Spreading Depression, Spreading Depolarizations, and the Cerebral Vasculature.

Spreading depression (SD) is a transient wave of near-complete neuronal and glial depolarization associated with massive transmembrane ionic and water shifts. It is evolutionarily conserved in the central nervous systems of a wide variety of species from locust to human. The depolarization spreads slowly at a rate of only millimeters per minute by way of grey matter contiguity, irrespective of functional or vascular divisions, and lasts up to a minute in otherwise normal tissue. As such, SD is a radically different breed of electrophysiological activity compared with everyday neural activity, such as action potentials and synaptic transmission. Seventy years after its discovery by Leão, the mechanisms of SD and its profound metabolic and hemodynamic effects are still debated. What we did learn of consequence, however, is that SD plays a central role in the pathophysiology of a number of diseases including migraine, ischemic stroke, intracranial hemorrhage, and traumatic brain injury. An intriguing overlap among them is that they are all neurovascular disorders. Therefore, the interplay between neurons and vascular elements is critical for our understanding of the impact of this homeostatic breakdown in patients. The challenges of translating experimental data into human pathophysiology notwithstanding, this review provides a detailed account of bidirectional interactions between brain parenchyma and the cerebral vasculature during SD and puts this in the context of neurovascular diseases.

Related papers:

title: Clinical Relevance of Cortical Spreading Depression in Neurological Disorders: Migraine, Malignant Stroke, Subarachnoid and Intracranial Hemorrhage, and Traumatic Brain Injury
abstract: Cortical spreading depression (CSD) and depolarization waves are associated with dramatic failure of brain ion homeostasis, efflux of excitatory amino acids from nerve cells, increased energy metabolism and changes in cerebral blood flow (CBF). There is strong clinical and experimental evidence to suggest that CSD is involved in the mechanism of migraine, stroke, subarachnoid hemorrhage and traumatic brain injury. The implications of these findings are widespread and suggest that intrinsic brain mechanisms have the potential to worsen the outcome of cerebrovascular episodes or brain trauma. The consequences of these intrinsic mechanisms are intimately linked to the composition of the brain extracellular microenvironment and to the level of brain perfusion and in consequence brain energy supply. This paper summarizes the evidence provided by novel invasive techniques, which implicates CSD as a pathophysiological mechanism for this group of acute neurological disorders. The findings have implications for monitoring and treatment of patients with acute brain disorders in the intensive care unit. Drawing on the large body of experimental findings from animal studies of CSD obtained during decades we suggest treatment strategies, which may be used to prevent or attenuate secondary neuronal damage in acutely injured human brain cortex caused by depolarization waves.

title: Delayed ischaemic neurological deficits after subarachnoid haemorrhage are associated with clusters of spreading depolarizations.
abstract: Progressive ischaemic damage in animals is associated with spreading mass depolarizations of neurons and astrocytes, detected as spreading negative slow voltage variations. Speculation on whether spreading depolarizations occur in human ischaemic stroke has continued for the past 60 years. Therefore, we performed a prospective multicentre study assessing incidence and timing of spreading depolarizations and delayed ischaemic neurological deficit (DIND) in patients with major subarachnoid haemorrhage (SAH) requiring aneurysm surgery. Spreading depolarizations were recorded by electrocorticography with a subdural electrode strip placed on cerebral cortex for up to 10 days. A total of 2110 h recording time was analysed. The clinical state was monitored every 6 h. Delayed infarcts after SAH were verified by serial CT scans and/or MRI. Electrocorticography revealed 298 spreading depolarizations in 13 of the 18 patients (72%). A clinical DIND was observed in seven patients 7.8 days (7.3, 8.2) after SAH. DIND was time-locked to a sequence of recurrent spreading depolarizations in every single case (positive and negative predictive values: 86 and 100%, respectively). In four patients delayed infarcts developed in the recording area. As in the ischaemic penumbra of animals, delayed infarction was preceded by progressive prolongation of the electrocorticographic depression periods associated with spreading depolarizations to >60 min in each case. This study demonstrates that spreading depolarizations have a high incidence in major SAH and occur in ischaemic stroke. Repeated spreading depolarizations with prolonged depression periods are an early indicator of delayed ischaemic brain damage after SAH. In view of experimental evidence and the present clinical results, we suggest that spreading depolarizations with prolonged depressions are a promising target for treatment development in SAH and ischaemic stroke.

title: Cortical spreading depression and peri-infarct depolarization in acutely injured human cerebral cortex.
abstract: Electrocorticographic (ECoG) activity was recorded for up to 129 h from 12 acutely brain-injured human patients using six platinum electrodes placed near foci of damaged cortical tissue. The method probes ECoG activity in the immediate vicinity of the injured cortex and in adjacent supposedly healthy tissue. Six out of twelve patients displayed a total of 73 spontaneous episodes of spreading depression of the ECoG. Of the remaining 6 patients 1 displayed an episode of synchronous depression of ECoG during surgery. Using the same electrodes we also measured the slow potential changes (SPC) (0.005-0.05 Hz) to test the hypothesis that the ECoG depressions were identical to Leao's cortical spreading depression (CSD), and to be able to record peri-infarct depolarisations (PIDs) in electrically 'silent' cortical tissue. Changes in the SPC indicate depolarization of brain tissue. For the analysis, the SPCs were enhanced by calculating the time integral of the ECoG signal. Spreading ECoG depressions were accompanied at every single recording site by stereotyped SPCs, which spread across the cortical mantle at 3.3 (0.41-10) mm/min (median, range), i.e. at the same speed of spread as the depression of the ECoG activity. The amplitude of the SPCs was 0.06-3 mV. In 4 out of 6 patients the ECoG recovered spontaneously. In 2 patients we subsequently recorded recurrent SPCs, but without recovery of the initial ECoG background activity until 2-5 h later. This represents the first direct recording of PIDs in acutely injured human brain. Evidence from this and our previous study of 14 brain-injured patients suggests that CSDs in acute brain disorders occur at higher incidence in patients <30 years (83%) than above (33%). CSD was recorded in 4 out of 5 traumatic brain injury patients, and in 2 out of 7 patients with spontaneous haemorrhages. We conclude that the spreading ECoG depressions recorded in patients are identical to CSDs recorded in animal experiments. We furthermore provide direct electrophysiological evidence for the existence of PIDs and hence a penumbra in the human brain. We hypothesize that the depolarization events might contribute to tissue damage in acute disorders in the human brain.

title: Spreading and Synchronous Depressions of Cortical Activity in Acutely Injured Human Brain
abstract: Cortical spreading depression (CSD) has been much studied experimentally but never demonstrated unequivocally in human neocortex by direct electrophysiological recording. A similar phenomenon, peri-infarct depolarization, occurs in experimental models of stroke and causes the infarct to enlarge. Our current understanding of the mechanisms of deterioration in the days after major traumatic or ischemic brain injury in humans has not yielded any effective, novel drug treatment. This study sought clear evidence for the occurrence and propagation of CSD in the injured human brain.  In 14 patients undergoing neurosurgery after head injury or intracranial hemorrhage, we placed electrocorticographic (ECoG) electrodes near foci of damaged cortical tissue.  Transient episodes of depressed ECoG activity that propagated across the cortex at rates in the range of 0.6 to 5.0 mm/min were observed in 5 patients; this rate of propagation is characteristic of CSD. We also observed, in 8 of the 14 patients, transient depressions of ECoG amplitude that appeared essentially simultaneous in all recording channels, without clear evidence of spread.  These results indicate that CSD or similar events occur in the injured human brain and are more frequent than previously suggested. On the basis of these observations, we suggest that the related phenomenon, peri-infarct depolarization, is indeed likely to occur in boundary zones in the ischemic human cerebral cortex.

title: Cortical Spreading Depression Triggers Migraine Attack: Pro
abstract: More than 60 years ago Aristides Leão coined the term spreading depression (SD) to describe a transient “depression” of electrocorticographic activity that lasts up to several minutes and slowly “spreads” in all directions in cortex by way of gray matter contiguity. 1 Today we know that SD is an intrinsic electrophysiological property of central nervous systems, evolutionarily preserved from locust to man. 2‐7 Largely based on the similarities between the symptomatology of migraine aura and the electrophysiological features of SD, a causal relationship between the two has long been hypothesized. 8‐10 Recently, the SD theory of migraine gained momentum by evidence emerging from both clinical and experimental studies despite being challenged by alternative mechanisms and hypotheses. Here, I will review the accumulated evidence supporting a causal relationship between SD and migraine aura and headache, and discuss the contested notion that SD may also be involved in migraine attacks without a “perceived” aura.

title: Membrane potential of cerebral cortical cells during reading depression and asyxia.
abstract: Changes in membrane potential were recorded intracellularly from cortical cells during spreading depression (SD) and asphyxiation. In fourteen cells with a mean membrane potential of 67 mv, SD caused a moderate to severe transient depolarization of about 2-min duration. The depolarization was relatively fast, the repolarization much slower. The mean value of the membrane potential at the maximum of depolarization was 35% of the original, with a range of 74 to 6%. A correction was made in a few instances for the effects of the slow potential change accompanying spreading depression on the membrane potential recorded between an intracellular and indifferent electrode. In one of these cases the corrected membrane potential approached zero. Asphyxiation caused, after a latency of 2 to 3 min, a fast depolarization to a low value of the membrane potential, preceded by a slow decline of the potential (6 mv/min) which started after a short latency (fraction of a minute).

title: Neuronal and glial activity during spreading depression in cerebral cortex of cat.
abstract: 1. Extra- and intracellular potentials were recorded from neurons and glia during spreading depression (SD) in cerebral cortex of cats. The glial membrane depolarized during SD and the time course of depolarization was concurrent with the surface DC change of SD. The glial depolarization evoked by 20-Hz repetitive cortical stimulation disappeared during the negative DC shift of SD. Simultaneous recording of the extra- and intracellular potentials from a single glial cell with a coaxial microelectrode showed that the extracellular DC potential change was of opposite polarity to the glial intracellular potential, which suggests that the slow glial depolarization concurrent with SD is not the field potential. In contrast to glial cells, the neuronal burst discharges as well as the neuronal membrane depolarization associated with SD did not show a close relationship to SD: the neuronal membrane depolarization and discharge were frequently delayed by 10-3- s from the onset of the SD slow wave. Sometimes SD was observed without accompanying neuronal depolarization. The degree of neuronal depolarization was not always correlated with the amplitude of the negative wave of SD. 2. The effect of tetrodotoxin (TTX) on the negative DC potential of SD was examined. Simultaneous recording of glial membrane potential and the neuronal unit activity as well as extracellular DC potential and surface DC potential during SD was performed and the TTX-treated cortex was compared with the normal state. TTX did not change the DC level of the cerebral cortex. SD could be evoked by KCl when neuronal discharge was completely abolished by TTX application...

title: Cytoarchitecture-Dependent Decrease in Propagation Velocity of Cortical Spreading Depression in the Rat Insular Cortex Revealed by Optical Imaging.
abstract: Cortical spreading depression (SD) is a self-propagating wave of depolarization accompanied by a substantial disturbance of the ionic distribution between the intra- and extracellular compartments. Glial cells, including astrocytes, play critical roles in maintenance of the extracellular environment, including ionic distribution. Therefore, SD propagation in the cerebral cortex may depend on the density of astrocytes. The present study aimed to examine the profile of SD propagation in the insular cortex (IC), which is located between the neocortex and paleocortex and is where the density of astrocytes gradually changes. The velocity of SD propagation in the neocortex, including the somatosensory, motor, and granular insular cortices (5.7 mm/min), was higher than that (2.8 mm/min) in the paleocortex (agranular insular and piriform cortices). Around thick vessels, including the middle cerebral artery, SD propagation was frequently delayed and sometimes disappeared. Immunohistological analysis of glial fibrillary acidic protein (GFAP) demonstrated the sparse distribution of astrocytes in the somatosensory cortex and the IC dorsal to the rhinal fissure, whereas the ventral IC showed a higher density of astrocytes. These results suggest that cortical cytoarchitectonic features, which possibly involve the distribution of astrocytes, are crucial for regulating the velocity of SD propagation in the cerebral cortex.

title: High-Resolution In Vivo Imaging of the Neurovascular Unit during Spreading Depression
abstract: Spreading depression (SD) is a propagating wave of neuronal depolarization and ionic shifts, seen in stroke and migraine. In vitro, SD is associated with astrocytic [Ca2+] waves, but it is unclear what role they play and whether they influence cerebral blood flow, which is altered in SD. Here we show that SD in vivo is associated with [Ca2+] waves in astrocytes and neurons and with constriction of intracortical arterioles severe enough to result in arrest of capillary perfusion. The vasoconstriction is correlated with fast astrocytic [Ca2+] waves and is inhibited when they are reduced. [Ca2+] waves appear in neurons before astrocytes, and inhibition of astrocytic [Ca2+] waves does not depress SD propagation. This suggests that astrocytes do not drive SD propagation but are responsible for the hemodynamic failure seen deep in the cortex. Similar waves occur in anoxic depolarizations (AD), supporting the notion that SD and AD are related processes.

title: Different Mechanisms Promote Astrocyte Ca2+ Waves and Spreading Depression in the Mouse Neocortex
abstract: Cortical spreading depression (CSD) is thought to play an important role in different pathological conditions of the human brain. Here we investigated the interaction between CSD and Ca2+ waves within the astrocyte population in slices from mouse neocortex (postnatal days 10–14). After local KCl ejection as a trigger for CSD, we recorded the propagation of Ca2+ increases within a large population of identified astrocytes in synchrony with CSD measured as intrinsic optical signal (IOS) or negative DC-potential shift. The two events spread with 39.2 ± 3.3 μm/sec until the IOS and negative DC-potential shift decayed after ∼1 mm. However, the astrocyte Ca2+ wave continued to propagate for up to another 500μm but with a reduced speed of 18.3 ± 2.5μm/sec that is also typical for glial Ca2+ waves in white matter or culture. While blocking CSD using MK-801 (40 μm), an NMDA-receptor antagonist, the astrocyte Ca2+ wave persisted with a reduced speed (13.2 ± 1.5μm/sec). The specific gap junction blocker carbenoxolon (100μm) did not prevent CSD but decelerated the speed (2.9 ± 0.9μm/sec) of the astrocyte Ca2+ wave in the periphery of CSD. We also found that interfering with intracellular astrocytic Ca2+ signaling by depletion of internal Ca2+ stores does not affect the spread of the IOS. We conclude that CSD determines the velocity of an accompanying astrocytic Ca2+ response, but the astrocyte Ca2+ wave penetrates a larger territory and by this represents a self-reliant phenomenon with a different mechanism of propagation.

title: The minimum volume of depolarized neural tissue required for triggering cortical spreading depression in rat
abstract: SummaryCortical spreading depression (CSD) was evoked in anaesthetized rats by intracortical microinjection of 3.4·10−8 mol KCl (the single injection threshold T1). With two simultaneous injections at 1 mm tip separation 59% T1 had to be applied to each point to elicit CSD. For interfocal distances 2, 3 and 4 mm the double injection thresholds T1,2 were 65%, 74% and 97% of T1 respectively. The spatial summation effect was still significant at 3 mm and undetectable at 4 mm tip separation. Recording electrodes placed 1–3 mm from the point of injection detected local slow potential changes which attained with subthreshold KCl injections 16% of the maximum CSD negativity at the 1.5 mm distance. The threshold amount of KCl required to trigger CSD at different intervals (30–480 sec) after initial injection of 0.8 T1, exponentially increased with time from 28.2% t1 at 30 sec to 88.9% at 480 sec with the slope 16.8% T1 for a twofold increase of the interinjection interval. Quantitative analysis of results based on equations describing diffusion from an instantaneous point source indicates that the critical volume of depolarization is reached 61 sec after injection. According to the value of the diffusion coefficient of potassium the critical K+ concentration lies between 45 and 12 mequ/l and is reached at a distance of 600–950 μ from the injection.

title: Minimum conditions for the induction of cortical spreading depression in brain slices.
abstract: Cortical spreading depression (CSD) occurs during various forms of brain injury such as stroke, subarachnoid hemorrhage, and brain trauma, but it is also thought to be the mechanism of the migraine aura. It is therefore expected to occur over a range of conditions including the awake behaving state. Yet it is unclear how such a massive depolarization could occur under relatively benign conditions. Using a microfluidic device with focal stimulation capability in a mouse brain slice model, we varied extracellular potassium concentration as well as the area exposed to increased extracellular potassium to determine the minimum conditions necessary to elicit CSD. Importantly, we focused on potassium levels that are physiologically plausible (≤145 mM; the intracellular potassium concentration). We found a strong correlation between the threshold concentration and the slice area exposed to increased extracellular potassium: minimum area of exposure was needed with the highest potassium concentration, while larger areas were needed at lower concentrations. We also found that moderate elevations of extracellular potassium were able to elicit CSD in relatively small estimated tissue volumes that might be activated under noninjury conditions. Our results thus show that CSD may be inducible under the conditions that expected in migraine aura as well as those related to brain trauma.

title: Responses of electrical potential, potassium levels, and oxidative metabolic activity of the cerebral neocortex of cats
abstract: We measured simultaneously the oxidative metabolic activity, monitored as the tissue fluorescence attribute to intramitochondrial NADH, the extracellular potassium level with ion-selective microelectrodes, and the focal extracellular electrical potential, of one site in intact cerebral cortex of cats. When the cerebral was stimulated by trains of repeated electric pulses applied either directly to its surface or to an afferent pathway, the corrected cortical fluorescence (F-R) declined indicating oxidation of NADH, the activity of extracellular potassium [K+]o increased, and the extracellular potential (Vec) shifted in the negative direction. When mild to moderate stimuli not exceeding 10-15 sec in duration were used, a 3-fold correlation was found between these three variables. The regression of F-R over either Vec, or over log [K+]o had a positive ordinal intercept. The results are in agreement with earlier suggestions 4,24,25,43,45,46 that (a) much but not all the oxidative metabolic response of cortex to electrical stimulation is expended in restoring disturbed ion balance; and (b) that sustained shifts of potential (SP) in response to repetitive electrical stimulation are generated by glia cells depolarized by excess potassium. The magnitude of SP shifts associated with a given elevation of [k+]o are smaller in cerebral cortex than in spinal cord48,49. The correlation of F-R with [K+]o breaks down when pathologic processes of either seizure activity or spreading depression set in. During paroxysmal activity [K+]o tends to remain confined below 10-12 mM, a level observed in non-convulsing cortex as well, but oxidation of NADH progresses beyond that seen in non-convulsing cortex as well, but oxidation of NADH progresses beyond that seen in non-convulsing tissue. This observation is hard to reconcile with the suggestion that excess potassium is a factor in the generation of seizures, at least of the type observed in this study. When [K+]o levels exceeded 10-12 mM, spreading depression invariably followed at least under the unanesthetized condition in these experiments. During spreading depression [K+]o levels rose to exceed 30 mM, sometimes 80 mM. NADH was oxidized during spreading depression to a level comparable to that seen in seizures. The observations are compatible with the suggestion13 that spreading depression occurs whenever the release of potassium into extracellular fluid is overloading its clearance therefrom.

title: Chronically Epileptic Human and Rat Neocortex Display a Similar Resistance Against Spreading Depolarization In Vitro
abstract: Experimental and clinical evidence suggests that prolonged spreading depolarizations (SDs) are a promising target for therapeutic intervention in stroke because they recruit tissue at risk into necrosis by protracted intracellular calcium surge and massive glutamate release. Unfortunately, unlike SDs in healthy tissue, they are resistant to drugs such as N-methyl-d-aspartate-receptor antagonists. This drug resistance of SD in low perfusion areas may be due to the gradual rise of extracellular potassium before SD onset. Brain slices from patients undergoing surgery for intractable epilepsy allow for screening of drugs, targeting pharmacoresistant SDs under elevated potassium in human tissue. However, network changes associated with epilepsy may interfere with tissue susceptibility to SD. This could distort the results of pharmacological tests.  We investigated the threshold for SD, induced by a gradual rise of potassium, in neocortex slices of patients with intractable epilepsy and of chronically epileptic rats as well as age-matched and younger control rats using combined extracellular potassium/field recordings and intrinsic optical imaging.  Both age and epilepsy significantly increased the potassium threshold, which was similarly high in epileptic rat and human slices (23.6±2.4 mmol/L versus 22.3±2.8 mmol/L).  Our results suggest that chronic epilepsy confers resistance against SD. This should be considered when human tissue is used for screening of neuroprotective drugs. The finding of similar potassium thresholds for SD in epileptic human and rat neocortex challenges previous speculations that the resistance of the human brain against SD is markedly higher than that of the rodent brain.

title: Maintenance of a constant brain extracellular potassium.
abstract: The development of potassium specific ion exchanger microelectrodes has enabled investigators to measure directly brain extracellular potassium ion activity. Although serum potassium in various species ranges between 3.5 and 6 mEq/l, brain extracellular potassium is maintained at a level close to 3 mEq/l independent of fluctuations in serum values. Despite this buffering of the internal brain environment by extracerebral changes, local variations in extracellular potassium occur in response to evoked neuronal activity, seizures, and spreading depression. Mechanisms involved in the maintenance of this ionic homeostasis in the brain include mediated transport at the level of the cerebral capillary and the choroid plexus epithelium. In addition, there are ouabain-sensitive clearance mechanisms presumably involving Na,K-ATPase that participate in the removal of excess potassium. The relative roles of simple diffusion, high glial cell conductance of potassium, and active ionic pumps in restoring basal potassium levels after activity are still controversial.

title: Extracellular ionic variations during spreading depression
abstract: Changes in the concentrations of K + , Ca 2+ , Na + and Cl − were measured during spreading depression in the exposed lissencephalic cerebellar molecular layer of the catfish, Corydoras aneus . Liquid ion exchanger ion-selective microelectrodes were used in pairs to monitor simultaneously changes in the concentrations of two ionic species in the extracellular space. Normothermic spreading depression in the catfish cerebellum consists of a slow negative potential shift that develops at a rate of 2–3mV/s, reaches an amplitude of −25 mV, lasts 1–6 min and propagates at a rate of 0.5–1.5 mm/min. [K + ] o rises from a resting level of 2.3–35 mM at the peak of spreading depression. Between 20 and 40s later [Ca 2+ ] o falls from 2.2 mM to 0.8 mM and [Na + ] o and [Cl − ] o decrease from 149 to 57 mM and 137 to 47 mM respectively at approximately the same time.  The earliest extracellular precursor of spreading depression is a rise in [K + ] o . In light of the equality of [Na + ] o and [Cl − ] o changes and the rise in [K + ] o , electroneutrality in extracellular space involved may be maintained by the net accumulation of some unidentified anion equivalent to the rise in [K + ] o . Alternatively, no net accumulation is needed if some extracellular anions are impermeant and the volume of extracellular space decreases. The sum of the extracellular ion concentrations suggests that the ionic strength of extracellular space decreases by greater than one-third during spreading depression. These results demonstrate that the brain is capable of establishing and recovering from local ionic inhomogenejties.

title: Calcium and potassium changes in extracellular microenvironment of cat cerebellar cortex.
abstract: 1. Local stimulus-evoked changes in concentration of extracellular calcium ions, [Ca2+]0, and potassium ions, [K+[0, were measured in the cerebellar cortex of the cat using paired ion-selected micropipettes. 2. Repetitive stimulation of 30 s duration decreased [Ca2+]0 from a base line of 1.2 mM to as low as 0.8 mM and increased [K+]0 from 3 mM to as much as 8 mM. The magnitude of the changes was directly related to stimulus frequency. Laminar analysis showed that the greatest ion changes occurred at the level of maximum parallel fiber-Purkinje cell dendrite stimulation, but that the [Ca2+]0 changes were more localized than the [K+]0 changes. 3. Combining real-time current-source density measurement with [K+]0 determination and local manganese application, showed that the Mn blocked parallel fiber-Purkinje cell synaptic transmission, but that much of the [K+]0 changes persisted. Thus, a large part of the [K+]0 flux most probably originated in the parallel fibers. In contrast, [Ca2+]0 changes were abolished by the Mn, indicating that the decrease in this ion was probably associated with synaptic transmission or dendritic events. 4. In a few cases, spreading depression occurred in the cat cerebellar cortex. This could be accompanied by decreases in [Ca2+]0 to as low as 0.12 mM and increases in [K+]0 in excess of 48 mM. 5. These results show that significant changes in [Ca2+]0 and [K+]0 occur during cerebellar stimulation and indicate possible origins of the ion fluxes in terms of neuronal elements. This work also shows that the cerebellar cortex of the cat can support spreading depression. The present results, together with those of earlier studies on [Ca2+]0 and [K+]0 changes in the presence of aminopyridine in the cat cerebellum, suggest that synaptic or dendritic electroresponsive properties may play a role in the observed [Ca2+]0 and [K+]0 changes.

title: Ion changes in spreading ischaemia induce rat middle cerebral artery constriction in the absence of NO.
abstract: In rats, cortical spreading hyperaemia is coupled to a spreading neuroglial depolarization wave (spreading depression) under physiological conditions, whereas cortical spreading ischaemia is coupled to it if red blood cell products are present in the subarachnoid space. Spreading ischaemia has been proposed as the pathophysiological correlate of the widespread cortical infarcts abundantly found in autopsy studies of patients with subarachnoid haemorrhage. The purpose of the present study was to investigate whether the extracellular ion changes associated with the depolarization wave may cause the vasoconstriction underlying spreading ischaemia. We induced spreading ischaemia in vivo with the nitric oxide (NO) scavenger oxyhaemoglobin and an elevated K+ concentration in the subarachnoid space while slow potential, pH, extracellular volume and concentrations of K+, Na+, Ca2+ and Cl- were measured in the cortex with microelectrodes. We then extraluminally applied an ionic cocktail (cocktail(SI)) to the isolated middle cerebral artery in vitro, matching the ionic composition of the extracellular space as measured during spreading ischaemia in vivo. Extraluminal application of cocktail(SI) caused middle cerebral artery dilatation in the absence and constriction in the presence of NO synthase inhibition in vitro, corresponding with the occurrence of spreading hyperaemia in the presence and spreading ischaemia in the absence of NO in vivo. The L-type Ca2+ inhibitor nimodipine caused the cocktail(SI)-induced vasoconstriction to revert to vasodilatation in the absence of NO in vitro similar to the reversal of spreading ischaemia to spreading hyperaemia in response to nimodipine in vivo. We found that K+ was the predominant vasoconstrictor contained in cocktail(SI). Its vasoconstrictor action was augmented by NO synthase inhibition. Our results suggest that, under elevated baseline K+ as a hallmark of any condition of energy deficiency, the extracellular ion changes represent the essential mediator of the vascular response to spreading neuroglial depolarization. In the presence of NO they mediate vasodilatation and in its absence they mediate constriction.

title: Electrical and vascular concomitants of spreading depression.
abstract: Spreading depression is accompanied by a slow potential change, a drop in cortical conductivity and by vascular changes. The latter were investigated in histological preparations of cortex frozen while a spreading depression was in progress. In the cat and rabbit a broad wave of vasodilatation was observed. In the rabbit this appeared to be preceded by a narrow region of vasoconstriction. Spreading depression can be changed into spreading convulsive activity by administering CO 2 in the respiratory air (7–12%). CO 2 markedly decreased the drop in cortical conductivity but affected the magnitude of the slow potential change only moderately. It is postulated that both the conductivity drop during spreading depression and a similar drop observed after asphyxiation of the brain are caused by a transport of ions from the intercellular compartment into cortical cellular elements. The relationship between the slow potential change, conductivity drop, vascular changes and the changes in the electrocorticogram during spreading depression is discussed.

title: Changes in extracellular space volume and geometry induced by cortical spreading depression in immature and adult rats.
abstract: Changes in extracellular space (ECS) diffusion parameters, DC potentials and extracellular potassium concentration were studied during single and repeated cortical spreading depressions (SD) in 13-15 (P13-15), 21 (P21) and 90-day-old (adult) Wistar rats. The real-time iontophoretic method using tetramethylammonium (TMA+)-selective microelectrodes was employed to measure three ECS parameters in the somatosensory cortex: the ECS volume fraction alpha (alpha = ECS volume/total tissue volume), ECS tortuosity lambda (increase in diffusion path length) and the nonspecific TMA+ uptake k'. SD was elicited by needle prick. SD was significantly longer at P13-15 than at P21 and in adults. During SD, alpha in all age groups decreased from 0.21-0.23 to 0.05-0.09; lambda increased from 1.55-1.65 to 1.95-2.07. Ten minutes after SD, alpha (in adults) and lambda (all age groups) increased compared to controls. This increase persisted even 1 hour after SD. When SD was repeated at 1 hour intervals, both alpha and lambda showed a gradual cumulative increase with SD repetition. Our study also shows that cortical SD is, as early as P13, accompanied by severe ECS shrinkage and increased diffusion path length (tortuosity) with values similar to adults, followed by a long-lasting increase in ECS volume and tortuosity when compared to pre-SD values.

title: Anion permeability in spreading depression investigated with ion-sensitive microelectrodes
abstract: Changes in the anion permeability of neurons within the mammalian central nervous system usually have been attributed to activation of synaptic inhibition, which is predominantly due to an increase in the chloride permeability of membranes11,12. Studies of the spreading depression (SD) of LeSo 1,1°, using ion-selective micropipettes (ISMs)S, 9 or a histochemical technique 22 have also revealed substantial chloride shifts accompanied by large changes in other extracellular ionsa,9,14 and an inferred reduction in extracellular space volume 20. It has been suggested 15 that postsynaptic inhibition is a component of SD and consequently this might account for the chloride changes, but this conjecture has received little experimental examination. In this paper we characterize the anion permeability change during SD in the rat cerebellum using ISMs sensitive to a sequence of 'probe anions' defined as anions not present in the brain which we can introduce into the extracellular space. The behavior of these probe anions, of graded size, during SD reveals whether or not membranes become permeable to them. Our experiments indicate an anion channel of defined size becomes active during SD and that the size is apparently larger than that of some, but not all, inhibitory channels found in the mammalian central nervous system. In addition we provide direct evidence that the extracellular space shrinks during SD. The probe anions were sodium salts of thiocyanate (SCN), hexafluorophosphate (PF6), hexafluoroarsenate (AsF6) and a-naphthalene sulfonate (a-NS) (PF6 and AsF6 obtained from ICN Pharmaceuticals; a-NS from Tridom-Fluka). Tetraethylammonium (TEA) chloride was used as a cation probe for volume measurement. Measurement of the diffusion of the anion probes by methods similar to those described elsewhere a3 indicates that they have an apparent diffusion constant reduced to 40 % of that in water and that the probes remain extracellular under normal conditions. Ion concentrations were measured with double-barrel ISMsS, ~a,~4 containing 150 mM NaCl in the reference side and 150 mM Na, 75 mM C1 and 75 mM of the anion to be detected as backfilling solution in the side containing the ion exchanger.

title: Influence of Plasma Glucose Concentration on Rat Brain Extracellular Calcium Transients during Spreading Depression
abstract: The objective of this study was to establish whether tissues that are energy compromised, but not energy depleted, demonstrate exaggerated calcium transients when subjected to membrane depolarizations of the spreading depression (SD) type. Anesthetized and artificially ventilated rats were given insulin in order to induce progressively lower plasma glucose concentrations. Spreading depression was elicited by local application of KCl; extracellular calcium concentration (Ca2+ e) as well as direct current (DC) potential were recorded. When plasma glucose concentration fell below ∼3 mM, the duration of the Ca2+e transient gradually increased to values exceeding 500% of control. The increase was associated with a corresponding increase in the duration of the DC potential shift, but the amplitude of the Ca2+e transient did not change. It is concluded that a restriction of glucose (or oxygen) supply, as occurs in hypoglycemia (or hypoxia), prolongs the calcium transient associated with depolarization of the SD type, even though tissue phosphocreatine and ATP concentrations are normal. The results support the contention that repeated depolarizations, occurring in the penumbral zone of a focal ischemic lesion, could lead to calcium-related damage.

title: Calcium modulation in brain extracellular microenvironment demonstrated with ion-selective micropipette.
abstract: Changes in extracellular Ca2+ concentration were directly measured in the rat cerebellum, using an ion-selective micropipette. Extracellular K+ was measured simultaneously with a second ion-selective micropipette. The potential reference barrels of the ion electrodes also provided fast field and slow potentials. During repetitive stimulation of the parallel fiber--Purkinje cell cerebellar circuit, extracellular Ca2+ fell to about 80% of base line concentration. During the spreading depression of Leão, extracellular Ca2+ fell to about 10% of base line; decreases of this magnitude also occurred during terminal anoxia. In all cases extracellular K+ increased substantially. These results show that extracellular Ca2+ is modulated during neuronal activity in the central nervous system and that under some conditions the Ca2+ change can be extreme. Given the well-established and antagonistic effects of reduce extracellular Ca2+ on axonal excitability and synaptic transmission, these results suggest that Ca2+ modulation in the brain cell microenvironment may be a significant parameter in the behavior of neuronal ensembles.

title: Microdialysis of interstitial amino acids during spreading depression and anoxic depolarization in rat neocortex
abstract: We have examined the effect of cortical spreading depression (SD) and anoxic depolarization (AD) on the interstitial concentration changes of amino acids (AA) in the neocortex of anesthetized rats using microdialysis and HPLC. Accompanying SD alanine increased to 126 +/- 11%, arginine to 116 +/- 3%, aspartate to 160 +/- 17%, glutamate to 163 +/- 9%, glycine to 158 +/- 21%, serine to 125 +/- 9%, and taurine to 172 +/- 15% (mean +/- 1 S.E.M.). The increases lasted for about 1 min. Histidine decreased to 74% +/- 4% at 1 min following SD, and returned to normal 4 min later. Cardiac arrest triggered AD after approximately 2 min, immediately followed by changes of interstitial AAs. At 5 min after AD alanine had increased to 183 +/- 13%, aspartate to 3,458 +/- 656%, GABA to 338 +/- 35%, glutamate to 1,696 +/- 546%, glycine to 297 +/- 37%, serine to 153 +/- 12%, and taurine to 1721 +/- 98% as compared to control values (mean +/- 1 S.E.M.). Histidine decreased to 78 +/- 2% at 3 min following AD while arginine exhibited insignificant variations around the baseline. The increase of glutamate during SD is consistent with activation of NMDA-receptors as an essential requirement for this reaction. The increase of AAs may also contribute to the sequence of events leading to AD, though the exact mechanism remains unknown. SD is an important pathophysiological mechanism of the ischemic penumbra associated with focal cerebral ischemia, while AD reflects the electrophysiological status of the infarct core.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Interstitial Concentrations of Amino Acids in the Rat Striatum During Global Forebrain Ischemia and Potassium-Evoked Spreading Depression
abstract: The early detection and appropriate treatment of brain ischemia is of paramount importance. The interstitial concentrations of neurotransmitter amino acids are often used as an index of neuronal injury. However, monitoring of non-neurotransmitter amino acids may be equally important. We have studied the behavior of 10 amino acids during K+-induced spreading depression (application of 70 mM KCl during 40 min) and global forebrain ischemia (two-vessel occlusion with hypotension during 20 min). The concentrations of glutamate, aspartate, taurine, GABA, glycine, and alanine, measured in the rat striatum by microdialysis, increased during both ischemia and spreading depression, whereas glutamine concentrations decreased in both cases. Only ischemia, but not spreading depression, led to enhanced release of serine, threonine, and asparagine. We thus conclude that an elevation in the interstitial concentrations of non-neurotransmitter amino acids is specific to deep ischemic injury to nervous tissue. We propose the monitoring of serine, asparagine, and threonine, together with excitatory amino acids, as an index of the degree of ischemic brain injury.

title: Adenosine receptor activation is responsible for prolonged depression of synaptic transmission after spreading depolarization in brain slices
abstract: Spreading depolarization (SD) is a slowly propagating, coordinated depolarization of brain tissue, which is followed by a transient (5-10min) depression of synaptic activity. The mechanisms for synaptic depression after SD are incompletely understood. We examined the relative contributions of action potential failure and adenosine receptor activation to the suppression of evoked synaptic activity in murine brain slices. Focal micro-injection of potassium chloride (KCl) was used to induce SD and synaptic potentials were evoked by electrical stimulation of Schaffer collateral inputs to hippocampal area Cornu Ammonis area 1 (CA1). SD was accompanied by loss of both presynaptic action potentials (as assessed from fiber volleys) and field excitatory postsynaptic potentials (fEPSPs). Fiber volleys recovered rapidly upon neutralization of the extracellular direct current (DC) potential, whereas fEPSPs underwent a secondary suppression phase lasting several minutes. Paired-pulse ratio was elevated during the secondary suppression period, consistent with a presynaptic mechanism of synaptic depression. A transient increase in extracellular adenosine concentration was detected during the period of secondary suppression. Antagonists of adenosine A1 receptors (8-cyclopentyl-1,3-dipropylxanthine [DPCPX] or 8-cyclopentyl-1,3-dimethylxanthine [8-CPT]) greatly accelerated fEPSP recovery and abolished increases in paired-pulse ratio normally observed after SD. The duration of fEPSP suppression was correlated with both the duration of the DC shift and the area of tissue depolarized, consistent with the model that adenosine accumulates in proportion to the metabolic burden of SD. These results suggest that in brain slices, the duration of the DC shift approximately defined the period of action potential failure, but the secondary depression of evoked responses was in large part due to endogenous adenosine accumulation after SD.

title: Spreading Depolarization-Induced Adenosine Accumulation Reflects Metabolic Status In Vitro and In Vivo
abstract: Spreading depolarization (SD), a pathologic feature of migraine, stroke and traumatic brain injury, is a propagating depolarization of neurons and glia causing profound metabolic demand. Adenosine, the low-energy metabolite of ATP, has been shown to be elevated after SD in brain slices and under conditions likely to trigger SD in vivo. The relationship between metabolic status and adenosine accumulation after SD was tested here, in brain slices and in vivo. In brain slices, metabolic impairment (assessed by nicotinamide adenine dinucleotide (phosphate) autofluorescence and O2 availability) was associated with prolonged extracellular direct current (DC) shifts indicating delayed repolarization, and increased adenosine accumulation. In vivo, adenosine accumulation was observed after SD even in otherwise healthy mice. As in brain slices, in vivo adenosine accumulation correlated with DC shift duration and increased when DC shifts were prolonged by metabolic impairment (i.e., hypoglycemia or middle cerebral artery occlusion). A striking pattern of adenosine dynamics was observed during focal ischemic stroke, with nearly all the observed adenosine signals in the periinfarct region occurring in association with SDs. These findings suggest that adenosine accumulation could serve as a biomarker of SD incidence and severity, in a range of clinical conditions.

title: Temporal relationship between neurotransmitter release and ion flux during spreading depression and anoxia.
abstract: Brain ion homeostasis is severely perturbed during spreading depression of Leao and during anoxia. The ionic composition of the extracellular space changes abruptly and approaches the intracellular concentrations owing to an increase in cell permeability. In spreading depression, synchronous transmitter efflux caused by a depolarization of the presynaptic terminals has been implicated as a possible mechanism that would explain the concomitant movement of ions. Anoxia, having many features in common with spreading depression, may follow the same mechanism. We have measured the concentrations of extracellular potassium with ion-selective microelectrodes and dopamine by in vivo voltammetry with carbon fiber microelectrodes during spreading depression and anoxia to compare the temporal relationship between the release of dopamine and ion movements in the striatum. There is a pronounced release of dopamine during both spreading depression and anoxia. In spreading depression, the sharp increase of potassium concentration that follows an initial smaller and slower increase of potassium is accompanied by the release of dopamine. In anoxia, the dopamine release clearly precedes the fast rise of extracellular potassium concentration. We conclude that in striatum, there is a pronounced dopamine release during spreading depression and anoxia, but that the relationships between ionic changes and transmitter release for these two phenomena are different and probably reflect different mechanisms.

title: Interstitial Ascorbate in Turtle Brain Is Modulated by Release and Extracellular Volume Change
abstract: The isolated turtle cerebellum was used as a model system to study effects of depolarizing conditions on interstitial ascorbic acid concentration. The depolarizing stimulus was Leão's spreading depression, which is characterized by transient negative extracellular potentials, high potassium levels (20–60 μM), and local depression of neuronal activity. Interstitial concentrations of ascorbate (200–400 μM) and other electroactive species were monitored voltammetrically, using graphite fiber microelectrodes. Total tissue ascorbate (1,810 nmol/g tissue wet weight) was similar to mammalian levels and was several orders of magnitude higher than catecholamine and indoleamine content. During spreading depression, a large (up to 200 μM) increase in concentration of interstitial electroactive species was monitored. Use of Nafion‐and ascorbate oxidase‐coated electrodes and uricase confirmed that ascorbate was the only substance detected. Simultaneous monitoring of ascorbate, extracellular potential, and extracellular volume (using tetramethylammonium and ion‐selective microelectrodes) indicated that (a) the ascorbate increase began with the decrease in extracellular volume during spreading depression, and (b) much of the increase was the result of extracellular volume decrease. In sucrose‐substituted medium, in which volume changes are eliminated, a 50 μM increase in interstitial ascorbate, caused by release from intracellular stores, was also seen. The ascorbate concentration increase was prolonged in sucrose medium, suggesting that an uptake process involving sodium may further regulate interstitial ascorbate concentration.

title: Glutamate release and spreading depression in the fascia dentata in response to microdialysis with high K+: role of glia
abstract: To see electrophysiological and neurochemical events during microdialysis with high [K+], direct current (DC) and excitatory postsynaptic field potentials (fEPSPs) due to perforant path stimulation were recorded in the granule cell layer of the fascia dentata, while 3, 25, 50 or 100 mM KCl was perfused through a microdialysis probe placed 1.5 mm from the recording electrode. Glutamate and glutamine content of the dialysate was measured by high performance liquid chromatography. Raising [K+] from 3 to 25 mM reduced the efflux of glutamine, without affecting that of glutamate or the electrical activity. In about 50% of experiments, 50 mM K+ induced large (20-30 mV) negative waves of spreading depression (SD), and a suppression of fEPSPs. In the other 50%, without SD, fEPSPs did not change. Glutamate efflux increased 3-fold in both groups. SD waves were produced in all experiments with 100 mM K+ which evoked a more than 10-fold increase in glutamate release. Glutamine efflux decreased equally, by about 50%, with the 3 concentrations of K+. Microdialysis with 20 mM fluoroacetate, a glial metabolic poison, decreased the spontaneous efflux of glutamine and glutamate and increased the incidence of SD waves. Results suggest that perfusion of 50 or 100 mM K+ through a microdialysis probe causes spreading depression which blocks surrounding electrical activity. The activity of glia partly protects against spreading depression caused by high [K+].

title: Evidence for a role of the N-methyl-d-aspartate (NMDA) receptor in cortical spreading depression in the rat
abstract: The neurotransmitter glutamate activates the N-methyl-D-aspartate (NMDA), quisqualate and kainate receptors. It has been proposed, but also disputed, that local release of glutamate would play a pivotal role in cortical spreading depression (SD). We tested this hypothesis by investigating the influence of NMDA antagonists on SD, using the non-competitive NMDA antagonists ketamine, phencyclidine (PCP) and MK-801 and the competitive NMDA antagonist DL-2-amino-7-phosphonoheptanoate (2-APH), injected intraperitoneally in rats anesthetized with alfentanil. SD was elicited by cathodal DC-stimulation of the frontal cortex. SD propagation was followed using two ion-sensitive microelectrodes placed in the parietal and occipital cortex. The NMDA antagonists increased SD threshold, decreased the propagation velocity and decreased the duration of the accompanying extracellular DC, K+ and Ca2+ changes at the following doses: 40 mg/kg ketamine, 10 mg/kg PCP, 0.63 mg/kg MK-801, 10 and 40 mg/kg 2-APH. With each NMDA antagonist failure of SD propagation between both microelectrodes could be observed. SD elicitation (or propagation) was inhibited completely with 80 mg/kg ketamine, 3.1 mg/kg MK-801 and 160 mg/kg 2-APH. These NMDA antagonists have also anticonvulsant properties. None of these effects on SD were observed with high doses of other anticonvulsants such as 80 mg/kg phenytoin or 40 mg/kg diazepam. These experiments indicate that endogenous release of excitatory amino acids and their action on the NMDA receptor play an important role in the initiation, propagation and duration of SD.

title: Low extracellular magnesium induces epileptiform activity and spreading depression in rat hippocampal slices.
abstract: The effect of low extracellular Mg2+ concentration ([Mg2+]o) on neuronal activity was studied in rat hippocampal slices. After 20-40 min of perfusion with Mg2+-free medium, when [Mg2+]o declined to approximately 0.1-0.4 mM, spontaneous field potentials developed in the CA1 and CA3 regions, but not in the dentate gyrus. In the CA3 pyramidal cell layer, these potentials consisted of repetitive (0.3-0.5 Hz), 40- to 120-ms-long positive deflections (2-5 mV) with superimposed population spikes. In the stratum (str.) pyramidale of the CA1 region, positive-negative deflections (less than 3 mV) lasting for 30-80 ms were observed, which occurred with a frequency of 0.3-0.5 Hz. In some cases, longer lasting and rapidly recurring events were also observed. In CA3 pyramidal cells, the intracellular correlates of the field potential transients were 20- to 30-mV paroxysmal depolarization shifts (PDS) with superimposed bursts of action potentials, followed by large (greater than 10 mV), 500- to 1,200-ms-long afterhyperpolarizations (AHP). In contrast, pyramidal neurons of the CA1 area did not show PDSs; instead, sequences of excitatory postsynaptic potentials (EPSPs)/inhibitory postsynaptic potentials (IPSPs) accompanied the transient field potential changes. Occasionally, spontaneous EPSPs/IPSPs, occurring with high frequencies, could also be observed in CA1 without any field potential transients. In both hippocampal regions, the epileptiform activity evolved without significant alterations in the resting membrane potential (RMP) and input resistance (RN) of the neurons, although a 2- to 5-mV reduction in action potential threshold was noted. The spontaneous activity in Mg2+-free medium was readily suppressed by raising the extracellular Ca2+ concentration ([Ca2+]o) from 1.6 to 3.6 mM. The perfusion of 10-30 microns DL-2-amino-5-phosphonovaleric acid (2-APV), an antagonist for the glutamate receptors of the N-methyl-D-aspartate (NMDA) type, also attenuated or reversibly blocked the spontaneous activity. Surgical isolation of area CA1 from CA3 ceased the occurrence of the transients in CA1 but not in CA3. The synaptic input/output curves were shifted to the left in the absence of [Mg2+]o. Threshold intensity for eliciting population spikes was 50-75% of that in normal medium. Paired-pulse facilitation was still present near threshold, but was reduced at higher stimulus intensities. Decreases in [Ca2+]o, produced by repetitive stimulation (20-Hz/5-10 s) of the Schaffer collateral/commissural pathway and monitored with ion-selective microelectrodes in the CA1 region, were enhanced in Mg2+-free medium.(ABSTRACT TRUNCATED AT 400

title: Brain tissue temperature: activation-induced changes determined with a new multisensor probe.
abstract: Local brain tissue oxygen tension, temperature, and electrical potential were continuously and simultaneously measured at each of two different depths in anesthetized, paralyzed rat brain. Brain tissue temperature increases up to 1 degree C were recorded in response to direct electrical stimulation, spreading depression, PTZ-induced seizures, hypercapnia, and hypoxia. An increase in brain tissue temperature was also recorded during reoxygenation after hypoxia. Thus, we have shown that, in this preparation, increases in either blood flow or oxidative metabolism lead to transient warming of the brain.

title: Stimulus-activated changes in brain tissue temperature in the anesthetized rat
abstract: A new thin-film, multisensor probe was used to determine tissue oxygen tension, tissue temperature, and electrical activity at two depths below the brain surface in chloral hydrateor nitrous oxide/halothane-anesthetized rats. Brain tissue temperature at both depths was found to be lower than core temperature by 1–2°C. Electrical activation, spreading depression, and pentylenetetrazol seizures all resulted in transient increases of brain tissue temperature of a few tenths degree centigrade. Vasodilation, induced by hypercapnia or hypoxia, caused a warming of brain tissue. Near-maximum oxygen metabolism, reached upon reoxygenation after severe hypoxia, was accompanied by tissue temperature rises of greater than 1°C. It was concluded that brain tissue temperature in the anesthetized rat is lower than core temperature due to extensive radiative and conductive heat loss to the environment through the head. Transient increases in tissue temperature during activation are caused by vasodilation and increased metabolism.

title: Demonstration of heat production associated with spreading depression in the amphibian retina.
abstract: Using thin film of synthetic pyroelectric material, polyvinylidene fluoride, sensitive heat-sensors were constructed for the purpose of detecting heat production associated with the phenomenon of spreading depression in isolated amphibian retinae. Measurements with these sensors revealed the existence of large heat production, which closely follows the electrical sign of spreading depression. Studies of the effects of chemical agents known to affect spreading depression have demonstrated the usefulness of heat measurements.

title: Changes in regional cortical temperature and cerebral blood flow after cortical spreading depression.
abstract: Regional cerebral blood flow (rCBF) measurement by laser Doppler flowmetry and cortical temperature measurement using thermoencephaloscopy (TES) were performed to investigate the relationship between the changes in rCBF and cortical temperature after induced cortical spreading depression (CSD) in rats. TES showed a gradually expanding thermoresponse like an extending circular wave after CSD induced by application of KCl. Similarly, a transient increase in rCBF spread from the site of stimulation with a velocity of propagation of 2.5 mm/min. Simultaneous monitoring of rCBF and cortical temperature showed that the transient increase in rCBF was associated with an initial decrease in cortical temperature, followed by an increase in cortical temperature. We suggest that the cortical temperature is regulated mainly by neurogenic control of the pial microvascular blood supply that is precisely adjusted to the metabolic needs of the cerebral cortex. Non-injured cortex with the fine vascular architecture must be preserved during neurosurgery to allow heat transfer from deep areas of the cortex.

title: Brain temperature and brain blood flow in unanesthetized rats.
abstract: Qualitative estimates of local cerebral blood flow have been obtained in conscious unrestrained rats by the heated thermocouple method. The reference thermojunction was implanted contralaterally at identical stereotaxic coordinates. Inhalation of a gas mixture containing 10% carbon dioxide produced consistent elevations in heat transfer from the heated probe; the response was reproducible for several weeks following implantation. Thermocouples were implanted also in the brain and aorta of some of the rats. Shifts in brain temperature during feeding and sleeping were paralleled by shifts in blood temperature. A parallelism in the two temperatures existed even during the elevation in blood flow associated with CO2 inhalation. In rats, variations in brain temperature are caused mainly by variations in arterial blood temperature.

title: Quisqualate, kainate and NMDA can initiate spreading depression in the turtle cerebellum
abstract: This study evaluated the role of excitatory amino acid (EAA) receptor activation in spreading depression (SD), using the in vitro turtle cerebellum as a model system. SD was triggered by electrical stimulation or by elevated K+ after the cerebellum had been conditioned for at least 30 min with physiological saline in which most of the chloride had been replaced by propionate. SD was recognized as a transient (1-3 min) negative shift of extracellular potential accompanied by depression of evoked potentials (15-30 min) and an increase of extracellular K+ up to 60 mM, which spread across the cerebellum at rates of 1-7 mm/min. SD usually commenced in the granular layer, which apparently contains the 3 major EAA receptor subtypes, quisqualate, kainate and N-methyl-D-aspartate (NMDA), then subsequently spread to the molecular layer, which is largely free of NMDA receptors. Glutamate, aspartate, NMDA, kainate and quisqualate all triggered SD. Kynurenic acid and 2-aminophosphonovaleric acid (APV) inhibited SD under certain conditions further suggesting involvement of EAA receptors. The initiation of SD was blocked by high Mg2+ and facilitated in low extracellular Mg2+, which also eliminated the delay in molecular layer SD onset. Our data suggest that no one EAA receptor subtype is singly responsible for SD.

title: Cortical spreading depression recorded from the human brain using a multiparametric monitoring system
abstract: The number of parameters (i.e., EEG or ICP-intracranial pressure) routinely monitored under clinical situations is limited. The brain function analyzer described in this paper enables simultaneous, continuous on-line monitoring of cerebral blood flow (CBF) and volume (CBV), intramitochondrial NADH redox state, extracellular K+ concentrations, DC potential, electrocorticography and ICP from the cerebral cortex. Brain function of 14 patients with severe head injury (GCS < or = 8), who were hospitalized in the neurosurgical or general intensive care unit was monitored using this analyzer. Leao cortical spreading depression (SD) has been reported in many experimental animals but not in the human cerebral cortex. In one of the patients monitored, spreading depression was observed. This is the first time that spontaneous repetitive cortical SD cycles have been recorded from the cerebral cortex of a patient suffering from severe head injury. Typical SD cycles appeared 4-5 h after the beginning of monitoring this patient. During the first 3-4 cycles the responses of this patient were very similar to the responses to SD recorded in normoxic experimental animals. Electrocorticography was depressed whereas extracellular K+ levels increased. The metabolic response to spreading depression was characterized by oxidation of intramitochondrial NADH concomitant to a large increase in CBF. During brain death, an ischemic depolarization, characterized by decrease in CBF and an irreversible increase in extracellular K+, was recorded.

title: Spreading depression in squirrel monkey lissencephalic cortex.
abstract: Spreading depression was elicited in the squirrel monkey's cerebral cortex to determine some parameters of cortical spreading depression (CSD) in a highly encephalized but semi-lissencephalic brain. Rate of CSD propagation, as indicated by a slow potential (SP) change, was slower than in other mammals but comparable to that reported in other primates. Frontal and occipital regions of the cortex differed in terms of SP amplitude, CSD threshold, SP waveform, and seizure threshold. It was concluded that the squirrel monkey would be an excellent preparation for studying the effects of CSD upon memory functions, interhemispheric transfer, and other phenomena in a highly encephalized brain.

title: Stress Preconditioning of Spreading Depression in the Locust CNS
abstract: Cortical spreading depression (CSD) is closely associated with important pathologies including stroke, seizures and migraine. The mechanisms underlying SD in its various forms are still incompletely understood. Here we describe SD-like events in an invertebrate model, the ventilatory central pattern generator (CPG) of locusts. Using K+ -sensitive microelectrodes, we measured extracellular K+ concentration ([K+]o) in the metathoracic neuropile of the CPG while monitoring CPG output electromyographically from muscle 161 in the second abdominal segment to investigate the role K+ in failure of neural circuit operation induced by various stressors. Failure of ventilation in response to different stressors (hyperthermia, anoxia, ATP depletion, Na+/K+ ATPase impairment, K+ injection) was associated with a disturbance of CNS ion homeostasis that shares the characteristics of CSD and SD-like events in vertebrates. Hyperthermic failure was preconditioned by prior heat shock (3 h, 45°C) and induced-thermotolerance was associated with an increase in the rate of clearance of extracellular K+ that was not linked to changes in ATP levels or total Na+/K+ ATPase activity. Our findings suggest that SD-like events in locusts are adaptive to terminate neural network operation and conserve energy during stress and that they can be preconditioned by experience. We propose that they share mechanisms with CSD in mammals suggesting a common evolutionary origin.

title: Unique Profile of Spreading Depression in a Primate Model
abstract: Spreading depression (SD) is considered to play a role in pathologic conditions of humans such as in the evolution of ischemic brain injury and migraine aura. Because many studies have demonstrated spreading hypoperfusion in patients with migraine and persistent hypoperfusion in nonprimate animal models of SD, these changes in cerebral blood flow (CBF) were regarded as an epiphenomenon of SD. However, there is no direct evidence of the occurrence of SD in primates. The authors attempted to elicit SD by applying 3.3 mol/L potassium chloride to the cerebral cortex of nine male cynomolgus monkeys. The CBF was monitored by positron emission tomography in five animals. Propagated direct-current shifts were found by the two neighboring microelectrodes only in one animal. The direct-current wave propagated at a speed of 4 mm/min and its amplitude was 20 mV, being consistent with the SD findings. Except in one animal with 6 SD episodes, SD waves were recorded infrequently at the rostral site (none in three animals, once in three, and twice in two). Focal hyperemia accompanied SD. Neither spreading hypoperfusion nor persistent hypoperfusion was found. These unique features of SD in primates raise a doubt as to whether the role of SD in nonprimate animals is the same as that in stroke and migraine in humans.

title: Spreading depression in elasmobranch cerebellum
abstract: Spreading depression (SD) occurs in the cerebellum of an elasmobranch fish, the skate (Raja erinacea, Raja ocellata). The elasmobranch cerebellum, because of its unique separation of granular form molecular layer, provides an excellent opportunity to study the characteristics of SD in two distinct neuronal populations. Both the DC potential shifts and changes in neuronal activity effected by SD were analyzed. The SD DC potential shifts in both layers closely resembled those in mammalian cerebral cortices. Consisting of a predominantly negative extracellular potential shift, they were typically 1--10 min in duration and reached 5--40 mV peak amplitudes. The largest negative shifts were found in the granular layer, without any consistent positive phases in the white matter, molecular, or granular layers. The SD propagated radially from surface electrical stimulation at 0.78 mm/min (+/- 0.16, n = 8) in the molecular layer and 0.43 mm/min (+/- 0.17, n = 8) in the granular layer at 15 degrees C. At 18 degrees C, the molecular layer propagatory velocity was 1.1 mm/min (+/- 0.12, n = 20) while, at 10 degrees C, it was 0.52 mm/min (+/- 0.21, n = 20), suggesting a temperature-dependent Q10 factor of 2. A profound depression of both spontaneous and evoked neuronal activity accompanied the DC potential shift. Activation of Purkinje cells antidromically, white matter, and granular layer neurons was typically abolished by the peak of the negative DC shift. However, a significant increase in granular layer excitability often followed the neuronal depression, remaining so far up to an hour. Repeated waves of SD sometimes occurred in the absence of neuronal recovery. A similar post-SD excitability increase was not seen in molecular layer neurons. Intracellular recordings from Purkinje cells revealed a spontaneous burst of action potentials at the onset of SD, closely followed by a depolarization of membrane potential from an average of -64 mV (+/- 12 mV, n = 3) to -11 mV (+/- 5 mV, n = 3).

title: Functional ablation by spreading depression: possible use in human stereotactic neurosurgery.
abstract: Spreading depression (SD) of EEG activity was elicited by microinjection (5 microliter) of 5% potassium chloride into the caudate nucleus (n = 7) or hippocampus (n = 3) during stereotactic brain surgery in patients with focal epilepsy. An electrode-cannula assembly for eliciting and recording the slow potential waves of SD is described. The parameters of SD in human brain are similar to those in lower mammals. Functional ablation by SD can be used as a diagnostic tool in neurosurgery.

title: [Spreading depression in the cortex and subcortical structures of the brain of the rat induced by exposure to focused ultrasound].
abstract: Steady potential shifts produced by focused ultrasound were recorded in the cerebral cortex, hippocampus, thalamus and caudate nucleus of the rat. Impulses of 50-100 ms duration were presented with frequency 5 and 10 Hz. Negative slow potential shifts gradually increased up to 3-7 mV during 10-30 s and were often followed by the spreading depression (SD) waves. In every analyzed structure the SD amplitude reached 20-30 mV; the SD duration in the cortex, caudate nucleus and thalamus was 30-40 s while in the hippocampus it was 80-120 s. Seizures initiated by the ultrasound influence proceded in some cases the SD. Threshold ultrasound doses were not effective for 5-7 min after every the SD wave but at the end of the refractory period they became effective again. So, local influence of the focused ultrasound may result in functional blockade of the brain structures due to the cortical and subcortical spreading depression.

title: Multiphoton Imaging of Ultrasound/Optison Mediated Cerebrovascular Effects in vivo
abstract: Ultrasound (US) enhanced with microbubble contrast agents may transiently disrupt the blood–brain barrier (BBB) with minimal damage, providing a technique for noninvasive, localized drug-delivery deep within the brain. The mechanism and temporal profile of disruption are not understood, owing to the limitations of imaging modalities used previously. In this study, we monitored US-induced BBB disruption with multiphoton microscopy, providing high-resolution temporal and spatial information about the permeabilization mechanism and immediate effects of US exposure. Anesthetized C57 mice were prepared with a craniotomy and injected intravenously with fluorescent dyes to permit visualization of the vasculature and BBB integrity. The animals were imaged through a cranial window while exposed to low-intensity US (f =1.029 MHz, power = 0.2 W) with a coincident intravenous injection of Optison (a microbubble contrast agent). We observed arteriolar vasoconstriction on US exposure that disrupted blood flow and lasted up to 5 mins; BBB disruption occurred via two characteristically distinct processes—perivascular fluorescence gradually increased (over minutes) along the length of the affected vessel without apparent rupture of the vessel wall or rapidly (seconds) increased in select, focal regions. These data corroborated previous studies suggesting increased endothelial transcytosis and breached tight junctions and demonstrated vasoconstriction, which might alter BBB permeability by modifying cerebral blood flow.

title: Real-Time Optical Diagnosis of the Rat Brain Exposed to a Laser-Induced Shock Wave: Observation of Spreading Depolarization, Vasoconstriction and Hypoxemia-Oligemia
abstract: Despite many efforts, the pathophysiology and mechanism of blast-induced traumatic brain injury (bTBI) have not yet been elucidated, partially due to the difficulty of real-time diagnosis and extremely complex factors determining the outcome. In this study, we topically applied a laser-induced shock wave (LISW) to the rat brain through the skull, for which real-time measurements of optical diffuse reflectance and electroencephalogram (EEG) were performed. Even under conditions showing no clear changes in systemic physiological parameters, the brain showed a drastic light scattering change accompanied by EEG suppression, which indicated the occurrence of spreading depression, long-lasting hypoxemia and signal change indicating mitochondrial energy impairment. Under the standard LISW conditions examined, hemorrhage and contusion were not apparent in the cortex. To investigate events associated with spreading depression, measurement of direct current (DC) potential, light scattering imaging and stereomicroscopic observation of blood vessels were also conducted for the brain. After LISW application, we observed a distinct negative shift in the DC potential, which temporally coincided with the transit of a light scattering wave, showing the occurrence of spreading depolarization and concomitant change in light scattering. Blood vessels in the brain surface initially showed vasodilatation for 3–4 min, which was followed by long-lasting vasoconstriction, corresponding to hypoxemia. Computer simulation based on the inverse Monte Carlo method showed that hemoglobin oxygen saturation declined to as low as ∼35% in the long-term hypoxemic phase. Overall, we found that topical application of a shock wave to the brain caused spreading depolarization/depression and prolonged severe hypoxemia-oligemia, which might lead to pathological conditions in the brain. Although further study is needed, our findings suggest that spreading depolarization/depression is one of the key events determining the outcome in bTBI. Furthermore, a rat exposed to an LISW(s) can be a reliable laboratory animal model for blast injury research.

title: Perspectives on spreading depression
abstract: Spreading depression (SD) consists of a transient suppression of all neuronal activity that spreads slowly across regions of gray matter. The paper is divided into three parts. Martins-Ferreira describes 30 years of research on SD in the isolated retina. Much of this work has relied on the prominent intrinsic optical signals that accompany SD in the retina. By inducing SD to propagate in circles with a velocity of 3.7 mm min(-1), it is possible to investigate the finely balanced electrochemical equilibrium that maintains the traveling wave. SD is accompanied by a slow negative extracellular voltage and ion movements that are greatest in the inner plexiform layer of the retina. Nedergaard discusses the role of astrocytes in SD propagation. Astrocytes mediate slowly moving waves of intracellular Ca(2+) increase, for which gap junctions are essential. SD is accompanied by entry of Ca(2+) into cells and fails when gap junctions are blocked. SD, however, is blocked by glutamate receptor antagonists but glial Ca(2+) waves are not. Astrocytic Ca(2+) waves are probably involved in the initiation of SD but other factors, including K(+), glutamate and purinergic receptors, are necessary for sustained propagation. Nicholson describes studies on the different preparations that helped clarify the role of extracellular space in SD. It has long been known that extracellular K(+) reaches levels of 50 mM or more during SD. Studies with ion-selective microelectrodes showed that extracellular Na(+) and Cl(-) fall by as much as 100 mM during SD, and water leaves the extracellular space. Further work showed that extracellular Ca(2+) falls 10-fold during SD and significant changes in extracellular pH and ascorbate occur. These studies imply that large perturbations of the extracellular milieu occur during SD and are an essential part of the interlocking cascade of events that produce this still mysterious phenomenon.

title: The role of spreading depression, spreading depolarization and spreading ischemia in neurological disease
abstract: The term spreading depolarization describes a wave in the gray matter of the central nervous system characterized by swelling of neurons, distortion of dendritic spines, a large change of the slow electrical potential and silencing of brain electrical activity (spreading depression). In the clinic, unequivocal electrophysiological evidence now exists that spreading depolarizations occur abundantly in individuals with aneurismal subarachnoid hemorrhage, delayed ischemic stroke after subarachnoid hemorrhage, malignant hemispheric stroke, spontaneous intracerebral hemorrhage or traumatic brain injury. Spreading depolarization is induced experimentally by various noxious conditions including chemicals such as potassium, glutamate, inhibitors of the sodium pump, status epilepticus, hypoxia, hypoglycemia and ischemia, but it can can also invade healthy, naive tissue. Resistance vessels respond to it with tone alterations, causing either transient hyperperfusion (physiological hemodynamic response) in healthy tissue or severe hypoperfusion (inverse hemodynamic response, or spreading ischemia) in tissue at risk for progressive damage, which contributes to lesion progression. Therapies that target spreading depolarization or the inverse hemodynamic response may potentially treat these neurological conditions.

title: Genetic and hormonal factors modulate spreading depression and transient hemiparesis in mouse models of familial hemiplegic migraine type 1.
abstract: Familial hemiplegic migraine type 1 (FHM1) is an autosomal dominant subtype of migraine with aura that is associated with hemiparesis. As with other types of migraine, it affects women more frequently than men. FHM1 is caused by mutations in the CACNA1A gene, which encodes the alpha1A subunit of Cav2.1 channels; the R192Q mutation in CACNA1A causes a mild form of FHM1, whereas the S218L mutation causes a severe, often lethal phenotype. Spreading depression (SD), a slowly propagating neuronal and glial cell depolarization that leads to depression of neuronal activity, is the most likely cause of migraine aura. Here, we have shown that transgenic mice expressing R192Q or S218L FHM1 mutations have increased SD frequency and propagation speed; enhanced corticostriatal propagation; and, similar to the human FHM1 phenotype, more severe and prolonged post-SD neurological deficits. The susceptibility to SD and neurological deficits is affected by allele dosage and is higher in S218L than R192Q mutants. Further, female S218L and R192Q mutant mice were more susceptible to SD and neurological deficits than males. This sex difference was abrogated by ovariectomy and senescence and was partially restored by estrogen replacement, implicating ovarian hormones in the observed sex differences in humans with FHM1. These findings demonstrate that genetic and hormonal factors modulate susceptibility to SD and neurological deficits in FHM1 mutant mice, providing a potential mechanism for the phenotypic diversity of human migraine and aura.

title: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy syndrome mutations increase susceptibility to spreading depression
abstract: Migraine with aura is often the first manifestation of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy syndrome (CADASIL), a disorder caused by NOTCH3 gene mutations expressed predominantly in vascular smooth muscle. Here, we report that cortical spreading depression (CSD), the electrophysiological substrate of migraine aura, is enhanced in mice expressing a vascular Notch 3 CADASIL mutation (R90C) or a Notch 3 knockout mutation. The phenotype was stronger in Notch 3 knockout mice, implicating both loss of function and neomorphic mutations in its pathogenesis. Our results link vascular smooth muscle Notch 3 mutations to enhanced spreading depression susceptibility, implicating the neurovascular unit in the development of migraine aura.

title: Nitric Oxide Modulates Spreading Depolarization Threshold in the Human and Rodent Cortex
abstract: Recent clinical data have suggested that prolonged cortical spreading depolarizations (CSDs) contribute to the pathogenesis of delayed ischemic neurologic deficits after subarachnoid hemorrhage. Elevated extracellular potassium concentrations and lowered nitric oxide (NO) levels have been detected in experimental and clinical subarachnoid hemorrhage. We investigated whether a similar extracellular composition renders the brain more susceptible to CSDs.  Electrophysiologic and blood flow changes were studied in vivo in rats. Intrinsic optical signals, alterations of NO level, and electrophysiologic changes were investigated in rodent and human brain slices.  Elevation of subarachnoid extracellular potassium in rats in vivo triggered CSDs. Using NO-sensitive dyes, we found that CSDs induce NO synthesis in neurons and endothelial cells. When we blocked NO synthesis in vivo, CSDs occurred at a significantly lower threshold and propagated with a wave of ischemia. This increased susceptibility for CSDs by a low NO level was confirmed in rat and human neocortical slices and depended on P/Q-type calcium channels and N-methyl-d-aspartate receptors, but not on guanylate cyclase. Mice deficient in endothelial NO synthase, in contrast to mice deficient in neuronal NO synthase, had an inherently lower threshold.  Basal NO production determined CSD threshold. The threshold effect depended predominantly on endothelial NO synthase. Reduced NO levels, as in patients with subarachnoid hemorrhage, may render the brain more susceptible to CSDs. Because CSDs have been linked to the pathogenesis of delayed ischemic neurologic deficits, raising its threshold by increasing NO availability may prove therapeutically beneficial in patients with subarachnoid hemorrhage.

title: Modulation of spreading depression by changes in extracellular pH.
abstract: Spreading depression (SD) and related phenomena have been implicated in hypoxic-ischemic injury. In such settings, SD occurs in the presence of marked extracellular acidosis. SD itself can also generate changes in extracellular pH (pH(o)), including a pronounced early alkaline shift. In a hippocampal slice model, we investigated the effect of interstitial acidosis on the generation and propagation of SD in the CA1 stratum radiatum. In addition, a carbonic anhydrase inhibitor (benzolamide) was used to decrease buffering of the alkaline shift to investigate its role in the modulation of SD. pH(o) was lowered by a decrease in saline HCO(3)(-) (from 26 to 13 to 6.5 mM at 5% CO(2)), or by an increase in the CO(2) content (from 5 to 15% in 26 mM HCO(3)(-)). Recordings with pH microelectrodes revealed respective pHo values of 7.23 +/- 0. 13, 6.95 +/- 0.10, 6.67 +/- 0.09, and 6.97 +/- 0.12. The overall effect of acidosis was an increase in the threshold for SD induction, a decrease in velocity, and a shortened SD duration. This inhibition was most pronounced at the lowest pH(o) (in 6.5 mM HCO(3)(-)) where SD was often blocked. The effects of acidosis were reversible on return to control saline. Benzolamide (10 microM) caused an approximate doubling of the early alkaline shift to an amplitude of 0.3-0.4 U pH. The amplified alkalosis was associated with an increased duration and/or increased velocity of the wave. These effects were most pronounced in acidic media (13 mM HCO(3)(-)/5% CO(2)) where benzolamide increased the SD duration by 55 +/- 32%. The initial velocity (including time for induction) and propagation velocity (measured between distal electrodes) were enhanced by 35 +/- 25 and 26 +/- 16%, respectively. Measurements of [Ca(2+)](o) demonstrated an increase in duration of the Ca(2+) transient when the alkaline shift was amplified by benzolamide. The augmentation of SD caused by benzolamide was blocked in media containing the N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonovaleric acid. These data indicate that the induction and propagation of SD is inhibited by a fall in baseline pH characteristic of ischemic conditions and that the early alkaline shift can remove this inhibition by relieving the proton block on NMDA receptors. Under ischemic conditions, the intrinsic alkalosis may therefore enable SD and thereby contribute to NMDA receptor-mediated injury.

title: Spreading Depression: From Serendipity to Targeted Therapy in Migraine Prophylaxis
abstract: Despite the relatively well-characterized headache mechanisms in migraine, upstream events triggering individual attacks are poorly understood. This lack of mechanistic insight has hampered a rational approach to prophylactic drug discovery. Unlike targeted abortive and analgesic interventions, mainstream migraine prophylaxis has been largely based on serendipitous observations (e.g. propranolol) and presumed class effects (e.g. anticonvulsants). Recent studies suggest that spreading depression is the final common pathophysiological target for several established or investigational migraine prophylactic drugs. Building on these observations, spreading depression can now be explored for its predictive utility as a preclinical drug screening paradigm in migraine prophylaxis.

title: Metabolic and Hemodynamic Activation of Postischemic Rat Brain by Cortical Spreading Depression
abstract: Following transient ischemia of the brain, the coupling between somatosensory activation and the hemodynamic-metabolic response is abolished for a certain period despite the partial recovery of somatosensory evoked responses. To determine whether this disturbance is due to alterations of the stimulus-induced neuronal excitation or to a breakdown of the coupling mechanisms, cortical spreading depression was used as a metabolic stimulus in rats before and after ischemia. Adult rats were subjected to 30 min of global forebrain ischemia and 3–6 h of recirculation. EEG, cortical direct current (DC) potential, and laser-Doppler flow were continuously recorded. Local CBF (LCBF), local CMRglc (LCMRglc), regional tissue contents of ATP, glucose, and lactate, and regional pH were determined by quantitative autoradiography, substrate-induced bioluminescence, and fluorometry. Amplitude and frequency of the DC shifts did not differ between groups. In control animals, spreading depression induced a 77% rise in cortical glucose consumption, a 66% rise in lactate content, and a drop in tissue pH of 0.3 unit. ATP and glucose contents were not depleted. During the passage of DC shifts, transient increases (<2 min) in laser-Doppler flow were observed, followed by a post-spreading depression hypoperfusion. A comparable although less expressed pattern of hemodynamic and metabolic changes was observed in the postischemic rats. Although baseline LCMRglc was depressed after ischemia, it was activated 47% during spreading depression. Lactate increased by 26%, pH decreased by 0.3 unit, and ATP and glucose remained unchanged. The extent of the transient increase in laser-Doppler flow did not differ from that of the control group, and a post–spreading depression hypoperfusion was also found. The results demonstrate that the postischemic brain may, although to a lesser degree, cover additional energy demands. The previously observed suppression of functional activation after ischemia is probably caused by both alterations in afferent synaptic transmission and subsequent neuronal excitation and the diminution of the metabolic response to a local stimulus as observed during spreading depression.

title: SOME METABOLIC CHANGES ACCOMPANYING LEÃO'S SPREADING CORTICAL DEPRESSION IN THE RAT
abstract: IN 1944 L E ~ O described a particular electrical reaction of the cerebral cortex to stimuli acting directly on its surface. Electrical, mechanical and chemical stimuli cause a local decrease in amplitude of the spontaneous EEG. This decrease spreads slowly at a rate 3-6 mm/min in all directions over the whole cortex. Complete recovery of the original activity occurs after from 10 to 20 min. The front of the wave of spreading depression is accompanied by a striking slow potential change. The initial surface negativity, attaining 5-10 mv in amplitude, is replaced after 1-2 min by a lower wave of longer lasting positivity. A new wave can be produced from the same focus after a minimum recovery period of 4-5 min (L&o, 1944). Since the discovery of this phenomenon various aspects of it have been studied (see recent review by MARSHALL, 1959). The electrophysiological properties of spreading depression are already well known but the mechanism of initiation and spreading is still obscure. Some properties of spreading depression seem to indicate that metabolical changes are involved: ( I ) The rate of spreading is slow; (2) the slow potential change is temperature dependent with a Qlo = 1.8 ( B u d , 1956); (3) the decrease of cortical PO, during spreading depression is not caused by vasoconstriction, as was assumed by VAN HARREVELD and STAMM (1952), but rather by increased oxygen utilization due to vasodilatation (BURFSOVA, 1957); (4) the analogy between the initiation of spreading depression in vivo and the increase in respiration and aerobic glycolysis of cerebral cortex slices in vitro (BUR&, 1956). A decrease in glycogen in the rat brain during spreading depression has been observed (K~IVANEK, 1958). In the experiments reported in the present paper a more precise correlation between electrical and chemical changes has been attempted.

title: Cortical Spreading Depression is Associated with Arachidonic Acid Accumulation and Preservation of Energy Charge
abstract: The present study aimed to study the relation between the release of arachidonic acid (AA) and the energy state in cerebral cortices of rats during single episodes of cortical spreading depression (CSD). The changes in concentrations of AA, labile phosphate compounds [ATP, ADP, AMP, and phosphocreatine (PCr)], and glycolytic metabolites (lactate, pyruvate, glucose, and glycogen) were studied during and following the large change of the local direct current (DC) potential. Free AA increased markedly during the DC shift, continued to increase during the subsequent 3 min, and returned to control levels at 4–5 min after CSD. PCr decreased by 38% in the first minutes following the DC shift, while ADP increased by 38%. Both returned to normal within a few minutes. ATP, AMP, and energy charge remained constant throughout the experimental period. Glucose decreased by 47% and glycogen by 34% for a few minutes following CSD, while lactate increased by 105% at 2–3 min and by 77% at 4–5 min after CSD. The metabolites returned to control levels at 10 min after CSD. Considering the constant energy charge at all time points during CSD, it is suggested that the AA rise reflects augmented phospholipase activity due to either increased intracellular [Ca2+] or receptor stimulation or both. The possibility that N-methyl-d-aspartate receptors play a role in the release of AA, and that free AA in turn could be part of the mechanism of CSD, is discussed.

title: Changes in energy metabolites, cGMP and intracellular pH during cortical spreading depression
abstract: The spatial and temporal distribution of cerebral metabolites and pHi were examined in the cortex during spreading depression. Acidification and marked depression in the energy status of the tissue was evident at the wavefront of spreading depression. In its aftermath, the residual activation of glycolysis and accumulation of cGMP persisted for minutes after a relatively rapid restoration of high-energy phosphates and pHi.

title: Regional changes of blood flow, glucose, and ATP content determined on brain sections during a single passage of spreading depression in rat brain cortex
abstract: Hemodynamic and biochemical substrate changes are associated with cortical spreading depression (CSD). Regional methods were used to measure blood flow, and glucose and ATP concentrations in intact brain sections in rats undergoing a single passage of cortical spreading depression. Changes were expressed as the percentages of the contralateral homotopic area of the unaffected cortex. A depression in tissue ATP content preceded the negative DC potential shift and ATP was reduced by 12% (P less than 0.01) despite unaltered blood flow and glucose concentration. When the negative shift of DC potential reached its maximum, glucose content decreased to 72% of control (P less than 0.01) and was accompanied by a further ATP decrease to 54%. When the cortical steady potential declined, blood flow was elevated twofold (P less than 0.01). The ATP content gradually returned to normal; however, cortical glucose concentrations remained at 55% of control values. The relationship of blood flow and glucose and ATP concentration with other known changes during spreading depression are discussed. With the advantage of higher resolution the provided techniques may be a useful tool for studies on hemodynamic and biochemical changes of other pathophysiologic conditions.

title: Compromised metabolic recovery following spontaneous spreading depression in the penumbra
abstract: Spreading depression (SD) has been demonstrated following focal ischemia, and the additional workload imposed by SD on a tissue already compromised by a marked reduction in blood flow may contribute to the evolution of irreversible damage in the ischemic penumbra. SD was elicited in one group of rats by injecting KCl directly into a frontal craniectomy and the wave of depolarization was recorded in two craniectomies 3 and 6 mm posterior to the first one. In a second group, the middle cerebral artery was occluded using the monofilament technique and a recording electrode was placed 5 mm lateral to the midline and 0.2 mm posterior to bregma. To determine the metabolic response in the penumbral region of the cortex ipsilateral to the occlusion, brains from both groups were frozen in situ when the deflection of the SD was maximal. The spatial metabolic response of SD in the ischemic cortex was compared to that in the non-ischemic cortex. Coronal sections of the brains were lyophilized, pieces of the dorsolateral cortex were dissected and weighed, and analyzed for ATP, P-creatine, inorganic phosphate (Pi), glucose, glycogen and lactate at varying distances anterior and posterior to the recording electrode. ATP and P-creatine levels were significantly decreased at the wavefront in both groups and the levels recovered after passage of the wavefront in the normal brain, but not in the ischemic brain. Glucose and glycogen levels were significantly decreased and lactate levels significantly increased in the tissue after the passage of the wavefront. While the changes in the glucose-related metabolites persisted during recovery even in anterior portions of the cortex in both groups in the aftermath of the SD, the magnitude of the changes was greater in the penumbra than in the normal cortex. SD appears to impose an equivalent increase in energy demands in control and ischemic brain, but the ability of the penumbra to recover from the insult is compromised. Thus, increasing the energy imbalance in the penumbra after multiple SDs may hasten the deterioration of the energy status of the tissue and eventually contribute to terminal depolarization and cell death, particularly in the penumbra.

title: ATP and Brain Function
abstract: The importance of A TP as the main source of chemical energy in living matter and its involve­ ment in cellular processes has long been recog­ nized. The primary mechanism whereby higher or­ ganisms, including humans, generate ATP is through mitochondrial oxidative phosphorylation. For the majority of organs, the main metabolic fuel is glucose, which in the presence of oxygen under­ goes complete combustion to CO2 and H20: C6H1206 + 602 � 602 + 6H20 + energy ( 1) The free energy (.:lG) liberated in this exergonic re­ action is partially trapped as ATP in two consecu­ tive processes: glycolysis (cytosol) and oxidative phosphorylation (mitochondria). The first produces 2 mol of ATP per mol of glucose, and the second 36 mol of ATP per mol of glucose. In the latter case, 6 mol of ATP are contributed from the oxidation of 2 mol of NADH generated in the cytosol during gly­ colysis and transferred into the mitochondria indi­ rectly through various "shuttle" systems. (In the a-glycerophosphate shuttle, the yield of ATP per NADH is reduced from 3 to 2 because the relevant mitochondrial dehydrogenase is a flavoprotein­ linked enzyme). Thus, oxidative phosphorylation yields 1718 times as much useful energy in the form of ATP as can be obtained from the same amount of glucose by glycolysis alone. It is there­ fore not surprising that limitation of O2 supply pro­ duces very damaging effects on cellular function. The brain is one of the organs that is particularly sensitive to lack of oxygen and in humans at rest is responsible for 20% of total O2 consumption al­ though it accounts for only 2% of the body weight. The role of energy in the maintenance of central

title: Extracellular changes of inorganic phosphate are different during spreading depression and global cerebral ischemia of rats
abstract: Tissue levels of inorganic phosphate (iP-) and lactate (lac) increase during cerebral ischemia and cortical spreading depression (SD). Since cell membranes become leaky during these insults, iP- and lac were expected to leak into the extracellular space (ECS). In order to find out whether this occurs or does not, a microdialysis (MD) fiber was implanted into the cortex of anesthetized rats and extracellular lactate (lac(e)) and extracellular iP- (iPe-) were determined during various insults. Extracellular lactate increased to about the same extent during ischemia and SD. In contrast, iPe- increased during ischemia but not during SD. Instead, iPe- started to rise after SD and reached its maximum about 45 min later. The distinct pattern of iPe- in comparison to lac(e) during the above mentioned insults points to a qualitative difference of the underlying mechanisms: whereas lac appears within the ECS at any stressful situation, elevation of iP- within the ECS indicates depletion of energy stores in parallel to the lack of control of ion homeostasis.

title: Blood‐Brain Glucose Transfer in Spreading Depression
abstract: Spreading depression in rat brain cortex is associated with a twofold increase of cerebral blood flow. It is not known whether this increase is coupled to increases of cerebral metabolic rate and glucose transport from blood to brain. During the passage of a single spreading depression, we measured blood‐brain glucose transport and glucose metabolism in rat cerebral cortex by single intravenous injection of tracer glucose. Blood flow and tissue content of glucose were measured as well. Reduction of tissue glucose and the consequent increase of net transfer of glucose from blood to brain were consistent with a threefold increase of the consumption of glucose before the increase of blood flow. There was no increase of unidirectional blood‐brain transfer.

title: Uncoupling of cerebral blood flow and metabolism after single episode of cortical spreading depression in the rat brain
abstract: The present study was undertaken to evaluate whether the persistent hypoperfusion following cortical spreading depression (CSD) in rat brain was accompanied by alterations of regional cortical glucose consumption (rCGU). rCGU was measured using 2-deoxy-[14C]glucose and autoradiography at 15-60 min after single CSD episodes. rCGU did not differ in cortical regions invaded by CSD as compared to the contralateral side and to sham-treated rats. The results suggested impairment of the metabolism-flow couple after CSD.

title: Device for simultaneous positron emission tomography, laser speckle imaging and RGB reflectometry: Validation and application to cortical spreading depression and brain ischemia in rats
abstract: Brain function critically relies on the supply with energy substrates (oxygen and glucose) via blood flow. Alterations in energy demand as during neuronal activation induce dynamic changes in substrate fluxes and blood flow. To study the complex system that regulates cerebral metabolism requires the combination of methods for the simultaneous assessment of multiple parameters. We developed a multimodal imaging device to combine positron emission tomography (PET) with laser speckle imaging (LSI) and RGB reflectometry (RGBR). Depending on the radiotracer, PET provides 3-dimensional quantitative information of specific molecular processes, while LSI and RGBR measure cerebral blood flow (CBF) and hemoglobin oxygenation at high temporal and spatial resolution. We first tested the functional capability of each modality within our system and showed that interference between the modalities is negligible. We then cross-calibrated the system by simultaneously measuring absolute CBF using (15)O-H2O PET (CBF(PET)) and the inverse correlation time (ICT), the LSI surrogate for CBF. ICT and CBF(PET) correlated in multiple measurements in individuals as well as across different animals (R(2)=0.87, n=44 measurements) indicating that ICT can be used for absolute quantitative assessment of CBF. To demonstrate the potential of the combined system, we applied it to cortical spreading depression (CSD), a wave of transient cellular depolarization that served here as a model system for neurovascular and neurometabolic coupling. We analyzed time courses of hemoglobin oxygenation and CBF alterations coupled to CSD, and simultaneously measured regional uptake of (18)F-2-fluoro-2-deoxy-D-glucose ((18)F-FDG) used as a radiotracer for regional glucose metabolism, in response to a single CSD and to a cluster of CSD waves. With this unique combination, we characterized the changes in cerebral metabolic rate of oxygen (CMRO2) in real-time and showed a correlation between (18)F-FDG uptake and the number of CSD waves that passed the local tissue. Finally, we examined CSD spontaneously occurring during focal ischemia also referred to as peri-infarct depolarization (PID). In the vicinity of the ischemic territory, we observed PIDs that were characterized by reduced CMRO2 and increased oxygen extraction fraction (OEF), indicating a limitation of oxygen supply. Simultaneously measured PET showed an increased (18)F-FDG uptake in these regions. Our combined system proved to be a novel tool for the simultaneous study of dynamic spatiotemporal alterations of cortical blood flow, oxygen metabolism and glucose consumption under normal and pathologic conditions.

title: Simultaneous Measurement of Blood Flow and Glucose Metabolism By Autoradiographic Techniques
abstract: A double tracer autoradiographic technique using 131I-iodo-antipyrine and 14C-deoxyglucose is presented for the simultaneous measurement of blood flow and cerebral glucose utilization in the same animal. 131I is a gamma emitting isotope with a half life of 8.06 days and can be detected with adequate resolution on standard autoradiographic films. Autoradlograms are made before and after decay of 131I; the time interval between the 2 exposures and the concentration of the 2 tracers is adjusted to avoid significant cross-contamination. In this way, 2 film exposures are obtained which can be processed quantitatively like single tracer autoradiograms. The validity of the method for the investigation of local coupling of flow and metabolism was tested under various physiological and pathophysiological conditions. Coupling was tight in barbiturate-anesthetized healthy animals, but not under halothane anesthesia where uncoupling occurred in various subcortical structures. Focal seizures induced by topical application of penicillin on the cortical surface led to a coupled increase of metabolism and flow in thalamic relay nuclei but not at the site of penicillin administration where increased glucose utilization was not accompanied by similar increase in blood flow. Both coupled and uncoupled increases in local glucose utilization were observed in spreading depression and in circumscribed areas of experimental brain tumors. The results obtained demonstrate that double tracer autoradiography allows the very precise local assessment of cerebral blood flow and glucose utilization, and, therefore, is particularly suited to the study of regional coupling processes under various experimental conditions.

title: Cerebral glucose utilization: local changes during and after recovery from spreading cortical depression.
abstract: Cerebral glucose utilization is markedly increased in most areas of the cerebral cortex and reduced in many subcortical structures during spreading cortical depression. During recovery, cortical glucose utilization is still elevated, but the increased metabolic activity is distributed in columns running perpendicularly through the cortex.

title: Rapid Efflux of Lactate from Cerebral Cortex during K+-Induced Spreading Cortical Depression
abstract: Rapid transport of lactate from activated brain regions to blood, perhaps reflecting enhanced metabolite trafficking, would prevent local trapping of labeled metabolites of [6-14C]glucose and cause underestimation of calculated CMRglc. Because the identities of glucose metabolites lost from activated structures and major routes of their removal are not known, arteriovenous differences across brains of conscious normoxic rats for derivatives of [6-14C]glucose were determined under steady-state conditions in blood during K+-induced spreading cortical depression. Lactate was identified as the major labeled product lost from brain. Its entry to blood was detected within 2 minutes after a pulse of [6-14C]glucose, and it accounted for 96% of the 14C lost from brain within approximately 8 minutes. Lactate efflux corresponded to 20% of glucose influx, but accounted for only half the magnitude of underestimation of CMRglc when [14C]glucose is the tracer, suggesting extensive [14C]lactate trafficking within brain. [14C]Lactate spreading within brain is consistent with (1) relatively uniform pattern labeling of K+-treated cerebral cortex by [6-14C]glucose contrasting heterogeneous labeling by [14C]deoxyglucose, and (2) transport of 14C-labeled lactate and inulin up to 1.5 and 2.4 mm, respectively, within 10 minutes. Thus, newly synthesized lactate exported from activated cells rapidly flows to blood and probably other brain structures.

title: Regional changes in tissue pH and glucose content during cortical spreading depression in rat brain
abstract: After eliciting a single passage of spreading depression in rat brain cortex, regional alterations in glucose content and tissue pH were studied in relation to changes in cortical steady potential. Migration of spreading depression into non-invaded cortex was accompanied by a drastic decrease in glucose concentration and tissue pH which persisted longer than the transient depolarization of cortical cells. This delay in metabolic recovery is probably accounted for by severe tissue acidosis which results from the stimulation of anaerobic glycolysis.

title: Extracellular pH Changes during Spreading Depression and Cerebral Ischemia: Mechanisms of Brain pH Regulation
abstract: We have examined the extracellular pH (pHe) during spreading depression and complete cerebral ischemia in rat parietal cortex utilizing double-barrelled H+ liquid ion exchanger microelectrodes. The baseline pHe of the parietal cortex was 7.33 at a mean arterial Pco2 of 38 mm Hg. Following spreading depression and cerebral ischemia, highly reproducible triphasic changes in pHe occurred, which were intimately related to the negative deflection in tissue potential (Ve). The changes in pHe for spreading depression (n = 23) were a small initial acidic shift, beginning before the rapid change in Ve, followed by a rapid transient alkaline shift of 0.16 pH units, the onset of which coincided with the negative deflection in Ve. A prolonged acidic shift of 0.42 pH units then occurred. The maximal decrease in pHe was to 6.97 and the mean duration of the triphasic pHe change was 7.8 min. The lactate concentration in brain cortex increased from baseline 1.2 mM to 7.0 mM (n = 6) during the maximal acidic change in spreading depression. In addition, lactate levels correlated well with resolution of the pHe changes during spreading depression. The triphasic pHe changes following complete cerebral ischemia were an initial acidic shift of 0.43 pH units which developed over 2 min, then an alkaline shift of 0.10 pH units coincident with the negative deflection in Ve, and a final acidic shift of 0.26 pH units. The terminal pHe was 6.75. Superfusion of the cortex with inhibitors of carbonic anhydrase (acetazolamide), Na+/H+ counter transport (amiloride), and Cl−/HCO3− countertransport (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) altered the triphasic pHe changes in a similar fashion for both spreading depression and cerebral ischemia, providing insights into the pHe regulatory mechanisms in mammalian brain.

title: Continuous Online Microdialysis Using Microfluidic Sensors: Dynamic Neurometabolic Changes during Spreading Depolarization
abstract: Microfluidic glucose biosensors and potassium ion selective electrodes were used in an in vivo study to measure the neurochemical effects of spreading depolarizations (SD), which have been shown to be detrimental to the injured human brain. A microdialysis probe implanted in the cortex of rats was connected to a microfluidic PDMS chip containing the sensors. The dialysate was also analyzed using our gold standard, rapid sampling microdialysis (rsMD). The glucose biosensor performance was validated against rsMD with excellent results. The glucose biosensors successfully monitored concentration changes, in response to SD wave induction, in the range of 10–400 μM with a second time-resolution. The data show that during a SD wave, there is a time delay of 62 ± 24.8 s (n = 4) between the onset of the increase in potassium and the decrease in glucose. This delay can be for the first time demonstrated, thanks to the high-temporal resolution of the microfluidic sensors sampling from a single tissue site (the microdialysis probe), and it indicates that the decrease in glucose is due to the high demand of energy required for repolarization.

title: Lactate and pH change in close correlation in the extracellular space of the rat brain during cortical spreading depression
abstract: pH sensitive microcelectrodes were used in combination with microdialysis (MD) technique to measure extracellular pH (pHe) and extracellular lactate (lace) within the cortex of rat brains during cortical spreading depression (SD). SD was induced by local K(+)-application and identified by DC recordings. It was accompanied by an extracellular acidification of 0.34 +/- 0.06 pH units and by a 2.8 +/- 0.80 fold increase of lace; the recovery of pHe took place within three phases, that of lace within 2 phases. The recovery of both parameters was complete about 45 min after the onset of SD. We conclude that the changes of lace and pHe are closely related. This indicates both lactate and protons to be transported in parallel.

title: Alkaline and acid transients in cerebellar microenvironment.
abstract: 1. Extracellular pH (pHo) was measured in the cerebellar cortex of the rat using a recently developed liquid membrane ion-selective micropipette (ISM). pHo was determined during stimulus-evoked neuronal activity, elevated extracellular potassium concentration, [K+]o, spreading depression (SD), and complete ischemia. In many experiments [K+]o was simultaneously determined. 2. A train of local surface stimuli (LOC) produced an initial alkaline shift in pHo from a base line of 7.20-7.30 to 7.25-7.35. This was followed by a long-lasting acid phase that reached a plateau of 7.05-7.15 after 64 s of stimulation. pHo decrease was related to stimulus frequency, intensity, and duration. 3. Superfusion with Ringer solution containing manganese ions rapidly abolished parallel fiber-induced Purkinje cell synaptic depolarization together with the alkaline shifts while enhancing the acid shifts. 4. Superfusion of the cerebellar cortex with Ringer solution containing increasingly elevated [K+] progressively lowered pHo to a plateau of 6.95-7.05. The acidification occurred in the presence of ouabain but was reversed on return to the normal [K+]o or with the addition of the glycolytic blocker, fluoride. Stimulus-evoked alkaline shifts were enhanced by K+-Ringer superfusion. These experiments suggested that the acid shift was due to the metabolic production of an anion, possibly lactate. 5. Elevation of [K+]o above 8-12 mM often produced oscillation in pHo and [K+]o with a period of about 40 s. Sometimes these oscillations ended in a spontaneous SD or SD could be evoked by stimulation. Under these conditions of raised [K+]o, the SD consisted of a very pronounced alkaline transient followed by a small, long-lasting acid shift. When SD was induced by conditioning the cerebellum with proprionate or lowered NaCl, the alkaline phase was reduced and the acid enhanced. 6. Complete ischemia began with a progressive decrease of pHo and rise in [K+]o. When [K+]o reached 12 mM, a second more rapid rise in [K+]o to 40 mM or more occurred. This was correlated with 0.1-0.2 pHo transient increase similar to that seen during SD. pHo eventually reached a plateau of 6.60-6.80, close to neutrality. 7. Superfusion with Ringer solution containing acetazolamide immediately altered pHo homeostasis by increasing base-line pHo by about 0.10 and enhanced the induced pHo changes. These results suggest that carbonic anhydrase (CA) is important for acute buffering of the brain extracellular microenvironment. 8. The above results were interpreted in terms of changes in extracellular strong ion concentration differences ( [SID]o), extracellular concentration of total weak acid ( [Atot]o) and partial pressure of CO2 (Pco2) in the brain microenvironment. The results indicate that neuronal activity produces changes in many of the constituents of the microenvironment.

title: MEASUREMENT OF CORTICAL PH IN SPREADING CORTICAL DEPRESSION.
abstract: The pH of the rabbit cortex was measured during the course of spreading cortical depression. Spreading cortical depression was elicited by chemical (group I) and by electrical (group II) means.

title: Simultaneous monitoring of intracellular pH changes and hemodynamic response during cortical spreading depression by fluorescence-corrected multimodal optical imaging
abstract: Cortical spreading depression (CSD) plays an important role in trauma, migraine and ischemia. CSD could induce pronounced hemodynamic changes and the disturbance of pH homeostasis which has been postulated to contribute to cell death following ischemia. In this study, we described a fluorescence-corrected multimodal optical imaging system to simultaneously monitor CSD associated intracellular pH (pH(i)) changes and hemodynamic response including hemoglobin concentrations and cerebral blood flow (CBF). CSD was elicited by application of KCl on rat cortex and direct current (DC) potential was recorded as a typical characteristic of CSD. The pH(i) shift was mapped by neutral red (NR) fluorescence which was excited at 516-556 nm and emitted at 625 nm. The changes in hemoglobin concentrations were determined by dual-wavelength optical intrinsic signal imaging (OISI) at 550 nm and 625 nm. Integration of fluorescence imaging and dual-wavelength OISI was achieved by a time-sharing camera equipped with a liquid crystal tunable filter (LCTF). CBF was visualized by laser speckle contrast imaging (LSCI) through a separate camera. Besides, based on the dual-wavelength optical intrinsic signals (OISs) obtained from our system, NR fluorescence was corrected according to our method of fluorescence correction. We found that a transient intracellular acidification followed by a small alkalization occurred during CSD. After CSD, there was a prolonged intracellular acidification and the recovery of pH(i) from CSD took much longer time than those of hemodynamic response. Our results suggested that the new multimodal optical imaging system had the potential to advance our knowledge of CSD and might work as a useful tool to exploit neurovascular coupling under physiological and pathological conditions.

title: Changes in cortical pH and blood flow accompanying spreading cortical depression and convulsion.
abstract: Local changes in cerebral cortex hydrogen ion concentration of as much as 0.5 ph units were observed to accompany the waves of cortical spreading depression or convulsion in cats and rabbits. A diphasic wave consisting of an initial alkaline followed by a more prolonged acid shift was observed in most cases. No significant differences were found between the ph changes accompanying spreading depression and those accompanying spreading convulsion. These ph shifts, like the abnormal ECG activity and the slowly changing potential wave which accompanied them, spread over the surface of the cerebral cortex with a velocity of 1–3 mm/min. The curve of cortical ph change is coincident with, and similar in shape to, the slowly changing potential difference measured between a point on the cortical surface and the jugular blood. For every unit change in ph, the cortex-blood P.D. is shifted approximately 30 mv. It is suggested that the slowly changing potential difference arises across the blood-brain barrier rather than as a result of depolarization of neuronal membranes. A significant but variable change in local blood flow accompanied the spreading depression.

title: Ischemic Brain Slice Glucose Utilization: Effects of Slice Thickness, Acidosis, and K+
abstract: Brain slices of varying thickness were used to modify retention of metabolic products in an in vitro model of ischemia. Past and present results reveal increased anaerobic glycolysis in 660-μm slices with accumulation of lactate as slice thickness reaches 1,000 μm. Brain slice glucose utilization and lactate content were measured in buffers of various extracellular K+ levels and pH in 540-, 660-, and 1,000-μm slices. Acidosis suppresses glucose utilization at all slice thicknesses without affecting tissue lactate. Studies of 2-deoxyglucose metabolites establish that the suppression of glucose utilization by acidosis is due entirely to inhibition of glucose phosphorylation without any effect on glucose uptake into tissue. The inhibition is reversible after 45 min at pH 6.1. The experiments with acidosis also suggest that persistent energy demands continue to stimulate phosphofructokinase despite the low pH so that glycolysis continues, with potential for injury. Increasing K+ increases glucose utilization and tissue lactate at all three thicknesses. Correlations of glucose utilization with lactate accumulation support the possibility that high K+ may exert a dual influence on the tissue metabolism, not only stimulating glucose utilization by inducing depolarization but also by influencing the removal of metabolic products.

title: Effect of pH on the kinetics of frog muscle phosphofructokinase.
abstract: Under appropriate conditions, the activity of phosphofructokinase of skeletal muscle from frog and mouse is extremely sensitive to small changes in pH in the physiological range, a low pH decreasing the affinity of the enzyme for fructose 6-phosphate. It is concluded that shifts in intracellular pH are important in the regulation of phosphofructokinase, but that this effect makes interpretation of data from intact muscle quite difficult.

title: CHANGES OF BRAIN GLYCOGEN IN THE SPREADING EEG—DEPRESSION OF LEAO
abstract: THE spreading depression of EEG activity is one of the manifestations of cerebral cortical functions which has not, so far, been chemically analysed. Various electrical, mechanical and chemical stimuli evoke at their point of action on the surface of the cerebral cortex a local decrease in the amplitude of the EEG, which spreads slowly at a rate of 3-6 mm/min along the surface of the hemisphere (LEAO, 1944). The front of the depression wave is accompanied by a negative potential lasting for 1 min and reaching an amplitude of 7-10 mv. The spreading depression (sp. D.) is independent of the depth of narcosis or of short-lasting anoxia (LEAO and MOWN, 1945; LEAO, 1947). According to some authors (SLOAN and JASPER, 1950; MARSHALL, ESSIG and DUBROFF, 1951) nerve contiguity is the chief requirement for the spreading. These findings suggest our seeking the basic mechanism of the EEG depression in humoral transmission and in the metabolic processes which underlie it. Some evidence in support of this is given by the work of BURE; (1956), in which it was shown that sp. D. is evoked by substances such as L-glutamine, NH4Cl, KCI, 2:4dinitrophenol and veratrin, which cause increased respiration and anaerobic glycolysis of brain slices in vitro (ASHFORD and DIXON, 1935; WEIL-MALHERBE, 1938; GHOSH and QUASTEL, 1954; WOLLENBERGER, 1955), if they are applied locally to the surface of the brain. Conversely substances that prevent the effects of increased potassium ion concentration on the respiration and glycolysis of brain slices, e.g. citrate, a-ketoglutarate, succinate and malonate (LIPSETT and CRESCITELLI, 1950; MCILWAIN, 1954; KIMURA and NIWA, 1953), prevent the onset of the sp. D. evoked by KCI, when added in suitable concentrations to the KCl solutions applied to the brain surface. The work of VAN HARREVELD and STAMM (1954), who found a decrease in the oxygen tension in the cerebral cortex during sp. D., gives further evidence in support of the view that there is a connection between the onset of sp. D. and the effects of the above substances on the metabolism of brain slices in vitro. This decrease is not caused by vasoconstriction, as was originally thought by these authors, since B U R E ~ V A (1957) has shown, by haemoglobin determinations, by measurements of the uptake of 24Na, 32P and 42K into cortical regions of the control and experimental hemisphere and by thermo-electric measurements, that the sp. D. is accompanied by a vasodilatation. The lowered oxygen tension during sp. D. is, therefore, caused by increased oxygen uptake by the brain tissue. In the present report an attempt was made to find a relationship between the action of potassium ions in vitro and in vivo and changes in the carbohydrate metabolism during sp. D. The study was commenced by determining the glycogen content of the rat brain in the course of the sp. D. evoked either mechanically or by local application of KCl at various concentrations to the surface of the brain.

title: Brain cyclic adenosine 3′,5′-monophosphate during depolarization of the cerebral cortical cells in vivo
abstract: Cyclic AMP (cAMP) was determined in that part of the rat cerebral cortex which was invaded by slow potential change (SPC) accompanying cortical spreading depression (CSD). cAMP was determined at various phases of SPC development and at several time intervals after SPC recovery. At maximum SPC, cAMP was increased by 100% above control and by 116% at the time of SPC recovery. Five, 10 and 15 min after SPC recovery, +54%, +34% and 0% increase in cAMP was found, respectively. The activity of phosphorylase a increased by 112% at SPC recovery (maximal cAMP increase), and by 13% 15 min later (complete cAMP recovery). Some depolarizing agents which differ in their ability to stimulate cAMP formation in vitro (veratridine, cyanide and glutamate) when applied topically onto the cerebral cortex in concentrations evoking CSD (2 mM veratridine, 10 mM cyanide and 100 mM glutamate), induce uniform increase of cAMP by about 100%. The same cAMP augmentation was found in the cortical region under maximum SPC induced by these agents.

title: Adenosine 3′,5′ ‐monophosphate in rat cerebral cortex: effect of potassium ions in vivo (cortical spreading depression)
abstract: THE REMARKABLE electrophysiological phenomenon, cortical spreading dcpression (LFAo, 1944) affects all basic types of brain activity-spike discharge of single neurons, synchronised synaptic potentials and steady potentials generated by neurons and glia (BURES et al., 1974). It is manifested by decreased EEG amplitude and by a steady potential difference developing between the depressed and intact part of the brain. Both changes spread from the place of cortical spreading depression induction (locus of CSD) in all directions over the cortex. CSD was shown to be accompanied by depolarisation of cortical cells (BROZEK, 1966; COLLEWUN & VAN HARREVELD, 1966). Spreading of depolarisation is mediated by neuronal discharge, preceding the wave of negativity and by release of a humoral factor probably consisting of potassium ions (BURES & KRIVANEK, 1958; KKIVANEK & BURES, 1960; BRINLEY et ai., 1960). Glutamate also has been suggested as a 'mediator' (VAN HARREVELD, 1959). CSD can be elicited by electrical stimulation, potassium ions, ammonia ions, some amino acids (aspartate, asparagine, glutamine, sometimes glutamate), by metabolic inhibitors (cyanide, azide, 2,4dinitrophenol, strophanthine, fluoride, iodoacetate-BuRES, 1956). Evidence has accumulated suggesting involvement of cyclic AMP in elementary functions of nerve cells like polarisation-depolarisation cycle and synaptic transmission (GREENGARD & COSTA, 1970). Most of the agents eliciting CSD have been shown to increase accumulation of cyclic AMP in brain slices in vitro (SATTIN & RALL, 1967; KAKIUCHI et al., 1969;  1970; SHIMIZU et a/.. 1970; HUANG & DALY, 1974; FERRENDELLI et al., 1974). In the present communication results are reported in which cyclic AMP was measured in the rat cerebral cortex during CSD. Tissue samples from the focus of CSD as well as from the portion of the cortex under the maximal SPC were analysed and compared with the samples of the intact cortex.

title: Neurons Have an Active Glycogen Metabolism that Contributes to Tolerance to Hypoxia
abstract: Glycogen is present in the brain, where it has been found mainly in glial cells but not in neurons. Therefore, all physiologic roles of brain glycogen have been attributed exclusively to astrocytic glycogen. Working with primary cultured neurons, as well as with genetically modified mice and flies, here we report that—against general belief—neurons contain a low but measurable amount of glycogen. Moreover, we also show that these cells express the brain isoform of glycogen Phosphorylase, allowing glycogen to be fully metabolized. Most importantly, we show an active neuronal glycogen metabolism that protects cultured neurons from hypoxia-induced death and flies from hypoxia-induced stupor. Our findings change the current view of the role of glycogen in the brain and reveal that endogenous neuronal glycogen metabolism participates in the neuronal tolerance to hypoxic stress.

title: Simultaneous imaging of total cerebral hemoglobin concentration, oxygenation, and blood flow during functional activation.
abstract: A simple instrument is demonstrated for high-resolution simultaneous imaging of total hemoglobin concentration and oxygenation and blood flow in the brain by combining rapid multiwavelength imaging with laser speckle contrast imaging. The instrument was used to image changes in oxyhemoglobin and deoxyhemoglobin and blood flow during cortical spreading depression and single whisker stimulation in rats through a thinned skull. The ability to image blood flow and hemoglobin concentration changes simultaneously with high resolution will permit detailed quantitative analysis of the spatiotemporal hemodynamics of functional brain activation, including imaging of oxygen metabolism. This is of significance to the neuroscience community and will lead to a better understanding of the interrelationship of neural, metabolic, and hemodynamic processes in normal and diseased brains.

title: Increased 20-HETE Synthesis Explains Reduced Cerebral Blood Flow But Not Impaired Neurovascular Coupling after Cortical Spreading Depression in Rat Cerebral Cortex
abstract: Cortical spreading depression (CSD) is associated with release of arachidonic acid, impaired neurovascular coupling, and reduced cerebral blood flow (CBF), caused by cortical vasoconstriction. We tested the hypothesis that the released arachidonic acid is metabolized by the cytochrome P450 enzyme to produce the vasoconstrictor 20-hydroxyeicosatetraenoic acid (20-HETE), and that this mechanism explains cortical vasoconstriction and vascular dysfunction after CSD. CSD was induced in the frontal cortex of rats and the cortical electrical activity and local field potentials recorded by glass microelectrodes, CBF by laser Doppler flowmetry, and tissue oxygen tension (tpO2) using polarographic microelectrodes. 20-HETE synthesis was measured in parallel experiments in cortical brain slices exposed to CSD. We used the specific inhibitor HET0016 (N-hydroxy-N′-(4-n-butyl-2-methylphenyl)formamidine) to block 20-HETE synthesis. CSD increased 20-HETE synthesis in brain slices for 120 min, and the time course of the increase in 20-HETE paralleled the reduction in CBF after CSD in vivo. HET0016 blocked the CSD-induced increase in 20-HETE synthesis and ameliorated the persistent reduction in CBF, but not the impaired neurovascular coupling after CSD. These findings suggest that CSD-induced increments in 20-HETE cause the reduction in CBF after CSD and that the attenuation of stimulation-induced CBF responses after CSD has a different mechanism. We suggest that blockade of 20-HETE synthesis may be clinically relevant to ameliorate reduced CBF in patients with migraine and acute brain cortex injuries.

title: Simultaneous Monitoring of Tissue Po2 and NADH Fluorescence During Synaptic Stimulation and Spreading Depression Reveals a Transient Dissociation between Oxygen Utilization and Mitochondrial Redox State in Rat Hippocampal Slices
abstract: Nicotinamide adenine dinucleotide (NADH) imaging can be used to monitor neuronal activation and ascertain mitochondrial dysfunction, for example during hypoxia. During neuronal stimulation in vitro, NADH normally becomes more oxidized, indicating enhanced oxygen utilization. A subsequent NADH overshoot during activation or on recovery remains controversial and reflects either increased metabolic activity or limited oxygen availability. Tissue Po2 measurements, obtained simultaneously with NADH imaging in area CA1 in hippocampal slices, reveal that during prolonged train stimulation (ST) in 95% O2, a persistent NADH oxidation is coupled with increased metabolic demand and oxygen utilization, for the duration of the stimulation. However, under conditions of either decreased oxygen supply (ST-50% O2) or enhanced metabolic demand (K+-induced spreading depression (K+-SD) 95% O2) the NADH oxidation is brief and the redox balance shifts early toward reduction, leading to a prolonged NADH overshoot. Yet, oxygen utilization remains elevated and is correlated with metabolic demand. Under these conditions, it appears that the rate of NAD+ reduction may transiently exceed oxidation, to maintain an adequate oxygen flux and ATP production. In contrast, during SD in 50% O2, the oxygen levels dropped to a point at which oxidative metabolism in the electron transport chain is limited and the rate of utilization declined.

title: Spreading depression induces prolonged reduction of cortical blood flow reactivity in the rat
abstract: The purpose of the present study was to examine the dynamic aspects of the cerebrovascular events occurring during and up to 2 h following cortical spreading depression (CSD) in the rat, using the mass spectrometry technique which enables continuous measurements of the cortical tissue PO2 and PCO2 and repeated blood flow measurements (CoBF) by helium clearance. We mostly sought to determine whether cortical perforation by a stimulation electrode induced long-lasting perturbation of the cortical vasoreactivity to hypercapnia and basal forebrain electrical stimulation. Cortical perforation in the animal under alpha-chloralose anesthesia, chronically implanted with mass spectrometry probes, was associated with biphasic changes in tissue gases. PO2 first briefly decreased (-7.8%) and then strongly increased (+79%) while PCO2 changed in the opposite direction (+7%, -13%) in the ipsilateral frontal cortex. Qualitatively similar changes occurred in the ipsilateral parietal cortex. The CoBF measurements showed a marked vasodilation (131 and 108% in the frontal and parietal cortex, respectively) in parallel with the PO2 increase, followed by a prolonged (60 min), moderate hypoperfusion (maximum -17% at 20 min after CSD). There was a pronounced reduction of vascular reactivity to both hypercapnia (20.3% of the control response) and substantia innominata stimulation (1/6 of the response obtained 80 min later) at 10 min after CSD. Both reactivities progressively recovered in approximately 2 h. Since the issue of CSD in human has become a popular hypothesis for migraine, the reduced cerebrovascular reactivity could constitute the basis of a test for the involvement of CSD in migraine.

title: Cerebral Blood Flow and Oxygen Consumption in Cortical Spreading Depression
abstract: We determined the effects of spreading depression on local cerebral O2 supply, oxygenation, and O2 consumption in the anesthetized rat. Spreading depression was induced by application of 0.5 M KCl to the frontal cortex. Regional cerebral blood flow was determined with [14C]iodoantipyrine and regional O2 extraction was determined microspectrophotometrically. The passage of the spreading depression wave was determined with a multiprobe assembly that recorded NADH redox state (surface fluorometry), extracellular K+ activity, and DC steady potential (surface minielectrodes). As the wave of spreading depression passed, there was an increase in extracellular K+ and a decrease in NADH. Cerebral blood flow was significantly increased (120 ± 51 ml/min/100 g, mean ± SD) during the wave as compared with other regions. In the affected cortex, blood flow was not different from that in the contralateral cortex (69 ± 28 ml/min/100 g) either before or after the wave of spreading depression passed. Arterial and venous O2 saturation were unaffected by the wave and the histogram of O2 saturations of examined veins followed a similar normal distribution in all regions. Oxygen extraction was not altered by the wave of spreading depression. Oxygen consumption was significantly increased during the wave to 7.4 ± 3.7 ml O2/min/100 g compared with the contralateral cortex (5.1 ± 2.6 ml/min/100 g) and other regions. It can be concluded that spreading depression caused an increase in cerebral O2 consumption that was adequately matched by an increase in local blood flow. Oxygen delivery was not limited during spreading depression and its effects were quickly over as evidenced by the lack of alteration in oxygenation after the wave of spreading depression passed.

title: Persistent Increase in Oxygen Consumption and Impaired Neurovascular Coupling after Spreading Depression in Rat Neocortex
abstract: Cortical spreading depression (CSD) is associated with a dramatic failure of brain ion homeostasis and increased energy metabolism. There is strong clinical and experimental evidence to suggest that CSD is the mechanism of migraine, and involved in progressive neuronal injury in stroke and head trauma. Here we tested the hypothesis that single episodes of CSD induced acute hypoxia, and prolonged impairment of neurovascular and neurometabolic coupling. Cortical spreading depression was induced in rat frontal cortex, whereas cortical electrical activity and local field potentials (LFPs) were recorded by glass microelectrodes, cerebral blood flow (CBF) by laser—Doppler flowmetry, and tissue oxygen tension (tpO2) with Polarographic microelectrodes. Cortical spreading depression increased cerebral metabolic rate of oxygen (CMRO2) by 71% ± 6.7% and CBF by 238% ± 48.1% for 1 to 2 mins. For the following 2 h, basal tpO2 and CBF were reduced whereas basal CMRO2 was persistently elevated by 8.1% ± 2.9%. In addition, within first hour after CSD we found impaired neurovascular coupling (LFP versus CBF), whereas neurometabolic coupling (LFP versus CMRO2) remained unaffected. Impaired neurovascular coupling was explained by both reduced vascular reactivity and suppressed function of cortical inhibitory interneurons. The protracted effects of CSD on basal CMRO2 and neurovascular coupling may contribute to cellular dysfunction in patients with migraine and acutely injured cerebral cortex.

title: Simultaneous imaging of cerebral partial pressure of oxygen and blood flow during functional activation and cortical spreading depression.
abstract: We developed a novel imaging technique that provides real-time two-dimensional maps of the absolute partial pressure of oxygen and relative cerebral blood flow in rats by combining phosphorescence lifetime imaging with laser speckle contrast imaging. Direct measurement of blood oxygenation based on phosphorescence lifetime is not significantly affected by changes in the optical parameters of the tissue during the experiment. The potential of the system as a novel tool for quantitative analysis of the dynamic delivery of oxygen to support brain metabolism was demonstrated in rats by imaging cortical responses to forepaw stimulation and the propagation of cortical spreading depression waves. This new instrument will enable further study of neurovascular coupling in normal and diseased brain.

title: Cortical spreading depression causes and coincides with tissue hypoxia
abstract: Cortical spreading depression (CSD) is a self-propagating wave of cellular depolarization that has been implicated in migraine and in progressive neuronal injury after stroke and head trauma. Using two-photon microscopic NADH imaging and oxygen sensor microelectrodes in live mouse cortex, we find that CSD is linked to severe hypoxia and marked neuronal swelling that can last up to several minutes. Changes in dendritic structures and loss of spines during CSD are comparable to those during anoxic depolarization. Increasing O2 availability shortens the duration of CSD and improves local redox state. Our results indicate that tissue hypoxia associated with CSD is caused by a transient increase in O2 demand exceeding vascular O2 supply.

title: Optical imaging of the spatiotemporal dynamics of cerebral blood flow and oxidative metabolism in the rat barrel cortex
abstract: Oxidative metabolism and cerebral blood flow (CBF) are two of the most important measures in neuroimaging. However, results from concurrent imaging of the two with high spatial and temporal resolution have never been published. We used flavoprotein autofluorescence (AF) and laser speckle imaging (LSI) in the anaesthetized rat to map oxidative metabolism and CBF in response to single vibrissa stimulation. Autofluorescence responses reflecting oxidative metabolism demonstrated a fast increase with a delay of 0.1 s. The sign‐reversed speckle contrast reflecting CBF started to rise with a delay of 0.6 s and reached its maximum 1.4 s after the stimulation offset. The fractional signal changes were 2.0% in AF and 9.7% in LSI. Pixelwise modelling revealed that CBF maps spread over an area up to 2.5‐times larger than metabolic maps. The results provide evidence that the increase in cerebral oxidative metabolism in response to sensory stimulation is considerably faster and more localized than the CBF response. This suggests that future developments in functional imaging concentrating on the metabolic response promise an increased spatial resolution.

title: The interrelation between CBF, energy metabolism and ECoG in a new awake brain model.
abstract: The measurement of intramitochondrial NADH oxidation-reduction state from the brain of an awake animal is a well established technique and is in use for the last few years. We had used this animal model in studying the effects of hypoxia, spreading depression, epileptiform activity (Mayevsky and Chance, 1975) or ischemia (Mayevsky, 1977) on the metabolic activity. In all of the studies made by our group or other groups, only one site or side of the brain was monitored fluorometrically. In the ischemia studies we found that under certain experimental conditions it is very important to measure metabolic activity from the “experimental” site as compared to the “control” site or side simultaneously. In our awake model we used a topical application technique to study the effects of drugs on the cortical tissue without any effects on the rest of the brain. This model also requires a bilateral measurement technique. We present in this presentation a new type of fluorometer/ reflectometer by which NADH fluorescence, as well as reflected light, can be measured simultaneously from two points of an awake brain model. This model was exposed to anoxia, spreading depression or ischemia and the results are presented. In another group of rats the effects of topical application of 2-Deoxyglucose were tested.

title: Dynamic Changes in Brain Glucose and Lactate in Pericontusional Areas of the Human Cerebral Cortex, Monitored with Rapid Sampling On-Line Microdialysis: Relationship with Depolarisation-Like Events
abstract: The pathophysiology of peri-lesion boundary zones in acute brain injury is highly dynamic, and it is now clear that spreading-depression-like events occur frequently in areas of cerebral cortex adjacent to contusions in the injured human brain. An automated method to assay microdialysate from peri-lesion cerebral cortex in 11 patients with intracranial haematomas requiring surgery was used. Perfusate (2 μL/min) flowed directly into a flow-injection system for assay of glucose and lactate at intervals typically of 30 secs each. Four channels of electrocorticogram (ECoG) were recorded from a subdural strip adjacent to the catheter. Several patterns of change in metabolites were identified in different time domains. Overall, the number of transient lactate events was significantly correlated with the number of glucose events (r2=0.48, P=0.027, n=10). Progressive reduction in dialysate glucose was very closely correlated with the aggregate number of ECoG events (r2=0.76, P=0.0004, n=11). It is proposed that the recently documented adverse impact of low dialysate glucose on clinical outcome may be because of recurrent, spontaneous spreading-depression-like events in the perilesion cortex.

title: Relationships among local functional activity, energy metabolism, and blood flow in the central nervous system.
abstract: The results of studies with the [14C]deoxyglucose technique establish that local energy metabolism in cerebral tissues is, as in other tissues, closely coupled to local functional activity. Stimulation of local functional activity increases the local rate of glucose utilization; reduced functional activity depresses it. Local cerebral blood flow is normally distributed among the cerebral structures in almost exact proportion to their rates of glucose utilization and changes together with local glucose consumption in response to altered local functional activity. These results demonstrate that the level of functional activity in the structural and functional components of the central nervous system regulates the local rate of energy metabolism, and local blood flow is adjusted to the local metabolic demand.

title: Transient swelling, acidification, and mitochondrial depolarization occurs in neurons but not astrocytes during spreading depression.
abstract: Cortical spreading depression (SD) is a propagating wave of neuronal and glial depolarization that manifests in several brain disorders. However, the relative contribution of neurons and astrocytes to SD genesis has remained controversial. This is in part due to a lack of utilizing sophisticated experimental methodologies simultaneously to quantify multiple cellular parameters. To address this, we used simultaneous two-photon imaging, intrinsic optical imaging, and electrophysiological recordings to ascertain the changes in cellular processes that are fundamental to both cell types including cell volume, pH, and metabolism during SD propagation. We found that SD was correlated in neurons with robust yet transient increased volume, intracellular acidification, and mitochondrial depolarization. Our data indicated that a propagating large conductance during SD generated neuronal depolarization, which led to both calcium influx triggering metabolic changes and H(+) entry. Notably, astrocytes did not exhibit changes in cell volume, pH, or mitochondrial membrane potentials associated with SD, but they did show alterations induced by changing external [K(+)]. This suggests that astrocytes are not the primary contributor to SD propagation but are instead activated passively by extracellular potassium accumulation. These data support the hypothesis that neurons are the crucial cell type contributing to the pathophysiological responses of SD.

title: Cortical Spreading Depression Impairs Oxygen Delivery and Metabolism in Mice
abstract: Cortical spreading depression (CSD) is associated with severe hypoperfusion in mice. Using minimally invasive multimodal optical imaging, we show that severe flow reductions during and after spreading depression are associated with a steep decline in cerebral metabolic rate of oxygen. Concurrent severe hemoglobin desaturation suggests that the oxygen metabolism becomes at least in part supply limited, and the decrease in cortical blood volume implicates vasoconstriction as the mechanism. In support of oxygen supply-demand mismatch, cortical nicotinamide adenine dinucleotide (NADH) fluorescence increases during spreading depression for at least 5 minutes, particularly away from parenchymal arterioles. However, modeling of tissue oxygen delivery shows that cerebral metabolic rate of oxygen drops more than predicted by a purely supply-limited model, raising the possibility of a concurrent reduction in oxygen demand during spreading depression. Importantly, a subsequent spreading depression triggered within 15 minutes evokes a monophasic flow increase superimposed on the oligemic baseline, which markedly differs from the response to the preceding spreading depression triggered in naive cortex. Altogether, these data suggest that CSD is associated with long-lasting oxygen supply-demand mismatch linked to severe vasoconstriction in mice.

title: Effects of age on brain oxidative metabolism in vivo
abstract: Non-invasive optical techniques were used to monitor the effects of increasing cerebral energy demand on metabolic capabilities and vascular reactivity in young and aged brain. Low level of electrical stimulation of the cortex, in both young (4--7 months) and aged (24--28 months) rat brain, were accompanied by transient oxidations of NADH and cytochrome oxidase (a,a3) as measured by microfluorometry and reflection spectrophotometry respectively. Stimulation sufficient to produce spreading cortical depression was accompanied by an oxidation of both NADH and cytochrome a,a3 in young brain together with an increase in local blood volume. There was either no change or a slight disoxygenation of hemoglobin. In aged brain, however, spreading depression was associated with an oxidation of NADH and a reduction of cytochrome a,a3 together with an increase in local blood volume and an oxygenation of hemoglobin. The present results indicate that the relationship between microcirculation and the terminal oxidase step of the respiratory chain is altered in aged brain when energy demand is high.

title: Systemic Nitric Oxide Synthase Inhibition Does Not Affect Brain Oxygenation during Cortical Spreading Depression in Rats: A Noninvasive Near-Infrared Spectroscopy and Laser-Doppler Flowmetry Study
abstract: Cortical spreading depression (CSD) has been implicated in the migraine aura and in stroke. This study demonstrates near-infrared spectroscopy (NIRS) for the first time as capable of noninvasive on-line detection of CSD in the pentobarbital-anesthetized rat. CSD was accompanied by a brief and rapid increase of regional CBF (by laser-Doppler flowmetry) to 200–400% baseline. NIRS demonstrates that this hyperperfusion is associated with concentration increases of oxyhemoglobin, while deoxyhemoglobin decreases. Simultaneously, oxygen partial pressure, measured on the brain surface with a solid-state Polarographic probe, was shown to be raised by at least 14 mm Hg during CSD. Oxygen-dependent phosphorescence life-time quenching measurements confirmed this finding. NIRS data on cytochrome aa3, however, showed a CSD-related shift toward a more reduced state, despite raised blood oxygenation. This may suggest either limited O2 transport from the blood to mitochondria or decreased oxygen utilization during CSD as supposed by theories about compartmentalization of energy metabolism favoring glycolytic rather than aerobic energy supply during CSD. However, the data on cytochrome aa3, warrant caution and are discussed critically. Nitric oxide synthase inhibition by systemic application of N′-nitro-l-arginine had no significant effect on the perfusion response or the tissue Po2 during CSD. During most CSD episodes, a brief decrease in MABP by 4–8 mm Hg was noted that might be caused by functional decortication during CSD.

title: Extra- and intracellular oxygen supply during cortical spreading depression in the rat.
abstract: Cortical Spreading Depression was discovered fifty years ago 15, but the complexity of its mechanisms is still far from being understood. It was then the high time of Wolff’s vascular theory of migraine 25 when Lashley first calculated the velocity of a supposed electrophysiological phenomenon in the primary visual cortex that could cause the optical hallucinations of the migraine aura as the same velocity that characterizes CSD 12. Arole for CSD in the pathophysiological scenario of migraine has become more and more attractive ever since, mainly by virtue of accumulating evidence for neuronal mechanisms as found in the pursuit of Moskowitz’ theory of neurogenic inflammation in migraine 14,l7.

title: Excessive oxygen or glucose supply does not alter the blood flow response to somatosensory stimulation or spreading depression in rats
abstract: We investigated the influence of hyperoxia (arterial pO2 446 +/- 43 mmHg) and hyperglycemia (blood glucose 19.4 mmol/l) on somatosensory stimulation (whisker deflection) employing laser Doppler flowmetry (LDF). Our aim was to test the hypothesis that a possible substrate-sensing mechanism for glucose and oxygen contributes to the coupling between cortical activity and regional cerebral blood flow (rCBF) in order to match increased demand with substrates. In addition, we looked at the influence of hyperglycemia (blood glucose 17.9 mmol/l) and hypercapnia (arterial pCO2 62 mmHg) on rCBF (LDF) and regional cerebral blood oxygenation changes (rCBO) in the even stronger metabolic stimulus of cortical spreading depression (CSD). For the latter we employed the new non-invasive technique of near infrared spectroscopy (NIRS). All experiments were done using chloralose/urethane-anesthetized rats. Somatosensory stimulation increased rCBF by about 20% of baseline, in the case of both norm- and hyperoxia as well as both normo- and hyperglycemia. The blood-flow response to CSD consisted of a temporary sharp increase in rCBF to more than 400%. At the same time, the concentration of oxyhemoglobin [HbO2] increased, while deoxyhemoglobin [Hb] decreased, indicating excessive oxygenation. Hyperglycemia altered neither the rCBF nor the rCBO response. Preexisting hypercapnia, however, produced reductions in both hyperperfusion (rCBF) and hyperoxygenation (rCBO) during CSD. We found that, for experimental hyperglycemia, i.v. may be superior to i.p. application of glucose because of the latter's side effects in connection with blood flow. Our findings cannot support the hypothesis of a substrate sensing mechanism in coupling.

title: Simultaneous detection of hemodynamics, mitochondrial metabolism and light scattering changes during cortical spreading depression in rats based on multi-spectral optical imaging
abstract: Cortical spreading depression (CSD) is a self-propagating wave of cellular depolarization that plays an important role in the development of cerebral pathology following ischemia or trauma. Optical intrinsic signal (OIS) imaging has been widely used to investigate CSD. Sources of OIS are complex and related to the changes in brain tissue absorption and scattering. The absorbing chromophores may include oxy-hemoglobin, deoxy-hemoglobin, cytochromes, flavin adenine dinucleotide (FAD) and nicotinamide adenine dinucleotide (NADH). Considering only one or part of these elements in studies involving OIS may cause inaccurate results. Thus, we simultaneously calculated changes in HbO, HbR, FAD, cytochrome c, cytochrome aa3 and light scattering during CSD by applying multi-spectral OIS imaging at 450, 470, 500, 530, 550, 570, 600, 630, and 650 nm in the rat brain. We also showed that the hemodynamic changes during CSD may not be correctly estimated if the scattering and other chromophores such as FAD, cytochrome c and cytochrome aa3, are not included in the fitting model of multi-wavelength data analysis. As shown in our results, if considering the changes in scattering and other chromophores in data fitting model, deoxy-hemoglobin (HbR) showed a triphasic change while only a monophasic decrease in HbR will be resolved without considering changes in scattering and other chromophores as reported in previous studies. Moreover, our results showed that changes in cytochrome c was tightly related to OIS at 550 nm, cytochrome aa3 was closely related to OIS at 450, 600 and 650 nm, and FAD was closely related to OIS at 450 and 470 nm during CSD. It indicates that if the contribution by these related chromophores is not considered, using OIS at these wavelengths to determine the hemoglobin changes during CSD may lead to inaccurate results.

title: Functional compartmentalization of energy production in neural tissue
abstract: Previous work in our laboratory has shown that neural trauma results in a disparity between oxidative and glycolytic rates. In non-neural tissue, glycolysis and oxidative phosphorylation have been shown to work independently of one another, a phenomenon known as "energy compartmentalization". We believe that functional compartmentalization of energy production may also occur in the brain with glycolysis providing energy for membrane bound ionic pumps. Spreading depression, induced in rodent brain by topical KCl application, results in K+ shifts. The restoration of K+ gradients is accomplished by energy dependent Na(+)-K+ pumps. If these pumps depend upon glycolysis, blocking glycolysis should prevent reconstitution of normal [K+]e levels. The present series of experiments were designed to suggest that energy compartmentalization may also exist in brain, and that glycolytic energy production is preferentially used by Na(+)-K+ pumps to maintain normal ionic homeostasis by observing the dynamics of spreading depression induced K+ shifts before and after glycolytic blockade. Spreading depression was associated with increased K+ (48.6 +/- 16.6 mM over control) that normalized within 2.9 +/- 0.3 minutes. Following superfusion with a glycolytic blocking agent, spreading depression produced similar increases in [K+]e (40.6 +/- 12.0 mM over control) but time for reconstitution of the normal [K+]e was 400% longer than controls (2.9 +/- 0.3 to 14.9 +/- 2.1 minutes, P less than 0.001). Time required for recovery of EEG was identical pre- and post-blockade. We believe these data suggest that energy compartmentalization may exist in neural tissue and that glycolytic pathways of energy production are functionally tied to membrane Na(+)-K+ pumps.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Nonoxidative glucose consumption during focal physiologic neural activity.
abstract: Brain glucose uptake, oxygen metabolism, and blood flow in humans were measured with positron emission tomography, and a resting-state molar ratio of oxygen to glucose consumption of 4.1:1 was obtained. Physiological neural activity, however, increased glucose uptake and blood flow much more (51 and 50 percent, respectively) than oxygen consumption (5 percent) and produced a molar ratio for the increases of 0.4:1. Transient increases in neural activity cause a tissue uptake of glucose in excess of that consumed by oxidative metabolism, acutely consume much less energy than previously believed, and regulate local blood flow for purposes other than oxidative metabolism.

title: The role of oxygen diffusivity in biochemical reactions
abstract: It has been shown that increasing protein concentrations can decrease oxygen diffusion in 3 in vitro systems. We postulate that it is possible, and in some circumstances probable, that diffusion might be a rate limiting step in both in vitro and in vivo biological systems.

title: Local tissue oxygen tension - cytochrome a,a3 redox relationships in rat cerebral cortex in vivo
abstract: Simultaneous measurements were made from rat cerebral cortex, in situ, of focal changes in both tissue oxygen tension (ptO2) and the reduction/oxidation ratio of cytochrome c oxidase (cytochrome a,a3) in order to study relationships between oxygen supply and consumption in small regions of tissue. Local ptO2 was measured with polarographic microelectrodes and the redox state of cytochrome a,a3 with a dual wavelength reflectance spectrophotometer. Increased ptO2, produced by respiration of gas mixtures with elevated O2 and/or CO2 content, was accompanied by increased oxidation of cytochrome a,a3. This confirms that cytochrome oxidase is not fully oxidized in focal brain tissue regions in vivo, as it is in mitochondria isolated in vitro. Decreased ptO2 was accompanied by cytochrome a,a3 reduction. The oxidative changes of cytochrome a,a3 with increases in ptO2 were smaller than the reductive changes associated with decreases in ptO2. Curves relating cytochrome a,a3 redox state to ptO2 were qualitatively alike, regardless of the initial ptO2 value from which they were generated. Thus, the reduction level of cytochrome a,a3 varied with ptO2 on a continuum. This consistent relationship demonstrates that changes in mitochondrial redox state provide an index of relative changes in tissue oxygenation in intact neocortex. The results suggest also that local rates of cerebral oxidative metabolism may not always be constant with changes in local ptO2.

title: Pronounced Hypoperfusion during Spreading Depression in Mouse Cortex
abstract: We studied unique cerebral blood flow (CBF) responses to cortical spreading depression in mice using a novel two-dimensional CBF imaging technique, laser speckle flowmetry. Cortical spreading depression caused a triphasic CBF response in both rat and mouse cortex. In rats, mild initial hypoperfusion (approximately 75% of baseline) was followed by a transient hyperemia reaching approximately 220% of baseline. In mice, the initial hypoperfusion was pronounced (40–50% of baseline), and the anticipated hyperemic phase barely reached baseline. The duration of hypoperfusion significantly correlated with the duration of the DC shift. As a possible explanation for the pronounced hypoperfusion, mouse cerebral vessels showed enhanced resistance to relaxation by acetylcholine (3 μM) after K+-induced preconstriction (20, 40, and 80 mM) but dilated normally in response to acetylcholine after preconstriction with U46619, a synthetic thromboxane A2 analog. By contrast, rat vessels dilated readily to acetylcholine after preconstriction by K+. The transient normalization of CBF after hypoperfusion in the mouse was abolished by L-NA but not 7-NI. In summary, the CBF response to cortical spreading depression in mice contrasts with the rat in that the initial hypoperfusion is pronounced, and the hyperemic phase is markedly diminished. The differences in CBF response between species may be in part caused by an increased sensitivity of mouse cerebral vessels to elevated extracellular K+.

title: Age-dependent cerebrovascular dysfunction in a transgenic mouse model of cerebral amyloid angiopathy.
abstract: The Tg2576 transgenic mouse model of human cerebral amyloid angiopathy is characterized by age-dependent cerebrovascular deposition of amyloid-beta (Abeta) starting from 9 months of age and progressively worsening to involve most pial arterioles by 18 months; soluble Abeta levels are elevated long before vascular deposition takes place in this model. It has been suggested that elevated soluble Abeta levels alone are sufficient to impair cerebral blood flow (CBF) regulation thereby contributing to the early progression of Alzheimer's disease. Using laser speckle flowmetry through an intact skull, we studied the impact of elevated soluble Abeta levels and vascular Abeta deposition on a wide range of CBF responses to evaluate vasodilation and vasoconstriction in young or aged Tg2576 mice. Nineteen-month-old Tg2576 with severe vascular Abeta deposits showed an attenuated hyperaemic response during hypercapnia and whisker stimulation compared to wild-type littermates. The anticipated increase in CBF due to isoflurane anaesthesia was also suppressed, as were the typical hypoperfusion responses during cortical spreading depression and alpha-chloralose anaesthesia. The responses of 8-month-old Tg2576 with elevated soluble Abeta levels, but without vascular Abeta deposition, did not differ from age-matched controls. In conclusion, our data suggest that vascular Abeta deposition is associated with impaired vasodilator as well as vasoconstrictor responses to a wide range of stimuli. These responses do not differ from controls when studied non-invasively prior to vascular Abeta deposition, thus challenging the view that elevated soluble Abeta levels are sufficient to cause cerebrovascular dysfunction.

title: Cerebral Oxygen/Glucose Ratio is Low during Sensory Stimulation and Rises above Normal during Recovery: Excess Glucose Consumption during Stimulation is Not Accounted for by Lactate Efflux from or Accumulation in Brain Tissue
abstract: Functional activation stimulates CMRglc more than CMRO2 and raises lactate levels in brain. This has been interpreted as evidence that brain work is supported mainly by energy derived from anaerobic glycolysis. To determine if lactate production accounts for the “excess” glucose consumption, cerebral arteriovenous differences were measured in conscious rats before, during, and 15 minutes after sensory stimulation; the brains were rapidly frozen in situ immediately after completion of blood sampling and assayed for metabolite levels. The molar O2/glucose uptake ratio fell from 6.1 ± 1.1 (mean ± SD) before stimulation to 5.0 ± 1.1 during activation (P < 0.01); lactate efflux from brain to blood was detectable at rest but not during stimulation. By 15 minutes after activation, O2 and lactate arteriovenous differences normalized, whereas that for glucose fell, causing the O2/glucose ratio to rise above preactivation levels to 7.7 ± 2.6 (P < 0.01). Brain glucose levels remained stable through all stages of activity. Brain lactate levels nearly doubled during stimulation but normalized within 15 minutes of recovery. Brain glycogen content fell during activation and declined further during recovery. These results indicate that brain glucose metabolism is not in a steady state during and shortly after activation. Furthermore, efflux from and increased content of lactate in the brain tissue accounted for less than 54% of the “excess” glucose used during stimulation, indicating that a shift to anaerobic glycolysis does not fully explain the disproportionately greater increases in CMRglc above that of CMRO2 in functionally activated brain. These results also suggest that the apparent dissociation between glucose utilization and O2 consumption during functional activation reflects only a temporal displacement; during activation, glycolysis increases more than oxidative metabolism, leading to accumulation of products in intermediary metabolic pools that are subsequently consumed and oxidized during recovery.

title: THE POSSIBLE MECHANISMS OF CONTRACTING AND PAYING THE OXYGEN DEBT AND THE RÔLE OF LACTIC ACID IN MUSCULAR CONTRACTION
abstract: Although direct evidence of a quantitative relationship between oxygen debt and lactic acid production in man has never been given, there is general agreement with A. V. Hill’s hypothesis that the oxygen debt is due to the delayed oxidation of a fraction of the lactic acid produced during the anaerobi .c processes of muscular activity. After the “revolution” produced in muscle physiology by the discoveries of the last few years, m ainiy after Lundsgaard’s work, and the further observations on men, it seemed to us that the lactic acid mechanism alone is inadequate to explain all the processes which occur in the payment of the oxygen debt, particularly for the following reasons: a. It has been observed in isolated muscle that most of the lactic acid is produced after the contraction is over, during the first minute of recovery; this does not seem to agree with the fact that the payment of the oxygen debt at the beginning shows no lag even if the exercise is of very short duration. b. In moderate exercise of long duration in man, involving an oxygen debt of 3 to 4 liters, the changes in lactic acid concentration or in pH of blood are negligible in comparison with the values implied by the assumption of an increment of lactic acid in the body corresponding to the amount of oxygen debt.

title: Association of seizures with cortical spreading depression and peri-infarct depolarisations in the acutely injured human brain
abstract: To test the co-occurrence and interrelation of ictal activity and cortical spreading depressions (CSDs) - including the related periinfarct depolarisations in acute brain injury caused by trauma, and spontaneous subarachnoid and/or intracerebral haemorrhage.



63 patients underwent craniotomy and electrocorticographic (ECoG) recordings were taken near foci of damaged cortical tissue for up to 10 days.



32 of 63 patients exhibited CSDs (5-75 episodes) and 11 had ECoGraphic seizure activity (1-81 episodes). Occurrence of seizures was significantly associated with CSD, as 10 of 11 patients with seizures also had CSD (p=0.007, 2-tailed Fishers exact test). Clinically overt seizures were only observed in one patient. Each patient with CSD and seizures displayed one of four different patterns of interaction between CSD and seizures. In four patients CSD was immediately preceded by prolonged seizure activity. In three patients the two phenomena were separated in time: multiple CSDs were replaced by ictal activity. In one patient seizures appeared to trigger repeated CSDs at the adjacent electrode. In 2 patients ongoing repeated seizures were interrupted each time CSD occurred.



Seizure activity occurs in association with CSD in the injured human brain.



ECoG recordings in brain injury patients provide insight into pathophysiological mechanisms, which are not accessible by scalp EEG recordings.

title: Pyridine nucleotide oxidation‐reduction state of the cerebral cortex in the awake gerbil
abstract: A new approach to study the effect of ischemia on the brain of the awake gerbil is described. The measurement of NADH fluorescence from the surface of the cortex is done by a time‐sharing fluorometer/reflectometer connected to the brain via a flexible light guide and an implanted cannula. The response of the gerbil brain to anoxia and spreading depression is described. By unilateral occlusion of the carotid artery and increase in NADH was measured in the ipsilateral hemisphere.

title: Metabolic responses of the awake cerebral cortex to anoxia hypoxia spreading depression and epileptiform activity
abstract: Using the time sharing fluorometer/reflectometer the measurement of NADH fluorescence as well as the reflected light was obtained from the surface of the awake rat brain cortex. The light was transferred to and from the brain via a flexible light pipe (made of quartz fibers) connected to a cannula implanted permanently above the brain. Exposing the rat to pure nitrogen atmosphere increased the fluorescence (reduction of NADH) by 32.3 +/- 6.1% in comparison to the normoxic fluorescence level. During cortical spreading depression (SD) the NADH fluorescence decreased (oxidation of NADH) by 17.3 +/- 2.8%. Exposing the rat to nitrogen after SD was elicited blocked the oxidation cycle observed during SD. Exposing the awake ras to 10, 7.5 or 5% O2 did not block the response of the brain to spreading depression or to Metrazol applied locally to the cortex. Under hypoxic conditions the brain showed a typical response to SD, namely, an oxidation cycle of NADH except that the duration of the cycle was longer and the decrease in the NADH level was smaller. The EEG activity recovered to normal even under 5%. The same effect of hypoxia was found when Metrazol was applied and epileptic activity was developed.

title: Simultaneous, live imaging of cortical spreading depression and associated cerebral blood flow changes, by combining voltage-sensitive dye and laser speckle contrast methods
abstract: Cortical spreading depression (i.e. waves of cellular depolarization, CSD) causes the aura symptoms in classical migraine, and may contribute to delayed cellular damage after an ischemic or traumatic insult to the brain. In the latter cases, secondary neuronal injury may be worsened by some of the cerebral blood flow (CBF) changes that are associated with CSD. Here, we describe a new method for the simultaneous, live imaging of local cellular depolarization and CBF changes (i.e. two variables with well-defined and important biological significance), through a closed cranial window prepared in anesthetized rats. This novel experimental strategy was validated by imaging the changes associated with CSD elicited by application of high K(+) medium on the cortical surface. CSD was visualized directly by using a fluorescent voltage-sensitive (VS) dye, whereas laser speckle contrast (LSC) imaging allowed the visualization of the corresponding CBF changes. In addition to the high temporal and spatial resolution of VS dye and LSC imaging, their novel combination allows to determine how CBF changes relate to a heterogeneous and evolving pattern of cellular depolarization, in any area of interest of the cortical region under study. This methodological development is especially pertinent and timely for investigations into the peri-lesion depolarizations that occur in models of focal brain injury, situations where their site of spontaneous elicitation and propagation pattern cannot be predicted. It should also help advance our knowledge in epilepsy, CBF pharmacology, and neurovascular coupling under normal and pathophysiological conditions.

title: Regional Cerebral Blood Flow during Spreading Cortical Depression in Conscious Rats
abstract: Spreading cortical depression (SCD) of EEG activity was induced in one cerebral hemisphere of conscious restrained rats by direct current stimulation of the lateral frontal cortex. Regional CBF was measured using [14C]iodoantipyrine and brain dissection. An early phase of increased CBF was not measured in conscious rats, but an early relative hyperperfusion was measured if the resting CBF was first reduced by treatment with pentobarbital or indomethacin. A long-lasting reduction in CBF was measured in conscious rats following the passage of SCD. This flow reduction resolved after 3 h. In conscious rats, CBF decreased in the striatum and thalamus ipsilateral to the SCD, paralleling the CBF changes occurring in the cortex. The CBF change in these deep structures was abolished by pentobarbital. An early transient increase in regional CBF was measured in the cerebral cortex contralateral to the hemisphere involved with SCD in conscious rats. This early contralateral hyperperfusion was also abolished by pentobarbital or indomethacin but not by atropine or propranolol. The vascular response to SCD in conscious rats differs from that which occurs in anesthetized rats.

title: Cortical hypoperfusion following spreading depression is not altered by tirilazad mesylate (U-74006F) in awake rats
abstract: The 21-aminosteroid antioxidant tirilazad mesylate (U-74006F) blocks the delayed hypoperfusion associated with spreading cortical depression (SCD) in anesthetized rats. Because the resting vascular tone influences the blood flow response to SCD, the effect of this drug was reassessed in awake rats. In this state, tirilazad mesylate did not eliminate cerebral hypoperfusion following SCD. Oxygen radical-induced lipid peroxidation may not mediate cerebral hypoperfusion after SCD in awake rats.

title: Subcortical Cerebral Blood Flow and Metabolic Changes Elicited by Cortical Spreading Depression in Rat
abstract: Changes in cerebral cortical perfusion (CBFLDF), local cerebral blood flow (ICBF) and local cerebral glucose utilization (ICGU) elicited by unilateral cortical spreading depression (SD) were monitored and measured in separate groups of rats anesthetized with a-chloralose. CBFLDF was recorded with laser Doppler flowmetry, while ICBF and ICGU were measured by the quantitative autoradiographic [14C]iodoantipyrine and [14C]-2-deoxyglucose methods, respectively. SD elicited a wave of hyperemia after a latency of 2 to 3 min followed by an oligemic phase. Ninety minutes following the onset of SD cortical (frontal, parietal and occipital) ICBF and ICGU were essentially the same as on the contralateral side and in sham-treated rats. However, alteration in the ICBF and ICGU in upper and lower brainstem persisted. The present results demonstrate, for the first time, that long-lasting cerebrovascular and metabolic alterations take place within the subcortical regions following SD. These regions provide an attractive site to integrate observations in man concerning spreading depression and the aura of migraine with the other features of the syndrome.

title: Glibenclamide enhances cortical spreading depression‐associated hyperemia in the rat
abstract: We investigated the contribution of ATP-sensitive potassium channels (KATP) and calcium-activated potassium channels (Kca2+) to cortical spreading depression (CSD)-associated hyperemia using the rat closed cranial window model. The peak CBF response was enhanced by 12 ± 5, 13 ± 4, and 28 ± 8% (p < 0.01) of the control with 10−6, 10−5 and 10−4 mol/l glibenclamide (glyb), a KATP antagonist, respectively. We also calculated the area under the CBF curve to fully represent the extent of hyperemia during CSD. The area increased by 30 ± 8 (p < 0.05), 72 ± 31 (p < 0.05) and 88 ± 20% (p < 0305) of the control with 10−6, 10−5 and 10−4 mol/l glyb, respectively. However, charybdotoxin (CTX), a Kca2+ antagonist showed no effect. The effect of glyb was inhibited by pretreatment with 5 mg/kg indomethacin. We conclude that activation of KATP, perhaps associated with neurons, plays an inhibitory role in the CSD-associated hyperemia via an indomethacin-sensitive mechanism.

title: Role of endothelium in hyperemia during cortical spreading depression (CSD) in the rat
abstract: The purpose of this study was to examine whether endothelium-mediated dilation is responsible for the cortical hyperemia that occurs during cortical spreading depression (CSD) in rats using three different approaches. The first approach taken was the acute pharmacological inhibition of the predominant endothelium-centered dilator systems, using indomethacin, a cyclooxygenase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, and miconazole, a cytochrome P-450 epoxygenase inhibitor. The second approach used was the acute general pharmacological impairment of endothelial function by the intravascular administration of phorbol 12, 13-dibutyrate (PDBu). The third approach taken was the chronic impairment of endothelium-dependent dilator responses by diet in insulin resistant (IR) rats. Cerebral blood flow (CBF) was measured using laser Doppler flowmetry. CSD was elicited by the topical application of potassium chloride. Pharmacological inhibition of endothelium-dependent dilator factors did not affect CSD. For example, with 20 mg/kg L-NAME, CBF peak of the first series of CSDs was 377 +/- 67% of baseline CBF. After drug administration, CBF peaks of the second and the third series of CSDs were 451 +/- 67% and 390 +/- 69% (n=5, P=n.s.), respectively. Control and IR animals and those treated with indomethacin, miconazole and PDBu showed similar results. We also calculated the area under the CBF curve to fully represent the extent of hyperemia during CSD. However, there were no significant differences in the CBF area with any treatment compared to control animals. Thus, our results provide strong evidence that endothelium-mediated mechanisms have minimal effects on the CSD-associated hyperemia.

title: Multiwavelength optical intrinsic signal imaging of cortical spreading depression.
abstract: Cortical spreading depression (CSD) is an important disease model for migraine and cerebral ischemia. In this study, we exploit the high temporal and spatial resolution of optical imaging to characterize perfusion-dependent and -independent changes in response to CSD and to investigate the etiology of reflectance changes during CSD. In this experiment, we characterized the optical response to CSD at wavelengths that emphasize perfusion-related changes (610 and 550 nm), and we compared these results with 850 nm and blood volume data. Blood volume changes during CSD were recorded using an intravascular fluorescent dye, Texas Red dextran. We observed triphasic optical signals at 850 and 550 nm characterized by spreading waves of increased, decreased, then increased reflectance  which expanded at a rate of approximately 3-5 mm/min. The signal at 610 nm had a similar initial phase, but the phase 2 response was slightly more complex, with a parenchymal decrease in reflectance but a vascular increase in reflectance. Reflectance values decreased in phase three. Blood volume signals were delayed relative to the optical intrinsic signals and corresponded temporally to phases 2 and 3. This is the first study to characterize optical imaging of intrinsic signal responses to CSD, in vivo, at multiple wavelengths. The data presented here suggest that changes in light scattering precede perfusion responses, the blood volume increase (phase 2) is accompanied by a reduction in deoxyhemoglobin, and the blood volume decrease (phase 3) is accompanied by an increase in deoxyhemoglobin. Previous studies have suggested the oligemia of spreading depression was a result of decreased metabolic demand. This study suggests that during the oligemic period there is a greater reduction in oxygen delivery than in demand.

title: Determinants of brain activation-induced cortical NAD/NADH responses in vivo
abstract: In order to elucidate that which are the factors that may influence the direction of brain activation-induced changes in the redox state of oxidized/reduced nicotinamide adenine dinucleotide (NAD/NADH), the brain cortex was electrically stimulated during arterial hypotension and following reinfusion of the shed blood, during arterial hyper- and hypoxia, and during the second phase of spreading cortical depression (SD). Cerebrocortical NADH fluorescence and vascular volume ( CVV ) of cats, anaesthetized by chloralose, were measured with a microscope fluororeflectometer . Under physiologically normal conditions electrical stimulation resulted in pronounced cortical NAD reduction and increase in CVV . These reactions were not altered by arterial hyperoxia and continuous superfusion of the brain cortex with oxygenated artificial cerebrospinal fluid (mock CSF). Arterial hypotension and SD (in phase II) increased NAD reduction and CVV markedly, and the superimposed electrical stimulation brought about NADH oxidation and greatly depressed CVV responses. Reinfusion of the shed blood did not restore NAD/NADH redox state and CVV to their reference levels, and electrical stimulation under this condition led to NADH oxidation and negligible vascular reactions. Since under physiologically normal conditions electrical activation of the brain cortex resulted in NAD reduction and marked increase in CVV and the magnitude of these reactions were not altered by arterial hyperoxia or by superfusion of the brain cortex with oxygenated CSF, it is very unlikely that the brain cortex became hypoxic during stimulation. Because when the steady NAD/NADH redox state of the brain cortex was shifted toward reduction by arterial hypotension and reinfusion and SD, electrical stimulation led to NADH oxidation, it is suggested that the prestimulatory steady redox state has great importance in determining the direction of NAD/NADH redox reactions evoked by activation of the brain cortex.

title: Separation of changes in light scattering and chromophore concentrations during cortical spreading depression in rats.
abstract: We used near-infrared spectroscopy to separate tissue scattering changes from changes in cerebral oxyhemoglobin and deoxyhemoglobin and the redox state of cytochrome- c -oxidase. A separate term of the transport scattering coefficient (micro(s)(?)) was included in a modified Lambert-Beer equation. It is shown by diffusion equation analysis that there is a simple relationship between the differential path-length factor (D(a)) and its scattering equivalent (D(s)) . The method was applied to cortical spreading depression (CSD) data recorded through the skulls of rats. Biphasic changes in micro(s)(?)of +/-0.1mm(-1)were observed during CSD's that spread with a velocity of ~5mm/min . The method proposed has the promise to permit monitoring of scattering changes noninvasively in humans during cortical activation or pathophysiological conditions.

title: Characterization of optical intrinsic signals and blood volume during cortical spreading depression
abstract: Cortical spreading depression (CSD) was imaged in vivo in a rodent model with optical intrinsic signals (OIS). This is the first study to identify a triphasic OIS response and to characterize the rate and timing of the response. The initial OIS phase had a highly uniform wavefront, which spread at a rate characteristic of CSD, 3.5 mm/min. Later phases were more diffuse and inhomogeneous. Blood volume changes, measured with intravascular fluorescent dye, correlated in time and location with the later phases of OIS reponse. This suggests that the inhomogeneity of the late OIS response may be due to complex residual hemodynamic contributions, as opposed to underlying cortical circuitry.

title: Fast vascular component of cortical spreading depression revealed in rats by blood pulsation imaging
abstract: Cortical spreading depression (CSD) is a slowly propagating wave of depolarization of neurons and glia and has a less characterized vascular component. CSD is a commonly used phenomenon to test new methods of live brain imaging. Application of a blood pulsations imaging (BPI) technique to study of CSD induced with high-potassium solution in rat cortex allowed us to visualize for the first time the novel vascular component of a CSD wave. In our study, this wave component propagated in the limited part of the cortex along the bow-shaped trajectory in sharp contrast with concentric development of CSD measured by concurrently applied optical intrinsic signal (OIS) imaging technique. It was associated with a significant increase of the blood pulsations amplitude (BPA), started with a delay of 20 to 90 s comparing to signal measured with OIS, and propagated 40% faster than OIS signal. These findings suggest that the BPA and slower change of the cerebral blood volume are not directly related to each other even though both characterize the same vascular system. Our study indicates that the BPI technique could be used for characterization of the new pulsatile vascular component of CSDs in animal models of migraine, stroke, and brain trauma.

title: Magnetic Resonance Imaging Assessment of Cerebral Hemodynamics during Spreading Depression in Rats
abstract: High-speed magnetic resonance imaging was used to perform simultaneous measurements of relative cerebral blood volume (rCBV) and water diffusion changes during spreading depression (SD) induced by cortical potassium chloride application. Rats were fitted epidurally with a rubber chamber. Potassium chloride was perfused through the chamber until SD was indicated by a negative direct current (DC) potential shift. Magnetic resonance imaging scans used echo planar diffusion and T2-weighted images. Iron dextran was injected as a blood pool contrast agent to make subsequent changes in T2 (or T2*) directly proportional to changes in CBV. Multislice maps of apparent diffusion coefficient (ADC) and rCBV were generated with 6- to 16-second time resolution, which revealed transient ADC and rCBV changes propagating over the cortex after potassium chloride application. Transient ADC declines appeared simultaneously with the DC shift, whereas rCBV increase followed with a delay of 16.4 ± 14.9 seconds. Prolonged rCBV decrease was observed after the initial increase during the SD in half of the animals. The delayed rCBV response after the ADC change supports the observation of increased energy demand because of repolarization. Simultaneous DC potential recording and ADC measurements in corresponding sites of the cortex indicate that transient ADC decreases during SD reflect water shifts associated with cell depolarization.

title: Vascular imprints of neuronal activity: relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation.
abstract: Modern functional neuroimaging methods, such as positron-emission tomography (PET), optical imaging of intrinsic signals, and functional MRI (fMRI) utilize activity-dependent hemodynamic changes to obtain indirect maps of the evoked electrical activity in the brain. Whereas PET and flow-sensitive MRI map cerebral blood flow (CBF) changes, optical imaging and blood oxygenation level-dependent MRI map areas with changes in the concentration of deoxygenated hemoglobin (HbR). However, the relationship between CBF and HbR during functional activation has never been tested experimentally. Therefore, we investigated this relationship by using imaging spectroscopy and laser-Doppler flowmetry techniques, simultaneously, in the visual cortex of anesthetized cats during sensory stimulation. We found that the earliest microcirculatory change was indeed an increase in HbR, whereas the CBF increase lagged by more than a second after the increase in HbR. The increased HbR was accompanied by a simultaneous increase in total hemoglobin concentration (Hbt), presumably reflecting an early blood volume increase. We found that the CBF changes lagged after Hbt changes by 1 to 2 sec throughout the response. These results support the notion of active neurovascular regulation of blood volume in the capillary bed and the existence of a delayed, passive process of capillary filling.

title: Scanning Laser-Doppler Flowmetry of Rat Cerebral Circulation during Cortical Spreading Depression
abstract: Scanning laser-Doppler flowmetry (SLDF) generates two-dimensional images of blood flow. This study compared SLDF to conventional laser-Doppler flowmetry (LDF) in the cerebral circulation. Test stimuli were episodes of cortical spreading depression (CSD) elicited in brains of halothane anaesthetised rats (n = 9). The LDF instrument used two wavelengths of laser light to record relative changes of cerebral blood flow (CBF) up to an approximate depth of 250 µm (543 nm) and 500 µm (780 nm). Under resting conditions, SLDF images showed a heterogeneous pattern of flow in pial vessels with high flow rates in arterioles, and lower rates in venules and small vessels (<30 µm). Arterioles constituted about 6%, venules 12% and small vessels 2% of the image area, while approximately 80% were background with a laser-Doppler signal corresponding to zero calibration. During CSD, the relative increase of area was largest for small vessels and less for venules and arterioles. Similar changes were observed for blood flow in the three vessel structures. For both wavelengths of LDF, flow changes correlated with SLDF (r ≈ 0.7). In conclusion, SLDF provides images of flow in pial vessels and capillaries at, or just beneath the cortical surface. SLDF and LDF are complementary, but cannot substitute for one another as they measure flow in different layers of the cortex.

title: Cerebral hemodynamics during cortical spreading depression in rabbits
abstract: Effects of a single cortical spreading depression (CSD), elicited by KCl microinjection, on diameter of pial arterioles and venules in the parieto-occipital cortex were examined in urethane-anesthetized adult rabbits using a closed cranial window. The velocity of CSD propagation was 2.7 +/- 0.1 mm/min (mean +/- S.E.M.). All arterioles (n = 39) except for those in the retrosplenial region (n = 6) increased their diameter significantly during CSD. The arteriolar dilation lasted for 1.5 +/- 0.1 min. Location of dilating arteriole and propagating CSD showed that they were always closely associated temporally. As a percentage change, diameters of smaller arterioles significantly increased (from 60 +/- 1 to 103 +/- 2 microns, 71%, n = 12) more than those of larger ones (from 82 +/- 2 to 129 +/- 3 microns, 57%, n = 27). While venules with initial diameter of 85 +/- 4 microns (n = 5) did not dilate, those with initial diameter of 49 +/- 3 microns increased to 57 +/- 3 microns (16%, n = 8) for 1.4 +/- 0.2 min during CSD. The majority of the dilated venules started to increase their diameter after nearby arterioles had dilated maximally. Pial arterioles, which dilated during ipsilateral CSD, decreased their diameter significantly from 78 +/- 2 to 72 +/- 3 microns (8%, n = 11) during contralateral CSD for 13.8 +/- 3.6 min with similar onset latencies as those observed for the dilation. Indomethacin pretreatment significantly enhanced arteriolar dilation during CSD (from 73 +/- 4 to 138 +/- 6 microns, 89%, n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

title: Investigating the effects of dimethylsulfoxide on hemodynamics during cortical spreading depression by combining laser speckle imaging with optical intrinsic signal imaging
abstract: Cortical spreading depression (CSD) is an important pathological model to study cerebral ischemia and migraine. In pharmacological studies of CSD, dimethylsulfoxide (DMSO) is an efficient solvent for water‐insoluble drugs. Previous studies indicated that DMSO could prevent pial arteriolar dilation induced by oxidants. Therefore, it was very important to study the effect of DMSO on hemodynamics during CSD so that optimization of dose of DMSO as solvent can be made.

title: Pial arteriolar constriction following cortical spreading depression is mediated by prostanoids
abstract: The mechanism of pial arteriolar constriction during post-cortical spreading depression (CSD) was examined in anesthetized adult rabbits. Using a closed cranial window and intravital microscopy, the diameter of a pial arteriole was determined. A single CSD was induced by KCl micro-injection and its propagation was monitored by recording slow potential changes accompanying CSD. Prostanoid levels in cortical cerebrospinal fluid (CSF) were determined by radioimmunoassay. Pial arteriolar diameter increased significantly from 76 +/- 6 to a maximum of 119 +/- 5 microns (57%, n = 8) for 1.6 +/- 0.1 min when CSD (velocity, 2.8 +/- 0.1 mm/min) reached the cortex just beneath the vessel irrespective of its location. Shortly after CSD expiration from the cortex, pial arteriolar diameter decreased from the pre-CSD level to a minimum of 67 +/- 5 microns (12%, n = 8) for 19.5 +/- 2.1 min. CSD was elicited again in the same animal while the cortical surface under the window was continuously superfused with artificial CSF at a flow rate of 3.2-4.5 ml/min. Pial arteriolar dilation (from 75 +/- 6 to 115 +/- 3 microns, 53 +/- 9%, for 1.6 +/- 0.1 min, n = 8) was observed again during CSD (velocity, 2.7 +/- 0.2 mm/min), however, no constriction of the vessel was seen after CSD expiration. Indomethacin pretreatment (n = 11) to inhibit prostanoid production enhanced the magnitude of CSD-induced vasodilation from the pretreatment levels of 59 +/- 9% (from 82 +/- 5 to 130 +/- 8 microns for 1.7 min) to the post-treatment levels of 82 +/- 13% (from 78 +/- 5 to 142 +/- 12 microns for 1.8 min).(ABSTRACT TRUNCATED AT 250 WORDS)

title: Change of cerebrovascular reactivity after cortical spreading depression in cats and rats
abstract: The purpose of the present study was to examine the pial arteriolar diameter and evoked vascular responses after single episodes of cortical spreading depression (CSD) in rats and cats in order to elucidate the mechanisms of the persistent change of cortical perfusion which succeeds CSD. This problem is of potential clinical interest also since CSD may be involved in migraine pathophysiology. Using an open cranial window technique, pial arteriolar diameters were measured with an image splitting method. Vascular reactivity was tested by local perivascular microapplication of mock cerebrospinal fluid (CSF) containing high and low levels of K+, high and low pH, adenosine and bradykinin before and after CSD which was triggered by intracortical injection of KCl. During CSD a monophasic vasodilatation of 26.0 +/- 3.7% (mean +/- S.E.M.; cat) or 64.6 +/- 3.9% (rat) was observed. Following CSD, the cat developed persistent vasodilatation (16.7 +/- 1.9%) while the rat exhibited vasoconstriction (12.1 +/- 1.8%). Both species displayed a severely impaired responsiveness to constrictor and dilating stimuli as compared to pre-CSD values. The responses were reduced by 28-84%, dependent on the substance tested. It is concluded that vascular reactivity is severely impaired after CSD (15-75 min) and that this might explain the impaired coupling between flow and metabolism after CSD.

title: Nitric Oxide Scavenging by Hemoglobin or Nitric Oxide Synthase Inhibition by N-Nitro-L-Arginine Induces Cortical Spreading Ischemia When K+ Is Increased in the Subarachnoid Space
abstract: We investigated the combined effect of increased brain topical K+ concentration and reduction of the nitric oxide(NO.) level caused by nitric oxide scavenging or nitric oxide synthase (NOS) inhibition on regional cerebral blood flow and subarachnoid direct current (DC) potential. Using thiopental-anesthetized male Wistar rats with a closed cranial window preparation, brain topical superfusion of a combination of the NO. scavenger hemoglobin(Hb; 2 mmol/L) and increased K+ concentration in the artificial cerebrospinal fluid ([K+]ACSF) at 35 mmol/L led to sudden spontaneous transient ischemic events with a decrease of CBF to 14 ± 7% (n = 4) compared with the baseline (100%). The ischemic events lasted for 53 ± 17 minutes and were associated with a negative subarachnoid DC shift of −7.3 ± 0.6 mV of 49 ± 12 minutes' duration. The combination of the NOS inhibitor N-nitro-L-arginine(L-NA, 1 mmol/L) with [K+]ACSF at 35 mmol/L caused similar spontaneous transient ischemic events in 13 rats. When cortical spreading depression was induced by KCl at a 5-mm distance, a typical cortical spreading hyperemia (CSH) and negative DC shift were measured at the closed cranial window during brain topical superfusion with either physiologic artificial CSF (n = 5), or artificial CSF containing increased [K+]ACSF at 20 mmol/L (n = 4), [K+]ACSF at 3 mmol/L combined with L-NA (n = 10), [K+]ACSF at 10 mmol/L combined with L-NA (five of six animals) or [K+]ACSF at 3 mmol/L combined with Hb (three of four animals). Cortical spreading depression induced long-lasting transient ischemia instead of CSH, when brain was superfused with either[K+]ACSF at 20 mmol/L combined with Hb (CBF decrease to 20± 20% duration 25 ± 21 minutes, n = 4), or [K+]ACSF at 20 mmol/L combined with L-NA (n = 19). Transient ischemia induced by NOS inhibition and [K+]ACSF at 20 mmol/L propagated at a speed of 3.4 ± 0.6 mm/min, indicating cortical spreading ischemia (CSI). Although CSH did not change oxygen free radical production, as measured on-line by in vivo lucigenin-enhanced chemiluminescence, CSI resulted in the typical radical production pattern of ischemia and reperfusion suggestive of brain damage (n = 4). Nimodipine (2 μg/kg body weight/min intravenously) transformed CSI back to CSH (n = 4). Vehicle had no effect on CSI(n = 4). Our data suggest that the combination of decreased NO. levels and increased subarachnoid K+ levels induces spreading depression with acute ischemic CBF response. Thus, a disturbed coupling of metabolism and CBF can cause ischemia. We speculate that CSI may be related to delayed ischemic deficits after subarachnoid hemorrhage, a clinical condition in which the release of Hb and K+ from erythrocytes creates a microenvironment similar to the one investigated here.

title: Ischaemia triggered by spreading neuronal activation is inhibited by vasodilators in rats
abstract: 1 It has been previously shown that spreading neuronal activation can generate a cortical spreading ischaemia (CSI) in rats. The purpose of the present study was to investigate whether vasodilators cause CSI to revert to a normal cortical spreading depression (CSD). 2 A KCl‐induced CSD travelled from an open cranial window to a closed window where the cortex was superfused with physiological artificial cerebrospinal fluid (ACSF). At the closed window, recordings revealed a short‐lasting negative slow potential shift accompanied by a variable, small and short initial hypoperfusion followed by hyperaemia and then oligaemia. 3 In contrast, spreading neuronal activation locally induced CSI at the closed window when ACSF contained a NO. synthase (NOS) inhibitor, NG‐nitro‐l‐arginine, and an increased K+ concentration ([K+]ACSF). CSI was characterised by a sharp and prolonged initial cerebral blood flow decrease to 29 ± 11 % of the baseline and a prolonged negative potential shift. 4 Co‐application of a NO. donor, S‐nitroso‐N‐acetylpenicillamine, and NOS inhibitor with high [K+]ACSF re‐established a short‐lasting negative potential shift and spreading hyperaemia typical of CSD. Similarly, the NO.‐independent vasodilator papaverine caused CSI to revert to a pattern characteristic of CSD. 5 In acute rat brain slices, NOS inhibition and high [K+]ACSF did not prolong the negative slow potential shift compared to that induced by high [K+]ACSF alone. 6 The data indicate that the delayed recovery of the slow potential was caused by vasoconstriction during application of high [K+]ACSF and a NOS inhibitor in vivo. This supports the possibility of a vicious circle: spreading neuronal activation induces vasoconstriction, and vasoconstriction prevents repolarisation during CSI. Speculatively, this pathogenetic process could be involved in migraine‐induced stroke.

title: Arginine-nitric oxide pathway and cerebrovascular regulation in cortical spreading depression.
abstract: Nerve cells release nitric oxide (NO) in response to activation of glutamate receptors of the N-methyl-D-aspartate (NMDA) subtype. We explored the hypothesis that NO influences the changes of cerebral blood flow (CBF) during cortical spreading depression (CSD), which is known to be associated with NMDA receptor activation. CBF was monitored in parietal cortex by laser-Doppler flowmetry in halothane-anesthetized rats. Under control conditions, CSD induced regular changes of CBF, which consisted of four phases: a brief hypoperfusion before the direct current (DC) shift; a marked CBF rise during the DC shift; followed by a smaller, but protracted increase of CBF; and a prolonged CBF reduction (the oligemia). NO synthase inhibition by intravenous and/or topical application of NG-nitro-L-arginine enhanced the brief initial hypoperfusion, but the CBF increases and the oligemia were unchanged. L-Arginine prevented the development of the prolonged oligemia after CSD but had no influence on the marked rise of CBF during CSD. Animals treated with L-arginine recovered the reduced vascular reactivity to hypercapnia after CSD much faster than control rats. Functional denervation of cortical and pial arterioles by tetrodotoxin accentuated the pre-CSD hypoperfusion and the oligemia but did not affect the CBF increases. The results suggest that NO is important for the changes of cerebrovascular regulation following CSD. The observations may have clinical importance, since CBF changes during migraine may be triggered by CSD.

title: Direct, Live Imaging of Cortical Spreading Depression and Anoxic Depolarisation Using a Fluorescent, Voltage-Sensitive Dye
abstract: Perilesion depolarisations, whether transient anoxic depolarisation (AD) or spreading depression (SD), occur in stroke models and in patients with acute brain ischaemia, but their contribution to lesion progression remains unclear. As these phenomena correspond to waves of cellular depolarisation, we have developed a technique for their live imaging with a fluorescent voltage-sensitive (VS) dye (RH-1838). Method development and validation were performed in two different preparations: chicken retina, to avoid any vascular interference; and cranial window exposing the cortical surface of anaesthetised rats. Spreading depression was produced by high-K medium, and AD by complete terminal ischaemia in rats. After dye loading, the preparation was illuminated at its excitation wavelength and fluorescence changes were recorded sequentially with a charge-coupled device camera. No light was recorded when the VS dye was omitted, ruling out the contribution of any endogenous fluorophore. With both preparations, the changes in VS dye fluorescence with SD were analogous to those of the DC (direct current) potential recorded with glass electrodes. Although some blood quenching of the emitted light was identified, the VS dye signatures of SD had a good signal-to-noise ratio and were reproducible. The changes in VS dye fluorescence associated with AD were more complex because of additional interferents, especially transient brain swelling with subsequent shrinkage. However, the kinetics of the AD-associated changes in VS dye fluorescence was also analogous to that of the DC potential. In conclusion, this method provides the imaging equivalent of electrical extracellular DC potential recording, with the SD and AD negative shifts translating directly to fluorescence increase.

title: Detecting tissue deterioration after brain injury: regional blood flow level versus capacity to raise blood flow
abstract: Regional cerebral blood flow (rCBF) is spatially and temporally adjusted to local energy needs. This coupling involves dilation of vessels both at the site of metabolite exchange and upstream of the activated region. Deficits in upstream blood supply limit the ‘capacity to raise rCBF’ in response to functional activation and therefore compromise brain function. We here demonstrate in rats that the ‘capacity to raise rCBF’ can be determined from real-time measurements of rCBF using laser speckle imaging during an energy challenge induced by cortical spreading depolarizations (CSDs). Cortical spreading depolarizations (CSDs) occur with high incidence in stroke and various other brain injuries and cause large metabolic changes. Various conditions of cerebral perfusion were induced, either by modifying microvascular tone, or by altering upstream blood supply independently. The increase in rCBF per unit of time in response to CSD was linearly correlated to the upstream blood supply. In an experimental model of stroke, we found that this marker of the capacity to raise rCBF which, in pathologic tissue may be additionally limited by impaired vasoactive signaling, was a better indicator of the functional status of cerebral tissue than local rCBF levels.

title: The oligemic phase of cortical spreading depression is not blocked by tirilazad mesylate (U-74006F)
abstract: Cortical spreading depression is characterised by a wave of depolarization that moves across the cortex leaving in its wake a state of hyperpolarization. Characteristic changes in cerebral blood flow are also seen and these consist of a wave of hyperemia followed by an oligemia, the latter lasting some hours in some experimental animals including the cat. In this study cerebral blood flow was measured using laser Doppler flowmetry in the anesthetised ventilated cat. Spreading depression was initiated with a pin-prick injury prior to or following administration of U74006F (tirilizad mesylate; 3 mg/kg, ivi) or an identical volume of vehicle. Laser Doppler probes were placed bilaterally and in each case studied both the hyperemic and oligemic phases of spreading depression were preserved after administration of either U74006F or its vehicle. These data suggest that free radical mechanisms have no significant role in mediating the blood flow changes of spreading depression and are consistent with data in the literature of a quantitative using single-point measurements that again U74006F does not affect spreading depression.

title: Nitric oxide synthesis couples cerebral blood flow and metabolism
abstract: The most fundamental aspect of the cerebral circulation is the well-described coupling of cerebral metabolic activity and cerebral blood flow. A number of substances have been proposed to link flow and metabolism, including K+, pH and adenosine. In the alpha-chloralose anaesthetised cat we studied simultaneously cerebral neuronal activity and local blood flow to attempt to dissociate the two and thus determine the coupling substance. Neuronal activity was determined by monitoring unit firing in the parietal cortex with tungsten in glass microelectrodes while local cerebral blood flow in the same area was monitored continuously using laser Doppler flowmetry. To initiate an increase in metabolic activity and, pari passu, blood flow spreading depression was elicited by needle stick injury. Spreading depression when initiated causes a wave of depolarization, measured as an increased firing rate and associated marked (400 +/- 95%) increase in local cerebral blood flow. Intravenous administration of NG-nitro-L-arginine methyl ester (1-NAME), a potent nitric oxide synthase inhibitor, produced a complete blockade of the hyperemia associated with spreading depression but no change in either resting cell firing or spreading depression-evoked increases in firing rate. These data demonstrate at least for spreading depression-elicited increases in metabolic activity, that nitric oxide (NO) is a key coupling compound that links changes in cerebral blood flow and metabolism. These data imply that NO may have a more general role in flow/metabolism coupling and further studies in other situations are required to determine the extent to which NO is responsible for this fundamental cerebrovascular phenomenon.

title: Regional cerebral blood flow during cortical spreading depression in rat brain: increased reactive hyperperfusion in low‐flow states
abstract: The purpose of the present study was to characterize the initial vascular events accompanying cortical spreading depression (CSD) of the rat brain. Regional cerebral blood flow (rCBF) was measured during the first 1–2 min of CSD using 14C‐iodoantipyrine autoradiography. The material included a reference group, and 4 groups where rCBF was altered by indomethacin treatment, hypo‐ or hypercapnia, or one previous episode of CSD. rCBF did not change prior to, or during the onset of CSD. Thirty seconds later, rCBF increased depending on the pre‐existing level of blood flow, i.e. the rise of rCBF was pronounced at depressed flow levels, but small or absent at normal or high flow levels. The prevalent view that CSD is intimately associated with vasodilatation was accordingly not supported. The activated rCBF in normocapnic rats ranged between 93 and 175 ml/100g/min, supra normal values were the exception rather than the rule. The rCBF rise, when present, probably succeeds a period of brain hypoxia, and should be classified as a reactive hyperfusion. The results together with earlier clinical and experimental findings, support that CSD may serve as experimental migraine model.

title: Real time laser-Doppler perfusion imaging of cortical spreading depression in rat neocortex.
abstract: Laser-Doppler perfusion imaging (LDPI) is a new technique which provides recordings of blood flow in rapid sequence. In this study we applied LDPI to the brain for the first time to demonstrate propagating waves of cortical spreading depression (CSD) elicited by a needle stab in the frontal cortex of barbiturate-anesthetized rats. Under resting conditions, LDPI recordings of the superficial cortex showed a heterogeneous pattern, partly due to the high flow rate in pial arteries compared with cortical tissue. Within 1 min after elicitation of the CSD a zone of increased signal intensity (96 +/- 5%) up to 6 mm across appeared in the exposed cortex. The rate of propagation away from the site of elicitation for 16 such waves was 2.8 +/- 0.1 mm min-1. The increased signal intensity was partly due to dilatation of pial arterioles and veins, partly to increased blood flow in the microvascular bed. The data are consistent with previous studies of CSD using other techniques for measurement of cortical blood flow. LDPI gives real time images of cerebral blood flow, and may be applied to demonstrate CSD or CSD-like phenomena during neurosurgical operations in man.

title: Cortical blood flow changes during spreading depression in cats.
abstract: Changes in cortical blood flow and cerebrovascular activity occurring during and after cortical spreading depression (CSD) were studied in alpha-chloralose-urethan-anesthetized cats. CSD was induced by superficial cortical pinprick, and laser-Doppler velocimetry (LDV) was used to measure cerebral blood flow (CBFLD). CSD resulted in a wave of cortical hyperemia during which there was a 215 +/- 48% peak increase in cortical blood flow that lasted for 2.7 +/- 0.4 min. This hyperemic phase was followed by prolonged cortical oligemia, with a reduction in flow of 20 +/- 4% at 1 h and 28 +/- 4% at 2 h. After CSD, cerebrovascular reactivity to the inhalation of CO2 was abolished and did not fully recover for at least 10 h. Spontaneous vasomotor activity in the cerebral microcirculation was significantly decreased after CSD, and autoregulation of cortical blood flow in response to hypotension was preserved. The abnormal cerebrovascular reactivity seen after CSD in the gyrencephalic cortex of the cat has possible significance for human migraine with aura.

title: The dynamics of nitric oxide release measured directly and in real time following repeated waves of cortical spreading depression in the anaesthetised cat
abstract: Cortical application of crystalline KCl in male cats anaesthetised with alpha-chloralose induced four transient negative deflections in cortical direct current (d.c.) potential. In vehicle treated animals d.c. shifts were associated with a hyperaemia and a multiphasic nitric oxide (NO) release. In these animals, the first negative shift in d.c. potential produced a significantly larger NO electrode current, when compared to subsequent cortical depolarisations. However, regional cerebrovascular laser Doppler flux (rCBF[LDF]) increases were similar for each event. In L-N(G)-nitro-L-arginine (L-NAME; 10 mg/kg i.v. infused over 30 min) treated animals, d.c. shifts were also associated with NO release following a multiphasic waveform and increase in rCBF(LDF), but were significantly attenuated when compared to controls.

title: Perivascular nerves contribute to cortical spreading depression-associated hyperemia in rats.
abstract: We investigated the contribution of perivascular nerves and neurotransmitters to cortical spreading depression (CSD)-associated hyperperfusion in the rat. Chronic transection of the nasociliary nerve (NCN, 2 wk before) decreased ipsilateral CSD-associated hyperperfusion by 23 +/- 13% (mean +/- SD; n = 5, P < 0.05), whereas acute transection of the NCN or sham surgery had no effect (n = 8). When the NCN and parasympathetic nerve fibers (PSN) were both chronically transected, CSD hyperperfusion was attenuated by 55 +/- 19% (n = 5, P < 0.05). Cerebrovascular reactivity to hypercapnia was not significantly affected. Brain topical superfusion of the muscarinic receptor antagonist atropine (10(-4) M) caused a reduction of CSD hyperperfusion by 41 +/- 13% (n = 5, P < 0.05). The competitive blockade of calcitonin gene-related peptide (CGRP) receptors by CGRP-(8-37) (5 x 10(-7) M) afforded a decrease by 49 +/- 19% (n = 5, P < 0.05), without affecting CO2 reactivity (n = 4). The combined application of both CGRP-(8-37) and atropine further attenuated CSD hyperperfusion (by 69 +/- 17%, n = 5, P < 0.05). After chronic NCN and PSN transection brain topical superfusion of CGRP-(8-37) (5 x 10(-7) M) reduced CSD hyperperfusion slightly by 9.5 +/- 5% (n = 3). Atropine (10(-4) M) afforded a decrease by 17 +/- 6% (n = 3). These reductions were not statistically significant. We conclude that CSD-associated hyperperfusion is mediated in part by a depolarization of trigeminal sensory and parasympathetic nerve fibers, resulting in a release of vasoactive trigeminal and parasympathetic neurotransmitters.

title: AN EXPERIMENTAL MODEL OF MIGRAINE WITH AURA: CORTICAL HYPOPERFUSION FOLLOWING SPREADING DEPRESSION IN THE AWAKE AND FREELY MOVING RAT
abstract: 1. Cortical spreading depression (CSD) was induced by direct current stimulation of the lateral frontal cortex in awake and freely moving rats.

title: Effects of anesthesia on the responses to cortical spreading depression in the rat brain in vivo
abstract: The aim of this study was to evaluate the effect of cortical spreading depression (CSD) on the metabolic, hemodynamic, electrical and ionic properties during anesthesia as compared with the awake state.  The mitochondrial NADH redox state, reflected light, direct current (DC) potential, electrocorticography (ECoG), cerebral blood flow (CBF) and volume (CBV), and extracellular K+ concentrations ([K+]e), were measured continuously and simultaneously in real time using two unique monitoring systems that evaluate brain function. Three consecutive CSD waves were initiated using a KCl solution in both awake and anesthetized rats.  CSD caused typical amplitude changes: biphasic waves in reflectance, oxidation cycles in NADH, an increase in CBF, CBV and in [K+]e, a negative shift in DC potential and depression in ECoG. Anesthesia by equithesin decreased significantly the baseline levels of CBF and [K+]e, showing a reduction in oxygen supply and demand. After anesthesia, CSD significantly decreased [K+]e and NADH oxidation cycles, indicating a reduction in oxygen demand and in oxygen balance, respectively. Furthermore, anesthesia reduced CSD wave frequencies by slowing the recovery period, showing a decline in energy production during brain activation, or by changing electrophysiological properties of the tissue. No changes were found in the propagation rate and in the initiation period of CSD, which may indicate that equithesin does not block CSD initiation. In addition, we found that the whole cerebral cortex reacts homogenously to CSD and that equithesin may reduce oxygen demand and energy production, which may have a protective effect on the brain exposed to pathophysiological conditions.

title: Hypoxia and Hypotension Transform the Blood Flow Response to Cortical Spreading Depression from Hyperemia into Hypoperfusion in the Rat
abstract: Cortical spreading depression (CSD) evokes a large cerebral blood flow (CBF) increase in normal rat brain. In contrast, in focal ischemic penumbra, CSD-like periinfarct depolarizations (PID) are mainly associated with hypoperfusion. Because PIDs electrophysiologically closely resemble CSD, we tested whether conditions present in ischemic penumbra, such as tissue hypoxia or reduced perfusion pressure, transform the CSD-induced CBF response in nonischemic rat cortex. Cerebral blood flow changes were recorded using laser Doppler flowmetry in rats subjected to hypoxia, hypotension, or both. Under normoxic normotensive conditions, CSD caused a characteristic transient CBF increase (74 ± 7%) occasionally preceded by a small hypoperfusion (−4 ± 2%). Both hypoxia (pO2 45 ± 3 mm Hg) and hypotension (blood pressure 42 ± 2 mm Hg) independently augmented this initial hypoperfusion (−14 ± 2% normoxic hypotension; −16 ± 6% hypoxic normotension; −21 ± 5% hypoxic hypotension) and diminished the magnitude of hyperemia (44 ± 10% normoxic hypotension; 43 ± 9% hypoxic normotension; 27 ± 6% hypoxic hypotension). Hypotension and, to a much lesser extent, hypoxia increased the duration of hypoperfusion and the DC shift, whereas CSD amplitude remained unchanged. These results suggest that hypoxia and/or hypotension unmask a vasoconstrictive response during CSD in the rat such that, under nonphysiologic conditions (i.e., mimicking ischemic penumbra), the hyperemic response to CSD becomes attenuated resembling the blood flow response during PIDs.

title: Sustained Decrease and Remarkable Increase in Red Blood Cell Velocity in Intraparenchymal Capillaries Associated With Potassium‐Induced Cortical Spreading Depression
abstract: Please cite this paper as: Unekawa M, Tomita M, Tomita Y, Toriumi H and Suzuki N. Sustained Decrease and Remarkable Increase in Red Blood Cell Velocity in Intraparenchymal Capillaries Associated With Potassium‐Induced Cortical Spreading Depression. Microcirculation 19: 166–174, 2012.

title: Potassium‐induced cortical spreading depression bilaterally suppresses the electroencephalogram but only ipsilaterally affects red blood cell velocity in intraparenchymal capillaries
abstract: Cortical spreading depression (CSD) is a repetitive, propagating profile of mass depolarization of neuronal and glial cells, followed by sustained suppression of spontaneous neuronal activity. We have reported a long‐lasting suppressive effect on red blood cell (RBC) velocities in intraparenchymal capillaries. Here, to test the hypothesis that the prolonged decrease of RBC velocity in capillaries is due to suppression of neuronal activity, we measured CSD‐elicited changes in the electroencephalogram (EEG) as an index of neuronal activity. In isoflurane‐anesthetized rats, DC potential, EEG, partial pressure of oxygen (PO2), and cerebral blood flow (CBF) were simultaneously recorded in the temporo‐parietal region. The velocities of fluorescently labeled RBCs were evaluated by high‐speed camera laser scanning confocal fluorescence microscopy with our original software, KEIO‐IS2. Transient deflection of DC potential and PO2 and increase of CBF were repeatedly detected only in the ipsilateral hemisphere following topical KCl application. On the other hand, the relative spectral power of EEG was reduced bilaterally, showing the lowest value at 5 min after KCl application, when the other parameters had already returned to the baseline after the passage of CSD. Mean RBC velocity in capillaries was slightly but significantly reduced during and after passage of CSD in the ipsilateral hemisphere but did not change in the contralateral hemisphere in the same rats. We suggest that mass depolarization of neuronal and glial cells might transiently decelerate RBCs in nearby capillaries, but the sustained reduction of ipsilateral RBC velocity might be a result of the prolonged effect of CSD, not of neuronal suppression alone.

title: Cortical spreading depression confounds concentration-dependent pial arteriolar dilation during N-methyl-D-aspartate superfusion.
abstract: Pial arterioles do not express N-methyl-D-aspartate (NMDA) receptors but dilate in response to topical NMDA application. We explored the mechanism underlying NMDA-mediated responses in murine pial arterioles (11-31 microm), using a closed cranial window preparation, and found that arteriolar dilation was not concentration dependent. Pial arteriolar diameter abruptly increased within 3 min of superfusing 50 or 100 microM NMDA. Dilation reached a peak within 1 min (46 +/- 14%) and then declined to a plateau (28 +/- 13%) for the duration of superfusion. Whereas a higher concentration (200 microM) did not produce further dilation, lower concentrations (1-10 microM) did not dilate the arterioles at all. MK-801 (10 microM) abrogated the dilation response, whereas Nomega-nitro-L-arginine (1 mM) attenuated the peak and abolished the sustained dilation during NMDA superfusion. We determined that NMDA-induced pial arteriolar responses were evoked by cortical spreading depression, because abrupt vasodilation during 50 or 100 microM NMDA superfusion was associated with a large negative slow potential shift and electrocorticogram suppression that spread from the superfusion window to distant cortical areas. Our data suggest that the responses of pial arterioles to NMDA are caused in part by neurovascular coupling due to cortical spreading depression.

title: Spindle-shaped constriction and propagated dilation of arterioles during cortical spreading depression
abstract: A dual illumination technique was used to examine the behavior of parenchymal arterioles of the cortex during cortical spreading depression in six cats. K+ produced a wave-ring spread of optical density changes concentrically from the injection site. At locations where the wave was passing, arterioles first constricted at one or two spots (55±43% of control), forming a spindle-shape in the early phase of cortical spreading depression, and then markedly dilated (155±57% of control) within 1 min. The dilation started at the constricted spots, propagated bidirectionally and finally resulted in full-length dilation of the arteriole. Although it varied in magnitude and time-course, this arteriolar behavior was observed in all six cats. Despite these changes, no associated downstream tissue microvascular flow changes were discernable.

title: Evidence against parenchymal metabolites directly promoting pial arteriolar dilation during cortical spreading depression in rabbits
abstract: The role of parenchymal metabolic factors in directly promoting pial arteriolar dilation during cortical spreading depression (CSD) in anesthetized rabbits was examined by direct measurement of periarachnoid cerebrospinal fluid (CSF) levels of a representative metabolite (i.e., K+) or superfusion of the cerebral cortical surface with artificial CSF. CSD was induced by KCl microinjection or tissue puncture and its movement was monitored electrophysiologically. Pial arteriolar diameter was determined using a closed cranial window and intravital microscopy. CSD propagated across the cortex under the window with a velocity of 2.9 +/- 0.2 mm/min, and caused pial arteriolar diameter to increase from 87 +/- 9 microns to 133 +/- 11 microns (53%, n = 23) for 1.6 +/- 0.1 min. At the same time, K+ concentration increased from 3.0 +/- 0.2 mM to a maximum of 4.6 +/- 0.3 mM. Topical application of 6 mM K+ increased pial arteriolar diameter by only 8%. Continuous superfusion of the cortical surface with aCSF at a rate of 3.0-4.5 ml/min (window volume = 0.5 ml) did not affect pial arteriolar dilation during CSD, but virtually abolished pial arteriolar dilation during inhalation of 10.2% CO2. These results suggest that pial arterioles dilate via a mechanism which does not involve diffusion of vasoactive metabolites released from the parenchyma during CSD.

title: Intracellular oxidation-reduction state measured in situ by a multichannel fiber-optic surface fluorometer.
abstract: The principles of the measurement in vivo of the oxidation-reduction state of intramitochrondrial pyridine nucleotides were used in establishing a multichannel fluorometer-reflectometer. This approach made possible the study of changes of mitochrondrial redox states in four different organs (brain, liver, kidney, and testis) of the same animal, as well as the monitoring of four different cortical areas of the same brain hemisphere. In the measurement of reduced nicotinamide adenine dinucleotide fluorescence, oximetric and movement artifacts are negligible, but blood volume changes and tissue absorption properties are a source of error. The corrected fluorescence is obtained by subtracting the reflectance from the fluorescence signed in 1:1 ratio., During graded hypoxia, the corrected fluorescence showed a gradual increase and was maximal during anoxia in all four organs tested.

title: Brain mitochondrial redox state, tissue haemodynamic and extracellular ion responses to four-vessel occlusion and spreading depression in the rat.
abstract: Fibre-optic surface fluorometer reflectrometry was used to monitor the NADH (nicotine adenine dinucleotide) redox state from rat brain during three- or four-vessel occlusion. To compare the completeness of the electrocauterization of the vertebral arteries and the effectiveness of the anterior cerebral arteries, two light guides were implanted above the cerebral hemispheres. The NADH level was measured and correlated with the changes in the intensity of the reflected light at the excitation wavelength (366 nm) and to the ECoG (electrocorticogram). In the present study, we used ten rats in which unilateral and bilateral carotid occlusion were performed. In a second group of rats we tested the effects of four-vessel occlusion on the metabolic and extracellular K+ and Ca2+ activities as compared with those recorded under spreading depression conditions. These experiments were done by using the multiprobe assembly (MPA) approach. The results could be summarized as follows: (1) in the four-vessel occlusion model, the level of cerebral ischaemia could be estimated quantitatively, in real-time, by monitoring the NADH redox state; (2) unilateral carotid occlusion (after vertebral coagulation) led to a variable level of ipsilateral ischaemia, depending upon the blood flow compensation between the two hemispheres; (3) fibre-optic fluorometry enabled the correlation of NADH redox state with other physiological parameters as well as during after-brain ischaemia; (4) using the MPA in rats exposed to four-vessel occlusion as well as spreading depression, we identified the differences between the two pathological states, although there were some similarities in the ion homeostasis responses.

title: Factors affecting the oxygen balance in the awake cerebral cortex exposed to spreading depression
abstract: Oxygen balance was evaluated in the cerebral cortex, using the surface fluorometry technique of the intramitochondrial NADH redox state, exposed to various physiological and pathological situations. Using flexible fiber optic light guide, connected to the brain surface via a cemented holder, the measurements were done continuously from the awake rat and gerbil. In few experiments the NADH redox state was correlated with the electrical and ionic activity (measured by surface K+ and DC electrodes). Three different animal models were used in the study: the adult rat, the very young rat (20 g) and the adult gerbil. Those 3 models were used in studying the effect of hypoxia, partial ischemia, and anesthesia on the metabolic and ionic activities measured from the awake brain. Spreading cortical depression (elicited by topical KCl solution) was used as a standard stimulation of the ionic and metabolic activities of the cerebral cortex. Two typical metabolic responses to spreading depression (SD) were recorded, namely 'oxidation cycle' and 'reduction cycle' depending upon the ability of the tissue to compensate for the extra amount of oxygen needed for the higher mitochondrial activity. It was found that the adult rat brain showed oxidation cycles in most conditions (besides partial ischemia), while the young rat and the gerbil brains were much more sensitive to the various perturbations of the brain and exhibited reduction cycle ( as a response to SD) under all pathological situations tested. We conclude from our detailed studies that the type of response to SD, as measured by NADH surface fluorometry, represents the oxygen balance which exists in the tissue under various conditions.

title: The effect of ethanol on metabolic, hemodynamic and electrical responses to cortical spreading depression
abstract: Alcohol induces a decrease in cerebral blood flow (CBF) and metabolic rate, mitochondrial damage and other impairments in brain function and structure. Cortical spreading depression (CSD) is a phenomenon causing changes in ion homeostasis and raises energy demand, mitochondrial activity and CBF. It is of great interest to study the effect of ethanol on brain response under a challenge of increasing oxygen demand by inducing CSD. A special multisite assembly (MSA) was constructed to evaluate metabolic (mitochondrial NADH), hemodynamic (reflectance) and electrical (DC potential) activities from four parasagittally adjacently arranged areas of the cerebral cortex, continuously and simultaneously in vivo. Three CSD cycles were initiated every 30 min before and after ethanol or saline infusion over 4.5 h. During CSD amplitude changes of reflectance, NADH and DC potential as well as propagation rates and wave frequency were calculated. After ethanol infusion CSD showed a decrease in the negative shift of the DC potential, and alterations in the biphasic responses in reflectance, which may indicate alteration in blood volume: unclear responses in the initial vasoconstriction phase and a significant increase in the subsequent vasodilatation phase. The reduction in the amplitude of the NADH oxidation cycle may depict a decrease in energy production, which could also be indicated by a decline in wave frequency (prolonging the recovery phase of the CSD). The decrease in propagation rate indicates a decline in tissue excitability and in the CSD initiation mechanism induced by ethanol treatment.

title: Effects of brain oxygenation on metabolic, hemodynamic, ionic and electrical responses to spreading depression in the rat
abstract: The effect of cortical spreading depression (CSD) on oxygen demand (extracellular K(+)), oxygen supply (cerebral blood flow - CBF) and oxygen balance (mitochondrial NADH) was studied by a special multiprobe assembly (MPA), during hypoxia and partial ischemia. The MPA was constructed and applied to monitor the CSD wave from its front line until complete recovery, continuously and simultaneously. CSD under hypoxia or partial ischemia led to an initial increase in NADH levels and a further decrease in CBF during the first phase of the CSD wave, indicating a decrease of tissue capability to compensate for an increase in oxygen demand. Furthermore, the special design of the MPA enabled identifying the close interrelation between oxygen demand, supply and balance during CSD propagation. In conclusion, brain oxygenation was shown to have a clear effect on tissue responses to CSD.

title: Initial Oligemia with Capillary Flow Stop Followed by Hyperemia during K+-Induced Cortical Spreading Depression in Rats
abstract: Local cerebral blood volume (CBV) and capillary flow changes in regions of depolarizing neurons during K+-induced cortical spreading depression (CSD) in the cerebral cortex of α-chloralose-urethane-anesthetized rats were examined employing a transillumination (550 nm) video system. Capillary flow was calculated as the reciprocal of mean transit times of blood in pixels of 40 μm × 40 μm, each of which contains a few capillaries. Potassium microinjection into the cortex evoked repetitive wave-ring spreads of oligemia at a speed of ca. 2.33±0.48 mm/min. During the spread of CSD, tracer (either saline or carbon black) was injected into the internal carotid artery. Colocated with the oligemic wave, we detected capillary flow stop as evidenced by disappearance of the hemodilution curves. At any location in the region of interest within the cerebral cortex, we observed cyclic changes of capillary flow stop/hyperperfusion in synchrony with oligemia/hyperemia fluctuations. The initial flow stop and oligemia were ascribed to capillary compression by astroglial cell swelling, presumably at the pericapillary endfeet, since the oligemia occurred before larger vessel changes. We conclude that local depolarizing neurons can decrease adjacent capillary flow directly and immediately, most likely via astroglial cell swelling, and that the flow stop triggers upstream arteriolar dilatation for capillary hyperperfusion.

title: Repetitive concentric wave-ring spread of oligemia/hyperemia in the sensorimotor cortex accompanying K+-induced spreading depression in rats and cats
abstract: Vascular changes accompanying spreading depression (SD) remain controversial. We examined dynamic alterations of local cerebral blood volume (CBV) during SD by observing light transmission at an isosbestic point of hemoglobin (550 nm) in seven rats and five cats under alpha-chloralose/urethane anesthesia. The two species were used for comparison between the lissencephalic and gyrencephalic brains. We found that a concentrated K(+) solution microinjected into the sensorimotor cortex provoked CBV changes that appeared as a repetitive propagation of concentric wave-rings of ischemia followed by hyperemia expanding peripherally from the injection site at speeds of 1.9-3.2 mm/min. The dynamic CBV changes continued repeatedly every 1-5 min for more than 30 min in three rats, ceased within 30 min in three rats and remained at the site of K(+) injection in one rat. Similar repeated CBV changes occurred in two out of five cats.

title: Oscillating neuro-capillary coupling during cortical spreading depression as observed by tracking of FITC-labeled RBCs in single capillaries
abstract: Coupling between capillary red blood cell (RBC) movements and neuronal dysfunction during cortical spreading depression (CSD) was examined in rats by employing a high-speed camera laser-scanning confocal fluorescence microscope system in conjunction with our Matlab domain software (KEIO-IS2). Following microinjection of K(+) onto the surface of the brain, changes in electroencephalogram (EEG), DC potential and tissue optical density were all compatible with the occurrence of a transient spreading neuronal depression. RBC flow in single capillaries was not stationary. Unpredictable redistribution of RBCs at branches of capillaries was commonly observed, even though no change in diameter was apparent at the reported site of the capillary sphincter and no change of arteriolar-venule pressure difference was detected. There appeared to be a slow morphological change of astroglial endfeet. When local neurons were stunned transiently by K(+) injection, the velocity and oscillation frequency of RBCs flowing in nearby capillaries started to decrease. The flow in such capillaries was rectified, losing oscillatory components. Sluggish floating movements of RBCs in pertinent capillaries were visualized, with occasional full stops. When CSD subsided, RBC movements recovered to the original state. We postulate that neuronal depolarization blocks oscillatory signaling to local capillaries via low-shear plasma viscosity increases in the capillary channels, and a complex interaction between the RBC surface and the buffy coat on the capillary wall surface increases the capillary flow resistance. Then, when CSD subsides and oscillatory neuronal function is recovered, the normal physiological conditions are restored.

title: Prostanoids attenuate pial arteriolar dilation induced by cortical spreading depression in rabbits.
abstract: The role of prostanoids in mediating cerebrovascular responses to cortical spreading depression (CSD) was examined in anesthetized rabbits. CSD was elicited by KCl microinjection, and its propagation was monitored electrophysiologically. Pial arterial diameter was determined using a closed cranial window and intravital microscopy, and regional cerebral blood flow (rCBF) was determined using laser flowmetry. Levels of peri-arachnoid cerebrospinal fluid prostanoids were determined by radioimmunoassay. CSF increased pial arteriolar diameter 62% and rCBF 354% over the baseline levels. Locations of propagating CSD, dilating pial arteriole, and increased rCBF were always closely associated spatiotemporally. Cerebrospinal fluid prostanoid levels increased during single CSD-induced arteriolar dilation, and they were further augmented during multiple CSDs. Indomethacin enhanced both CSD-induced vasodilation (88%) and rCBF increase (580%), but it decreased the cerebrospinal fluid levels of prostanoids below the baseline levels and prevented their increase during CSD-induced vasodilation. These results indicate that prostanoids are synthesized from neurons or glial cells and/or the brain vessels and, as the net result, counteract pial arteriolar dilation and rCBF increase during CSD. In addition, they support the hypothesis that the vasodilation is caused primarily by neurogenic factors associated with CSD.

title: Cortical Spreading Depression Causes a Long-Lasting Decrease in Cerebral Blood Flow and Induces Tolerance to Permanent Focal Ischemia in Rat Brain
abstract: Cortical spreading depression (CSD) has previously been shown to induce tolerance to a subsequent episode of transient cerebral ischemia. The objective of the present study was to determine whether CSD also induces tolerance to permanent focal ischemia and, if so, whether tolerance may be mediated by alterations in cerebral blood flow (CBF). Sprague-Dawley rats were preconditioned by applying potassium chloride to one hemisphere for 2 hours, evoking 19 ± 5 episodes of CSD (mean ± SD, n = 19). Three days later, the middle cerebral artery (MCA) was permanently occluded using an intraluminal suture. In a subset of animals, laser Doppler blood flow (LDF) was monitored over the parietal cortex before and during the first 2 hours of MCA occlusion. Preconditioning with CSD reduced the hemispheric volume of infarction from 248 ± 115 mm3 (n = 18) in sham-conditioned animals to 161 ± 81 mm3 (n = 19, P < 0.02). Similarly, CSD reduced the neocortical volume of infarction from 126 ± 82 mm3 to 60 ± 61 mm3 (P < 0.01). Moreover, preconditioning with CSD significantly improved LDF during MCA occlusion from 21% ± 7% (n = 9) of preischemic baseline in sham-conditioned animals to 29% ± 9% (n = 7, P < 0.02). Preconditioning with CSD therefore preserved relative levels of CBF during focal ischemia and reduced the extent of infarction resulting from permanent MCA occlusion. To determine whether CSD may have altered preischemic baseline CBF, [14C]iodoantipyrine was used in additional animals to measure CBF 3 days after CSD conditioning or sham conditioning. CSD, but not sham conditioning, significantly reduced baseline CBF in the ipsilateral neocortex to values 67% to 75% of those in the contralateral cortex. Therefore, CSD causes a long-lasting decrease in baseline CBF that is most likely related to a reduction in metabolic rate. A reduction in the rate of metabolism may contribute to the induction of tolerance to ischemia after preconditioning with CSD.

title: Hyperperfusion Counteracted by Transient Rapid Vasoconstriction Followed by Long-Lasting Oligemia Induced by Cortical Spreading Depression in Anesthetized Mice
abstract: Cortical spreading depression (CSD) involves mass depolarization of neurons and glial cells accompanied with changes in regional cerebral blood flow (rCBF) and energy metabolism. To further understand the mechanisms of CBF response, we examined the temporal diametric changes in pial arteries, pial veins, and cortical capillaries. In urethane-anesthetized mice, the diameters of these vessels were measured while simultaneously recording rCBF with a laser Doppler flowmeter. We observed a considerable increase in rCBF during depolarization in CSD induced by application of KCl, accompanied by a transient dip of rCBF with marked vasoconstriction of pial arteries, which resembled the response to pin-prick-induced CSD. Arterial constriction diminished or disappeared during the second and third passages of CSD, whereas the rCBF increase was maintained without a transient dip. Long-lasting oligemia with a decrease in the reciprocal of mean transit time of injected dye and mild constriction of pial arteries was observed after several passages of the CSD wave. These results indicate that CSD-induced rCBF changes consist of initial hyperemia with a transient dip and followed by a long-lasting oligemia, partially corresponding to the diametric changes of pial arteries, and further suggest that vessels other than pial arteries, such as intracortical vessels, are involved.

title: In Vivo NADH Fluorescence Imaging Indicates Effect of Aquaporin-4 Deletion on Oxygen Microdistribution in Cortical Spreading Depression
abstract: Using in vivo two-photon imaging, we show that mice deficient in aquaporin-4 (AQP4) display increased fluorescence of nicotinamide adenine dinucleotide (NADH) when subjected to cortical spreading depression. The increased NADH signal, a proxy of tissue hypoxia, was restricted to microwatershed areas remote from the vasculature. Aqp4 deletion had no effects on the hyperemia response, but slowed [K+]o recovery. These observations suggest that K+ uptake is suppressed in Aqp4−/- mice as a consequence of decreased oxygen delivery to tissue located furthest away from the vascular source of oxygen, although increased oxygen consumption may also contribute to our observations.

title: Mechanisms of migraine aura revealed by functional MRI in human visual cortex
abstract: Cortical spreading depression (CSD) has been suggested to underlie migraine visual aura. However, it has been challenging to test this hypothesis in human cerebral cortex. Using high-field functional MRI with near-continuous recording during visual aura in three subjects, we observed blood oxygenation level-dependent (BOLD) signal changes that demonstrated at least eight characteristics of CSD, time-locked to percept/onset of the aura. Initially, a focal increase in BOLD signal (possibly reflecting vasodilation), developed within extrastriate cortex (area V3A). This BOLD change progressed contiguously and slowly (3.5 ± 1.1 mm/min) over occipital cortex, congruent with the retinotopy of the visual percept. Following the same retinotopic progression, the BOLD signal then diminished (possibly reflecting vasoconstriction after the initial vasodilation), as did the BOLD response to visual activation. During periods with no visual stimulation, but while the subject was experiencing scintillations, BOLD signal followed the retinotopic progression of the visual percept. These data strongly suggest that an electrophysiological event such as CSD generates the aura in human visual cortex.

title: Propagation of cortical spreading depolarization in the human cortex after malignant stroke
abstract: To investigate hemodynamic response pattern and spatiotemporal propagation of cortical spreading depolarization in the peri-infarct region of malignant hemispheric stroke.  In this prospective observational case study we used intraoperative laser speckle technology to measure cerebral blood flow in patients with malignant hemispheric stroke. Additionally, postoperative occurrence of cortical spreading depolarization was monitored using a subdural recording strip for electrocorticography and infarct progression was assessed by serial MRI.  In 7 of 20 patients, 19 blood flow changes typical of cortical spreading depolarizations occurred during a 20-minute period. Thirteen events were characterized by increase, 2 by biphasic response, and 4 by decrease of blood flow. Propagation velocity ranged from 1.7 to 9.2 mm/min and propagation area from 0.1 to 4.8 cm2. Intrinsic optical signal alterations preceded and low-frequency vascular fluctuations were suppressed during the hemodynamic responses. A mean number of 56 ± 82 cortical spreading depolarizations per patient was recorded and a mean infarct progression of 30 ± 13 cm3 was detected in 5 of 7 patients.  We visualize the spatiotemporal propagation of spreading depolarizations in the human cerebral cortex intraoperatively. In patients with focal ischemia, multiple cortical spreading depolarizations with either hyperemic or hypoemic flow responses occurred. Our data suggest that, in patients with focal ischemia, cortical spreading depolarizations are associated with both unfavorable and protective hemodynamic responses.

title: Laminar Analysis of Cerebral Blood Flow in Cortex of Rats by Laser-Doppler Flowmetry: A Pilot Study
abstract: Laser-Doppler flowmetry (LDF) is a reliable method for estimation of relative changes of CBF. The measurement depth depends on wavelength of the laser light and the separation distance of transmitting and recording optical fibers. We designed an LDF probe using two wavelengths of laser light (543 nm and 780 nm), and three separation distances of optical fibers to measure CBF in four layers of the cerebral cortex at the same time. In vitro comparison with electromagnetic flow measurements showed linear relationship between LDF and blood flow velocity at four depths within the range relevant to physiologic measurements. Using artificial brain tissue slices we showed that the signal for each channel decreased in a theoretically predictable fashion as a function of slice thickness. Application of adenosine at various depths in neocortex of halothane-anesthetized rats showed a predominant CBF increase at the level of application. Electrical stimulation at the surface of the cerebellar cortex demonstrated superficial predominance of increased CBF as predicted from the distribution of neuronal activity. In the cerebellum, hypercapnia increased CBF in a heterogeneous fashion, the major increase being at apparent depths of approximately 300 and 600 μm, whereas in the cerebral cortex, hypercapnia induced a uniform increase. In contrast, the CBF response to cortical spreading depression in the cerebral cortex was markedly heterogeneous. Thus, real-time laminar analysis of CBF with spatial resolution of 200 to 300 μm may be achieved by LDF. The real-time in depth resolution may give insight into the functional organization of the cortical microcirculation and adaptive features of CBF regulation in response to physiologic and pathophysiologic stimuli.

title: Diffuse optical correlation tomography of cerebral blood flow during cortical spreading depression in rat brain.
abstract: Diffuse optical correlation methods were adapted for three-dimensional (3D) tomography of cerebral blood flow (CBF) in small animal models. The image reconstruction was optimized using a noise model for diffuse correlation tomography which enabled better data selection and regularization. The tomographic approach was demonstrated with simulated data and during in-vivo cortical spreading depression (CSD) in rat brain. Three-dimensional images of CBF were obtained through intact skull in tissues(~4mm) deep below the cortex.

title: Propofol hemisuccinate suppresses cortical spreading depression
abstract: Propofol is a rapidly acting water-insoluble non-barbiturate anesthetic agent that is widely used as an intravenous sedative-hypnotic agent. Anecdotal evidence indicates that propofol may be effective at terminating intractable migraine headache. Cortical spreading depression (CSD) is believed to be the neural correlate of migraine aura and may be a trigger for migraine pain. Agents that block the induction or slow the spread of CSD may be of utility in treating migraine. Here we examined the ability of propofol hemisuccinate (PHS), a water-soluble prodrug of propofol, to affect CSD in mice. For comparison, we examinined dizocilpine, an NMDA receptor antagonist, that is well recognized to inhibit CSD. When administered 15min prior to activation of CSD by KCl application to the cortex, intraperitoneal PHS at doses of 120 and 200mg/kg decreased the number of CSD deflections without an effect on CSD amplitude, and at 200mg/kg caused a 77% reduction in CSD velocity. The minimally-effective dose of PHS (120mg/kg) did not cause sedation or motor impairment and while some animals receiving 200mg/kg did demonstrate motor impariment none exhibited loss-of-righting reflex (anesthesia). Dizocilpine produced comparable inhibition of CSD at doses of 0.5 and 2.5mg/kg. We conclude that acute PHS treatment inhibits CSD. Our results indicate that propofol, or its prodrug PHS, are worthy of further investigation as a treatment for migraine.

title: The impact of anesthetics and hyperoxia on cortical spreading depression
abstract: Cortical spreading depression (CSD), a transient neuronal and glial depolarization that propagates slowly across the cerebral cortex, is the putative electrophysiological event underlying migraine aura. It negatively impacts tissue injury during stroke, cerebral contusion and intracranial hemorrhage. Susceptibility to CSD has been assessed in several experimental animal models in vivo, such as after topical KCl application or cathodal stimulation. Various combinations of anesthetics and ambient conditions have been used by different laboratories making comparisons problematic and differences in data difficult to reconcile. We systematically studied CSD susceptibility comparing commonly used experimental anesthetics (isoflurane, alpha-chloralose, and urethane) with or without N(2)O or normobaric hyperoxia (100% O(2) inhalation). The frequency of evoked CSDs, and their propagation speed, duration, and amplitude were recorded during 2 h topical KCl (1 M) application. We found that N(2)O reduced CSD frequency when combined with isoflurane or urethane, but not alpha-chloralose; N(2)O also decreased CSD propagation speed and duration. Urethane anesthesia was associated with the highest CSD frequency that was comparable to pentobarbital. Inhalation of 100% O(2) did not alter CSD frequency, propagation speed or duration in combination with any of the anesthetics tested. Our data show anesthetic modulation of CSD susceptibility in an experimental model of human disease, underscoring the importance of proper study design for hypothesis testing as well as for comparing results between studies.

title: Anesthetic effects on susceptibility to cortical spreading depression
abstract: Cortical spreading depression (CSD) is a transient neuronal and glial depolarization and disruption of membrane ionic gradients that propagates slowly across the cerebral cortex. Recent clinical and experimental evidence has implicated CSD in the pathophysiology of migraines and neuronal injury states. In the current study, we examined the influence of four different anesthetics (propofol, dexmedetomidine, isoflurane, pentobarbital) on CSD susceptibility in a KCl application animal model. We found that isoflurane and dexmedetomidine suppressed CSD frequency, and tended to reduce the CSD propagation speed. Our data suggest that these anesthetics may be therapeutically beneficial in preventing CSD in diverse neuronal injury states.

title: Inhalational Anesthetics Inhibit Spreading Depression: Relevance to Migraine
abstract: Cortical spreading depression (SD) has not been shown in the human neocortex by direct cortical recordings. However, animal studies suggest that cortical injury, such as that occurring during neurosurgical procedures, should result in the initiation of SD. It is possible that inhibition of SD by volatile anesthetic agents may partially explain the failure to observe SD in the human neocortex during surgery. This study examines the effect of the anesthetic agents α-chloralose, halothane, nitrous oxide and isoflurane on the initiation of cortical SD in the cat neocortex. SD was seen in 100% of cats anesthetized with α-chloralose (n = 15), in 3 of 7 (42%) animals anesthetized with isoflurane (p < 0.05, χ2 with Yates correction) and none of the animals (n = 4, 6 hemispheric preparations) anesthetized with halothane (p < 0.005, χ2 with Yates correction, halothane vs α-chloralose group). In all cases this inhibitory effect was reversible. In four animals the administration of nitrous oxide (66%) reduced the inspired concentration of isoflurane required to inhibit SD by 0.75%. This study suggests that halothane, and to a lesser extent isoflurane and nitrous oxide, protect against the initiation of cortical SD. This observation may partially explain why SD has not been demonstrated in human neocortex during surgery. Further studies are needed to determine if SD may occur under pathological conditions, such as during migraine with aura, where the cortex may be predisposed to SD.

title: Halothane, but not alpha-chloralose, blocks potassium-evoked cortical spreading depression in cats.
abstract: The effects of two anesthetics, halothane and alpha-chloralose, on induction of spreading depression and on extracellular glutamate elevation after intracortical potassium administration were investigated in artificially ventilated (30% oxygen/70% nitrous oxide) cats. High potassium concentrations were achieved using either direct KCl injections (7 microliters, 150 mM via a micropipette) or microdialysis by supplementing 100, 300 or 500 mM KCl, respectively, for 10 min to the perfusion solution (Ringer's). Changes of the cortical DC potential were recorded adjacent (1-2 mm: electrode DC1) and distant (6-7 mm: electrode DC2) to the injection site. Either under halothane (0.75% in the respiratory gas mixture) or under alpha-chloralose (60 mg/kg i.v.) anesthesia, prolonged negative shifts of the DC potential reflecting the elevated potassium levels after KCl injection were measured near the injection site (electrode DC1). In contrast, spreading depressions (transient short DC deflections) were almost exclusively observed under alpha-chloralose. Spreading depressions recorded with electrode DC1 were superimposed on the prolonged negative DC shifts and they propagated frequently to the more distant site (DC2). Upon KCl administration, dose dependent elevations of extracellular glutamate were measured. These elevations were not significantly altered by the type of anesthesia. Our results suggest that in cats, spreading depression induction is affected by anesthesia, i.e., spreading depression induction is inhibited by halothane as compared to alpha-chloralose. Furthermore, factors other than glutamate or high potassium seem to contribute to spreading depression induction.

title: Isoflurane suppresses cortical spreading depolarizations compared to propofol — Implications for sedation of neurocritical care patients
abstract: Sedatives in the neurointensive care unit can strongly influence patients' risks of developing secondary brain damage. In particular, isoflurane, a volatile anesthetic, has been recently re-introduced to the neurointensive care unit, and first clinical studies suggest beneficial effects due to elevation of cerebral blood flow and reduction of metabolism. In contrast, propofol is a commonly used intravenous sedative that reduces cerebral blood flow and intra-cranial pressure. We have here studied the influence of these two sedatives on the occurrence of cortical spreading depolarizations (CSDs), which have emerged over the last decade as a major mechanism of delayed brain injury in stroke and brain trauma, constituting a substantial vascular and metabolic threat to peri-infarct tissue and being associated with poor patient outcome. Two experimental models were tested in Wistar rats anesthetized either with isoflurane or with propofol: KCl-evoked CSDs (n=10) and spontaneous CSDs after occlusion of the middle cerebral artery (n=14). Spatiotemporal patterns of CSD waves were observed by real-time laser speckle imaging of regional cerebral blood flow changes associated with the CSDs. During 30 min of cortical KCl application, 5.2±0.7 CSDs were induced under isoflurane compared to 10.2±1.8 CSDs under propofol (p<0.001). After focal ischemia, 2.43±1.0 CSDs/h emerged spontaneously under isoflurane versus 6.83±2.5 CSDs/h under propofol (p<0.001). Furthermore, baseline blood flow and glycemia were much higher under isoflurane compared to propofol, which may set the tissue in better metabolic conditions to recover from the occurrence of CSD waves. We conclude that isoflurane, in comparison to propofol, decreases the occurrence of CSDs and may improve recovery from these metabolically demanding waves. To reduce CSD induced secondary tissue damage, we suggest isoflurane to be favored over propofol to sedate acute stroke and trauma patients in the neurointensive care unit.

title: The Role of Electrode Size on the Incidence of Spreading Depression and on Cortical Cerebral Blood Flow as Measured by H2 Clearance
abstract: Cerebral blood flow was measured by the H2 clearance method 30 and 60 min after the implantation of 300, 250, 125, or 50 μm diameter platinum–iridium electrodes 2 mm deep into the right parietal cortex of normothermic, normocarbic halothane-anesthetized rats. Another group of animals had 50 μm electrodes inserted 1 mm. In all animals, the presence or absence of a wave of spreading depression (SD) was noted at the time of implantation, with recordings made with glass micropipettes. H2 flow values were compared with those measured in gray matter from the same anatomical region (but from different rats), using [3H]nicotine. The incidence of SD ranged from 60% following insertion of 300 μm electrodes to 0% with 50 μm electrodes. H2 clearance flows also varied with electrode size, from 77 ± 21 ml 100 g−1 min−1 (mean ± standard deviation) with 300 μm electrodes to 110 ± 31 and 111 ± 16 ml 100 g−1 min−1 with 125 and 50 μm electrodes, respectively (insertion depth of 2 mm). A CBF value of 155 ± 60 ml 100 g−1 min−1 was obtained with 50 μm electrodes inserted only 1 mm. Cortical gray matter blood flow measured with [3H]nicotine was 154 ± 35 ml 100 g−1 min−1. When the role of SD in subsequent flow measurements was examined, there was a gradual increase in CBF between 30 and 60 min after electrode insertion in those animals with SD, while no such change was seen in rats without SD. These results indicate that the choice of electrode size and implantation depth influences the measurement of CBF by H2 clearance. CBF values equivalent to those obtained with isotopic techniques can be acutely obtained with small (50 μm diameter) electrodes inserted 1 mm into the cortex. While the occurrence of SD does influence CBF in the period immediately after implantation, a relationship between electrode size and measured flow is present that is independent of SD.

title: Effects of early aging and cerebral hypoperfusion on spreading depression in rats
abstract: Cortical spreading depression (CSD) is a feature of stroke pathophysiology. As stroke incidence increases with age, we have examined the effects of early aging and chronic cerebral hypoperfusion on CSD in rats. Three groups were studied: Young, 2-month-old animals; Middle-aged-2VO, subjected to 8 months of bilateral carotid occlusion from 2-month-of-age; and Middle-aged-SHAM, sham-operated. At 2- and 10-month-of-age for the Young and Middle-aged groups, recurrent CSD were induced under halothane anesthesia, by sustained application of 1 M KCl to the cortex for 2 h. Propagating CSD (i.e., cortical EEG, direct current potential) and associated laser Doppler blood flow changes were recorded anteriorly. Susceptibility to CSD and event duration were both decreased by early aging (frequency: 21±0.5 and 6±0.5 CSD/h; duration: 139±7 and 63±8 s; in Young and Middle-aged-SHAM, respectively). There was also a tendency for CSD-associated hyperemia to be reduced in the Middle-aged-2VO group (8.9±2.1 vs. 32.8±12.6% × min in Young). These data suggest reduced sensitivity of the cortex to CSD elicitation with early aging, and a less responsive cerebrovascular system with chronic hypoperfusion.

title: Responses to Cortical Spreading Depression under Oxygen Deficiency
abstract: The effect of cortical spreading depression (CSD) on extracellular K+ concentrations ([K+]e), cerebral blood flow (CBF), mitochondrial NADH redox state and direct current (DC) potential was studied during normoxia and three pathological conditions: hypoxia, after NOS inhibition by L-NAME and partial ischemia.  A special device (MPA) was used for monitoring CSD wave propagation, containing: mitochondrial NADH redox state and reflected light, by a fluorometry technique; DC potential by Ag/AgCl electrodes; CBF by laser Doppler flowmetry; and [K+]e by a mini-electrode.  CSD under the 3 pathological conditions caused an initial increase in NADH and a further decrease in CBF during the first phase of CSD, indicating an imbalance between oxygen supply and demand as a result of the increase in oxygen requirements. The hyperperfusion phase in CBF was significantly reduced during hypoxia and ischemia showing a further decline in oxygen supply during CSD. CSD wave duration increased during the pathological conditions, showing a disturbance in energy production. Extracellular K+ levels during CSD, increased to identical levels during normoxia and during the three pathological groups, indicating correspondingly increase in oxygen demand. 5. The special design of the MPA enabled identifying differences in the simultaneous responses of the measured parameters, which may indicate changes in the interrelation between oxygen demand, oxygen supply and oxygen balance during CSD propagation, under the conditions tested. 6. In conclusion, brain oxygenation was found to be a critical factor in the responses of the brain to CSD.

title: Perfusion Pressure-Dependent Recovery of Cortical Spreading Depression is Independent of Tissue Oxygenation over a Wide Physiologic Range
abstract: Spreading depression (SD) is a slowly propagating wave of transient neuronal and glial depolarization that develops after stroke, trauma and subarachnoid hemorrhage. In compromised tissue, repetitive SD-like injury depolarizations reduce tissue viability by worsening the mismatch between blood flow and metabolism. Although the mechanism remains unknown, SDs show delayed electrophysiological recovery within the ischemic penumbra. Here, we tested the hypothesis that the recovery rate of SD can be varied by modulating tissue perfusion pressure and oxygenation. Systemic blood pressure and arterial pO2 were simultaneously manipulated in anesthetized rats under full physiologic monitoring. We found that arterial hypotension doubled the SD duration, whereas hypertension reduced it by a third compared with normoxic normotensive rats. Hyperoxia failed to shorten the prolonged SD durations in hypotensive rats, despite restoring tissue pO2. Indeed, varying arterial pO2 (40 to 400 mm Hg) alone did not significantly influence SD duration, whereas blood pressure (40 to 160 mm Hg) was inversely related to SD duration in compromised tissue. These data suggest that cerebral perfusion pressure is a critical determinant of SD duration independent of tissue oxygenation over a wide range of arterial pO2 levels, and that hypotension may be detrimental in stroke and subarachnoid hemorrhage, where SD-like injury depolarizations have been observed.

title: Acute hyperglycemia compromises cerebral blood flow following cortical spreading depression in rats monitored by laser speckle imaging.
abstract: Hyperglycemia and cortical spreading depression (CSD) are possible factors that worsen the outcome of ischemic stroke, and it is probable that there is a longterm cooperative effect of hyperglycemia and CSD on cerebral blood flow (CBF). Long-lasting and full-field observation of changes in CBF following CSD in vivo during acute hyperglycemia in rats might show whether this is the case. Here, we utilized laser speckle imaging to study influences of acute hyperglycemia on CBF at the level of individual vascular compartments for 3 h in normal rats and those with CSD. It is shown that there are extensive increases of CBF at the arteriole and parenchyma over the normal rat cortex during acute hyperglycemia, whereas there is no significant change in CBF at the venule. We also find that, at all vascular compartments, after the glucose administration there is a stepwise reduction of CBF following CSD, but after saline injection CBF following CSD is close to the baseline. Our results indicate that acute hyperglycemia could aggravate the severity of decrease in CBF following CSD, suggesting possible mechanisms by which hyperglycemia exacerbates cerebral damage after ischemic stroke.

title: Neurovascular Coupling in Rat Brain Operates Independent of Hemoglobin Deoxygenation
abstract: Recently, a universal, simple, and fail-safe mechanism has been proposed by which cerebral blood flow (CBF) might be coupled to oxygen metabolism during neuronal activation without the need for any tissue-based mechanism. According to this concept, vasodilation occurs by local erythrocytic release of nitric oxide or ATP wherever and whenever hemoglobin is deoxygenated, directly matching oxygen demand and supply in every tissue. For neurovascular coupling in the brain, we present experimental evidence challenging this view by applying an experimental regime operating without deoxy-hemoglobin. Hyperbaric hyperoxygenation (HBO) allowed us to prevent hemoglobin deoxygenation, as the oxygen that was physically dissolved in the tissue was sufficient to support oxidative metabolism. Regional CBF and regional cerebral blood oxygenation were measured using a cranial window preparation in anesthetized rats. Hemodynamic and neuronal responses to electrical forepaw stimulation or cortical spreading depression (CSD) were analyzed under normobaric normoxia and during HBO up to 4 ATA (standard atmospheres absolute). Inconsistent with the proposed mechanism, during HBO, CBF responses to functional activation or CSD were unchanged. Our results show that activation-induced CBF regulation in the brain does not operate through the release of vasoactive mediators on hemoglobin deoxygenation or through a tissue-based oxygen-sensing mechanism.

title: Focal physiological uncoupling of cerebral blood flow and oxidative metabolism during somatosensory stimulation in human subjects.
abstract: Coupling between cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) was studied using multiple sequential administrations of 15O-labeled radiotracers (half-life, 123 sec) and positron emission tomography. In the resting state an excellent correlation (mean r, 0.87) between CBF and CMRO2 was found when paired measurements of CBF and CMRO2 from multiple (30-48) brain regions were tested in each of 33 normal subjects. Regional uncoupling of CBF and CMRO2 was found, however, during neuronal activation induced by somatosensory stimulation. Stimulus-induced focal augmentation of cerebral blood flow (29% mean) far exceeded the concomitant local increase in tissue metabolic rate (mean, 5%), when resting-state and stimulated-state measurements were obtained in each of 9 subjects. Stimulus duration had no significant effect on response magnitude or on the degree of CBF-CMRO2 uncoupling observed. Dynamic, physiological regulation of CBF by a mechanism (neuronal or biochemical) dependent on neuronal firing per se, but independent of the cerebral metabolic rate of oxygen, is hypothesized.

title: Calcium transients in astrocyte endfeet cause cerebrovascular constrictions
abstract: Cerebral blood flow (CBF) is coupled to neuronal activity and is imaged in vivo to map brain activation. CBF is also modified by afferent projection fibres that release vasoactive neurotransmitters in the perivascular region, principally on the astrocyte endfeet that outline cerebral blood vessels. However, the role of astrocytes in the regulation of cerebrovascular tone remains uncertain. Here we determine the impact of intracellular Ca2+ concentrations ([Ca2+]i) in astrocytes on the diameter of small arterioles by using two-photon Ca2+ uncaging to increase [Ca2+]i. Vascular constrictions occurred when Ca2+ waves evoked by uncaging propagated into the astrocyte endfeet and caused large increases in  The vasoactive neurotransmitter noradrenaline increased [Ca2+]i in the astrocyte endfeet, the peak of which preceded the onset of arteriole constriction. Depressing increases in astrocyte [Ca2+]i with BAPTA inhibited the vascular constrictions in noradrenaline. We find that constrictions induced in the cerebrovasculature by increased [Ca2+]i in astrocyte endfeet are generated through the phospholipase A2–arachidonic acid pathway and 20-hydroxyeicosatetraenoic acid production. Vasoconstriction by astrocytes is a previously unknown mechanism for the regulation of CBF.

title: Neuron-to-astrocyte signaling is central to the dynamic control of brain microcirculation
abstract: The cellular mechanisms underlying functional hyperemia—the coupling of neuronal activation to cerebral blood vessel responses—are not yet known. Here we show in rat cortical slices that the dilation of arterioles triggered by neuronal activity is dependent on glutamate-mediated [Ca2+]i oscillations in astrocytes. Inhibition of these Ca2+ responses resulted in the impairment of activity-dependent vasodilation, whereas selective activation—by patch pipette—of single astrocytes that were in contact with arterioles triggered vessel relaxation. We also found that a cyclooxygenase product is centrally involved in this astrocyte-mediated control of arterioles. In vivo blockade of glutamate-mediated [Ca2+]i elevations in astrocytes reduced the blood flow increase in the somatosensory cortex during contralateral forepaw stimulation. Taken together, our findings show that neuron-to-astrocyte signaling is a key mechanism in functional hyperemia.

title: Brain metabolism dictates the polarity of astrocyte control over arterioles
abstract: Calcium signalling in astrocytes couples changes in neural activity to alterations in cerebral blood flow by eliciting vasoconstriction or vasodilation of arterioles. However, the mechanism for how these opposite astrocyte influences provide appropriate changes in vessel tone within an environment that has dynamic metabolic requirements remains unclear. Here we show that the ability of astrocytes to induce vasodilations over vasoconstrictions relies on the metabolic state of the rat brain tissue. When oxygen availability is lowered and astrocyte calcium concentration is elevated, astrocyte glycolysis and lactate release are maximized. External lactate attenuates transporter-mediated uptake from the extracellular space of prostaglandin E2, leading to accumulation and subsequent vasodilation. In conditions of low oxygen concentration extracellular adenosine also increases, which blocks astrocyte-mediated constriction, facilitating dilation. These data reveal the role of metabolic substrates in regulating brain blood flow and provide a mechanism for differential astrocyte control over cerebrovascular diameter during different states of brain activation.

title: Rapid stimulus-evoked astrocyte Ca2+ elevations and hemodynamic responses in mouse somatosensory cortex in vivo
abstract: The morphology of astrocytes places them as likely contributors to communication between nerve cells and blood vessels. They are reported to respond with few and slow Ca2+ elevations, which exclude them as possible participants in initiation of blood flow responses or synapse communication. We establish that astrocytes have fast responses in addition to the slow. These rapid, brief Ca2+ responses were present in a large proportion of astrocytes. We were able to observe these changes due to a signal enhancement analysis, which is useful when responses are small compared with baseline activity. Our findings indicate a higher sensitivity than generally believed of astrocytes. Increased neuron and astrocyte activity triggers increased brain blood flow, but controversy exists over whether stimulation-induced changes in astrocyte activity are rapid and widespread enough to contribute to brain blood flow control. Here, we provide evidence for stimulus-evoked Ca2+ elevations with rapid onset and short duration in a large proportion of cortical astrocytes in the adult mouse somatosensory cortex. Our improved detection of the fast Ca2+ signals is due to a signal-enhancing analysis of the Ca2+ activity. The rapid stimulation-evoked Ca2+ increases identified in astrocyte somas, processes, and end-feet preceded local vasodilatation. Fast Ca2+ responses in both neurons and astrocytes correlated with synaptic activity, but only the astrocytic responses correlated with the hemodynamic shifts. These data establish that a large proportion of cortical astrocytes have brief Ca2+ responses with a rapid onset in vivo, fast enough to initiate hemodynamic responses or influence synaptic activity.

title: Astrocytic endfoot Ca2+ and BK channels determine both arteriolar dilation and constriction
abstract: Neuronal activity is thought to communicate to arterioles in the brain through astrocytic calcium (Ca2+) signaling to cause local vasodilation. Paradoxically, this communication may cause vasoconstriction in some cases. Here, we show that, regardless of the mechanism by which astrocytic endfoot Ca2+ was elevated, modest increases in Ca2+ induced dilation, whereas larger increases switched dilation to constriction. Large-conductance, Ca2+-sensitive potassium channels in astrocytic endfeet mediated a majority of the dilation and the entire vasoconstriction, implicating local extracellular K+ as a vasoactive signal for both dilation and constriction. These results provide evidence for a unifying mechanism that explains the nature and apparent duality of the vascular response, showing that the degree and polarity of neurovascular coupling depends on astrocytic endfoot Ca2+ and perivascular K+.

title: Pyramidal Neurons Are “Neurogenic Hubs” in the Neurovascular Coupling Response to Whisker Stimulation
abstract: The whisker-to-barrel cortex is widely used to study neurovascular coupling, but the cellular basis that underlies the perfusion changes is still largely unknown. Here, we identified neurons recruited by whisker stimulation in the rat somatosensory cortex using double immunohistochemistry for c-Fos and markers of glutamatergic and GABAergic neurons, and investigated in vivo their contribution along with that of astrocytes in the evoked perfusion response. Whisker stimulation elicited cerebral blood flow (CBF) increases concomitantly with c-Fos upregulation in pyramidal cells that coexpressed cyclooxygenase-2 (COX-2) and GABA interneurons that coexpressed vasoactive intestinal polypeptide and/or choline acetyltransferase, but not somatostatin or parvalbumin. The evoked CBF response was decreased by blockade of NMDA (MK-801, −37%), group I metabotropic glutamate (MPEP+LY367385, −40%), and GABA-A (picrotoxin, −31%) receptors, but not by GABA-B, VIP, or muscarinic receptor antagonism. Picrotoxin decreased stimulus-induced somatosensory evoked potentials and CBF responses. Combined blockade of GABA-A and NMDA receptors yielded an additive decreasing effect (−61%) of the evoked CBF compared with each antagonist alone, demonstrating cooperation of both excitatory and inhibitory systems in the hyperemic response. Blockade of prostanoid synthesis by inhibiting COX-2 (indomethacin, NS-398), expressed by ∼40% of pyramidal cells but not by astrocytes, impaired the CBF response (−50%). The hyperemic response was also reduced (−40%) after inhibition of astroglial oxidative metabolism or epoxyeicosatrienoic acids synthesis. These results demonstrate that changes in pyramidal cell activity, sculpted by specific types of inhibitory GABA interneurons, drive the CBF response to whisker stimulation and, further, that metabolically active astrocytes are also required.

title: Cyclooxygenase-2 Contributes to Functional Hyperemia in Whisker-Barrel Cortex
abstract: The prostanoid-synthesizing enzyme cyclooxygenase-2 (COX-2) is expressed in selected cerebral cortical neurons and is involved in synaptic signaling. We sought to determine whether COX-2 participates in the increase in cerebral blood flow produced by synaptic activity in the somatosensory cortex. In anesthetized mice, the vibrissae were stimulated mechanically, and cerebral blood flow was recorded in the contralateral somatosensory cortex by a laser–Doppler probe. We found that the COX-2 inhibitor NS-398 attenuates the increase in somatosensory cortex blood flow produced by vibrissal stimulation. Furthermore, the flow response was impaired in mice lacking the COX-2 gene, whereas the associated increase in whisker-barrel cortex glucose use was not affected. The increases in cerebral blood flow produced by hypercapnia, acetylcholine, or bradykinin were not attenuated by NS-398, nor did they differ between wild-type and COX-2 null mice. The findings provide evidence for a previously unrecognized role of COX-2 in the mechanisms coupling synaptic activity to neocortical blood flow and provide an insight into one of the functions of constitutive COX-2 in the CNS.

title: Astroglial and Vascular Interactions of Noradrenaline Terminals in the Rat Cerebral Cortex
abstract: Noradrenaline (NA) has been shown to influence astrocytic and vascular functions related to brain homeostasis, metabolism, local blood flow, and blood-brain barrier permeability. In the current study, we investigate the possible associations that exist between NA-immunoreactive nerve terminals and astrocytes and intraparenchymal blood vessels in the rat frontoparietal cortex, both at the light and electron microscopic levels. As a second step, we sought to determine whether the NA innervation around intracortical microvessels arises from peripheral or central structures by means of injections of N-(2-chloroethyl-N-ethyl-2-bromobenzylamine) (DSP-4), a neurotoxin that specifically destroys NA neurons from the locus ceruleus. At the light microscopic level, 6.8% of all NA-immunoreactive nerve terminals in the frontoparietal cortex were associated with vascular walls, and this perivascular noradrenergic input, together with that of the cerebral cortex, almost completely disappeared after DSP-4 administration. When analyzed at the ultrastructural level in control rats, NA terminals in the neuropil had a mean surface area of 0.53 ± 0.03 µm2 and were rarely junctional (synaptic incidence close to 7%). Perivascular terminals (located within a 3-µm perimeter from the vessel basal lamina) counted at the electron microscopic level represented 8.8% of the total NA terminals in the cortical tissue. They were smaller (0.29 ± 0.01 µm2, P < 0.05) than their neuronal counterparts and were located, on average, 1.34 ± 0.08 µm away from intracortical blood vessels, which consisted mostly of capillaries (65%). None of the perivascular NA terminals engaged in junctional contacts with surrounding neuronal or vascular elements. The primary targets of both neuronal and perivascular NA nerve terminals consisted of dendrites, nerve terminals, astrocytes, and axons, whereas in the immediate vicinity (0.25 µm or less) of the microvessels, astrocytic processes represented the major target. The results of the current study show that penetrating arteries and intracortical microvessels receive a central NA input, albeit parasynaptic in its interaction, originating from the locus ceruleus. Particularly, they point to frequent appositions between both neuronal and perivascular NA terminals and astroglial cells and their processes. Such NA neuronal-glial and neuronal-glial-vascular associations could be of significance in the regulation of local metabolic and vascular functions under normal and pathologic situations.

title: Evidence for central innervation of intracerebral blood vessels: Local cerebral blood flow measurements and histofluorescence analysis by the sucrose-phosphate-glyoxylic acid (SPG) method
abstract: Local cerebral blood flow using a hydrogen clearance technique and a histofluorescent modification of the glyoxylic acid method (SPG method) were used in rats to study the influence of brain stem centers on intracerebral flood flow. Recording of local cerebral blood flow following stimulation of the locus coeruleus but not of the ventrocaudal nucleus of the lateral lemniscus showed a significant blood flow decrease in anterior brain regions where innervation of ascending adrenergic pathways are known to occur. Adrenergic innervation using the SPG method (sucrose-potassium phosphate-glyoxylic acid) histofluorescence could not be verified in the rat but was evident in the dog and rhesus monkey brain sections examined. The results provide additional evidence suggestive of a role for the locus coeruleus in modulating or controlling intracerebral blood flow in these animals. In addition, histofluorescent visualization of intracerebral vessels in dog and monkey show an association between adrenergic varicosities and arterioles in bilaterally ganglion-ectomized animals. This adrenergic-vascular association was not seen in the rat. The results provide further evidence that central adrenergic innervation from the brain stem may control intracerebral blood flow independent of sympathetic influence.

title: Ultrastructural relationships between noradrenergic nerve fibers and non‐neuronal elements in the rat cerebral cortex
abstract: Pharmacological and biochemical data suggest that noradrenaline (NA)‐containing fibers not only regulate the activity of cortical neurons but also influence the functional state of non‐neuronal elements. In the present study, immunocytochemistry with an antiserum against NA, followed by silver‐gold intensification of the immunoreaction end‐product, was employed to examine the ultrastructural relationships between the NA fiber system and the intraparenchymal blood vessels, oligodendrocytes, and astrocytes in the rat visual cortex.

title: Central noradrenergic regulation of cerebral blood flow and vascular permeability.
abstract: Anatomical studies employing the immunofluorescence localization of dopamine-beta-hydroxylase [= dopamine beta-monooxygenase; 3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating); EC 1.14.17.1] have demonstrated in brain central noradrenergic nerve fibers on small intraparenchymal blood vessels, including capillaries. This system is distinct from the peripheral noradrenergic system inervating the large extraparenchymal blood vessels. From these anatomical findings evolved the working hypothesis that the central noradrenergic system is analogous to the peripheral sympathetic system except that it is specialized for performing specific functions related to the brain microvasculature. To test this hypothesis cerebral blood flow and the brain vascular permeability of water (H215O) were measured in four adult rhesus monkeys (three with bilateral superior cervical ganglionectomies) with stereotaxically placed cannulae permanently located in the lateral ventricles and the locus coeruleus for the injection of drugs. Our data demonstrate that stimulation of the noradrenergic cell bodies in the locus coeruleus with carbachol (8 mug) produces a prompt reduction in hemispheric cerebral blood flow and an increase in brain vascular permeability of water. The intraventricular administration of the alpha-adrenergic blocker phentolamine (25--50 mug) has the opposite effect. These preliminary data support the hypothesis that the central noradrenergic system is analogous to the peripheral sympathetic system with the special function of regulating brain vascular permeability as well as blood flow.

title: Perivascular nerves and the regulation of cerebrovascular tone.
abstract: Brain perfusion is tightly coupled to neuronal activity, is commonly used to monitor normal or pathological brain function, and is a direct reflection of the interactions that occur between neuronal signals and blood vessels. Cerebral blood vessels at the surface and within the brain are surrounded by nerve fibers that originate, respectively, from peripheral nerve ganglia and intrinsic brain neurons. Although of different origin and targeting distinct vascular beds, these "perivascular nerves" fulfill similar roles related to cerebrovascular functions, a major one being to regulate their tone and, therein, brain perfusion. This utmost function, which underlies the signals used in functional neuroimaging techniques and which can be jeopardized in pathologies such as Alzheimer's disease, stroke, and migraine headache, is thus regulated at several levels. Recently, new insights into our understanding of how neural input regulate cerebrovascular tone resulted in the rediscovery of the functional "neurovascular unit." These remarkable advances suggest that neuron-driven changes in vascular tone result from interactions that involve all components of the neurovascular unit, transducing neuronal signals into vasomotor responses not only through direct interaction between neurons and vessels but also indirectly via the perivascular astrocytes. Neurovascular coupling is thus determined by chemical signals released from activated perivascular nerves and astrocytes that alter vascular tone to locally adjust perfusion to the spatial and temporal changes in brain activity.

title: Demonstration of Neuropeptide Containing Nerves and Vasomotor Responses to Perivascular Peptides in Human Cerebral Arteries
abstract: A rich supply of nerve fibers containing neuropeptide Y-like (NPY-LI) and tyrosine hydroxylase-like immunoreactivity was seen in human cerebral arteries, arterioles and veins. Only a sparse supply of vasoactive intestinal polypeptide (VIP-LI), substance P (SP-LI), and calcitonin gene-related peptide (CGRP-LI) was demonstrated in the walls of human cerebral vessels. In isolated ring segments of human cerebral arteries, NPY and noradrenaline caused vasoconstriction but did not potentiate each other. VIP, peptide histidine methionine, SP, neurokinin A, and CGRP relaxed arteries precontracted by prostaglandin F2a. The degree of innervation and the vasomotor responses are discussed in relation to migraine pathophysiology.

title: Selective Electrical Stimulation of Postganglionic Cerebrovascular Parasympathetic Nerve Fibers Originating from the Sphenopalatine Ganglion Enhances Cortical Blood Flow in the Rat
abstract: Recently, the origins and pathways of cerebrovascular acetylcholine- and vasoactive intestinal polypeptide-containing nerves have been elucidated in detail in the rat: The sphenopalatine ganglion is the major source for postganglionic parasympathetic fibers to the vascular beds of the cerebral hemispheres. To clarify the functional role of the nerves on cerebral blood vessels in vivo, brain cortical microvascular blood flow was measured in rats during electrical stimulation of these particular postganglionic fibers. Animals were subjected to transection of the right nasociliary nerve 2 weeks before the flow measurements to eliminate activation of peptidergic sensory fibers. Relative change in microvascular blood flow was continuously recorded by a laser-Doppler flowmeter system under α-chloralose anesthesia. The postganglionic fibers were electrically stimulated just proximal to the ethmoidal foramen by a bipolar platinum electrode (5 V; 0.5 ms; 3, 10, 30, 60 Hz; as a continuous stimulation for 90 s). Stimulation at 10 Hz induced a marked increase of the cortical blood flow (CoBF) on the ipsilateral side, whereas no change was observed on the contralateral side. It reached a maximum mean value of 42.5% at 46 s, and then slightly declined during the remaining stimulation period. No significant changes were observed in the mean arterial blood pressure or blood gases during or after stimulation. Both atropine and scopolamine failed to alter this flow increase. Electrical stimulation of the postganglionic fibers at different frequencies revealed a maximal increase in the CoBF at 30 Hz in the control situation (47.2%), but at 10 Hz after scopolamine administration (51.6%). This provides the first report showing that selective postganglionic stimulation of the parasympathetic nerve fibers markedly enhances blood flow in the brain, and it supports the view that the neurogenic vasodilatation is primarily noncholinergic.

title: Control of Brain Capillary Blood Flow
abstract: While it has been widely confirmed that cerebral blood flow is closely coupled with brain metabolism, it remains a matter of controversy whether capillary flow is directly controlled to meet the energy demands of the parenchyma. Since the capillary is known to lack smooth muscle cells, it has generally been considered that capillary flow is not regulated in situ. However, we now have increasing data supporting the physiological control of capillary flow. The observation of heterogeneity in the microcirculation in vivo has suggested that intravascular factors may be involved in the flow control, including non-Newtonian rheology, red blood cell flow, leukocyte adhesion, release of vasoactive mediators, and expression of glycoproteins on the endothelial cells. Astrocytes, a key mediator of the neurovascular unit, and intrinsic innervation may also regulate capillary flow. In addition, recent findings on pericyte contractility have attracted the attention of many researchers. Finally, based on these findings, we present a new model of flow control, the proximal integration model, in which localized neural activity is detected at nearby capillaries and the vasodilation signal is transmitted proximally along the vessel. Signals are then integrated at the precapillary arterioles and other arterioles further upstream and regulate the capillary flow.

title: Pericyte contraction induced by oxidative-nitrative stress impairs capillary reflow despite successful opening of an occluded cerebral artery
abstract: Here we show that ischemia induces sustained contraction of pericytes on microvessels in the intact mouse brain. Pericytes remain contracted despite successful reopening of the middle cerebral artery after 2 h of ischemia. Pericyte contraction causes capillary constriction and obstructs erythrocyte flow. Suppression of oxidative-nitrative stress relieves pericyte contraction, reduces erythrocyte entrapment and restores microvascular patency; hence, tissue survival improves. In contrast, peroxynitrite application causes pericyte contraction. We also show that the microvessel wall is the major source of oxygen and nitrogen radicals causing ischemia and reperfusion–induced microvascular dysfunction. These findings point to a major but previously not recognized pathophysiological mechanism; ischemia and reperfusion-induced injury to pericytes may impair microcirculatory reflow and negatively affect survival by limiting substrate and drug delivery to tissue already under metabolic stress, despite recanalization of an occluded artery. Agents that can restore pericyte dysfunction and microvascular patency may increase the success of thrombolytic and neuroprotective treatments.

title: Capillary pericytes regulate cerebral blood flow in health and disease
abstract: Increases in brain blood flow, evoked by neuronal activity, power neural computation and form the basis of BOLD (blood-oxygen-level-dependent) functional imaging. Whether blood flow is controlled solely by arteriole smooth muscle, or also by capillary pericytes, is controversial. We demonstrate that neuronal activity and the neurotransmitter glutamate evoke the release of messengers that dilate capillaries by actively relaxing pericytes. Dilation is mediated by prostaglandin E2, but requires nitric oxide release to suppress vasoconstricting 20-HETE synthesis. In vivo, when sensory input increases blood flow, capillaries dilate before arterioles and are estimated to produce 84% of the blood flow increase. In pathology, ischaemia evokes capillary constriction by pericytes. We show that this is followed by pericyte death in rigor, which may irreversibly constrict capillaries and damage the blood–brain barrier. Thus, pericytes are major regulators of cerebral blood flow and initiators of functional imaging signals. Prevention of pericyte constriction and death may reduce the long-lasting blood flow decrease that damages neurons after stroke.

title: Pericytes in capillaries are contractile in vivo, but arterioles mediate functional hyperemia in the mouse brain
abstract: Modern functional imaging techniques of the brain measure local hemodynamic responses evoked by neuronal activity. Capillary pericytes recently were suggested to mediate neurovascular coupling in brain slices, but their role in vivo remains unexplored. We used two-photon microscopy to study in real time pericytes and the dynamic changes of capillary diameter and blood flow in the cortex of anesthetized mice, as well as in brain slices. The thromboxane A2 analog, 9,11-dideoxy-9α,11α-methanoepoxy Prostaglandin F2α (U46619), induced constrictions in the vicinity of pericytes in a fraction of capillaries, whereas others dilated. The changes in vessel diameter resulted in changes in capillary red blood cell (RBC) flow. In contrast, during brief epochs of seizure activity elicited by local administration of the GABAA receptor antagonist, bicuculline, capillary RBC flow increased without pericyte-induced capillary diameter changes. Precapillary arterioles were the smallest vessels to dilate, together with penetrating and pial arterioles. Our results provide in vivo evidence that pericytes can modulate capillary blood flow in the brain, which may be important under pathological conditions. However, our data suggest that precapillary and penetrating arterioles, rather than pericytes in capillaries, are responsible for the blood flow increase induced by neural activity.

title: The effects of potassium on the rat middle cerebral artery
abstract: After traumatic brain injury, extracellular K(+) in brain can dramatically increase. We studied the effects of increased K(+) on the isolated pressurized rat middle cerebral artery (MCA). MCAs (200-250 microm OD) were isolated, cannulated with glass micropipettes, and pressurized. K(+) was increased in the extraluminal bath using three paradigms: (1) isotonic K(+) (K(iso)) where increases in K(+) were offset by decreases in Na(+), (2) hypertonic K(+) (K(hyper)) where K(+) was increased without a concomitant adjustment of Na(+), and (3) K(suc), a solution using K(iso) but with the addition of sucrose to obtain a hypertonic solution. Increases in K(+) in the extraluminal bath produced significant dilations (approximately 20%) at 21 mM K(+) in all three groups (K(iso), K(hyper), and K(suc)). With the K(hyper) and K(suc) groups, the magnitude of the dilation diminished with further increases in K(+). L-NAME (10(-5) M), an inhibitor of nitric oxide synthase, had no effect on the response of the K(hyper) and K(suc) groups at 21 mM but significantly enhanced constrictions of the MCAs above 40 mM K(+) compared to the control. The K(iso) group was not affected by L-NAME at any K(+) concentration and showed profound constrictions above 40 mM K(+). We conclude that changes in the K(+) concentration and osmolality of the extracellular fluid may have profound effects on the cerebral vasculature.

title: Extracellular K(+)‐induced hyperpolarizations and dilatations of rat coronary and cerebral arteries involve inward rectifier K(+) channels.
abstract: 1. The hypothesis that inward rectifier K(+) channels are involved in the vasodilatation of small coronary and cerebral arteries (100‐200 microm diameter) in response to elevated [K+]o was tested. The diameters and membrane potentials of pressurized arteries from rat were measured using a video‐imaging system and conventional microelectrodes, respectively. 2. Elevation of [K+]o from 6 to 16 mM caused the membrane potential of pressurized (60 mmHg) arteries to hyperpolarize by 12‐14 mV. Extracellular Ba(2+) (Ba2+(o)) blocked K(+)‐induced membrane potential hyperpolarizations at concentrations (IC(50), 6 microM) that block inward rectifier K(+) currents in smooth muscle cells isolated from these arteries. 3. Elevation of [K+]o from 6 to 16 mM caused sustained dilatations of pressurized coronary and cerebral arteries with diameters increasing from 125 to 192 microm and 110 to 180 microm in coronary and cerebral arteries, respectively. Ba2+(o) blocked K(+)‐induced dilatations of pressurized coronary and cerebral arteries (IC50, 3‐8 microM). 4. Elevated [K+]o‐induced vasodilatation was not prevented by blockers of other types of K(+) channels (1 mM 4‐aminopyridine, 1 mM TEA+, and 10 mu M glibenclamide), and blockers of Na(+)‐K(+)‐ATPase. Elevated [K+]o‐induced vasodilatation was unaffected by removal of the endothelium. 5. These findings suggest that K+(o) dilates small rat coronary and cerebral arteries through activation of inward rectifier K(+) channels. Furthermore, these results support the hypothesis that inward rectifier K(+) channels may be involved in metabolic regulation of coronary and cerebral blood flow in response to changes in [K+]o.

title: Perivascular Potassium and pH as Determinants of Local Pial Arterial Diameter in Cats: A MICROAPPLICATION STUDY
abstract: The effects of and the interaction between local perivascular variation in potassium and bicarbonate concentration on the diameter of pial arteries were studied in cats by the microapplication technique. At 11 mEq/liter of bicarbonate, a direct correlation existed between vascular diameter and K+ concentrations between 0 and 10 mEq/liter. At K+ concentrations between 10 and 20 mEq/liter, no further increase in vascular diameter was observed. At a K+ concentration of 5 mEq/liter, an inverse relationship existed between pial arterial diameter and perivascular bicarbonate concentrations between 0 and 22 mEq/liter. At K+ concentrations of 0 and 10 mEq/liter, the pial arterial diameter was determined strongly by the K+ concentration and was only slightly, if at all, influenced by bicarbonate concentrations between 5 and 22 mEq/liter. At lower bicarbonate concentrations the local acidity induced a marked vasodilation. The results indicate that the diameter of pial arterioles in cats is affected by periarteriolar concentrations of K+ and H+; the degree of the vasoreaction induced by H+ is modulated by K+.

title: Potassium dilates rat cerebral arteries by two independent mechanisms.
abstract: Cerebral blood flow is regulated by brain metabolism, and there is evidence to suggest that changes in extracellular potassium concentration are important in linking brain metabolic activity with blood supply. In this study, the effect of low concentrations of potassium on the spontaneous tone of resistance-sized isolated posterior cerebral arteries from Wistar-Kyoto rats was examined. At a transmural pressure of approximately 58 mmHg, the vessels developed spontaneous tone that was 69 +/- 2% of their fully relaxed diameter of 184 +/- 2 microns (n = 50). Introduction of potassium (less than 5 mM) after a 5-min period in potassium-free physiological saline solution resulted in transient dilations, which were not attenuated by barium or cesium but abolished by ouabain. However, potassium concentrations between 7 and 15 mM produced dilations that lacked a transient component and were sensitive to barium, cesium, and ouabain. Maintained dilations to 10 mM K+ persisted in tetrodotoxin, tetraethylammonium, and glibenclamide and after endothelium removal. These results suggest that potassium dilation of cerebral arteries has two independent components, the first of which may be caused by stimulation of the electrogenic sodium pump (0-5 mM K+), whereas the second (greater than 7 mM K+) results from activation of a ouabain-, barium-, and cesium-sensitive process. The latter process describes a means by which potassium may effect prolonged changes in cerebral blood flow.

title: Effects of Ca2+ channel blockers on cortical hypoperfusion and expression of c‐Fos‐like immunoreactivity after cortical spreading depression in rats
abstract: 1 We examined the effects of two Ca2+ channel blockers, lomerizine (KB‐2796) and flunarizine, on the cortical hypoperfusion (measured by hydrogen clearance and laser Doppler flowmetry methods) and cortical c‐Fos‐like immunoreactivity that follow KCl‐induced cortical spreading depression in anaesthetized rats. Cortical spreading depression was induced by application of 1 m KC1 for 30 s to the cortical surface, 3.0 mm posterior to the area of cerebral blood flow measurement. 2 In control rats, KB‐2796 (0.3 and 1 mg kg−1, i.v.) dose‐dependently increased cerebral blood flow significantly at 30 min and 15 min, respectively, after its administration. Flunarizine (1 mg kg“1, i.v.) significantly increased cerebral blood flow 15 min after its administration. In contrast, dimetotiazine (3 mg kg−1, i.v.), a 5‐HT2 and histamine H1 antagonist, failed to affect cerebral blood flow significantly. 3 After KC1 application to the cortex, cerebral blood flow monitored by the laser Doppler flowmetry method increased transiently, for a few minutes, then fell and remained approximately 20 to 30% below control for at least 60 min. Cerebral blood flow monitored by the hydrogen clearance method was also approximately 20 to 30% below baseline for at least 60 min after KC1 application. KB‐2796 (0.3 and 1 mg kg“1, i.v.) and flunarizine (1 and 3 mg kg−1, i.v.) administered 5 min before KC1 application inhibited the cortical hypoperfusion that followed KC1 application, but dimetotiazine (1 and 3 mg kg−1, i.v.) did not. 4 An indicator of neuronal activation, c‐Fos‐like immunoreactivity, was detected in the ipsilateral, but not in the contralateral frontoparietal cortex 2 h after KC1 application. No c‐Fos‐like immunoreactivity was seen on either side of the brain in the hippocampus, thalamus, striatum or cerebellum. 5 KB‐2796 (1 mg kg−1, i.v.) and flunarizine (3 mg kg−1, i.v.), but not dimetotiazine (3 mg kg−1, i.v.), significantly attenuated the expression of c‐Fos‐like immunoreactivity in the ipsilateral frontoparietal cortex. 6 These findings suggest that the inhibitory effects of KB‐2796 and flunarizine on the cortical hypoperfusion and expression of c‐Fos‐like immunoreactivity induced by spreading depression are mediated via the effects of Ca2+‐entry blockade, which may include an increase in cerebral blood flow and the prevention of excessive Ca2+ influx into brain cells. KB‐2796 and flunarizine may prove useful as inhibitors of cortical spreading depression in migraine.

title: Comparison of the effects of potassium and pH on the calibre of cerebral veins and arteries
abstract: The vasomotor responses of individual pial veins and arteries on the convexity of the cerebral cortex to perivascular microinjection of mock cerebrospinal fluid (CSF) containing various concentrations of potassium (K+) and of various pH (achieved by altering the bicarbonate, HCO3− concentration) have been examined in cats anaesthetised with α-chloralose.Microapplication of CSF containing 0 mM HCO3− (pH 4.80) effected significant increases in calibre of pial veins and arteries of 9.3±2.4% and 38.2±4% respectively (mean calibre change ±SE), whereas CSF containing 22 mM HCO3− (pH 7.45) which constricted pial arteries significantly (−18.5±2.9%) minimally altered venous calibre (−4.3 ±2.2%).Microapplication of CSF containing 0 mM potassium resulted in a significant reduction in pial arterial calibre (−11.4±2.8%) but failed to alter pial venous calibre (−0.3 ±0.6%). Perivascular microapplication of CSF containing moderately elevated potassium concentrations (10 mM) which effected marked, significant increases in pial arterial calibre (49.3±3.9%) did not significantly alter the calibre of the pial veins (mean response −1.6±2.4%). The perivascular administration of CSF containing a high concentration of potassium (40 mM) resulted in the significant constriction of both pial veins (−13.5±0.9%) and pial arteries (−47.2±6.3%). The magnitude of the response was significantly smaller in the pial veins.The relative insensitivity to K+ and pH of the pial veins as compared to pial arteries suggests that alteration in the chemical composition of the perivascular fluid are of lesser importance in the control of cerebrovascular capacitance than for the regulation of cerebrovascular resistance.

title: Micropuncture Evaluation of the Importance of Perivascular pH for the Arteriolar Diameter on the Brain Surface
abstract: A micropipette technique was used to induce local changes of the bicarbonate concentration of the cerebro-spinM fluid surrounding arterioles on the exposed cerebral cortex of anaesthetized rats and cats. Injection volumes of a few nanoliters caused circumscribed and pronounced changes of the diameter of the arterioles under study: mock spinal fluid without bicarbonate dilated, while a solution containing 25 meq/1 of bicarbonate constricted the vessels. In such experiments the local pCO2 of the artcriolar wall remains practically constant, since it is set by the pCO 2 of the arterial blood and of the cerebral tissue. Hence the microinjections essentially consisted in a local change of the pH of the fluid surrounding a small segment of a cerebral arteriole. Since metabolic changes of the nervous tissue changes the periarteriolar ptI, it is probable that local pH induced vasomotor changes of the type reported here participate in the so called metabolic regulation of the cerebral blood flow which underlies the local adaptation of the cerebral blood flow to changing functional demands.  Cerebral Circulation -Cerebral Arteriolar Resistance -Local Arteriolar Reactions -Smooth Kuscles -Hydrogen Ions. Schl~sselwSrter: Gehirndurchblutung -Widerstand der Gehirnateriolen -Lokale arteriolgre Gef~Breaktion -Glatte Muskelzelle -Wasserstoffionen.

title: Nitric oxide is the predominant mediator of cerebellar hyperemia during somatosensory activation in rats.
abstract: Crus II is an area of the cerebellar cortex that receives trigeminal afferents from the perioral region. We investigated the mechanisms of functional hyperemia in cerebellum using activation of crus II by somatosensory stimuli as a model. In particular, we sought to determine whether stimulation of the perioral region increases cerebellar blood flow (BFcrb) in crus II and, if so, whether the response depends on activation of 2-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-kainate receptors and nitric oxide (NO) production. Crus II was exposed in anesthetized rats, and the site was superfused with Ringer. Field potentials were recorded, and BFcrb was measured by laser-Doppler flowmetry. Crus II was activated by electrical stimulation of the perioral region (upper lip). Perioral stimulation evoked the characteristic field potentials in crus II and increased BFcrb (34 +/- 6%; 10 Hz-25 V; n = 6) without changing arterial pressure. The BFcrb increases were associated with a local increase in glucose utilization (74 +/- 8%; P < 0.05; n = 5) and were attenuated by the AMPA-kainate receptor antagonist 2, 3-dihydroxy-6-nitro-7-sulfamoylbenzo-[f]quinoxaline (-71 +/- 3%; 100 microM; P < 0.01; n = 5). The neuronal NO synthase inhibitor 7-nitroindazole (7-NI, 50 mg/kg; n = 5) virtually abolished the increases in BFcrb (-90 +/- 2%; P < 0.01) but did not affect the amplitude of the field potentials. In contrast, 7-NI attenuated the increase in neocortical cerebral blood flow produced by perioral stimulation by 52 +/- 6% (P < 0.05; n = 5). We conclude that crus II activation by somatosensory stimuli produces localized increases in local neural activity and BFcrb that are mediated by activation of glutamate receptors and NO. Unlike in neocortex, in cerebellum the vasodilation depends almost exclusively on NO. The findings underscore the unique role of NO in the mechanisms of synaptic function and blood flow regulation in cerebellum.

title: Specific coupling of NMDA receptor activation to nitric oxide neurotoxicity by PSD-95 protein.
abstract: The efficiency with which N-methyl-D-aspartate receptors (NMDARs) trigger intracellular signaling pathways governs neuronal plasticity, development, senescence, and disease. In cultured cortical neurons, suppressing the expression of the NMDAR scaffolding protein PSD-95 (postsynaptic density-95) selectively attenuated excitotoxicity triggered via NMDARs, but not by other glutamate or calcium ion (Ca2+) channels. NMDAR function was unaffected, because receptor expression, NMDA currents, and 45Ca2+ loading were unchanged. Suppressing PSD-95 blocked Ca2+-activated nitric oxide production by NMDARs selectively, without affecting neuronal nitric oxide synthase expression or function. Thus, PSD-95 is required for efficient coupling of NMDAR activity to nitric oxide toxicity, and imparts specificity to excitotoxic Ca2+ signaling.

title: Nitric oxide mediates vasodilatation in response to activation of N-methyl-D-aspartate receptors in brain.
abstract: Neurons release nitric oxide (NO) in response to activation of receptors for the excitatory amino acid N-methyl-D-aspartate (NMDA). We examined the hypothesis that activation of receptors for NMDA produces dilatation of the cerebral microcirculation that is mediated by NO. Diameters of cerebral arterioles were measured using a closed cranial window in anesthetized rabbits. Under control conditions, topical NMDA produced concentration-related dilatation of pial arterioles. Dilatation in response to NMDA was inhibited selectively by MK-801 (an NMDA receptor antagonist) and tetrodotoxin, suggesting that responses to NMDA were receptor mediated and dependent on neuronal activation. Increases in arteriolar diameter in response to NMDA were not affected by L-arginine but were inhibited by NG-nitro-L-arginine, suggesting that the vasodilatation was mediated by NO. Dilatation of cerebral arterioles in response to NMDA was not inhibited by indomethacin, suggesting that cyclooxygenase products do not mediate the response. Using isolated cerebral arteries, we also examined whether NMDA elicited direct cerebral vascular effects. In intact arteries studied in vitro, NMDA had no effect on vascular tone, suggesting that cerebral arteries lack receptors for NMDA. These findings suggest that NO generated in response to activation of receptors for NMDA in vivo is neuronally derived and not due to a direct vascular effect. Thus, NO may mediate increases in local blood flow during increases in neuronal activity in response to excitatory amino acids.

title: Glutamate-induced cerebral vasodilation is mediated by nitric oxide through N-methyl-D-aspartate receptors.
abstract: It was found that glutamate, a major neurotransmitter, is vasoactive in the cerebral circulation. However, the mechanism is unclear. This study was designed to investigate the role of nitric oxide (NO) and N-methyl-D-aspartate (NMDA) receptors in cerebral arteriolar dilation to glutamate.



Newborn, chloralose-anesthetized pigs were equipped with a closed cranial window. The diameter of pial arterioles was measured by means of intravital microscopy, and NO synthase (NOS) activity in brain cortex was determined by the conversion assay of [14C]arginine to [14C]citrulline.



Topical application of glutamate at 10(-7), 10(-6), and 10(-5) mol/L (n = 5) increased the mean diameter by 12 +/- 3%, 13 +/- 2%, and 18 +/- 3% (+/- SEM), respectively (baseline, 91 +/- 10 microns; P < .05). Similarly, NMDA application at the above doses (n = 5) dilated arterioles by 10 +/- 2%, 16 +/- 3%, and 18 +/- 6%, respectively (baseline, 97 +/- 4 microns; P < .05). Topical application of 10(-4) mol/L NG-nitro-L-arginine (L-NNA), which inhibited NOS activity by 93%, blocked the arteriolar dilation to glutamate or NMDA. Furthermore, administration of MK-801, a potent inhibitor of NMDA receptors, blocked glutamate-induced vasodilation completely in both topical application (10(-5) mol/L; n = 6) and intravenous administration (5 to 10 mg/kg; n = 5). In addition, neither L-NNA nor MK-801 attenuated the vasodilation to hypercapnia (PCO2 = 40 to 68 mm Hg).



Glutamate-induced cerebral arteriolar dilation is mediated by NO through NMDA receptors, and NO does not play a major role in the cerebral arteriolar dilation to hypercapnia (PCO2 = 40 to 68 mm Hg) in newborn pigs.

title: In vivo production of nitric oxide correlates with NMDA-induced cerebral hyperemia in newborn sheep.
abstract: Stimulation of N-methyl-D-aspartate (NMDA) receptors in brain increases nitric oxide production in vitro. We tested the hypothesis that nitric oxide participates in the increase in local cerebral blood flow (CBF) caused by infusion of NMDA in anesthetized newborn sheep. We used the combined hydrogen clearance and microdialysis technique for simultaneous measurement of local CBF, infusion of drugs, and measurement of interstitial levels of L-[14C]citrulline in the parietal cortex. Release of L-[14C]citrulline into the dialysate during continuous infusion of L-[14C]arginine was used as a marker of nitric oxide production in vivo. Citrulline recovery and CBF were measured hourly during a 4-h infusion of cerebrospinal fluid containing either 1) no additional drugs, 2) 1 mM NMDA, 3) 1 mM NG-nitro-L-arginine methyl ester (L-NAME, a nitric oxide synthase inhibitor), 4) 1 mM NMDA + 1 mM L-NAME, 5) 0.1 mM 2-chloroadenosine (adenosine receptor agonist), or 6) 0.1 mM 2-chloroadenosine + 1 mM L-NAME. At 240 min of perfusion, CBF (ml.min-1.100 g-1; means +/- SE) was as follows: control 52 +/- 3, NMDA 116 +/- 11, L-NAME 32 +/- 5, NMDA+L-NAME 40 +/- 4,2-chloroadenosine 201 +/- 63, and 2-chloroadenosine+L-NAME 129 +/- 18. Citrulline recovery (fmol/min) at 240 min of perfusion was as follows: control 38 +/- 12, NMDA 149 +/- 21, L-NAME 9 +/- 1, NMDA+L-NAME 39 +/- 5, 2-chloroadenosine 13 +/- 5, and 2-chloroadenosine+L-NAME 17 +/- 1.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Nitric oxide does not mediate cerebral blood flow changes during cortical spreading depression in the anaesthetised rat
abstract: To date, the role of nitric oxide (NO) in mediation of cerebrovascular regulation during spreading depression (SD) in rats remains controversial. Studies are compromised by indirect assay of 'regional' nitric oxide synthase activity (NOS) and/or inappropriate doses of antagonists. The present study utilises direct electrochemical detection in the pia to demonstrate a local, biphasic release of NO associated with each wave of cortical depolarisation. The mean peak of SD-induced NO release was 0.35 microM, which was significantly inhibited by L-N(G)-nitroarginine methyl ester (L-NAME) pre-treatment. Changes in cerebrovascular flux remained intact following treatment with L-NAME, indicating little role for NO in mediation of rat SD blood-flux changes. Mean peak NO release was found to be lower than that observed in rat cerebral ischaemia studies (approximately 4 microM) and in SD in the cat gyrencephalic brain (approximately 0.8 microM).

title: Sumatriptan modifies cortical free radical release during cortical spreading depression A novel antimigraine action for sumatriptan?
abstract: Increases in concentration of brain NO are proposed to initiate and mediate migraine headache. Triggered by focal depolarisation, spreading depression (SD) represents a suitable mechanism for eliciting widespread release of nitric oxide. The current study examines the effect of sumatriptan, a 5-HT(1B/1D) agonist and effective antimigraine therapy, on free radical release (nitric oxide and superoxide) in SD in the simple and complex cortices of the rat and cat. Following initiation of SD, sumatriptan pretreatment (300 microg kg(-1) i.v., 15 min prior to SD) modulated all phases of nitric oxide release associated with each SD in both cats and rats. As a result, superoxide levels were observed to significantly (ANOVA, post hoc LSD) increase versus vehicle treated animals (saline 1 ml kg(-1) i.v. 15 min prior to SD) during specific phases of each SD depolarisation. Averaged over all SD depolarisations, mean peak SD nitric oxide levels per depolarisation were 0.73+/-0.23 microM (n=29) in cats, and 0.42+/-0.09 microM (n=34) in rats. Sumatriptan significantly (Students t-test, P<0.05, two tailed hypothesis, P<0.05) modulated this increase in cortical nitric oxide concentrations to 0.32+/-0.06 microM (n=25) and 0. 22+/-0.07 microM (n=37) in cats and rats. Sumatriptan appears to decrease the amplitude of nitric oxide release but enhances extracellular superoxide concentrations in both lissencephalic and gyrencephalic cortices during SD.

title: SB-220453, A Potential Novel Antimigraine Agent, Inhibits Nitric Oxide Release Following Induction of Cortical Spreading Depression in the Anaesthetized Cat
abstract: Profound nitric oxide release associated with cortical spreading depression (SD), has been implicated in stroke, traumatic brain injury and migraine pathophysiology. SB-220453 represents a mechanistically novel, well-tolerated class of compounds which may have therapeutic potential in the treatment of conditions associated with neuronal hyperexcitability and inflammation. The aim of the present study was to investigate the effects of SB-220453 on the nitric oxide (NO) release associated with SD in the anaesthetized cat. In vehicle treated animals, KCl application for 6 min to the cortical suface produced repeated changes in extracellular direct current field potential with associated NO release. This activity was sustained for a median duration of 55 min (25–75% range, 32–59 min) and 59 min (25–75% range, 34–59 min), respectively. SB-220453 (1, 3 and 10 mg/kg i.p.) produced a dose-related inhibition of this activity and at the highest dose tested, the median duration of changes in extracellular field potential and NO release were reduced to 4 min (25–75% range, 4–5min) and 5 min (25–75% range, 5–5min), respectively. No effect was observed on basal systemic haemodynamic parameters or resting cerebral laser Doppler blood flux at any of the doses of SB-220453 tested. SB-220453 therefore represents a novel compound to assess the potential benefit of inhibiting SD associated nitric oxide release in neurological disease.

title: Local NADPH—Diaphorase Neurons Innervate Pial Arteries and Lie Close or Project to Intracerebral Blood Vessels: A Possible Role for Nitric Oxide in the Regulation of Cerebral Blood Flow
abstract: Electrical stimulation of perivascular nerves induced a relaxation of endothelium-denuded cat pial arteries that was significantly reduced by nitric oxide (NO) synthase inhibition, indicating that NO was involved in the neurogenic relaxation of these vessels. Histochemical staining of the pial arteries for NADPH-diaphorase (NADPH-d), used as a marker for NO synthase, showed positive nerve fibers in the adventitial layer. Interestingly, in some restricted areas stained neuronal cell bodies were also observed. These neurons were scattered or distributed in small groups in a ganglion-like manner, and they sent fibers to the vessel wall. No NADPH-d-positive nerve fibers or cell bodies were detected in forelimb, pulmonary, or coronary arteries. Within the brain parenchyma, blood vessels also showed positive fibers around their walls. These fibers were organized in a branching pattern and presented varicosities. NADPH-d-positive neurons were found in the proximity of the intracerebral vascular profiles, sending processes to the vessels and/or being directly apposed to their wall. The neurovascular contacts were preferentially located close to the interface between the cerebral cortex and white matter. The anatomical relationship between NADPH-d-positive neurons and fibers and the cerebral blood vessels, together with the participation of NO in the neurogenic relaxation of pial arteries, suggests that NO is involved in the regulation of cerebral blood flow.

title: Nitric oxide synthase-containing neural processes on large cerebral arteries and cerebral microvessels
abstract: We studied whether neural processes containing nitric oxide synthase (NOS) are associated with large cerebral arteries and/or intraparenchymal microvessels. The presence of NOS-positive nerves on large cerebral arteries was examined in whole-mount preparations processed for NADPH diaphorase histochemistry, a procedure that stains NOS-containing neurons. The association between NOS-containing neural processes and intracerebral microvessels was studied by electron microscopy in ultrathin brain sections reacted with antibodies against NOS. A dense perivascular plexus of NADPH diaphorase positive axons was observed in the anterior portion of the circle of Willis and its branches while in the basilar artery the innervation was less dense. Lesions of the major sources of perivascular innervation of the cerebral arteries indicated that these nerve fibers arise from the sphenopalatine ganglia. Within the brain parenchyma, NOS immunoreactivity was observed in dendrites and axonal terminals closely associated with the basal lamina of arterioles and capillaries. We conclude that NOS-containing nerves of peripheral origin innervate large cerebral arteries while NOS-containing neural processes of central origin, especially dendrites, are closely associated with cerebral arterioles and capillaries. The presence of NOS in perivascular dendrites raises the possibility that these structures are a major source of NO during neural activity. These findings, collectively, provide morphological evidence supporting the hypothesis that NOS neurons participate in the mechanisms that match neural activity to cerebral blood flow.

title: Nitric Oxide Synthase Inhibition and Cerebrovascular Regulation
abstract: There is increasing evidence that nitric oxide (NO) is an important molecular messenger involved in a wide variety of biological processes. Recent data suggest that NO is also involved in the regulation of the cerebral circulation. Thus, NO participants in the maintenance of resting cerebrovascular tone and may play an important role in selected vasodilator responses of the cerebral circulation. Furthermore, evidence has been presented suggesting that NO participates in the mechanisms of cerebral ischemic damage. Despite the widespread attention that NO has captured in recent years and the large number of studies that have been published on the subject, there is considerable controversy regarding the role of this agent in cerebrovascular regulation and in ischemic damage. In this paper the results of investigations on NO and the cerebral circulation are reviewed and the evidence for and against a role of NO is critically examined.

title: Possible Origins and Distribution of Immunoreactive Nitric Oxide Synthase-Containing Nerve Fibers in Cerebral Arteries
abstract: The distribution of perivascular nerve fibers expressing nitric oxide synthase (NOS)-immunoreactivity was examined in Sprague–Dawley and Long–Evans rats using affinity-purified rabbit antisera raised against NOS from rat cerebellum. NOS immunoreactivity was expressed within the endothelium and adventitial nerve fibers in both rat strains. Labeled axons were abundant and dense in the proximal anterior and middle cerebral arteries, but were less numerous in the caudal circle of Willis and in small pial arteries. The sphenopalatine ganglia were the major source of positive fibers in these vessels. Sectioning postganglionic parasympathetic fibers from both sphenopalatine ganglia reduced the density of NOS-immunoreactive (IR) nerve fibers by >75% in the rostral circle of Willis. Moreover, NOS-IR was present in 70–80% of sphenopalatine ganglion cells. Twenty percent of these neurons also contained vasoactive intestinal polypeptide (VlP)-immunoreactivity. By contrast, the superior cervical ganglia did not contain NOS-IR cells. In the trigeminal ganglion, NO-IR neurons were found chiefly within the ophthalmic division; ∼10–15% of neurons were positively labeled. Colocalization with calcitonin gene-related peptide (CGRP) was not observed. Sectioning the major trigeminal branch innervating the circle of Willis decreased positive fibers by ≤25% in the ipsilateral vessels. In the nodose ganglion, 20–30% of neurons contained NOS-immunoreactivity, whereas less than 1% were in the C2 and C3 dorsal root ganglia. Three human circles of Willis obtained at autopsy showed sparse immunoreactive fibers, chiefly within vessels of the posterior circulation. Postmortem delay accounted for some of the reduced density. Our findings indicate that nerve fibers innervating cerebral arteries may serve as a nonendothelial source of the vasodilator nitric oxide (NO). The coexistence of NOS and VIP within sphenopalatine ganglion cells raises the possibility that two vasodilatory agents, one, a highly diffusable short-lived, low-molecular-weight molecule, and the other, a polar 28 amino acid-containing peptide, may serve as coneuromediators within the cerebral circulation.

title: Nitric Oxide Promotes Arteriolar Dilation During Cortical Spreading Depression in Rabbits
abstract: Pial arterioles transiently dilate during cortical spreading depression (CSD), although the mechanisms are unclear. We tested the hypothesis that increased production of nitric oxide (NO) promotes arteriolar dilation.  Urethane-anesthetized rabbits were equipped with cranial windows, and the diameter (reported in micrometers) of a pial arteriole was determined via intravital microscopy. In each rabbit, a baseline CSD was elicited by microapplication of KC1 onto the cortex, and resultant pial arteriolar dilation was measured. Either 100 μmolfL Nw-nitro-L-arginine methyl ester (L-NAME) or 50 μmol/L NG-nitro-L-arginine (L-NA), both competitive NO synthase inhibitors, was then applied to the brain surface. A CSD was elicited as before. The L-NAME and L-NA were then removed by artificial cerebrospinal fluid washes. An additional CSD was induced with KC1 as before.  Control CSD in the L-NAME group dilated pial arterioles: baseline diameter, 66±7 mm, with CSD=106±8 mm (59% increase). After topically applied L-NAME, CSD dilated pial arterioles less: baseline diameter, 61 ±7 mm, with CSD=77±6 mm (26% increase), P<.05 compared with control CSD diameter. Topical L-NA had similar effects on CSD: control CSD dilated pial arterioles 51%; after topical L-NA, only 14% (P<.05). After removal of L-NAME or L-NA, CSD-induced pial arteriolar dilation was similar to original control values.  The reversible inhibition of CSD-induced pial arteriolar dilation by either L-NAME or L-NA suggests that NO contributes to arteriolar dilation observed with CSD.

title: Neuronal NO promotes cerebral cortical hyperemia during cortical spreading depression in rabbits.
abstract: Temporary elevations in cortical cerebral blood flow (CBF) accompany cortical spreading depression (CSD) in anesthetized animals. We tested the hypothesis that nitric oxide (NO) is an important promotor of CSD-induced cortical hyperemia in urethan-anesthetized rabbits. CBF was measured at four time points by administration of 15-microm microspheres with the reference withdrawal technique. Intravenous administration of the nonspecific NO synthase (NOS) inhibitor N(omega)-nitro-L-arginine increased mean arterial blood pressure and resting cerebrovascular resistance and attenuated CSD-induced hyperemia. Cortical CBF before intraperitoneal 7-nitroindazole (7-NI), a neuronal NOS inhibitor, was 42 +/- 8 and 124 +/- 19 ml x 100 g(-1) x min(-1) at baseline and during CSD, respectively (P < 0.05 by repeated-measures analysis of variance). After 7-NI administration, mean arterial blood pressure, CBF, and cerebrovascular resistance were unchanged from baseline values; cortical CBF was 38 +/- 4 and 90 +/- 8 ml x 100 g(-1) x min(-1) post-7-NI at rest and during a second CSD, respectively. Similar to N(omega)-nitro-L-arginine, 7-NI decreased the cortical hyperemic response during CSD (P < 0.05 by repeated-measures analysis of variance). We conclude that neuronal NOS promotes the temporary cortical hyperemia observed during CSD.

title: Oxygen Radicals Do Not Play a Role in Arteriolar Dilation during Cortical Spreading Depression
abstract: This study examined the role of oxygen radicals in pial arteriolar changes during cortical spreading depression (CSD). CSD was induced by microinjection of 5% KCl in anesthetized adult rabbits. Pial diameter was measured with a closed cranial window and intravital microscopy. During control CSD (n = 12), the dilation amplitude and area were 55 ± 14% and 693 ± 69 mm2 (baseline = 76 ± 14 μm), respectively. Oxygen radical scavengers, superoxide dismutase (SOD; 105 U/ml, topical application; n = 5) or oxypurinol (50 mg/kg i.v.; n = 7), did not alter the dilation amplitude and area or change onset latency during CSD. Further, SOD and oxypurinol did not prevent NG-nitro-L-arginine from attenuating arteriolar dilation during CSD (n = 12). We conclude that oxygen radicals do not play a role in the transient dilation of cerebral arterioles during CSD.

title: Nitric oxide and prostaglandins interact to mediate arteriolar dilation during cortical spreading depression.
abstract: We examined whether blockade of prostaglandin synthesis by indomethacin could attenuate the effect of nitric oxide synthase (NOS) inhibition on cerebral arteriolar dilation during cortical spreading depression (CSD). CSD was induced by microinjection of 5% (670 mM) KCl onto the cerebral cortex of anesthetized adult rabbits. A closed cranial window and intravital microscopy were used to measure pial arteriolar diameter, and NOS activity was determined by the conversion assay of [14C]arginine to [14C]citrulline. CSD dilated pial arterioles by 47 +/- 3% (baseline = 80-88 microns) (n = 21, P < 0.05), and inhibition of NOS by NG-nitro-L-arginine (L-NNA) (15 mg/kg iv) reduced dilation during CSD by over one-half (n = 8, P < 0.05) without altering the onset latency to CSD. After indomethacin administration (15 mg/kg iv), CSD dilated arterioles from 73 +/- 2 to 152 +/- 6 microns (n = 4, P < 0.05). However, after administration of both indomethacin and L-NNA (n = 5), CSD-induced arteriolar dilation was not different from the situation where indomethacin alone was given. Thus indomethacin completely abolished the inhibitory effect of L-NNA on CSD-induced dilation. Administration of L-NNA inhibited NOS activity in brain cortex almost completely (n = 8, P < 0.05), whereas indomethacin itself had no effect (n = 8). In addition, L-NNA inhibited topical acetylcholine (10(-5) M)-induced arteriolar dilation (n = 3, P < 0.05), and this effect was not altered by indomethacin (n = 4). In summary, L-NNA reduced arteriolar dilation during CSD. However, after administration of indomethacin, L-NNA does not reduce CSD-induced arteriolar dilation.

title: Examination of the role of nitric oxide for the hypercapnic rise of cerebral blood flow in rats.
abstract: We examined the effect of nitric oxide synthase (NOS) inhibition and tetrodotoxin (TTX) on the increase of cerebral blood flow (CBF) in parietal (CoBF) and cerebellar cortex (CeBF) in response to hypercapnia. Rats were anesthetized with halothane and artificially ventilated. Hypercapnia was induced by adding 5% CO2 to the inhalation mixture. CoBF and CeBF were measured by laser-Doppler flowmetry. NOS inhibition was achieved by intravenous (30 mg/kg) and/or topical application (1 mM) of NG-nitro-L-arginine (L-NNA). Activity in perivascular nerves around pial and cortical vessels was inhibited by topical application of TTX (20 microM). Under control conditions, hypercapnia (66 +/- 1 mmHg) increased CoBF by 70 +/- 4% and CeBF by 96 +/- 5%. Systemic L-NNA decreased the baseline level of CoBF and CeBF by 11 +/- 3%, but topical L-NNA did not affect baseline flow. Intravenous L-NNA attenuated the hypercapnic increase of CoBF by 77 +/- 5% and CeBF by 63 +/- 4% within 10-20 min. Topical L-NNA attenuated the hypercapnic increase of CoBF by 52 +/- 6% and CeBF by 29 +/- 5% after 45-min exposure. Both CoBF and CeBF decreased rapidly when L-NNA was infused during sustained hypercapnia, but not when L-NNA was applied topically. Effect of intravenous L-NNA was partially prevented by pretreatment with intravenous L-arginine. Intravenous or topical L-NNA enhanced the rise of CBF elicited by cortical spreading depression, adenosine (1 mM), or sodium nitroprusside (300 microM), except in the cerebellum where topical L-NNA attenuated the rise of CBF elicited by adenosine by 53%.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Characteristics of induced spreading depression after transient focal ischemia in the rat
abstract: We examined characteristics of spreading depression (SD) induced on the rat cortex 1 day after transient focal ischemia. Male Wistar rats (n=21) were subjected to transient intraluminal thread occlusion of the right middle cerebral artery for 75 min. Twenty-four hours after the reperfusion, cerebral blood flow (CBF) was determined using laser Doppler flowmeter during multiple SDs elicited on both non-stroke (left) and stroke (right) cortex by the topical application of 2 M KCl. We also examined CBF responses before and after the intravenous administration of the nonspecific NOS inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg) in normal and stroke cortex. Animals were divided into two groups; Group 1 (n=12), animals with subcortical infarction and Group 2 (n=9), animals with subcortical plus cortical infarction. There were no differences between non-stroke and stroke sides in the duration or amplitude of the DC potential shifts in either group. The transient CBF hyperemia during SD was not different between non-stroke (372+/-23% of baseline, mean+/-S.E.) and stroke sides (383+/-30%) in Group 1. However, in Group 2, CBF was significantly restricted on the stroke side (192+/-15% vs. non-stroke side, 374+/-33%). In four normal animals without ischemia, there were no differences in CBF response between both sides. L-NAME had no effect on the transient CBF hyperemia during SD in any of the groups. These data suggest that the CBF responses during SD in the peri-infarction area is restricted 1 day after the transient focal ischemia, while CBF responses are intact in normal cortex overlapping a subcortical infarct. Further, our results indicate that nitric oxide does not promote CBF responses during SD in normal cortex or in tissue surrounding infarction.

title: Cerebral Blood Flow Changes during Cortical Spreading Depression are Not Altered by Inhibition of Nitric Oxide Synthesis
abstract: CBF increases concomitantly with cortical spreading depression (CSD). We tested the hypothesis that CBF changes during CSD are mediated by nitric oxide (NO). Male Wistar rats (n = 23) were subjected to KCl-induced CSD before and after administration of nitric oxide synthase (NOS) inhibitors N-nitro-l-arginine (L-NNA) or N-nitro-l-arginine methyl ester (L-NAME) and in nontreated animals. CBF, CSD, and mean arterial blood pressure were recorded. Brain NOS activity was measured in vitro in control, L-NNA, and L-NAME-treated rats by the conversion of [3H]arginine to [3H]citrulline. Our data show that the NOS inhibitors did not significantly change regional CBF (rCBF) during CSD, even though cortical NOS activity was profoundly depressed and systemic arterial blood pressure was significantly increased. Our data suggest that rCBF during CSD in rats is not regulated by NO.

title: A brief hypoperfusion precedes spreading depression if nitric oxide synthesis is inhibited
abstract: Spreading cortical depression (SCD) alters cerebral blood flow by mechanisms that are not well understood. To investigate the role of the likely endothelium-derived relaxing factor, nitric oxide, in the blood flow changes occurring during SCD in awake rats, nitric oxide synthesis was blocked using N omega-nitro-L-arginine methyl ester (L-NAME). During SCD there is an initial hyperperfusion followed by a longer-lasting hypoperfusion. Treatment with L-NAME, 30 mg/kg, reduced resting cerebral blood flow globally. During SCD, L-NAME treatment produced an additional brief phase of hypoperfusion which preceded the initial hyperperfusion. The magnitude of the initial hyperperfusion was less than expected. The subsequent longer-lasting hypoperfusion was unchanged. Nitric oxide plays an important role in the regulation of cerebral blood flow during SCD.

title: Nitric Oxide Modulates the CBF Response to Increased Extracellular Potassium
abstract: The response of the regional cerebral blood flow (rCBF) to brain topical superfusion of 20 mM K+ was characterized in a closed cranial window preparation in barbiturate anesthetized and ventilated rats; Increasing K+ in the artificial cerebrospinal fluid (ACSF) induced a rCBF elevation (measured by laser–Doppler flowmetry) of +85 ± 37% above baseline (n = 19). This elevation was stable for >3 h with continuous superfusion of increased K+ (n = 5) and partially reversible to a level of + 18 ± 19% above baseline when returning to a physiological K+ concentration. Nitric oxide synthase (NOS) inhibition by brain topical superfusion with Nω-nitro-L-arginine (L-NA) revealed (a) Addition of L-NA to high-potassium ACSF reduced the rCBF increase from + 94 ± 36% to + 21 ± 18% (p ≤ 0.01, n = 7). (b) When L-NA was superfused for 60 min before increasing K+, rCBF decreased to – 17 ± 7% below baseline. Subsequent coapplication of L-NA and increased K+ induced only an elevation of +7 ± 4% above baseline (n = 4). (c) When the NO donor S-nitroso-N-acetylpenicillamine (SNAP) was added during NOS inhibition to restore basal tissue NO levels, the resultant level of rCBF was +28 ± 54% above baseline. Subsequent increase of K+ in the presence of NOS inhibition and SNAP elevated rCBF to + 137 ± 89% above baseline (n = 4). Statistical analysis comparing K+-induced elevation of rCBF (a) without any added drugs, (b) in the presence of NOS inhibition with L-NA, and (c) in the presence of both NOS inhibition and SNAP revealed that K+-induced elevation in the presence of NOS inhibition was significantly reduced (p ≤ 0.05) whereas no statistical difference was found between K+-induced elevation of rCBF without drugs compared with the K+-induced elevation of rCBF in the presence of L-NA and SNAP. We conclude that NO is a modulator of the rCBF elevation to increased extracellular K+ concentration.

title: Modulation of extraluminally induced vasoconstrictions by endothelium-derived nitric oxide in the canine basilar artery.
abstract: The present study was undertaken to investigate the role of endothelium in extraluminally induced vasospasm of the cerebral artery using isolated perfused canine basilar arteries. The extraluminal applications of high K+ and prostaglandin F2 alpha (PGF2 alpha) induced concentration-dependent vasoconstriction. Both constrictive responses were significantly enhanced by denuding endothelium. Additionally, the responses in the endothelium-intact arteries were markedly augmented by intraluminal perfusion with NG-monomethyl-L-arginine (L-NMMA). These results suggest that the inhibition of nitric oxide (NO) synthase in endothelium enhances increase in transmembrane Ca(2+)-influx which is a common constrictive mechanism to the vasoconstrictors. The augmentative action induced by L-NMMA was inhibited by intraluminal perfusion of L-arginine, but not by D-arginine. Furthermore, the augmentation was not observed in the arteries without endothelium. These results suggest that the endothelium may have a great significance on responsiveness to extraluminal vasoactive substances and that endothelium-derived NO may modulate the extraluminally induced vasoconstriction which is responsible for cerebral vasospasm after subarachnoid hemorrhage.

title: Nitric oxide in the potassium-induced response of the rat middle cerebral artery: a possible permissive role
abstract: In the middle cerebral artery (MCA), the presence of nitric oxide (NO) is responsible for maintaining a more dilated state than in its absence during increases in extracellular K(+) and osmolality. The purpose of the present study was to determine whether the involvement of NO was due to (a) a direct effect of the K(+)/osmolality (K(hyper)) on the endothelium or (b) a 'permissive' role of NO. MCAs (approximately 210 microm o.d.) were isolated, cannulated with glass micropipettes, and pressurized to 85 mmHg. When K(+) (KCl) in the extraluminal bath was increased to 21 mM, the diameter increased by 15-20% with the magnitude of dilation diminishing with further increases in K(hyper). The addition of N(G)-nitro-L-arginine methyl ester (L-NAME, 10(-5) mM), an inhibitor of nitric oxide synthase, had no significant effect on dilations at lower K(hyper) concentrations but constricted the arteries relative to the control at 51, 66, and 81 mM K(hyper). In the presence of L-NAME, the addition of an exogenous NO donor, S-nitroso-N-acetylpenicillamine (SNAP, 10(-8) M) or an analog of cGMP, 8-bromo-cGMP (6x10(-5) M), tended to restore the response of K(hyper)to near the original response. We conclude that the basal release of NO from the endothelium plays a permissive role in the K(hyper)-induced response.

title: Impaired cerebrovascular reactivity after cortical spreading depression in rats: Restoration by nitric oxide or cGMP
abstract: We investigated the role of the NO/cGMP system in the vasodilatory response to hypercapnia after cortical spreading depression (CSD) in barbiturate anesthetized rats in vivo. Regional cerebral blood flow (rCBF) was measured by laser Doppler flowmetry (LDF). Hypercapnia (arterial pCO2 50-60 mm Hg) increased rCBF by 2.8+/-1.0%/mm Hg (n = 34). Fifteen minutes after CSD, resting rCBF was reduced to 87%, and rCBF response to hypercapnia was abolished (p < 0.001, n = 28). Within 1 h after CSD, only little restoration of vascular reactivity occurred. Topical application of the NO-donors S-nitroso-N-acetylpenicillamine (SNAP), 3-morpholinosydnonimine (SIN1), or spermine/NO complex (Sperm/NO), or of the cell permeable guanosine 3',5'-cyclic monophosphate (cGMP) analogue 8-Br-cGMP reestablished resting rCBF to values measured before CSD, and reversed CSD-induced attenuation of the cerebrovascular response to hypercapnia. Restoration of resting rCBF to pre-CSD level by the NO-independent vasodilator papaverine had no effect on the attenuated hypercapnic response. In conclusion, we have shown that the compromised vascular reactivity to hypercapnia after CSD can be reversed to normal reactivity by restoration of the basal NO or cGMP concentration in the cortex, suggesting a reduction of the cerebrovascular NO or cGMP concentration following CSD.

title: Cerebrospinal Fluid 20-HETE Is Associated With Delayed Cerebral Ischemia and Poor Outcomes After Aneurysmal Subarachnoid Hemorrhage
abstract: Delayed cerebral ischemia (DCI) is a major complication after aneurysmal subarachnoid hemorrhage (aSAH); it is manifested by changes in cerebral blood flow accompanied by neurological decline, and it results in long-term functional and neuropsychological impairment. Preclinical evidence has demonstrated that the arachidonic acid metabolite, 20-hydroxyeicosatetraenoic acid (20-HETE), affects cerebral microvascular tone and cerebral blood flow after aSAH. The purpose of this study was to determine whether cerebrospinal fluid 20-HETE levels were associated with DCI and long-term neuropsychological outcomes in aSAH patients.  Cerebrospinal fluid samples were collected twice daily through 14 days after hemorrhage on 108 acute, adult, aSAH patients. Samples were analyzed for 20-HETE via HPLC MSQ single quadrupole mass spectrometry. DCI was defined as the presence of impaired cerebral blood flow (angiographic vasospasm, elevated transcranial Dopplers, abnormal computed tomography or magnetic resonance perfusion scans) accompanied by neurological deterioration. Outcomes, including death and neuropsychological testing, were completed at 3 months after hemorrhage.  Detectable 20-HETE levels were observed in 31% of patient samples and were associated with severity of hemorrhage (Hunt & Hess [HH], P=0.04; Fisher, P=0.05). Detection of 20-HETE was not associated with angiographic vasospasm (P=0.34); however, detectable 20-HETE was significantly associated with DCI (P=0.016). Our data also suggest that detectable 20-HETE was associated with decreased performance in 5 neuropsychological domains.  These results provide the first clinical evidence that cerebrospinal fluid 20-HETE concentrations are associated with DCI and poor outcomes, and this provides impetus for future studies to elucidate the clinical utility of inhibiting 20-HETE formation as a novel therapeutic intervention in patients with aSAH.

title: 20-HETE contributes to the acute fall in cerebral blood flow after subarachnoid hemorrhage in the rat.
abstract: This study examined the effects of blocking the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) on the acute fall in cerebral blood flow after subarachnoid hemorrhage (SAH) in the rat. In vehicle-treated rats, regional cerebral blood flow (rCBF) measured with laser-Doppler flowmetry fell by 30% 10 min after the injection of 0.3 ml of arterial blood into the cisterna magna, and it remained at this level for 2 h. Pretreatment with inhibitors of the formation of 20-HETE, 17-octadecynoic acid (17-ODYA; 1.5 nmol intrathecally) and N-hydroxy-N'-(4-butyl-2-methylphenyl)formamidine (HET0016; 10 mg/kg iv), reduced the initial fall in rCBF by 40%, and rCBF fully recovered 1 h after induction of SAH. The concentration of 20-HETE in the cerebrospinal fluid rose from 12 +/- 2 to 199 +/- 17 ng/ml after SAH in vehicle-treated rats. 20-HETE levels averaged only 15 +/- 11 and 39 +/- 13 ng/ml in rats pretreated with 17-ODYA or HET0016, respectively. HET0016 selectively inhibited the formation of 20-HETE in rat renal microsomes with an IC(50) of <15 nM and human recombinant CYP4A11, CYP4F2, and CYP4F3 enzymes with an IC(50) of 42, 125, and 100 nM, respectively. These results indicate that 20-HETE contributes to the acute fall in rCBF after SAH in rats.

title: HET0016, a potent and selective inhibitor of 20‐HETE synthesizing enzyme
abstract: The present study examined the inhibitory effects of N‐Hydroxy‐N′‐(4‐butyl‐2‐methylphenyl)‐formamidine (HET0016) on the renal metabolism of arachidonic acid by cytochrome P450 (CYP) enzymes. HET0016 exhibited a high degree of selectivity in inhibiting the formation of 20‐hydroxy‐5,8,11,14‐eicosatetraenoic acid (20‐HETE) in rat renal microsomes. The IC50 value averaged 35±4 nM, whereas the IC50 value for inhibition of the formation of epoxyeicosatrienoic acids by HET0016 averaged 2800±300 nM. In human renal microsomes, HET0016 potently inhibited the formation of 20‐HETE with an IC50 value of 8.9±2.7 nM. Higher concentrations of HET0016 also inhibited the CYP2C9, CYP2D6 and CYP3A4‐catalysed substrates oxidation with IC50 values of 3300, 83,900 and 71,000 nM. The IC50 value for HET0016 on cyclo‐oxygenase activity was 2300 nM. These results indicate that HET0016 is a potent and selective inhibitor of CYP enzymes responsible for the formation of 20‐HETE in man and rat.

title: P-450 metabolites of arachidonic acid in the control of cardiovascular function.
abstract: Recent studies have indicated that arachidonic acid is primarily metabolized by cytochrome P-450 (CYP) enzymes in the brain, lung, kidney, and peripheral vasculature to 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) and that these compounds play critical roles in the regulation of renal, pulmonary, and cardiac function and vascular tone. EETs are endothelium-derived vasodilators that hyperpolarize vascular smooth muscle (VSM) cells by activating K(+) channels. 20-HETE is a vasoconstrictor produced in VSM cells that reduces the open-state probability of Ca(2+)-activated K(+) channels. Inhibitors of the formation of 20-HETE block the myogenic response of renal, cerebral, and skeletal muscle arterioles in vitro and autoregulation of renal and cerebral blood flow in vivo. They also block tubuloglomerular feedback responses in vivo and the vasoconstrictor response to elevations in tissue PO(2) both in vivo and in vitro. The formation of 20-HETE in VSM is stimulated by angiotensin II and endothelin and is inhibited by nitric oxide (NO) and carbon monoxide (CO). Blockade of the formation of 20-HETE attenuates the vascular responses to angiotensin II, endothelin, norepinephrine, NO, and CO. In the kidney, EETs and 20-HETE are produced in the proximal tubule and the thick ascending loop of Henle. They regulate Na(+) transport in these nephron segments. 20-HETE also contributes to the mitogenic effects of a variety of growth factors in VSM, renal epithelial, and mesangial cells. The production of EETs and 20-HETE is altered in experimental and genetic models of hypertension, diabetes, uremia, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of this pathway in the control of cardiovascular function, it is likely that CYP metabolites of arachidonic acid contribute to the changes in renal function and vascular tone associated with some of these conditions and that drugs that modify the formation and/or actions of EETs and 20-HETE may have therapeutic benefits.

title: Role of cGMP versus 20-HETE in the vasodilator response to nitric oxide in rat cerebral arteries.
abstract: This study examined the response to nitric oxide (NO) in rat middle cerebral arteries (MCA). NO donors increased the activity of a 205-pS K(+) channel recorded from vascular smooth muscle (VSM) cells isolated from MCA 10-fold. Blockade of guanylyl cyclase activity with 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10(-5) M) did not alter the effect of NO on this channel. In contrast, adding 20-hydroxyeicosatetraenoic acid (20-HETE) to the bath (10(-7) M) abolished the response to NO. NO donors also increased the diameter of serotonin-preconstricted MCA to 85% of control. Blockade of K(+) channels with iberiotoxin or a high-K(+) medium reduced this response by 50%. ODQ (10(-5) M) reduced this response by 47 +/- 3%, whereas preventing the fall of 20-HETE levels reduced the response by 59 +/- 2% (n = 5). Blockade of both pathways eliminated the response to NO donors. These results indicate that activation of K(+) channels contributes 50% to vasodilator response to NO in rat MCA. This is mediated by a fall in 20-HETE levels rather than a rise in cGMP levels or a direct effect of NO.

title: Inhibition of calcitonin gene-related peptide by h-CGRP(8–37) antagonizes the cerebral dilator response from nasociliary nerve stimulation in the cat
abstract: The head is innervated by neurons with cell bodies in the trigeminal ganglion that contain both calcitonin gene-related peptide (CGRP) and substance P. The CGRP-containing neurons preferentially innervate the cerebral vessels and when activated produce both an increase in blood flow and local release of CGRP. In this study, the CGRP antagonist h-CGRP(8-37) was examined for its ability to interfere with trigeminal-evoked cerebral vasodilator responses in the alpha-chloralose anaesthetised cat. Nasociliary nerve stimulation produced a characteristic frequency-dependent increase in cerebral cortical blood flow with a mean maximum of 35 +/- 7% at 20 Hz. Following administration of h-CGRP(8-37), this response was reduced by half with a general shift to the right of the frequency-response curve. These data further support the view that CGRP is an important transmitter agent in the trigeminovascular system that is responsible for a great part of the vasodilator capacity of trigeminal neurons.

title: Ischemia reduces CGRP-induced cerebral vascular dilation in piglets.
abstract: Effects of anoxic stress on cerebrovascular responses to calcitonin gene-related peptide (CGRP) have not been examined previously. We determined the effects of total global ischemia on cerebral arteriolar responses to CGRP in newborn pigs.



Piglets were anesthetized and ventilated with a respirator. Pial arteriolar diameter was determined using a closed cranial window and intravital microscopy. Baseline arteriolar diameters ranged from 80 to 100 microns. Arteriolar responses to 10(-9) and 10(-8) mmol/L CGRP applied topically were determined before and 1, 2, and 4 hours after a 10-minute period of total global ischemia. Ischemia was caused by increasing intracranial pressure.



Before ischemia, CGRP dilated arterioles by 14 +/- 2% (n = 6) and 24 +/- 3% (n = 7) at 10(-9) and 10(-8) mmol/L, respectively. However, after ischemia, arteriolar responses to 10(-9) mmol/L CGRP were reduced at 1 hour to 4 +/- 1%, at 2 hours to 3 +/- 2%, and at 4 hours to 5 +/- 4% (P < .05 for all comparisons). Similarly, arteriolar responses to 10(-8) mmol/L CGRP were reduced to 5 +/- 2% at 1 hour, 5 +/- 2% at 2 hours, and 10 +/- 6% at 4 hours (P < .05 for all comparisons). In time control animals, arteriolar responses to CGRP did not change over time. In other animals, we examined effects of pretreatment with indomethacin (5 mg/kg IV) on ischemia-induced decreases in arteriolar responses to CGRP. Indomethacin administration did not preserve arteriolar dilation to CGRP at 1 hour after ischemia, but responses were normal at 2 hours.



Total global ischemia leads to prolonged attenuated dilator responses of cerebral arterioles to CGRP. In addition, indomethacin treatment alters effects of ischemia on CGRP-induced dilation.

title: Is there a correlation between spreading depression, neurogenic inflammation, and nociception that might cause migraine headache?
abstract: The time course of propagation of scotoma and blood flow changes during migraine aura parallels the phenomenon of cortical spreading depression (CSD). It was proposed that CSD generates a sterile neurogenic inflammation in the meninges, which may then lead to the activation or sensitization of nociceptors, thus generating headache. We performed rat experiments in which the effect of CSD on plasma extravasation in the dura mater and on neuronal activity in deep laminae of the trigeminal nucleus was assessed in vivo. CSD did not alter dural plasma extravasation measured by means of bovine serum albumin–coupled flourescein (n = 17 rats) compared to the CSD‐free contralateral side. In an in vitro model, the application of KCl to the dura at concentrations extracellularly found during CSD did not alter the release of calcitonin gene–related peptide and prostaglandin E2 from the dura. In 33 rats, neither single CSDs nor a series of CSDs altered ongoing neuronal activity or mechanical and/or thermal sensitivity of the deeply located neurons to stimulation of their receptive fields in the dura mater. These results are at variance with data that showed increased c‐Fos labeling in superficial laminae of the trigeminal nucleus following CSD. They do not suggest that CSD initiates migraine headache via neurogenic inflammation.

title: Critical role of calcitonin gene-related peptide receptors in cortical spreading depression
abstract: Cortical spreading depression (CSD) is a key pathogenetic step in migraine with aura. Dysfunctions of voltage-dependent and receptor-operated channels have been implicated in the generation of CSD and in the pathophysiology of migraine. Although a known correlation exists between migraine and release of the calcitonin gene-related peptide (CGRP), the possibility that CGRP is involved in CSD has not been examined in detail. We analyzed the pharmacological mechanisms underlying CSD and investigated the possibility that endogenous CGRP contributes to this phenomenon. CSD was analyzed in rat neocortical slices by imaging of the intrinsic optical signal. CSD was measured as the percentage of the maximal surface of a cortical slice covered by the propagation of intrinsic optical signal changes during an induction episode. Reproducible CSD episodes were induced through repetitive elevations of extracellular potassium concentration. AMPA glutamate receptor antagonism did not inhibit CSD, whereas NMDA receptor antagonism did inhibit CSD. Blockade of voltage-dependent sodium channels by TTX also reduced CSD. CSD was also decreased by the antiepileptic drug topiramate, but not by carbamazepine. Interestingly, endogenous CGRP was released in the cortical tissue in a calcium-dependent manner during CSD, and three different CGRP receptor antagonists had a dose-dependent inhibitory effect on CSD, suggesting a critical role of CGRP in this phenomenon. Our findings show that both glutamate NMDA receptors and voltage-dependent sodium channels play roles in CSD. They also demonstrate that CGRP antagonism reduces CSD, supporting the possible use of drugs targeting central CGRP receptors as antimigraine agents.

title: Calcitonin gene-related peptide promotes cerebrovascular dilation during cortical spreading depression in rabbits.
abstract: We examined the role of calcitonin gene-related peptide (CGRP) in cortical spreading depression (CSD)-induced dilation of rabbit pial arterioles. In urethan-anesthetized rabbits instrumented with a closed cranial window, CSD induction with KCl dilated pial arterioles from 86 +/- 10 to 132 +/- 13 (mean +/- SE, n = 6) microns (a 54 +/- 9% increase). Topical administration of 12.8 microM CGRP-(8-37), a competitive inhibitor of the CGRP receptor, reduced CSD-induced pial dilation from 54 +/- 9% baseline to 33 +/- 9% (P < 0.05). Removal of the receptor antagonist from the brain surface restored CSD-induced dilation to 59 +/- 11% (P < 0.05, compared with the response with the antagonist present). In other animals, we showed that this dose of the CGRP antagonist attenuated arteriolar dilation to topically applied 10(-7) M CGRP (n = 5), but it did not alter arteriolar dilation to arterial hypercapnia. We also evaluated the dilator potency of substance P (SP) compared with CGRP. Dilation with 10(-7) M SP was only 22 +/- 11%, whereas arterioles dilated to 57 +/- 7% above baseline diameter with 10(-7) M CGRP. We conclude that CGRP contributes to the transient arteriolar dilation that is characteristic of CSD.

title: Involvement of calcitonin gene-related peptide (CGRP) and nitric oxide (NO) in the pial artery dilatation elicited by cortical spreading depression
abstract: The aim of the present study was to examine whether the initial transient arterial dilatation during cortical spreading depression (CSD) was mediated by the release of calcitonin gene-related peptide (CGRP) and/or nitric oxide (NO). This question is of interest as the initial phase of CSD appears to be a model of events occurring during functional hyperemia and during the first period of classic migraine. Using an open cranial window technique, pial arterial diameter in the parietal cortex of cats was recorded with an image splitting method. Employing micropuncture technique, perivascularly applied CGRP8-37 did not alter the resting diameter of pial arteries but antagonized concentration dependently (5 x 10(-9)-10(-6) M) the dilatation (35%) due to 5 x 10(-8) M CGRP. NG-Nitro-L-Arginine (NOLAG, 10(-4) M) also had no effect on resting diameter of pial arteries, indicating that their resting tone is neither mediated by a continuous release of CGRP nor of NO. CSD was triggered by a remote intracortical injection of KCl (150 mM) and recorded by a microelectrode placed adjacent to the artery under investigation. CSD elicited a transient negative DC shift which was accompanied by a peak dilatation of 44 +/- 5.2% (S.E.M.). This dilatation was reduced by approximately 50% during topical application of 10(-7) M CGRP8-37 and 10(-4) M NOLAG each. A 75% inhibition of the CSD-induced dilatation was found during simultaneous application of both compounds. These data indicate that the initial dilatation during CSD is mediated, at least in part, by a release of CGRP and NO.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Neuronal NOS-cGMP-dependent ACh-induced relaxation in pial arterioles of endothelial NOS knockout mice.
abstract: We evaluated the effects of superfusing 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), eNOS null ( B)an inhibitor of soluble guanylyl cyclase, and 7-nitroindazole sodium (7-NI), a selective neuronal nitric oxide synthase (nNOS) inhibitor, on the acetylcholine (ACh) response in endothelial NOS (eNOS) null mice. Pial arteriolar diameter was measured by intravital microscopy through a closed cranial window under α-chloralose anesthesia. NOS activity was measured by [3H]arginine-to-[3H]citrulline conversion in subjacent cortex in vitro. The density and distribution of muscarinic receptors in the brain were determined by quantitative [3H]quinuclidinyl benzilate autoradiography and did not differ between the eNOS mutants and wild-type mice. ACh superfusion (1 and 10 μM) dose dependently dilated pial arterioles in eNOS null and wild-type mice. ODQ (10 μM) attenuated ACh-induced dilation in both eNOS mutants (41% decrease at 10 μM ACh, P < 0.01, n = 6) and wild-type strains ( n = 5 per group). By contrast, topical superfusion of 7-NI (100 μM) attenuated the ACh response in eNOS mutants only (66%, P < 0.05, and 25% decrease, P < 0.05, at 1 and 10 μM ACh, respectively). Our findings suggest that nNOS-guanosine 3',5'-cyclic monophosphate (cGMP)-dependent pathways dilate pial arterioles by compensatory mechanisms after eNOS gene disruption.

title: ACh dilates pial arterioles in endothelial and neuronal NOS knockout mice by NO-dependent mechanisms.
abstract: We used mice with deletions in either the endothelial nitric oxide synthase (eNOS) or neuronal NOS (nNOS) gene to investigate the role of eNOS and nNOS in acetylcholine (ACh)-induced relaxation of pial arterioles (20-30 microns). Pial arteriolar diameter was measured by intravital microscopy through a closed cranial window, and NOS activity was determined by the conversion of [3H]arginine to [3H]citrulline in subjacent cortex. ACh superfusion (1, 10 microM) caused atropine-sensitive dose-dependent arteriolar dilation in all three mouse strains. At 10 microM, increases of 20 +/- 2, 31 +/- 3, and 23 +/- 3% were recorded in wild-type (n = 25), nNOS mutant (n = 15), and eNOS mutant (n = 20) mice, respectively. NG-nitro-L-arginine (L-NNA, 1 mM) superfusion inhibited cortical NOS activity by > 70% and abrogated the response in wild-type mice while blocking the dilation by approximately 50% in eNOS mutant and nNOS mutant mice. Only in the eNOS mutant did tetrodotoxin (TTX) superfusion (1 microM) attenuate ACh-induced dilation (n = 6). The residual dilation after L-NNA in eNOS mutant mice could be blocked completely by TTX-plus L-NNA. Our findings indicate that 1) ACh dilates pial arterioles of wild-type mice by NOS-dependent mechanisms as reported in other species, 2) the response in nNOS mutant mice resembles the wild-type response except for enhanced dilation to ACh and reduced L-NNA sensitivity, and 3) surprisingly, the response in eNOS mutant mice is partially NOS dependent and attenuated by both TTX and L-NNA. Because nNOS is constitutively expressed in eNOS mutants, these findings coupled with the TTX results suggest that an nNOS-dependent mechanism may compensate for the chronic loss of eNOS activity after targeted gene disruption.

title: Cholinergic Control of Blood Flow in the Cerebral Cortex of the Rat
abstract: Local blood flow was measured in the somatosensory cortex of urethanized rats by means of the hydrogen clearance method. The variations of cortical blood flow in the course of the anesthesia and the effects of the topical application of atropine, eserine and cholinomimetic drugs were studied. During urethan anesthesia, the electrical activity of the cerebral cortex fluctuated between a synchronized and a desynchronized state. During desynchronization, local cortical blood flow increased significantly. This increase in blood flow could be prevented by topical application of atropine and exaggerated by topical eserine. Topical application of arecoline, carbaminoylcholine, pilocarpine or acetylcholine with eserine significantly increased cortical blood flow. It is concluded that the increase in cortical blood flow that accompanies cortical desynchronization in the urethanized rat is mediated, at least in part, by a neurogenic mechanism that involves a cholinergic step at the cortical level.

title: Effect of Serotonin and its Antagonist Ketanserin on Pial Vessels
abstract: The effect of serotonin (5-HT) and its antagonist ketanserin on the cerebral circulation was investigated in two series totaling 24 cats using the cranial window technique. 5-HT elicited a marked dilatation of small pial arteries, whereas large arteries tended to constrict. Intravenous administration of ketanserin reversed the constriction of large arteries, causing dilatation, and reduced the extent of small arteries' dilatation. In a randomized study, i.v. administration of ketanserin in its solvent versus the solvent alone revealed a strong dilatatory effect of the solvent on pial arteries (17 ± 1.8%), which partly jeopardized a possible constrictory effect of ketanserin, as ketanserin plus solvent induced less dilatation of small pial arteries than the solvent alone. The present data support the view that serotonin exerts a dual effect on cerebral arteries, namely, dilatation of small and constriction of large vessels. The antagonist ketanserin reverses this effect, but the strong dilatatory effect of the solvent alone masks the antiserotoninergic effect.

title: Cortical spreading depression-associated hyperemia in rats: involvement of serotonin
abstract: We investigated whether the vasoactive neurotransmitter serotonin (5-HT) is involved in cortical spreading depression (CSD)-associated hyperemia in the rat. We focused on the 5-HT2 receptor, which is engaged in 5-HT induced small arteriolar relaxation in cats, as well as on the 5-HT1D/1B receptor, the binding site of the potent antimigraine drug sumatriptan. In male barbiturate anaesthetized Wistar rats (n=25) CSDs were elicited by brain topical application of 1 M KCl, and the DC-potential and regional cerebral blood flow (rCBF, by Laser Doppler flowmetry) were measured over the same hemisphere through dura and thinned bone, respectively. Intravenous application of 8 mg/kg of the 5-HT2A/2C receptor antagonist ritanserin (group I; n=8) significantly reduced the hyperperfusion amplitude during CSD by approximately 44% (p<0.05, from 342+/-124 to 194+/-97%, baseline before CSD=100%), and prolonged its duration by approx. 30%. Vehicle alone (group II; n=4) did not affect CSD hyperperfusion. The highly selective 5-HT1D/1B receptor agonist 311C90 was given in two doses: 100 micrograms/kg i.v. (n=5) had no effect on CSD hyperperfusion, while 800 micrograms/kg (n=5) increased hyperperfusion significantly (p<0.05, from 224+/-86 to 310+/-148%). We conclude that serotonin is, probably via 5-HT2 receptors, involved in the modulation of the regional cerebral blood flow increase during CSD. Novel highly selective receptor antagonists may help to discriminate the differential contribution of various 5-HT receptor subspecies.

title: Endogenous adenosine exerts inhibitory effects upon the development of spreading depression and glutamate release induced by microdialysis with high K+ in rat hippocampus
abstract: Spreading depression (SD) is known to be involved in the N-methyl-D-aspartate receptor-mediated neuronal damage. In urethane-anesthetized rats, we examined the release of adenosine and glutamate during SD induced by microdialysis of high K+ perfusate through the hippocampal CA1 area. The effects of endogenous adenosine upon SD were studied by applying an adenosine antagonist, theophylline (1 mM) and by a simultaneous application of adenosine uptake blockers, dipyridamole (DPR) (100 microM) and nitrobenzylthioinosine (NBI) (50 microM). The dialysates were sampled every 5 or 10 min and analyzed by HPLC. SD was identified by flattening of background EEg and disappearance of population spikes recorded from the pyramidal cell layer of CA1 area by a glass microelectrode. Adenosine and glutamate release was enhanced significantly in association with the occurrence of SD. Theophylline increased the release of glutamate and the incidence of SD and decreased the latency of the SD occurrence. DPR+NBI decreased the release of glutamate and the occurrence of SD, but increased extracellular adenosine concentration. The effects of DPR+NBI were blocked by application of a selective antagonist of adenosine A1 receptor, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 0.1 microM). These findings suggest that endogenous adenosine exerts inhibitory influences upon the development of SD and the glutamate release through the A1 receptor in rat hippocampus.

title: Relationship between adenosine concentration and oxygen supply in rat brain.
abstract: Since adenosine is present in normal brain tissue and cerebrosipinal fluid and since it dilates the pial vessels, it is possible that adenosine, in addition to H-+, is also a mediator of the metabolic regulation of cerebral blood flow. Evidence supporting this hypothesis was obtained under various experimental conditions characterized by achange in brain oxygen supply. The brain was frozen in situ by means of a small bonerongeur precooled in liquid N2 and the tissue was processed for adenosine determination (nmol/g of tissue). Electrical stimulation of the cortex at 0, 15, 30, and 45 Hz yielded adenosine levels of 5.4 plus or minus 0.7, 10.5 plus or minus 1.7, 13.0 plusor minus 1.2, and 9.0 plus or minus 2.1 nmol/g. Arterial pressures of 87, 60, and 40mmHg gave adenosine levels of 7.5 plus or minus 0.76, 13 plus or minus 2.6, and 26.6plus or minus 3.3, respectively. Ventilation with 29.7, 20, 10.7, and5.5% O2 significantly increased the adenosine levels to 9.4 plus or minus 3.0, 6.4 plus or minus 1.2, 30.0 plus or minus 9.3, and 63.3 plus or minus 18.2 nmol/g, respectively. Hyperventilation significantly increased adenosine form 6.7 plus or minus 1.0 to 11.8 plus or minus 1.4 nmol/g. This increased adenosine level was reduced by additionof CO2 to the ventilating gas mixture. Lactate, the main H-+ donor, pyruvate, and cAMP changed in a fashion parallel to adenosine. However, cAMP showedonly a small increase in adenosine. These findings are in accordance with the concept that adenosine and H-+ may act synergistally to regulate cerebral blood flow and that endogenous adenosine may exert a small effect on cAMP formation.

title: Alpha‐Receptor Stimulation by Endogenous and Exogenous Norepinephrine and Blockade by Phentolamine in Pial Arteries of Cats
abstract: The question regarding the existence of an alpha-adrenergic component of pial arterial tone was investigated using a microapplication technique combined with the measurement of vascular diameter. Concentration-response curves for the alpha-receptor blocker, phentolamine, revealed no vascular reaction for a concentration range from 2.5 x 10−11 to 2.5 x 10−7M. At higher concentrations (up to 1.3 x 10−3M) concentration-dependent dilations were observed. Constrictions of pial arteries induced by perivascular injection of 2.5 x 10−6M norepinephrine could be reduced by 38% and 73% when phentolamine was applied simultaneously in concentrations of 2.5 x 10−7 and 2.5 x 10−6M, respectively, whereas constrictions due to 2.5 x 10−4M norepinephrine were not reduced by 2.5 x 10−6M phentolamine, indicating a competitive antagonism between norepinephrine and phentolamine for pial arteries. Stimulation of the cervical sympathetic chain (90 seconds, 10 v, 1.4 msec, 20 Hz) induced constrictions of pial arteries (mean 12%) which could be reduced by two-thirds during the simultaneous application of 2.5 x 10−7M phentolamine. Since the constriction induced by norepinephrine applied exogenously or released endogenously could be reduced by a concentration of phentolamine which had no vascular effect per se, we conclude that the resting tone of the pial arteries is not influenced by an alpha-adrenergic component under our experimental conditions. The dilations induced by high concentrations of phentolamine are believed to be nonspecific.

title: The Effect of Glutamate Receptor Blockade on Anoxic Depolarization and Cortical Spreading Depression
abstract: We examined the effect of blockade of N-methyl-d-aspartate (NMDA) and non-NMDA subtype glutamate receptors on anoxic depolarization (AD) and cortical spreading depression (CSD). [K+]e and the direct current (DC) potential were measured with microelectrodes in the cerebral cortex of barbiturate-anesthetized rats. NMDA blockade was achieved by injection of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate [MK-801; 3 and 10 mg/kg] or amino-7-phosphonoheptanoate (APH; 4.5 and 10 mg/kg). Non-NMDA receptor blockade was achieved by injection of 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX; 10 and 20 mg/kg). MK-801 and APH blocked CSD, while NBQX did not. In control rats, the latency from circulatory arrest to AD was 2.1 ± 0.1 min, while the amplitude of the DC shift was 21 ± 1 mV, and [K+]e increased to 50 ± 6 mM. All variables remained unchanged in animals treated with MK-801, APH, or NBQX. Finally, MK-801 (14 mg/kg) and NBQX (40 mg/kg) were given in combination to examine the effect of total glutamate receptor blockade on AD. This combination slightly accelerated the onset of AD, probably owing to circulatory failure. In conclusion, AD was unaffected by glutamate receptor blockade. In contrast, NMDA receptors play a crucial role for CSD.

title: Regulation of cerebral microvessels by glutamatergic mechanisms
abstract: This study examined the role of glutamate receptor activation in the regulation of microvascular tone in the hippocampus and neocortex of the rat. Microvascular and neuronal responses were simultaneously recorded in brain slices using videomicroscopic analysis in conjunction with electrophysiological recording. Glutamate and other glutamate receptor agonists, including NMDA, kainic acid, and ACPD elicited dose-dependent dilation in preconstricted hippocampal microvessels. The lower concentrations of NMDA elicited dilation with an increase in neuronal excitability while dilatory responses to other agonists were associated with substantial depolarization. NMDA-mediated dilation was inhibited completely with a sodium channel blocker (TTX), an NOS inhibitor (L-NNA), or a specific inhibitor of neuronal NOS (7-NI). Inhibition of the GABA(A) or the A2 adenosine receptor did not attenuate the NMDA-induced dilation. The role of spontaneous glutamate receptor activation by endogenous glutamate in the regulation of resting dilatory tone was also examined. Blocking AMPA or metabotropic glutamate receptors did not induce significant responses in resting hippocampal vessels. However, the NMDA receptor antagonist, APV, elicited a dose-dependent constriction. In surface vessels of the neocortex, NMDA elicited a comparable dose-dependent dilation, and APV elicited a significantly smaller dose-dependent constriction. A 60 min period of hypoxia elicited a significant dilation of preconstricted hippocampal microvessels. APV did not significantly influence this dilatory response indicating that hypoxia-induced dilation is not mediated by NMDA receptor activation. Taken together, these results indicate that glutamate contributes to the dilatory tone of cerebral microvessels under physiologic conditions and that this effect is mediated by NMDA receptors. Glutamatergic vasodilation is dependent on neuronal discharge activity and the neuronal production of NO. The tonic influence is more pronounced in hippocampal microvessels than in neocortical vessels suggesting that the contribution of NMDA receptor activation to resting dilatory tone is dependent on the location of vessels within the brain.

title: 7-Nitroindazole inhibits brain nitric oxide synthase and cerebral vasodilatation in response to N-methyl-D-aspartate.
abstract: N-Methyl-D-aspartate (NMDA) produces dilatation of cerebral arterioles that is dependent on production of nitric oxide (NO). In these experiments we examined the hypothesis that cerebral vasodilatation in response to NMDA is mediated by the neuronal isoform of NO synthase.



We measured diameters of cerebral arterioles (baseline diameter, 89 +/- 7 microns) using a closed cranial window in anesthetized rabbits that received either vehicle (10 mL/kg IP peanut oil) or 7-nitroindazole (7-NI; 50 mg/kg IP). 7-NI is reported to be a selective inhibitor of neuronal NO synthase.



Two hours after administration of 7-NI, activity of brain NO synthase (measured by conversion of L-arginine to L-citrulline) was reduced by 33% compared with vehicle (24 +/- 1 versus 16 +/- 3 pmol/min per milligram protein; n = 7; P < .05). Dilatation of cerebral arterioles in response to NMDA (100 and 300 mumol/L) was inhibited by 30% to 40% by 7-NI compared with responses in the presence of vehicle (23 +/- 6% versus 14 +/- 5% and 30 +/- 4% versus 21 +/- 5%, respectively; P < .05 for both concentrations; n = 10). In contrast, vasodilatation in response to acetylcholine (1 mumol/L) was similar in vehicle- and 7-NI-treated animals (17 +/- 5% versus 21 +/- 4%; P > .05).



These findings suggest that vasodilatation in response to NMDA is mediated by neuronally derived NO. 7-NI appears to produce selective inhibition of brain NO synthase but not endothelial NO synthase.

title: Insulin‐like growth factor‐1 abrogates microglial oxidative stress and TNF‐α responses to spreading depression
abstract: Spreading depression (SD), the most likely cause of migraine aura and perhaps migraine, occurs with increased oxidative stress (OS). SD increases reactive oxygen species (ROS), and ROS, in turn, can signal to increase neuronal excitability, which includes increased SD susceptibility. SD also elevates tumor necrosis factor‐α (TNF‐α), which increases neuronal excitability. Accordingly, we probed for the cellular origin of OS from SD and its relationship to TNF‐α, which might promote SD, using rat hippocampal slice cultures. We observed significantly increased OS from SD in astrocytes and microglia but not in neurons or oligodendrocytes. Since insulin‐like growth factor‐1 (IGF‐1) mitigates OS from SD, we determined the cell types responsible for this effect. We found that IGF‐1 significantly decreased microglial but not astrocytic OS from SD. We also show that IGF‐1 abrogated the SD‐induced TNF‐α increase. Furthermore, TNF‐α application increased microglial but not astrocytic OS, an effect abrogated by IGF‐1. Next, we showed that SD increased SD susceptibility, and does so via TNF‐α. This work suggests that microglia promote SD via increased and interrelated ROS and TNF‐α signaling. Thus, IGF‐1 mitigation of microglial ROS and TNF‐α responses may be targets for novel therapeutics development to prevent SD, and perhaps migraine.

title: Insulin‐like growth factor‐1 lowers spreading depression susceptibility and reduces oxidative stress
abstract: (2012) 122, 221–229.

title: Cortical spreading depression affects reactive oxygen species production
abstract: Cortical spreading depression (CSD) is a reversible electrophysiological phenomenon that is not associated with tissue damage under normal blood supply. The induction of CSD during ischemia causes an increase in tissue damage, while pre-conditioning with CSD decreases the damage induced by a subsequent episode of ischemia. The mechanisms underlying these effects are not clear. Because the production of reactive oxygen species (ROS) is involved in tissue damage during ischemia-reperfusion, the aim of the present study was to evaluate the effects of CSD on superoxide production (O(2)(-)), on hydrogen peroxide (H(2)O(2)) production and on superoxide dismutase (SOD) activity in the cerebral cortex. CSD was induced by KCl application on the cortical surface in rats. O(2)(-) production was evaluated using dihydroethidium (DHE) that is oxidized to the fluorescent dye ethidium (HEt) by O(2)(-). The extracellular level of H(2)O(2) was evaluated by microdialysis sampling and HPLC analysis. SOD activity was evaluated with a histochemical assay. The results showed an increase in H(2)O(2) production, an increase in SOD activity and a decrease in O(2)(-) concentration 1h after CSD induction.

title: The 21-aminosteroid antioxidant tirilazad mesylate, U-74006F, blocks cortical hypoperfusion following spreading depression
abstract: Cortical spreading depression (SD) has been implicated in the pathophysiology of classical migraine headache and cerebral ischemia. A reduction in cerebral blood flow (CBF), mimicking that seen during the aura and headache phase of migraine, is typically observed following SD in the rat. This phenomenon may also play a role in potentiating ischemic brain damage. In the present study, brief cortical exposure to 1 M KCl produced a marked suppression of EEG amplitude which persisted 20 min in the rat. Upon normalization of the EEG, cortical blood flow declined 20-30% and remained low for at least 2 h. Treatment with a 1 mg/kg i.v. dose of the 21-aminosteroid antioxidant tirilazad mesylate (U-74006F), 2 min following KCl application, completely blocked the hypoperfusion while leaving the magnitude and duration of the EEG suppression and mean arterial pressure unchanged. Tirilazad mesylate is a potent inhibitor of oxygen radical-mediated lipid peroxidation both in vitro and in vivo. Thus, based on present results, an oxygen radical hypothesis is proposed to account for the SD-induced cerebral hypoperfusion.

title: Spreading depression is not associated with neuronal injury in the normal brain
abstract: This study was performed in order to evaluate whether waves of spreading depression (SD) induces irreversible neuronal injury. SD was elicited by topical application of 3 M KCl to the exposed cortex for 4-5 h and the resulting change of the cortical electrical potential showing the occurrence of SD, was recorded by glass microelectrodes. Histological examination of cerebral cortex revealed no signs of neuronal injury outside the area of KCl application as examine after 4 days recovery. The results indicate that recurrent waves of SD do not induce irreversible neuronal injury in the otherwise normal rat brain.

title: Mitochondrial permeability transition in acute neurodegeneration.
abstract: Acute neurodegeneration in man is encountered during and following stroke, transient cardiac arrest, brain trauma, insulin-induced hypoglycemia and status epilepticus. All these severe clinical conditions are characterized by neuronal calcium overload, aberrant cell signaling, generation of free radicals and elevation of cellular free fatty acids, conditions that favor activation of the mitochondrial permeability transition pore (mtPTP). Cyclosporin A (CsA) and its analog N-methyl-valine-4-cyclosporin A (MeValCsA) are potent blockers of the mtPTP and protect against neuronal death following excitotoxicity and oxygen glucose deprivation. Also, CsA and MeValCsA diminish cell death following cerebral ischemia, trauma, and hypoglycemia. Here we present data that strongly imply the mtPT in acute neurodegeneration in vivo. Compounds that readily pass the blood-brain-barrier (BBB) and block the mtPT may be neuroprotective in stroke.

title: Mitochondrial permeability transition in CNS trauma: Cause or effect of neuronal cell death?
abstract: Experimental traumatic brain injury (TBI) and spinal cord injury (SCI) result in a rapid and significant necrosis of neuronal tissue at the site of injury. In the ensuing hours and days, secondary injury exacerbates the primary damage, resulting in significant neurologic dysfunction. It is believed that alterations in excitatory amino acids (EAA), increased reactive oxygen species (ROS), and the disruption of Ca2+ homeostasis are major factors contributing to the ensuing neuropathology. Mitochondria serve as the powerhouse of the cell by maintaining ratios of ATP:ADP that thermodynamically favor the hydrolysis of ATP to ADP + Pi, yet a byproduct of this process is the generation of ROS. Proton‐pumping by components of the electron transport system (ETS) generates a membrane potential (ΔΨ) that can then be used to phosphorylate ADP or sequester Ca2+ out of the cytosol into the mitochondrial matrix. This allows mitochondria to act as cellular Ca2+ sinks and to be in phase with changes in cytosolic Ca2+ levels. Under extreme loads of Ca2+, however, opening of the mitochondrial permeability transition pore (mPTP) results in the extrusion of mitochondrial Ca2+ and other high‐ and low‐molecular weight components. This catastrophic event discharges ΔΨ and uncouples the ETS from ATP production. Cyclosporin A (CsA), a potent immunosuppressive drug, inhibits mitochondrial permeability transition (mPT) by binding to matrix cyclophilin D and blocking its binding to the adenine nucleotide translocator. Peripherally administered CsA attenuates mitochondrial dysfunction and neuronal damage in an experimental rodent model of TBI, in a dose‐dependent manner. The underlying mechanism of neuroprotection afforded by CsA is most likely via interaction with the mPTP because the immunosuppressant FK506, which has no effect on the mPT, was not neuroprotective. When CsA was administrated after experimental SCI at the same dosage and regimen used TBI paradigms, however, it had no beneficial neuroprotective effects. This review takes a comprehensive and critical look at the evidence supporting the role for mPT in central nervous system (CNS) trauma and highlights the differential responses of CNS mitochondria to mPT induction and the implications this has for therapeutically targeting the mPT in TBI and SCI.

title: Cyclosporine A, FK506, and NIM811 ameliorate prolonged CBF reduction and impaired neurovascular coupling after cortical spreading depression
abstract: Cortical spreading depression (CSD) is associated with mitochondrial depolarization, increasing intracellular Ca2+, and the release of free fatty acids, which favor opening of the mitochondrial permeability transition pore (mPTP) and activation of calcineurin (CaN). Here, we test the hypothesis that cyclosporine A (CsA), which blocks both mPTP and CaN, ameliorates the persistent reduction of cerebral blood flow (CBF), impaired vascular reactivity, and a persistent rise in the cerebral metabolic rate of oxygen (CMRO2) following CSD. In addition to CsA, we used the specific mPTP blocker NIM811 and the specific CaN blocker FK506. Cortical spreading depression was induced in rat frontal cortex. Electrocortical activity was recorded by glass microelectrodes, CBF by laser Doppler flowmetry, and tissue oxygen tension with polarographic microelectrodes. Electrocortical activity, basal CBF, CMRO2, and neurovascular and neurometabolic coupling were unaffected by all three drugs under control conditions. NIM811 augmented the rise in CBF observed during CSD. Cyclosporine A and FK506 ameliorated the persistent decrease in CBF after CSD. All three drugs prevented disruption of neurovascular coupling after CSD; the rise in CMRO2 was unchanged. Our data suggest that blockade of mPTP formation and CaN activation may prevent persistent CBF reduction and vascular dysfunction after CSD.

title: Postischemic Augmentation of Conducted Dilation in Cerebral Arterioles
abstract: Conducted vasomotor responses likely play an important role in cerebrovascular regulation, but it is unclear how these responses may be affected by ischemia. The purpose of this study was to evaluate the hypothesis that cerebral ischemia and reperfusion (I/R) alters vascular conduction in cerebral arterioles.  Middle cerebral artery occlusion (MCAO) was induced by an intraluminal filament technique in 4 groups of rats: (A) 2-hour MCAO/24-hour reperfusion (n=14); (B) 2-hour MCAO/1-hour reperfusion (n=7); (C) 1-hour MCAO/24-hour reperfusion (n=6); and (D) 1-hour MCAO/1-hour reperfusion (n=5). Neurological status and infarction (2,3,5-triphenyltetrazolium chloride staining) were evaluated after I/R. Conducted vasomotor responses were assessed in intracerebral branches of the MCA, by following the longitudinal spread of vasodilation or vasoconstriction to localized microapplication of ATP or adenosine.  Local microapplication of ATP evoked a biphasic constriction (17±3%) and dilation (7±2%) response, whereas adenosine elicited only dilation (11±2%). These local responses spread longitudinally along sham-control arterioles (1 mm conduction distance) with rapid spatial decay. Ischemia followed by 24-hour reperfusion (groups A and C) led to a marked potentiation of conducted dilation responses: dilation to ATP conducted with virtually no decay in I/R arterioles. Augmentation of conductivity was not observed in the 1-hour reperfusion groups (B and D). Moreover, I/R did not alter conducted constriction.  Ischemia-reperfusion led to a specific augmentation of conducted vasodilation in cerebral arterioles. Presumably, enhanced conductivity may improve cerebral perfusion after ischemia.

title: Electrical communication in branching arterial networks.
abstract: Electrical communication and its role in blood flow regulation are built on an examination of charge movement in single, isolated vessels. How this process behaves in broader arterial networks remains unclear. This study examined the nature of electrical communication in arterial structures where vessel length and branching were varied. Analysis began with the deployment of an existing computational model expanded to form a variable range of vessel structures. Initial simulations revealed that focal endothelial stimulation generated electrical responses that conducted robustly along short unbranched vessels and to a lesser degree lengthened arteries or branching structures retaining a single branch point. These predictions matched functional observations from hamster mesenteric arteries and support the idea that an increased number of vascular cells attenuate conduction by augmenting electrical load. Expanding the virtual network to 31 branches revealed that electrical responses increasingly ascended from fifth- to first-order arteries when the number of stimulated distal vessels rose. This property enabled the vascular network to grade vasodilation and network perfusion as revealed through blood flow modeling. An elevation in endothelial-endothelial coupling resistance, akin to those in sepsis models, compromised this ascension of vasomotor/perfusion responses. A comparable change was not observed when the endothelium was focally disrupted to mimic disease states including atherosclerosis. In closing, this study highlights that vessel length and branching play a role in setting the conduction of electrical phenomenon along resistance arteries and within networks. It also emphasizes that modest changes in endothelial function can, under certain scenarios, impinge on network responsiveness and blood flow control.

title: Integrated Ca2+ Signaling Between Smooth Muscle and Endothelium of Resistance Vessels
abstract: Cell-cell communication in the arteriolar wall was examined using the Ca2+-sensitive indicator fura-2 and the Ca2+ buffer BAPTA as means of measuring and buffering cellular Ca2+. The experiments focused on the role of endothelial cell [Ca2+]i in modulating phenylephrine (PE)-induced contractions in in vitro arterioles of the hamster cremaster. Fura-2-AM and BAPTA-AM were applied intraluminally to accomplish endothelium-specific loading. PE was applied to short segments of arterioles using pressure-pulse ejection from a micropipette. Under control conditions at the site of stimulation, PE elicited a strong vasoconstriction preceded by an increase in endothelial cell [Ca2+]i. A very small biphasic conducted response was observed at sites upstream from the stimulation site. BAPTA sharply reduced the measured Ca2+ response in the endothelium. This was associated with an enhanced local contractile response. In addition, the biphasic conducted response was converted into a strong conducted vasoconstriction. PE caused an initial rise in smooth muscle [Ca2+]i at the stimulated site, which was followed by a rapid decrease below baseline. Endothelial cell loading of BAPTA had minimal effect on the initial [Ca2+]i peak but eliminated the secondary decrease in smooth muscle [Ca2+]i. Intraluminal application of charybdotoxin plus apamin mimicked the change in vasomotor state induced by BAPTA. These data lead us to hypothesize that, after smooth muscle stimulation, intercellular Ca2+ signaling between smooth muscle and endothelium causes a secondary rise in endothelial cell Ca2+, which triggers a hyperpolarizing event and initiates a conducted vasodilation. We conclude that smooth muscle and endothelium operate as a functional unit in these vessels.

title: Impaired Vascular Reactivity of Isolated Rat Middle Cerebral Artery after Cortical Spreading Depression in Vivo
abstract: Cortical spreading depression (CSD) is accompanied by hyperemia followed by long-lasting hypoperfusion and impaired cerebrovascular reactivity. The authors show that vasodilation to extraluminal acidosis (pH 7.0) and increased concentrations of extraluminal potassium (12, 20, 40 mmol/L) was significantly reduced in isolated rat middle cerebral arteries after CSD in vivo before the artery was isolated, compared with sham-operated controls. Application of 80-mmol/L potassium induced vasoconstriction after CSD. Therefore, the impairment of vascular reactivity after CSD in vivo occurs, at least in part, at the vascular level itself.

title: Spreading depression reversibly impairs autoregulation of cortical blood flow.
abstract: The experiment examines whether the mechanisms responsible for the autoregulation of cerebral blood flow (CBF) in response to hypotension were affected during the initial phase of cortical spreading depression (CSD). CSD was induced by a cortical pinprick in anesthetized rabbits, and CBF was measured by laser-Doppler flowmetry through a chronically implanted Plexiglas window. The reactivity to CO2 and papaverine was also studied before and after CSD. Fifteen minutes after CSD, autoregulatory vasodilation was reduced (P < 0.01). This impairment was reversible, since the autoregulatory response was restored 35 min after CSD. The time course of the reactivity to papaverine after CSD paralleled the autoregulatory response, with a significant correlation between the two reactivities (r = 0.47; P < 0.01). Conversely, the reactivity to CO2 was significantly reduced after CSD (P < 0.001) and remained affected for at least 95 min. We conclude that the mechanisms underlying autoregulation are transiently disturbed by CSD and that these mechanisms are not mediated by an accumulation of CO2 but seem instead to be related to an increase in adenosine 3',5'-cyclic monophosphate concentration.

title: Effects of single and repetitive spreading depression on cerebral blood flow and glucose metabolism in cats: a PET study
abstract: To clarify the effects of spreading depression (SD) on cerebral circulation and metabolism, we elicited a single or repetitive episode of SD and evaluated CBF and CMRglc three-dimensionally in normal cats (n=4, in each group) using a high-resolution positron emission tomography (PET) scanner. SD was evoked by applying KCl to the left occipital cortex. We then monitored DC potential changes with tungsten electrodes inserted into the left temporal cortex. CBF was measured twice before and three times (immediately, 30-60 min, and 60-120 min) following KCl application using [15O]H(2)O, and CMRglc was determined using 2-[18F]fluoro-2-deoxy-D-glucose immediately following the last CBF measurement. The following results were obtained: (1) a single episode of SD produced a temporary CBF increase, followed by a long-lasting hypoperfusion in the cortex, with no significant changes to CBF observed in the subcortex; (2) no significant CMRglc changes were observed in either cortical or subcortical regions following a single episode of SD; (3) a flow-metabolism uncoupling was observed in the cortical regions concurrently with persistent hypoperfusion; (4) repetitive SD produced significant CBF changes in the cortex; and (5) the cortical CMRglc increased as a result of repeated episodes of SD, with no significant changes observed in the subcortex. Thus, we succeeded in determining three-dimensionally the effects of single and repetitive SD on CBF and CMRglc in cats using a high-resolution PET scanner. The present study provides the first direct evidence of CBF-CMRglc uncoupling occurring concurrently with persistent hypoperfusion following SD.

title: Cortical spreading depression produces long-term disruption of activity-related changes in cerebral blood volume and neurovascular coupling.
abstract: Cortical spreading depression (CSD) is a pronounced depolarization of neurons and glia that spreads slowly across the cortex followed by a period of depressed electrophysiological activity. The vascular changes associated with CSD are a large transient increase in blood flow followed by a prolonged decrease lasting greater than 1 h. Currently, the profile of functional vascular activity during this hypovolemic period has not been well characterized. Perfusion-based imaging techniques such as functional magnetic resonance imaging (fMRI) assume a tight coupling between changes in neuronal and vascular activity. Under normal conditions, these variables are well correlated. Characterizing the effect of CSD on this relationship is an important step to understand the impact acute pathophysiological events may have on neurovascular coupling. We examine the effect of CSD on functional changes in cerebral blood volume (CBV) evoked by cortical electrophysiological activity for 1 h following CSD induction. CBV signal amplitude, duration, and time to peak show little recovery at 60 min post-induction. Analysis of spontaneous vasomotor activity suggests a decrease in vascular reactivity may play a significant role in the disruption of normal functional CBV responses. Electrophysiological activity is also attenuated but to a lesser degree. CBV and evoked potentials are not well correlated following CSD, suggesting a breakdown of the neurovascular coupling relationship.

title: Pathway-Specific Variations in Neurovascular and Neurometabolic Coupling in Rat Primary Somatosensory Cortex
abstract: Functional neuroimaging signals are generated, in part, by increases in cerebral blood flow (CBF) evoked by mediators, such as nitric oxide and arachidonic acid derivatives that are released in response to increased neurotransmission. However, it is unknown whether the vascular and metabolic responses within a given brain area differ when local neuronal activity is evoked by an activity in the distinct neuronal networks. In this study we assessed, for the first time, the differences in neuronal responses and changes in CBF and oxygen consumption that are evoked after the activation of two different inputs to a single cortical area. We show that, for a given level of glutamatergic synaptic activity, corticocortical and thalamocortical inputs evoked activity in pyramidal cells and different classes of interneurons, and produced different changes in oxygen consumption and CBF. Furthermore, increases in stimulation intensities either turned off or activated additional classes of inhibitory interneurons immunoreactive for different vasoactive molecules, which may contribute to increases in CBF. Our data imply that for a given cortical area, the amplitude of vascular signals will depend critically on the type of input, and that a positive blood oxygen level-dependent (BOLD) signal may be a consequence of the activation of both pyramidal cells and inhibitory interneurons.

title: Repetitive spreading depression causes selective suppression of GABAergic function.
abstract: Cortical spreading depression (SD) represents a pathophysiological signal that has been associated with the induction of migraine and ischaemic brain damage. The properties of repetitive SDs and their effects on excitatory and inhibitory synaptic transmission were analysed in neocortical slices obtained from adult rats. The SD showed only small variations in amplitude, duration and integral when elicited four times at intervals of 30 min. Extracellularly recorded paired pulse inhibition was, however, significantly reduced by approximately 10% with each SD episode. Since excitatory synaptic transmission was unaffected, our data indicate that repetitive SD causes a selective reduction of intracortical inhibition.

title: Key role of tissue plasminogen activator in neurovascular coupling
abstract: The increase in blood flow evoked by synaptic activity is essential for normal brain function and underlies functional brain imaging signals. Nitric oxide, a vasodilator released by NMDA receptor activation, is critical for the flow increase, but the factors linking NMDA receptor activity to nitric oxide-dependent hyperemia are poorly understood. Here, we show that tissue plasminogen activator (tPA), a serine protease implicated in NMDA receptor signaling, is required for the flow increase evoked by somatosensory stimulation. tPA acts by facilitating neuronal nitric oxide release, but this effect does not involve enhancement of NMDA currents or the associated intracellular Ca2+ rise. Rather, the evidence suggests that tPA controls NMDA-dependent nitric oxide synthesis by influencing the phosphorylation state of neuronal nitric oxide synthase. These findings unveil a previously unrecognized role of tPA in vital homeostatic mechanisms coupling NMDA receptor signaling with nitric oxide synthesis and local cerebral perfusion.

title: Reversal of attenuation of cerebrovascular reactivity to hypercapnia by a nitric oxide donor after controlled cortical impact in a rat model of traumatic brain injury.
abstract: Traumatic brain injury (TBI) attenuates the cerebral vasodilation to hypercapnia. Cortical spreading depression (CSD) also transiently reduces hypercapnic vasodilation. The authors sought to determine whether the CSD elicited by a controlled cortical impact (CCI) injury masks the true effect of TBI on hypercapnic vasodilation, and whether a nitric oxide (NO) donor can reverse the attenuation of hypercapnic vasodilation following CCI.



Anesthetized rats underwent moderate CCI. Cerebral blood flow was monitored with laser Doppler flowmetry and the response to hypercapnia was determined for injured and sham-injured animals. The effect of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), on this response was also assessed. At an uninjured cortical site ipsilateral to the CCI, a single wave of CSD was recorded and the CO2 response at this location was significantly attenuated for up to 30 minutes (seven rats, p < 0.05). At the injured cortex, hypercapnic vasodilation continued to be attenuated for 7 hours. The cerebral vasodilation to CO2 was 37 +/- 5% in injured rats (six) compared with 84 +/- 10% in the sham-injured group (five rats, p < 0.05). After 30 minutes of topical superfusion with SNAP, hypercapnic vasodilation was restored to 74 +/- 7% (nine rats, p > 0.1 compared with that in the sham-injured group). In contrast, papaverine, an NO-independent vasodilator, failed to reverse the attenuation of the CO2 response to CCI.



The authors conclude that CSD elicited by CCI can mask the true effect of TBI on hypercapnic vasodilation for at least 30 minutes. Exogenous NO, but not papaverine, can reverse the attenuation of cerebrovascular reactivity to CO2 caused by TBI. This result supports the hypothesis that NO production is reduced after TBI and that the NO donor has a potential beneficial role in the clinical management of head injury.

title: Cerebrovascular Reactivity Remains Intact after Cortical Depolarization in Newborn Piglets
abstract: Cerebrovascular reactivity is severely affected by ischemia, and changes in vascular responses have been reported after cortical spreading depression and head trauma as well. Cortical depolarization (CD) occurs during ischemia, cortical spreading depression, and head trauma, but its effects on cerebrovascular reactivity are unclear. We tested the hypothesis that CD induced by KCl diminishes the vascular responsiveness to various vasodilatory stimuli in piglets. Responses of pial arterioles were determined by changes in vascular diameter by use of a closed cranial window and intravital microscopy. Baseline arteriolar diameters were 105 ± 3 µm (mean ± SEM, n = 27). CD was elicited by topical administration of 1 mol/L KCl for 3 min. Vascular responses were measured before and 1 h after CD. KCl elicited CD and constricted arterioles by 54 ± 4% (n = 27). N-methyl-D-aspartate induced dose-dependent vasodilation that was unaffected by CD; the percent changes were 9 ± 1 versus 8 ± 1 (before and after CD) at 10-5 mol/L, 19 ± 2 versus 18 ± 3 at 5 × 10-5 mol/L, and 29 ± 2 versus 26 ± 3 at 10-4 mol/L (n = 9). Hypercapnic vasodilation was not diminished by CD; the percent changes were 15 ± 2 versus 16 ± 4 at 5%, and 27 ± 5 versus 27 ± 6 at 10% inspired CO2 (n = 8). Aprikalim and forskolin caused dilation that was also resistant to prior CD; the percent change values were 21 ± 4 versus 18 ± 3 and 16 ± 2 versus 16 ± 4 at 10-6 mol/L, 36 ± 5 versus 34 ± 5 and 34 ± 7 versus 37 ± 7 at 10-5 mol/L (n = 8), respectively. Finally, calcitonin gene-related peptide-induced vasodilation was unaffected by CD; percent changes were 15 ± 3 versus 16 ± 2 at 10-7 mol/L and 26 ± 4 versus 22 ± 3 at 10-6 mol/L (n = 8). The intact vascular responses after CD suggest that this component is not responsible for decreased cerebrovascular reactivity after ischemia, head trauma, or cortical spreading depression.

title: for Myogenic Activity Middle Cerebral Artery Function After Stroke : The Threshold Duration of Reperfusion
abstract: Myogenic activity of the cerebral arteries is an important contributor to autoregulation of cerebral blood flow. Previous studies have demonstrated that increasing periods of ischemia diminished the amount of myogenic tone in cerebral arteries. In the present study, we investigated the effect of different periods of postischemic reperfusion on the myogenic behavior of middle cerebral arteries (MCAs). We measured both the amount of spontaneous myogenic tone that developed at 75 mm Hg and the contractile response to increased transmural pressure (TMP), ie, myogenic reactivity. The MCA occlusion model was used in male Wistar rats (n 45) to induce 30 minutes of temporary ischemia, followed by different periods of reperfusion (0 or sham; 30 minutes; and 6, 12, 18, 20, and 22 hours), confirmed by laser Doppler flowmetry. MCAs were studied in vitro using an arteriograph system that allowed control of TMP and measurement of lumen diameter. After equilibration for 1 hour at 75 mm Hg, TMP was increased stepwise in 25–mm Hg increments to 125 mm Hg and lumen diameter measured at each pressure. The amount of spontaneous myogenic tone was determined in both ischemic and contralateral arteries for each reperfusion period and compared with the right and left MCAs in the sham group. Arteries were then fixed with 10% formalin pressurized in the arteriograph bath and stained for filamentous (F)–actin with fluorescently labeled phalloidin, a specific probe for F-actin. The amount of F-actin was quantified using confocal microscopy. MCAs from the sham-operated control group possessed considerable myogenic tone (35%). However, the amount of tone in ischemic MCAs progressively diminished as the reperfusion duration increased. In addition, sham-operated control arteries responded myogenically to increases in TMP, decreasing diameter as pressure increased. There was a similar response in arteries exposed to 30 minutes and 6 hours of reperfusion, all producing a negative slope on the pressure-diameter curve; however, myogenic reactivity was diminished at the longer periods of reperfusion, producing a positive slope of the graph. The slopes of the pressure-diameter curves were as follows: 0.10 0.06 (sham), 0.07 0.12 (30 minutes), 0.08 0.11 (6 hours), 0.09 0.09 (12 hours), 0.25 0.16 (18 hours), 0.38 0.09 (20 hours), and 0.57 0.09 (22 hours). F-actin content was significantly less only in ischemic MCAs at 6 and 12 hours of reperfusion. These results demonstrate that longer periods of reperfusion significantly diminish myogenic activity of MCAs. Understanding how different periods of ischemia and reperfusion affect the function of the cerebral circulation may promote more effective treatment of ischemic stroke.

title: Autoregulation and CO2 responses of cerebral blood flow in patients with acute severe head injury.
abstract: Regional cerebral blood flow (rCBF), cerebral intraventricular pressure (IVP), systemic arterial blood pressure, and cerebral ventricular fluid (CSF) lactate and pH were studied repeatedly in 23 patients during the acute phase of severe brain injury lasting from 3 to 21 days after the trauma. Cerebrovascular autoregulation was tested repeatedly by means of angiotensin infusion in 21 of the patients, and CO2 response in 14 by means of passive hyperventilation. The pressure in the brain ventricles was measured continuously in all patients and kept below 45 mm Hg during the study. If the IVP increased more than 10 mm Hg during the angiotensin infusion (as in one case), the autoregulation test was considered contraindicated and the angiotensin infusion was discontinued. Dissociation between cerebrovascular autoregulation and CO2 response was a common phenomenon. Typically, autoregulation appeared preserved in the most severely injured areas of the cerebral cortex when the patient was deeply comatose, but deteriorated concomitantly with recovery; by the time the patient became alert, the autoregulation was always impaired. The CO2 response was impaired only in patients who were deeply comatose and had attacks of decerebrate rigidity; during recovery the CO2 response became normal. Thus, preserved autoregulation associated with imparied CO2 response indicated very severe brain damage, whereas impaired autoregulation associated with preserved CO2 response suggested moderate or severe brain damage in recovery. These paradoxical observations raise the question whether the preserved autoregulation seen in severely injured brain tissue is a true autoregulation caused by an active vasoconstrictor response to an increase in blood pressure.

title: Regulation of regional cerebral blood flow during and between migraine attacks
abstract: Cerebrovascular reactivity to voluntary hyperventilation, moderate hypertension, and physiological activation was studied in nine patients during induced migraine attacks and in four patients between their attacks. Regional cerebral blood flow was measured by the xenon 133 injection technique in 254 areas of one hemisphere. The partly hypoperfused hemisphere allowed for comparison of adjacent hypoperfused and normally perfused brain areas. During attacks the carbon dioxide reactivity was decreased to 2.8 ± 0.8% per mm Hg in the oligemic regions compared with 5.8 ± 0.8% per mm Hg in the normally perfused brain. Blood pressure autoregulation was normal in all brain regions. Regional blood flow increase in response to physiological activation was severely impaired in the hypoperfused brain areas, whereas neighboring normally perfused regions reacted normally. Confinement of the regulation abnormalities to the area of the oligemia supports our suggestion that the blood flow changes are caused by a change in local metabolism. Between attacks of migraine, the patients had normal regulation of brain circulation.

title: Global Ischemia in Dogs: Cerebrovascular CO2 Reactivity and Autoregulation
abstract: One hypothesis on the pathogenesis of post-ischemic-anoxic encephalopathy is impaired cerebral perfusion or the no-reflow phenomenon. Therapies aimed at preventing the development of this phenomenon are increased cerebral perfusion pressure (CPP) and hyperventilation or hypercapnia. Using a dog model in which we have described the progressive development of post-ischemic (PI) cerebral hypoperfusion after 15 minutes of global ischemia induced by aortic and vena cavae clamping, our aims in this study were to determine during the PI cerebral hypoperfusion period: (1) cerebrovascular reactivity to CO2, and (2) cerebral blood flow (CBF) autoregulation. Post-ischemic cerebral hypoperfusion to about 50% of normal was not accompanied by raised intracranial pressure (ICP) but cerebrovascular CO2 reactivity was markedly attenuated while maintaining some kind of autoregulatory phenomenon. Cerebral uptake of oxygen was not significantly affected by changing Paco2 from 20 to 60 torr at constant CPP or by changing CPP from 64 to 104 torr at constant Paco2. These results suggest that increasing both CPP and hypocapnia/hypercapnia would not significantly attenuate PI neurological deficit after global cerebral ischemia. However, in two dogs inadvertently hemodiluted in the PI period, increasing CPP from 50 to 200 torr increased CBF by 200%, suggesting that hemodilution plus increased CPP may be effective therapy for amelioration of post-ischemic-anoxic encephalopathy. The significance of our findings on cerebrovascular CO2 reactivity and autoregulation with respect to the mechanism of the no-reflow phenomenon is discussed.

title: Functional Activation of Cerebral Blood Flow after Cardiac Arrest in Rat
abstract: After a period of global cerebral ischemia, CO2 reactivity and the hemodynamic–metabolic activation to functional stimulation are transiently suppressed. This raises the question of whether the impaired functional coupling reflects disturbances of functional integrity of the brain or an impaired cerebrovascular reactivity. We, therefore, compared the recovery of CO2 reactivity with that of somatosensory evoked potentials, functional flow activation and neurologic deficits in a rodent model of cardiac arrest-induced cerebral ischemia, followed by up to 7 days of reperfusion. Cardiac arrest of 10 minutes' duration was produced in 24 animals by electrical fibrillation of the heart. Five animals were sham-operated controls. Resuscitation was performed by external cardiac massage, using standard resuscitation procedures. Functional activation was carried out under chloralose anesthesia by electrical stimulation of forepaws. CO2 reactivity was tested by ventilation of animals with 6% CO2. During functional and hypercapnic stimulation CBF was measured in the somatosensory cortex using laser–Doppler flowmetry, and at the end of the experiment by 14C-iodoantipyrine autoradiography. Neurologic deficits were scored by evaluating consciousness and various sensory and motor functions. In control animals 6% CO2 increased CBF measured by laser–Doppler flowmetry by 28.8% ± 8.7%. Forepaw stimulation generated somatosensory evoked potentials with an amplitude of 750 ± 217 μV and increased CBF measured by laser–Doppler flowmetry by 86.0% ± 18.1%. After return of spontaneous circulation, CO2 reactivity was transiently reduced to about 30% of control at 1 hour of reperfusion (P < 0.05) but returned to near control at 5 hours. Somatosensory evoked potential amplitudes were reduced to 15% of control at 45 minutes of reperfusion and returned to only 50% to 60% at 3 and 7 days after return of spontaneous circulation (P < 0.05). Functional activation of blood flow was completely suppressed during the first hour after return of spontaneous circulation but also recovered to 50% to 60% of control at 3 days after return of spontaneous circulation (P < 0.05). Linear regression analysis revealed a significant correlation between recovery of functional activation of blood flow and both recovery of the amplitude of somatosensory evoked potentials (P = 0.03) and the neurologic deficit score (P = 0.02), but not between neurologic deficit score and recovery of CO2 reactivity or somatosensory evoked potential amplitudes. These data demonstrate that the suppression of functional activation of blood flow after 10 minutes cardiac arrest is not related to impairment of coupling mechanisms but reflects ongoing disturbances of the functional integrity of the brain. Assessment of functional flow coupling is a reliable way to study postischemic recovery of the brain.

title: Cortical spreading depression activates and upregulates MMP-9.
abstract: Cortical spreading depression (CSD) is a propagating wave of neuronal and glial depolarization and has been implicated in disorders of neurovascular regulation such as stroke, head trauma, and migraine. In this study, we found that CSD alters blood-brain barrier (BBB) permeability by activating brain MMPs. Beginning at 3-6 hours, MMP-9 levels increased within cortex ipsilateral to the CSD, reaching a maximum at 24 hours and persisting for at least 48 hours. Gelatinolytic activity was detected earliest within the matrix of cortical blood vessels and later within neurons and pia arachnoid (> or =3 hours), particularly within piriform cortex; this activity was suppressed by injection of the metalloprotease inhibitor GM6001 or in vitro by the addition of a zinc chelator (1,10-phenanthroline). At 3-24 hours, immunoreactive laminin, endothelial barrier antigen, and zona occludens-1 diminished in the ipsilateral cortex, suggesting that CSD altered proteins critical to the integrity of the BBB. At 3 hours after CSD, plasma protein leakage and brain edema developed contemporaneously. Albumin leakage was suppressed by the administration of GM6001. Protein leakage was not detected in MMP-9-null mice, implicating the MMP-9 isoform in barrier disruption. We conclude that intense neuronal and glial depolarization initiates a cascade that disrupts the BBB via an MMP-9-dependent mechanism.

title: Unexpected effects of peripherally administered kynurenic acid on cortical spreading depression and related blood–brain barrier permeability
abstract: Cortical spreading depression (CSD) involves a slowly-propagating depolarization wave in the cortex, which can appear in numerous pathophysiological conditions, such as migraine with aura, stroke, and traumatic brain injury. Neurons and glial cells are also depolarized transiently during the phenomena. CSD is followed by a massive increase in glutamate release and by changes in the brain microcirculation. The aim of this study was to investigate the effects of two N-methyl-D-aspartate receptor antagonists, endogenous kynurenic acid (KYNA) and dizocilpine, on CSD and the related blood–brain barrier (BBB) permeability in rats. In intact animals, KYNA hardly crosses the BBB but has some positive features as compared with its precursor L-Kynurenine, which is frequently used in animal studies (KYNA cannot be metabolized to excitotoxic agents such as 3-hydroxy-L-kynurenine and quinolinic acid). We therefore investigated the possible effects of peripherally administered KYNA.  CSD waves were elicited by the application of 1 M KCl solution to the cortex. Direct current-electrocorticograms were measured for 1 hour. Four parameters of the waves were compared. Evans blue dye and fluorescent microscopy were used to study the possible changes in the permeability of the BBB. The results demonstrated that N-methyl-D-aspartate receptor antagonists can reduce the number of CSD waves and decrease the permeability of the BBB during CSD. These results suggest that KYNA itself or its derivatives may offer a new approach in the therapy of migraines.

title: The interrelation between brain PO2 and NADH oxidation‐reduction state in the gerbil
abstract: The present investigation was aimed at studying the interrelation between hemodynamic, metabolic and oxygen tension in the brain of the gerbil exposed to various physiological and pathological conditions in the awake and anesthetized states. The hemodynamic and metabolic activities were evaluated by the DC fluorometer/reflectometer and were correlated to the pO2 values obtained by a surface electrode.

title: Differences in O2 availability resolve the apparent discrepancies in metabolic intrinsic optical signals in vivo and in vitro

abstract: Monitoring changes in the fluorescence of metabolic chromophores, reduced nicotinamide adenine dinucleotide and flavin adenine dinucleotide, and the absorption of cytochromes, is useful to study neuronal activation and mitochondrial metabolism in the brain. However, these optical signals evoked by stimulation, seizures and spreading depression in intact brain differ from those observed in vitro. The responses in vivo consist of a persistent oxidized state during neuronal activity followed by mild reduction during recovery. In vitro, however, brief oxidation is followed by prolonged and heightened reduction, even during persistent neuronal activation. In normally perfused, oxygenated and activated brain tissue in vivo, partial pressure of oxygen (P(O2)) levels often undergo a brief 'dip' that is always followed by an overshoot above baseline, due to increased blood flow (neuronal-vascular coupling). By contrast, in the absence of blood circulation, tissue P(O2)in vitro decreases more markedly and recovers slowly to baseline without overshooting. Although oxygen is abundant in vivo, it is diffusion-limited in vitro. The disparities in mitochondrial and tissue oxygen availability account for the different redox responses.

title: Cortical NADH during pharmacological manipulations of the respiratory chain and spreading depression in vivo
abstract: The nicotinamide adenine dinucleotide (NADH) is one of the main means for energy transfer in the mitochondrial respiratory chain and is an important parameter of cellular metabolism. NADH can be measured by its fluorescence and various fluorometric methods have been developed. In this study, a pulsed nitrogen laser combined with a fibreoptic set‐up and photomultipliers was used to induce and measure NADH fluorescence on the cortical surface. The aim of the study was to assess the suitability of the laser induced spectroscopy for in vivo and on‐line measurement of NADH in neuroscience and particularly for the assessment of neuronal metabolism. Changes in cerebral blood flow may affect fluorescence measurement. To assess the consequences of alterations in blood flow, the vasodilators glyceryl trinitrate and nimodipine and the vasoconstrictor endothelin‐1 were applied. The induced hemodynamic changes were verified by colour Doppler sonography. The tests using the vasodilators showed that an increased blood flow in the brain increased not only NADH fluorescence but also the scattered light measured. The vasoconstrictor caused opposite effects. Insertion of a compensation method (subtraction of the scattered light) allowed the exclusion of hemodynamic artifacts. Effects of changes in the cellular metabolism were induced by sodium cyanide, an inhibitor of the mitochondrial respiratory chain, or by 2,4‐dinitrophenol (2,4‐DNP), an uncoupler of the oxidative phosphorylation. Sodium cyanide induced a transient increase of NADH fluorescence and 2,4‐DNP decreased intracellular NADH fluorescence. Furthermore, the repercussions of cortical spreading depressions (CSD), a response of the brain to noxious stimuli, on cortical NADH fluorescence were determined. A single CSD decreased cortical NADH fluorescence for about 1 min, followed by a 5‐ to 10‐min increase. The changes in NADH levels seem to correspond with the excitation and inhibition of neuronal metabolism, respectively. In summary, the measurement of NADH fluorescence using the laser technique allows the determination of changes in oxidative phosphorylation with high regional selectivity and time resolution.  1999.

title: Ischemia-induced alterations in oxidative “recovery” metabolism after spreading cortical depression in situ
abstract: Surface electrical stimulation was used to provoke direct cortical responses, spreading cortical depression, and concomitant increases in oxidative metabolic activity in cat neocortex in situ during and after short periods of incomplete and complete ischemia. These metabolic changes were recorded continuously in the intact tissue by monitoring the fluorescence of NADH (as NAD + does not fluoresce under these optical conditions). Ischemic effects were unidirectional and progressive with the degree of perfusion decrease. Incomplete ischemia was accompanied by decreased excitability and amplitude of metabolic responses to stimulation. During incomplete ischemia when the NADH:NAD + ratio was increased, the brain continued to respond to spreading cortical depression with oxidation of NADH indicating that the capability for increased respiration still resided within the tissue. In cats that survived complete ischemia, these reaction rates became unchanged from control. In other cats, the rate of NAD + re-reduction after spreading depression continued to decrease and death inevitably followed. These findings confirm that short ischemic periods produce alterations in oxidative metabolic capabilities indicative of respiratory uncoupling, resulting in decreased excitability and decreased capacity to respond to increased metabolic demand.

title: Brain oxygen balance under various experimental pathophysiologycal conditions.
abstract: Normally, brain tissue copes with negative oxygen balance by increasing cerebral blood flow (CBF). We examined the effects of increasing oxygen demand, by inducing spreading depression (SD) under various oxygen balance states, on brain O2 balance. The Tissue Vitality Monitoring System was used, which enables real time simultaneous in vivo monitoring of CBF, mitochondrial NADH and tissue HbO2 from the same region of the cerebral cortex. SD was induced during normoxia, hypoxia, hyperoxia, ischemia, and in normal and ischemic brain after systemic epinephrine administration. Under normoxia, hyperoxia and ischemia & epinephrine, the compensation of energy demand induced by SD, was carried out by increasing CBF. The higher oxygen delivery under hyperoxia and epinephrine did not change the pattern of recovery from SD as compared to normoxia, whereas in the ischemic and hypoxic brain, the recovery from SD was prolonged, indicating a lake in oxygen delivery. Epinephrine infusion in the ischemic rat, decreased oxyhemoglobin utilization during SD, indicating that tissue oxygen balance improves even under higher oxygen demand induced by SD.

title: The Use of In Vivo Fluorescence Image Sequences to Indicate the Occurrence and Propagation of Transient Focal Depolarizations in Cerebral Ischemia
abstract: A method for the detection and tracking of propagated fluorescence transients as indicators of depolarizations in focal cerebral ischemia is described, together with initial results indicating the potential of the method. The cortex of the right cerebral hemisphere was exposed for nonrecovery experiments in five cats anesthetized with chloralose and subjected to permanent middle cerebral artery (MCA) occlusion. Fluorescence with 370-nm excitation (attributed to the degree of reduction of the NAD/H couple) was imaged with an intensified charge-coupled device camera and digitized. Sequences of images representing changes in gray level from a baseline image were examined, together with the time courses of mean gray levels in specified regions of interest. Spontaneous increases in fluorescence occurred, starting most commonly at the edge of areas of core ischemia; they propagated usually throughout the periinfarct zone and resolved to varying degrees and at varying rates, depending on proximity of the locus to the MCA input. When a fluorescence transient reached the anterior cerebral artery territory, its initial polarity reversed from an increase to a decrease in fluorescence. An initial increase in fluorescence in response to the arrival of a transient may characterize cortex that will become infarcted, if pathophysiological changes in the periinfarct zone are allowed to evolve naturally.

title: Factors influencing the frequency of fluorescence transients as markers of peri-infarct depolarizations in focal cerebral ischemia.
abstract: Peri-infarct depolarizations (PIDs) that occur in ischemic boundary zones of the cerebral cortex of experimental animals have been shown to promote rather than simply to indicate the evolution of the lesion and are especially prominent in the rat. To study the influence of one factor, species, on PID incidence, we compared the frequency of PIDs in a primate species, the squirrel monkey, with that in the cat after middle cerebral artery occlusion. Plasma glucose was reviewed as a possible cause of interexperiment variability in the cat experiments.



In open-skull experiments under chloralose anesthesia, changes in cortical fluorescence believed to indicate NADH/NAD(+) redox state, as markers of PIDs, were recorded by serial imaging of the cortical surface in vivo for 4 hours after middle cerebral artery occlusion.



Fluorescence transients occurred in squirrel monkeys at a frequency (mean+/-SD) of 0.7+/-0.8 hours(-1) (n=5), which was not significantly less than in that observed in cats (1.3+/-1.6 hours(-1), n=8). Data from the cat experiments indicated a relationship between number of transients (dependent) and plasma glucose, with a striking increase in PID frequency in association with values of mean postocclusion plasma glucose <4.1 mmol/L (Mann-Whitney U=15.0, P=0.034); this observation agrees well with other published findings.



Transient changes in fluorescence strongly suggestive of peri-infarct depolarizations, either transient or terminal, occur and propagate in the ischemic cerebral cortex of a nonhuman primate. The results also suggest that the relationship of frequency of peri-infarct depolarizations with plasma glucose requires further examination, to confirm the finding and to determine a safe lower limit for a target range for control of plasma glucose if insulin is used in the management of patients with cerebral ischemia.

title: Light scattering in rat neocortical slices differs during spreading depression and ischemia
abstract: Spreading depression (SD) and ischemia are different pathophysiological events but have similar characteristics. This study investigated whether similarity exists in the light scattering (LS) properties during SD and ischemia in rat neocortical slices. SD was induced by injection of K(+) while ischemia was simulated by removing oxygen and glucose. LS was simultaneously recorded with changes in extracellular direct current (DC) potential and extracellular space (ECS) volume. LS was measured using a photon counting fiber optic system and the ECS volume change was determined by measuring the ECS concentration of tetramethylammonium (TMA(+)). Slices maintained in normal artificial cerebrospinal fluid (ACSF) showed a consistent LS increase during SD, but exhibited two different LS behaviors during 6 min of ischemia. In eight slices, LS decreased and remained so until the end of the ischemic challenge. In another 10 slices, LS diminished initially but, after 2 min, suddenly reversed sign, accompanied by a rapid negative shift in extracellular DC potential. When 50 or 91% of Cl(-) in the ACSF was replaced by membrane-permeable propionate, LS retained its increase during SD, but always showed the sudden LS reversal during ischemia. In contrast, when Cl(-) was substituted with membrane-impermeant methylsulfate, the SD-induced LS increase was replaced by an LS decrease, and the sudden LS reversal during ischemia was absent. While the LS signal showed different characteristics during SD and ischemia, the DC potential always presented negative shifts and the ECS volume always exhibited similar decreases. These results suggest that the polarity of the LS signal is determined by the competition of at least two factors: cell swelling and anion influx.

title: Two-photon high-resolution measurement of partial pressure of oxygen in cerebral vasculature and tissue
abstract: Measurements of oxygen partial pressure (pO2) with high temporal and spatial resolution in three dimensions is crucial for understanding oxygen delivery and consumption in normal and diseased brain. Among existing pO2 measurement methods, phosphorescence quenching is optimally suited for the task. However, previous attempts to couple phosphorescence with two-photon laser scanning microscopy have faced substantial difficulties because of extremely low two-photon absorption cross-sections of conventional phosphorescent probes. Here we report to our knowledge the first practical in vivo two-photon high-resolution pO2 measurements in small rodents' cortical microvasculature and tissue, made possible by combining an optimized imaging system with a two-photon–enhanced phosphorescent nanoprobe. The method features a measurement depth of up to 250 μm, sub-second temporal resolution and requires low probe concentration. The properties of the probe allowed for direct high-resolution measurement of cortical extravascular (tissue) pO2, opening many possibilities for functional metabolic brain studies.

title: Induced spreading depressions in energy-compromised neocortical tissue: calcium transients and histopathological correlates
abstract: Mechanisms causing gradual recruitment of damaged cells in the penumbra zone around the core of a focal ischaemic lesion may encompass irregularly occurring depolarization waves of the spreading depression (SD) type, each leading to transient loading of cells with calcium. It has been speculated that, when elicited in an underperfused or otherwise energy-compromised tissue, such depolarization waves lead to cell damage. We assessed under what conditions the calcium transients during KCl-induced SDs are prolonged, and explored if marked prolongation of the transients leads to brain damage. Cerebral blood flow (CBF) was reduced by marked hypocapnia. Tissue oxygenation was reduced by arterial hypoxia, without or with unilateral carotid artery occlusion, or by occlusion of the carotid arteries in normoxic, anaesthetized rats. In all animals the DC potential and extracellular calcium concentration (Ca2+e) were measured before and during a series of SDs. The animals were recovered for histopathological assessment. Hypoxia alone (Pao2, 32.5 +/- 3.8 mmHg) increased mean and total depolarization times, but repeated SDs elicited over 1.7 (+/-0.4) h failed to induce cell damage. Unilateral carotid artery occlusion further prolonged the SD waves but, in spite of total depolarization times of up to 40 min during 2 h, only two out of seven animals showed damage, localized to caudoputamen and parietal cortex, as well as to the subiculum, CA1 and CA3 sectors of the hippocampus. Bilateral carotid artery occlusion was associated with the most pronounced prolongation of the DC potential shifts and Ca2+ transients, with total depolarization times of up to 70 min. In spite of this, only four out of 13 animals showed brain damage and in two of these the damage was contralateral. The results justify modification of the hypothesis stating that SD-like depolarizations in the perifocal penumbra zone per se is what leads to gradual recruitment of such tissues in the infarction process. It is suggested that additional factors are required, such as a larger reduction in CBF, or the proximity of cells at risk to necrotic tissue.

title: Nitric Oxide Formation during Cortical Spreading Depression is Critical for Rapid Subsequent Recovery of Ionic Homeostasis
abstract: Cortical spreading depression (CSD) is a temporary disruption of local ionic homeostasis that propagates slowly across the cerebral cortex. Cortical spreading depression promotes lesion progression in experimental stroke, and may contribute to the initiation of migraine attacks. The purpose of this study was to investigate the roles of the marked increase of nitric oxide (NO) formation that occurs with CSD. Microdialysis electrodes were implanted in the cortex of anesthetized rats to perform the following operations within the same region: (1) elicitation of CSD by perfusion of high K+ medium; (2) recording of CSD elicitation; (3) application of the NO synthase inhibitor, NG-nitro-l-arginine methyl ester (l-NAME); and (4) recording of dialysate pH changes. The primary effect of l-NAME (0.3 to 3.0 mmol/L in the perfusion medium) was a marked widening of individual CSD wave, resulting essentially from a delayed initiation of the repolarization phase. This change was due to NO synthase inhibition because it was not observed with the inactive isomer d-NAME, and was reversed by l-arginine. This effect did not appear to be linked to the suppression of a sustained, NO-mediated vascular change associated with the superposition of NO synthase inhibition on high levels of extracellular K+. The delayed initiation of repolarization with local NO synthase inhibition may reflect the suppression of NO-mediated negative feedback mechanisms acting on neuronal or glial processes involved in CSD genesis. However, the possible abrogation of a very brief, NO-mediated vascular change associated with the early phase of CSD cannot be ruled out.

title: The use of spreading depression waves for acute and long-term monitoring of the penumbra zone of focal ischemic damage in rats.
abstract: Slow potential recording was used for long-term monitoring of the penumbra zone surrounding an ischemic region produced by middle cerebral artery (MCA) occlusion in adult hooded rats (n = 32). Four capillary electrodes (El-E4) were chronically implanted at 2-mm intervals from AP -3, L 2 (El) to AP 0, L 5 (E4). Spontaneous or evoked slow potential waves of spreading depression (SD) were recorded during and 4 h after a 1-h MCA occlusion and at 2- to 3-day intervals afterward for 3 weeks. Duration of the initial focal ischemic depolarization was maximal at E4 and decreased with distance from the focus. SD waves in the penumbra zone were high at El and E2, low and prolonged at E3, and almost absent at E4. Amplitude of elicited SD waves was further reduced 3 days later and slowly increased in the following week. Cortical areas displaying marked reduction of SD waves in the first days after MCA occlusion either remained low or showed substantial (60%) recovery, the probability of which decreased with the duration of the initial focal ischemic depolarization and increased with the distance from the focus. It is concluded that the outcome of ischemia monitored by long-term SD recovery in the perifocal region can be partly predicted from the acute signs of MCA occlusion.

title: A Paravascular Pathway Facilitates CSF Flow Through the Brain Parenchyma and the Clearance of Interstitial Solutes, Including Amyloid β
abstract: Cerebrospinal fluid flows through channels around brain blood vessels that are bounded by astrocytic endfeet, mediated by water transport through aquaporin-4. A New Footing for Waste Clearance in the Brain Where are the lymph vessels of the brain? The lymphatic system’s complex network of vessels extends throughout most of the body, transporting excess fluid and waste products from the interstitial spaces between cells to the blood. Such vessels are notably absent from the brain, however, leading to long-standing questions about how interstitial fluid in this organ is cleared of waste. Now, Iliff et al. describe an anatomically distinct clearing system in the brain that serves a lymphatic-like function. The researchers first investigated the fate of tracer molecules introduced into the cerebrospinal fluid (CSF) in mice. Produced in ventricular cavities deep within the brain, the CSF fills the subarachnoid space—a gap between two of the membranes that encase the brain and spinal cord. Whereas tracers infused into the ventricle remained near that site, those injected into the subarachnoid space rapidly entered the brain itself. By visualizing fluorescent tracers through a cranial window in live mice, the authors found that CSF enters the brain in specific channels that are defined by features of small blood vessels in the brain. Such vessels are almost entirely ensheathed by astrocytic endfeet (terminal enlargements of long processes that project from astrocytes). The CSF tracers readily flow inward to the brain matter in a compartment between the outside of vessels—in this case small arteries entering the brain—and the astrocytic endfeet. At later time points, the tracer exits the brain in similar channels surrounding veins, having apparently circulated through the brain interstitium. Such CSF flux—and the clearance of tracers injected into the brain itself—were markedly reduced in mice lacking aquaporin-4, a water channel localized to astrocytic endfeet, indicating that these channels mediate this flux. These findings may have relevance for understanding or treating neurodegenerative diseases that involve the mis-accumulation of soluble proteins, such as amyloid β in Alzheimer’s disease. Indeed, Iliff et al. found that normal clearance of amyloid β (previously injected into the brain) requires aquaporin-4. Because it lacks a lymphatic circulation, the brain must clear extracellular proteins by an alternative mechanism. The cerebrospinal fluid (CSF) functions as a sink for brain extracellular solutes, but it is not clear how solutes from the brain interstitium move from the parenchyma to the CSF. We demonstrate that a substantial portion of subarachnoid CSF cycles through the brain interstitial space. On the basis of in vivo two-photon imaging of small fluorescent tracers, we showed that CSF enters the parenchyma along paravascular spaces that surround penetrating arteries and that brain interstitial fluid is cleared along paravenous drainage pathways. Animals lacking the water channel aquaporin-4 (AQP4) in astrocytes exhibit slowed CSF influx through this system and a ~70% reduction in interstitial solute clearance, suggesting that the bulk fluid flow between these anatomical influx and efflux routes is supported by astrocytic water transport. Fluorescent-tagged amyloid β, a peptide thought to be pathogenic in Alzheimer’s disease, was transported along this route, and deletion of the Aqp4 gene suppressed the clearance of soluble amyloid β, suggesting that this pathway may remove amyloid β from the central nervous system. Clearance through paravenous flow may also regulate extracellular levels of proteins involved with neurodegenerative conditions, its impairment perhaps contributing to the mis-accumulation of soluble proteins.

title: Cerebral Arterial Pulsation Drives Paravascular CSF–Interstitial Fluid Exchange in the Murine Brain
abstract: CSF from the subarachnoid space moves rapidly into the brain along paravascular routes surrounding penetrating cerebral arteries, exchanging with brain interstitial fluid (ISF) and facilitating the clearance of interstitial solutes, such as amyloid β, in a pathway that we have termed the “glymphatic” system. Prior reports have suggested that paravascular bulk flow of CSF or ISF may be driven by arterial pulsation. However, cerebral arterial pulsation could not be directly assessed. In the present study, we use in vivo two-photon microscopy in mice to visualize vascular wall pulsatility in penetrating intracortical arteries. We observed that unilateral ligation of the internal carotid artery significantly reduced arterial pulsatility by ∼50%, while systemic administration of the adrenergic agonist dobutamine increased pulsatility of penetrating arteries by ∼60%. When paravascular CSF–ISF exchange was evaluated in real time using in vivo two-photon and ex vivo fluorescence imaging, we observed that internal carotid artery ligation slowed the rate of paravascular CSF–ISF exchange, while dobutamine increased the rate of paravascular CSF–ISF exchange. These findings demonstrate that cerebral arterial pulsatility is a key driver of paravascular CSF influx into and through the brain parenchyma, and suggest that changes in arterial pulsatility may contribute to accumulation and deposition of toxic solutes, including amyloid β, in the aging brain.

title: Diffusion in brain extracellular space.
abstract: Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding, or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix, and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is approximately 20% and the tortuosity is approximately 1.6 (i.e., free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge, and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases, and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties is valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain.

title: Analysis of potassium dynamics in mammalian brain tissue.
abstract: Equations are derived for potassium (K+) dynamics in simplified models of brain tissue. These describe K+ movement in extracellular space, transfer of K+ associated with current flow through cells (the so‐called spatial buffer mechanism) and equilibration between extracellular space and cytoplasm. Numerical calculations show that the principal data on K+ dynamics from various laboratories can be accounted for with simple assumptions about spatial buffer action and uptake. Much of the data is inconsistent with extracellular diffusion being the main mechanism for K+ flux through brain tissue, including some that has earlier been cited in support of this hypothesis. The buffering actions of spatial buffer transfer of K+ and of cytoplasmic equilibration, in which these mechanisms reduce rises of [K+]o that would otherwise occur, are analysed quantitatively for specific K+ source distributions and for spatial and temporal frequency components of general disturbances. Spatial buffer action has most effect in reducing [K+]o rises with net release over extensive zones of tissue (greater than ca. 200 micron in diameter) for periods of the order of minutes. Reductions greater than 75% may be achieved. With localized but prolonged release, the maximum [K+]o rise is little affected but the volume of tissue affected by more moderate rises is substantially reduced. Cytoplasmic K+ uptake also has most effect with widespread release, but its effect diminishes with prolonged periods of release. The effects of the buffering mechanisms and of K+ re‐uptake into active neurones in determining the decline of [K+]o after a period of stimulation are considered. Re‐uptake is unlikely to be the major factor responsible for [K+]o decline when this has a time course of only a few seconds. The properties necessary for the cells mediating the spatial buffer mechanisms, possibly glial cells, are assessed.

title: A study of the mechanisms by which potassium moves through brain tissue in the rat.
abstract: The flux of K+ produced by electric current across the pia‐arachnoid surface of the neocortex of anaesthetized rats has been studied with K+‐selective electrodes in a cup at the surface and with flame photometry. The potential differences developed across three regions of the rat brain (neocortex, cerebellum, hippocampus) have been measured as [K+] was altered in fluid at the surface. The experimental results have been related to those that would be expected (i) if K+ moved principally by diffusion in extracellular space and (ii) if current flow through cells makes a significant contribution to K+ transfer. K movement produced by current across the neocortical surface accounted for 0.06 of the transfer of electric charge with small currents in either direction (ca. 5 microA mm‐2) and with larger currents out of the tissue. Large currents (ca. 20 microA mm‐2) into the tissue produced less K+ movement, but still more than the fraction 0.012 expected for purely extracellular flux. Alternating current pulses (5 Hz) with zero net transfer of charge produced no flux of K+ across the surface, while alternation with unequal durations produced the same effects as the equivalent steady charge transfer. The K+ flux lagged behind the onset and cessation of current with a time constant ca. 45 sec, approximately as expected from calculations with a model of the tissue. A surface‐negative potential shift averaging 2 mV was observed when [K+ ]at the brain surface was increased from 3 to 12 mM. The time for development of half of the full potential change was 20 sec, with the solution changes complete in less than 4 sec. These results are inconsistent with the hypothesis that K+ movement through brain tissue occurs principally through intercellular clefts, except where these movements involve very localized gradients. They are consistent with the conclusion that ca. 5 times as much K+ flux passes through cells (probably largely glial cells) as through extracellular space, with fluxes driven by either extracellular voltage or concentration gradients.

title: Characterization of Cortical Depolarizations Evoked in Focal Cerebral Ischemia
abstract: Cortical tissue surrounding acute ischemic infarcts undergoes repetitive spontaneous depolarizations. It is unknown whether these events are episodes of spreading depression (SD) elicited by the elevated interstitial K+ ([K+]e) in the ischemic core or whether they are evoked by transient decreases of the local blood flow. Electrophysiologically, depolarization caused by SD or by ischemia (ID) can be distinguished by their characteristic patterns of [K+]e rise: During SD, [K+]e rises abruptly, while in ID, this fast rate of increase is preceded by a slow rate lasting minutes. To characterize the depolarizations, we occluded the right middle cerebral artery (MCA) in rats and inserted two K+-sensitive microelectrodes into the cortex surrounding the evolving infarct. Repeated increases in [K+]e arose spontaneously following MCA occlusion. [K+]e increased during these transients from a resting level of 3–6 to 60 mM. One-third of these transient increases in [K+]e were biphasic, consisting of a slow initial increase to 10–12 mM, which lasted for minutes, followed by an abrupt increase, a pattern characteristic of ID. The remaining two-thirds exhibited a steep monotonic increase in [K+]e (>10 s), characteristic of SD. The duration of the transients was a function of the pattern of [K+]e increase: ID-like transients lasted an average 10.7 ±5.1 min, whereas the duration of SD-like transients was 5.7 ± 3.4 min. Both types of K+ transients occurred in an apparently random fashion in individual animals. A K+ transient was never observed solely at one electrode. In 40% of the cases, the K+ transients occurred simultaneously at the two electrode sites, and in the remaining a temporal separation of 20–420 s was observed. Our data suggest that the majority of the spontaneous depolarizations evoked by focal ischemia are SD-like phenomena probably evoked by the high values of [K+]e or glutamate in the ischemic focus, while the rest are elicited by independent foci of low blood flow within the ischemic border areas.

title: Thresholds in cerebral ischemia - the ischemic penumbra.
abstract: COMPLETE ARREST of the cerebral circulation leads within seconds to cessation of neuronal electrical activity and within a few minutes to deterioration of the energy state and ion homeostasis. Depletion of high energy phosphates, membrane ion pump failure, efflux of cellular potassium, influx of sodium, chloride and water, and membrane depolarization occur swiftly. If such chaos persists for longer than 5-10 minutes, irreversible cell damage is likely. Such is the inevitable sequence of events if blood flow to the brain is arrested. If, however, the ischemia is incomplete the outcome is more difficult to predict and is largely dependent on residual perfusion and oxygen availability. It is in large measure the outcome of incomplete cerebral ischemia, which is of particular interest in cerebrovascular disease. With occlusion of a cere-bral vessel and signs of acute stroke, ischemia is hardly ever total. Some residual perfusion persists in the ischemic area dependent on collateral vessels and local perfusion pressures. Recent evidence indicates that immediate failure of basic functions such as synaptic transmission, ion pumping and energy metabolism in the ischemic brain, is critically dependent on residual blood flow, and that these functions fail at certain critical flow thresholds. It appears, further, that the development of infarction is critically correlated to residual per-fusion, and there is a lethal threshold of residual blood flow below which tissue infarction develops after a certain time. Such knowledge provides the theoretical background for application of the instrumentation now being developed for repeated non-invasive 3-dimensional imaging of residual flow in the ischemic brain. By these means one hopes it will become possible to conduct treatment and to evaluate prognosis in the acute stroke patient by reproducible repeatable measurement in man. In man, flattening of the EEG occurs immediately if hemispheric flow falls below 0.16-0.17 ml-g^min 1 as evidenced by measurements of cerebral blood flow and EEG during clamping of one carotid artery in end-arterectomy. 1-* The critical relationship between cere-bral electrical activity and blood flow which such clinical observation suggested has been amply proven in exDerimental studies. Svmon and Branston and co-workers' demonstrated that the evoked somato-sensory potential recorded in baboon cortex was abolished at local flows below about 0.15 ml'gr^mirr 1. This flow level could be regarded as critical in the sense that electrical function in the cortex was abolished below but sustained above this level. It has, therefore, been referred to as the flow threshold of electrical …

title: Normobaric hyperoxia improves cerebral blood flow and oxygenation, and inhibits peri-infarct depolarizations in experimental focal ischaemia.
abstract: Normobaric hyperoxia is under investigation as a treatment for acute ischaemic stroke. In experimental models, normobaric hyperoxia reduces cerebral ischaemic injury and improves functional outcome. The mechanisms of neuroprotection are still debated because, (i) inhalation of 100% O2 does not significantly increase total blood O2 content; (ii) it is not known whether normobaric hyperoxia increases O2 delivery to the severely ischaemic cortex because of its short diffusion distance; and (iii) hyperoxia may reduce collateral cerebral blood flow (CBF) to ischaemic penumbra because it can cause vasoconstriction. We addressed these issues using real-time two-dimensional multispectral reflectance imaging and laser speckle flowmetry to simultaneously and non-invasively determine the impact of normobaric hyperoxia on CBF and oxygenation in ischaemic cortex. Ischaemia was induced by distal middle cerebral artery occlusion (dMCAO) in normoxic (30% inhaled O2, arterial pO2 134 +/- 9 mmHg), or hyperoxic mice (100% inhaled O2 starting 15 min after dMCAO, arterial pO2 312 +/- 10 mmHg). Post-ischaemic normobaric hyperoxia caused an immediate and progressive increase in oxyhaemoglobin (oxyHb) concentration, nearly doubling it in ischaemic core within 60 min. In addition, hyperoxia improved CBF so that the area of cortex with < or =20% residual CBF was decreased by 45% 60 min after dMCAO. Furthermore, hyperoxia reduced the frequency of peri-infarct depolarizations (PIDs) by more than 60%, and diminished their deleterious effects on CBF and metabolic load. Consistent with these findings, infarct size was reduced by 45% in the hyperoxia group 2 days after 75 min transient dMCAO. Our data show that normobaric hyperoxia increases tissue O2 delivery, and that novel mechanisms such as CBF augmentation, and suppression of PIDs may afford neuroprotection during hyperoxia.

title: Correlation between peri-infarct DC shifts and ischaemic neuronal damage in rat.
abstract: The effect of peri-infarct depolarizations on ischaemic injury was studied in rats submitted to 3 h occlusion of the left middle cerebral artery (MCA). The number of depolarizations varied from 1 to 8 and infarct volume from 37 to 159 mm3. The correlation between the two variables revealed a highly significant linear relationship (r = 0.800; p < 0.005), each depolarization accounting for an increase in infarct volume by about 13 mm3. The aggravating effect of repeated depolarizations was also demonstrated by the gradual increase in cortical DC shift duration, in EEG amplitude recovery time, and in EEG delta power with increasing number of depolarizations. Suppression of peri-infarct depolarizations is a rational approach for reducing the severity of ischaemic stroke.

title: Correlation between tissue depolarizations and damage in focal ischemic rat brain
 1
 Published on the World Wide Web on 12 July 1999.
 
 
 1
 

abstract: Ischemia-induced depolarizations may play a key role in the development of cerebral ischemic injury. Our goal was to assess the relationship between tissue depolarizations and tissue damage in focal ischemia. We performed multi-electrode cortical direct current (DC) potential recording and, subsequently, diffusion-weighted and T(2)-weighted magnetic resonance imaging (MRI) in rats after i) cortical application of KCl, and ii) permanent and transient middle cerebral artery (MCA)-occlusion in rats. Cortical KCl application induced 10.0+/-2.2 transient negative DC potential shifts per h on the ipsilateral hemisphere (i.e. cortical spreading depressions) (n=4). During 6 h of permanent MCA-occlusion (n=9) 1-10 DC potential shifts were observed, dependent on the brain location. Anoxic depolarization developed in the ischemic core. Outside ischemic areas DC potential shifts resembled cortical spreading depressions. Depolarizations in cortical ischemic borderzones were also transient, but generally long-lasting. Reperfusion induced 1 (n=5) or 3 h (n=6) after MCA-occlusion resulted in repolarization in 2.9+/-1.5 min. Ischemic lesion volumes after 7 h, calculated from diffusion-weighted and T(2)-weighted MR images, correlated significantly with total depolarization time in cortical perifocal zones (R=0.741, p<0.05), but not with the number of depolarizations. The extent of ischemic damage, as measured from alterations in the water diffusion coefficient and T(2), was also significantly related to the total time of depolarization (R=0.762 and 0.738, respectively, p<0.01). We conclude that early ischemic tissue injury is related to the total duration of tissue depolarization and not to the frequency of depolarizations.

title: Induction of Spreading Depression in the Ischemic Hemisphere following Experimental Middle Cerebral Artery Occlusion: Effect on Infarct Morphology
abstract: This study was undertaken to test whether transient depolarizations occurring in periinfarct regions are important in contributing to infarct spread and maturation. Following middle cerebral artery (MCA) occlusion we stimulated the ischemic penumbra with recurrent waves of spreading depression (SD) and correlated the histopathological changes with the electrophysiological recordings. Halothane-anesthetized, artificially ventilated Sprague–Dawley rats underwent repetitive stimulation of SD in intact brain (Group 1; n = 8) or photothrombotic MCA occlusion coupled with ipsilateral common carotid artery occlusion (Groups 2 and 3, n = 9 each). The electroencephalogram and direct current (DC) potential were recorded for 3 h in the parietal cortex, which represented the periinfarct border zone in ischemic rats. In Group 2, only spontaneously occurring negative DC shifts occurred; in Group 3, the (nonischemic) frontal pole of the ischemic hemisphere was electrically stimulated to increase the frequency of periinfarct DC shifts. Animals underwent perfusion-fixation 24 h later, and volumes of complete infarction and scattered neuronal injury (“incomplete infarction”) were assessed on stained coronal sections by quantitative planimetry. Electrical induction of SD in Group 1 did not cause morphological injury. During the initial 3 h following MCA occlusion, the number of spontaneous periinfarct depolarizations in Group 2 (7.0 ±1.5 DC shifts) was doubled in Group 3 by frontal current application (13.4 ± 2.7 DC shifts; p < 0.001). The duration as well as the integrated negative amplitude of DC shifts over time were significantly greater in Group 3 than in Group 2 rats (duration, 5.7 ± 3.8 vs. 4.1 ± 2.5 min; p < 0.05). Histopathological examination disclosed well-defined areas of pannecrosis surrounded by a cortical rim exhibiting selectively damaged acidophilic neurons and astrocytic swelling in otherwise normal-appearing brain. Induction of SD in the ischemic hemisphere led to a significant increase in the volume of incomplete infarction (19.0 ± 6.1 mm3 in Group 3 vs. 10.3 ± 5.1 mm3 in Group 2; p < 0.01) and of total ischemic injury (100.7 ± 41.0 mm3 in Group 3 vs. 66.5 ± 24.7 mm3 in Group 2; p < 0.05). The integrated magnitude of DC negativity per experiment correlated significantly with the volume of total ischemic injury (r = 0.780, p < 0.0001). Thus, induction of SD in the ischemic hemisphere accentuated the development of scattered neuronal injury and increased the volume of total ischemic injury. This observation may be explained by the fact that, with limited perfusion reserve, periinfarct depolarizations are associated with episodic energy failure in the acute ischemic penumbra.

title: The Effect of MK-801 on Cortical Spreading Depression in the Penumbral Zone following Focal Ischaemia in the Rat
abstract: Cortical spreading depression (CSD) is a transient depression of neuronal activity that spreads across the cortical surface. In the present studies, we have investigated CSD activity in the penumbral zone following permanent middle cerebral artery (MCA) occlusion in the rat (n = 16/group), using double-barreled Ca2+ -sensitive microelectrodes. Measurements of CSD activity were made for 3 h in each animal. During this time, a varying number of spontaneous CSDs were seen in the control group (total was 30, with a range of 0–7/rat). These CSDs were of varying duration: “small” (∼1 min) and “big” (5–45 min) CSDs. During a CSD, the extracellular [Ca2+] decreased to 0.11 ± 0.07 mM (mean ± SD). After 3 h, the extracellular [Ca2+] in the cortex (penumbral zone) was either normal (10/16 rats) or lowered to 0.5 mM (2/16 rats) or to 0.1 mM (4/16 rats). In the caudate nucleus (ischaemic core area), all rats had an extracellular [Ca2+] of ∼0.1 mM when measured after the 3 h recording period. Neuropathological evaluation of the brains of the animals, which had been allowed to survive for 24 h after MCA occlusion, revealed ischaemic damage in the dorsolateral cortex and caudate nucleus. Administration of the noncompetitive NMDA antagonist, MK-801 (3 mg/kg i.p.), 30 min after MCA occlusion resulted in 24 and 29% reductions in the volume of hemispheric and cortical damage, respectively, which was highly significant (p < 0.0001); no protection was seen against caudate damage. MK-801 also significantly (p < 0.05) reduced the number of CSDs (total was 10 with a range of 0–2/rat) and the degree of decrease in extracellular [Ca2+] during CSDs (low level was 0.19 ± 0.15 mM, mean ± SD). Both the number of “small CSDs” and significantly the “big CSDs” were reduced by MK-801. The “small CSDs” were present in the border zone and also deeper within the infarct, whereas “big CSDs” and anoxic depolarisations only occurred closer to the infarct core. CSDs were not seen outside the border zone of the infarct. In conclusion, there was a good correlation between extracellular [Ca2+] changes and ischaemic damage in the infarcted region following MCA occlusion. MK-801 reduced the ischaemic damage in the penumbral zone in parallel with attentuation of the number and amplitude of CSDs and thereby a reduced intracellular Ca2+ overload.

title: Repeated Negative DC Deflections in Rat Cortex following Middle Cerebral Artery Occlusion are Abolished by MK-801: Effect on Volume of Ischemic Injury
abstract: Following permanent occlusion of the left middle cerebral artery (MCA) in rats, electrophysiological and hemodynamic characteristics of the periinfarct border zone were investigated in sham-operated (n = 6), untreated (n = 6), and MK-801-treated (3.0 mg/kg; n = 6) animals. For this purpose, direct current potential (DC), EEG, and blood flow (laser-Doppler flowmetry) were recorded from the cortex in the periphery of the MCA territory. In sham-operated rats, a single negative cortical DC deflection was observed after electrocoagulation of the cortex, whereas in untreated MCA-occluded animals, three to eight transient DC deflections were monitored during the initial 3 h of ischemia. The duration of these cortical DC shifts gradually increased from 1.2 ± 0.3 to 3.7 ± 2.7 min (mean ± SD; p < 0.05) during this time. In animals treated intraperitoneally with MK-801 (3.0 mg/kg) immediately after MCA occlusion, the number of cortical DC shifts significantly declined to one to three deflections (p < 0.005). The EEG of the treated animals revealed low-amplitude burst-suppression activity. In the untreated and treated experimental group, the reduction of cortical blood flow amounted to 69 ± 25 and 49 ± 13% of control, respectively. Despite the more pronounced cortical oligemia, MK-801 treatment resulted in a significant decrease of the volume of the ischemically injured tissue from 108 ± 38.5 (untreated group) to 58 ± 11.5 (p < 0.05) mm3. Our results suggest that repetitive cortical DC deflections in the periinfarct border zone contribute to the expansion of ischemic brain infarcts.

title: Vasoconstrictive Neurovascular Coupling during Focal Ischemic Depolarizations
abstract: Ischemic depolarizing events, such as repetitive spontaneous periinfarct spreading depolarizations (PIDs), expand the infarct size after experimental middle cerebral artery (MCA) occlusion. This worsening may result from increased metabolic demand, exacerbating the mismatch between cerebral blood flow (CBF) and metabolism. Here, we present data showing that anoxic depolarization (AD) and PIDs caused vasoconstriction and abruptly reduced CBF in the ischemic cortex in a distal MCA occlusion model in mice. This reduction in CBF during AD increased the area of cortex with 20% or less residual CBF by 140%. With each subsequent PID, this area expanded by an additional 19%. Drugs that are known to inhibit cortical spreading depression (CSD), such as N-methyl-D-aspartate receptor antagonists MK-801 and 7-chlorokynurenic acid, and σ-1 receptor agonists dextromethorphan and carbetapentane, did not reduce the frequency of PIDs, but did diminish the severity of episodic hypoperfusions, and prevented the expansion of severely hypoperfused cortex, thus improving CBF during 90 mins of acute focal ischemia. In contrast, AMPA receptor antagonist NBQX, which does not inhibit CSD, did not impact the deterioration in CBF. When measured 24 h after distal MCA occlusion, infarct size was reduced by MK-801, but not by NBQX. Our results suggest that AD and PIDs expand the CBF deficit, and by so doing negatively impact lesion development in ischemic mouse brain. Mitigating the vasoconstrictive neurovascular coupling during intense ischemic depolarizations may provide a novel hemodynamic mechanism of neuroprotection by inhibitors of CSD.

title: Impact of aging on spreading depolarizations induced by focal brain ischemia in rats
abstract: Spreading depolarization (SD) contributes to the ischemic damage of the penumbra. Although age is the largest predictor of stroke, no studies have examined age dependence of SD appearance. We characterized the electrophysiological and hemodynamic changes in young (6 weeks old, n = 7), middle-aged (9 months old, n = 6), and old (2 years old, n = 7) male Wistar rats during 30 minutes of middle cerebral artery occlusion (MCAO), utilizing multimodal imaging through a closed cranial window over the ischemic cortex: membrane potential changes (with a voltage-sensitive dye), cerebral blood volume (green light reflectance), and cerebral blood flow (CBF, laser-speckle imaging) were observed. The initial CBF drop was similar in all groups, with a significant further reduction during ischemia in old rats (p < 0.01). Age reduced the total number of SDs (p < 0.05) but increased the size of ischemic area displaying prolonged SD (p < 0.01). The growth of area undergoing prolonged SDs positively correlated with the growth of ischemic core area (p < 0.01) during MCAO. Prolonged SDs and associated hypoperfusion likely compromise cortical tissue exposed to even a short focal ischemia in aged rats.

title: Dynamic perfusion and diffusion MRI of cortical spreading depolarization in photothrombotic ischemia
abstract: Cortical spreading depolarization (CSD) is known to exacerbate ischemic damage, as the number of CSDs correlates with the final infarct volumes and suppressing CSDs improves functional outcomes. To investigate the role of CSD in ischemic damage, we developed a novel rat model of photothrombotic ischemia using a miniature implantable optic fiber that allows lesion induction inside the magnetic resonance imaging (MRI) scanner. We were able to precisely control the location and the size of the ischemic lesion, and continuously monitor dynamic perfusion and diffusion MRI signal changes at high temporal resolution before, during and after the onset of focal ischemia. Our model showed that apparent diffusion coefficient (ADC) and cerebral blood flow (CBF) in the ischemic core dropped immediately after lesion onset by 20±6 and 41±23%, respectively, and continually declined over the next 5h. Meanwhile, CSDs were observed in all animals (n=36) and displayed either a transient decrease of ADC by 17±3% or an increase of CBF by 104±15%. All CSDs were initiated from the rim of the ischemic core, propagated outward, and confined to the ipsilesional cortex. Additionally, we demonstrated that by controlling the size of perfusion-diffusion mismatch (which approximates the penumbra) in our model, the number of CSDs correlated with the mismatch area rather than the final infarct volume. This study introduces a novel platform to study CSDs in real-time with high reproducibility using MRI.

title: Distinct Spatiotemporal Patterns of Spreading Depolarizations during Early Infarct Evolution: Evidence from Real-Time Imaging
abstract: Experimental and clinical studies indicate that waves of cortical spreading depolarization (CSD) appearing in the ischemic penumbra contribute to secondary lesion growth. We used an embolic stroke model that enabled us to investigate inverse coupling of blood flow by laser speckle imaging (CBFLSF) to CSD as a contributing factor to lesion growth already in the early phase after arterial occlusion. Embolization by macrospheres injected into the left carotid artery of anesthetized rats reduced CBFLSF in the territories of the middle cerebral artery (MCA) (8/14 animals), the posterior cerebral artery (PCA) (2/14) or in less clearly defined regions (4/14). Analysis of MCA occlusions (MCAOs) revealed a first CSD wave starting off during ischemic decline at the emerging core region, propagating concentrically over large portions of left cortex. Subsequent recurrent waves of CSD did not propagate concentrically but preferentially circled around the ischemic core. In the vicinity of the core region, CSDs were coupled to waves of predominantly vasoconstrictive CBFLSF responses, resulting in further decline of CBF in the entire inner penumbra and in expansion of the ischemic core. We conclude that CSDs and corresponding CBF responses follow a defined spatiotemporal order, and contribute to early evolution of ischemic territories.

title: Characterization of periinfarct flow transients with laser speckle and Doppler after middle cerebral artery occlusion in the rat
abstract: Little information exists on the role and the characteristics of perfusion changes related to periinfarct depolarization. Our aim was to visualize and monitor periinfarct flow transients (PIFTs) in Sprague‐Dawley rats (n = 10) with two different laser methods in a closed‐skull model of filament middle cerebral artery occlusion. A laser Doppler probe was placed over the ischemic cortex 5 mm lateral to Bregma, and a 5 × 5 mm area centered 5 mm posterior and 4 mm lateral to Bregma was thinned for laser speckle imaging. Both neurological and histological evaluations were performed at 72 hr postinjury. Mean flow during 90‐min ischemia was 29% of baseline measured by laser Doppler and 36–54% by laser speckle. Flow transients occurred in all rats, the number of PIFTs being 4.6 ± 1.8/90 min. By both methods, 95.6% of them occurred with temporal correlation. The average duration of PIFTs was also identical (162 ± 24 and 162 ± 34 sec, respectively). Five different morphologies of flow transients ranging from hypoperfusive to hyperemic were identified by laser speckle. The PIFTs changed their morphology dynamically over certain regions. All of the animals showed an infarct (178.5 ± 26 mm3) in the middle cerebral artery territory. Laser Doppler in itself can be a reliable method for counting/detecting PIFTs, but laser speckle is capable of monitoring the dynamic changes in PIFT morphology over the penumbral and periischemic cortex.

title: Peri-infarct depolarizations lead to loss of perfusion in ischaemic gyrencephalic cerebral cortex.
abstract: In the light of accumulating evidence for the occurrence of spontaneous cortical spreading depression and peri-infarct depolarizations in the human brain injured by trauma or aneurysmal subarachnoid haemorrhage, we used DC electrode recording and laser speckle imaging to study the relationship between depolarization events and perfusion in the ischaemic, gyrencephalic brain. In 14 adult male cats anaesthetized with chloralose, one cerebral hemisphere was exposed and the middle cerebral artery occluded. Surface cortical perfusion in core and penumbral territories was imaged semiquantitatively at intervals of 13 s for 4 h. Cortical surface DC potential was recorded. Time interval between changes in DC potential and in perfusion was examined, and this comparison was repeated using microelectrodes for DC potential in five similar experiments in a second laboratory. Mean pre-occlusion perfusion was 11707 +/- 4581 units (equivalent to CBF (cerebral blood flow) approximately 40.5 +/- SD 14.4 ml/100 g/min), and fell on occlusion to 5318 +/- 2916 (CBF approximately 17.1 +/- 8.3), 5291 +/- 3407 (CBF approximately 17.0 +/- 10.1), and 6711 +/- 3271 (CBF approximately 22.2 +/- 9.6), quickly recovering to 8704 +/- 4581 (CBF approximately 29.5 +/- 14.4), 9741 +/- 4499 (CBF approximately 33.3 +/- 14.1) and 10 314 +/- 3762 (CBF approximately 35.4 +/- 11.4) on the core, intermediate and outer penumbral gyri, respectively. Mean perfusion later fell secondarily on core and intermediate gyri but, overall, was preserved on the outer (upper level of perfusion) gyrus during the period of observation. Pattern and severity of transient changes in perfusion associated with depolarization events varied with gyral location; falls in perfusion were sometimes profound and irreversible, and followed rather than preceded depolarization. In this model of occlusive stroke, reductions in perfusion linked to peri-infarct depolarization events contribute to secondary deterioration in penumbral areas. The findings suggest that such events play a central rather than a subsidiary role in cerebral infarction in the gyrencephalic brain.

title: Metabolic and Perfusion Responses to Recurrent Peri-Infarct Depolarization during Focal Ischemia in the Spontaneously Hypertensive Rat: Dominant Contribution of Sporadic CBF Decrements to Infarct Expansion
abstract: Peri-infarct depolarizations (PIDs) contribute to the evolution of focal ischemic lesions. Proposed mechanisms include both increased metabolic demand under conditions of attenuated perfusion and overt vasoconstrictive responses to depolarization. The present studies investigated the relative contributions of metabolic and perfusion effects to PID-associated infarct expansion during middle cerebral artery (MCA) occlusion in the Spontaneously Hypertensive Rat. The initial distribution of ischemic depolarization (ID) was established within minutes after MCA occlusion at a cerebral blood flow threshold of ∼40 mL/100 g per minute, with expansion of the depolarized territory during 3hours detected in half of the animals. Peri-infarct depolarizations were associated with transient metabolic responses, comparable to those observed after spreading depression, with no evidence of cumulative energy failure after multiple transient depolarizations during 1 hour. Speckle contrast imaging of PID-associated flow transients documented prominent distal hyperemic flow responses that became progressively attenuated in regions of already impaired perfusion, with modest propagated flow decreases more proximal to the ischemic core. However, sporadic PIDs were associated with persistent decrements in perfusion, increasing tissue volume below the threshold for energy failure, ID and infarction. These latter, comparatively rare, events can account for the pattern of stepwise infarct expansion in this model.

title: Noninvasive near Infrared Spectroscopy Monitoring of Regional Cerebral Blood Oxygenation Changes during Peri-Infarct Depolarizations in Focal Cerebral Ischemia in the Rat
abstract: Intermittent peri-infarct depolarizations (PID), which spread from the vicinity of the infarction over the cortex, have been reported in focal ischemia. These depolarizations resemble cortical spreading depression except that they damage the cortex and enlarge the infarct volume possibly because of compromised oxygen delivery. The main purpose of this study was to evaluate the noninvasive technique of near-infrared spectroscopy (NIRS) for the identification of PID and to evaluate its capability for further pathophysiological studies. We used male barbiturate-anesthetized Wistar rats (n = 10) in which middle cerebral artery occlusion had been performed with a surgical thread. Middle cerebral artery occlusion resulted in a drop in parietally measured regional cerebral blood flow (laser Doppler flowmetry) to 31 ± 8% of baseline flow. Six ± 4 minutes after the induction of focal ischemia, 5 ± 2 direct current deflections were recorded during a one-hour measurement period which may be regarded as PID. Measuring regional cerebral blood oxygenation changes with a NIRO 500 revealed dynamic concentration changes in the three chromophores oxyhemoglobin [HbO2], deoxyhemoglobin [Hb], and the oxidized form of cytochrome aa3 [CytO] during PID. Typically, an initial slight decrease of [HbO2] (−6.1 ± 1.7 arbitrary units [AU]) and an increase of [Hb] (+1 1.5 ± 7.7 AU) were followed by an increase of [HbO2] (+10.8 ± 4.7 AU) and a decrease of [Hb] (−4.7 ± 5.5 AU); [CytO] decreased during the depolarizations (−2.0 ± 1.2 AU). We conclude that NIRS can detect typical PID-associated changes in blood oxygenation. We hypothesize that during the course of PID, unlike “normal” spreading depression, hypoxygenation precedes hyperoxygenation of the microcirculation in a given cortex volume as the depolarization wave propagates through hemodynamically compromised to intact tissue. This would accord with the known damaging effect of PID. The NIRS “fingerprint” of PID encourages the search for PID during early stroke in patients.

title: Normobaric hyperoxia improves cerebral blood flow and oxygenation, and inhibits peri-infarct depolarizations in experimental focal ischaemia.
abstract: Normobaric hyperoxia is under investigation as a treatment for acute ischaemic stroke. In experimental models, normobaric hyperoxia reduces cerebral ischaemic injury and improves functional outcome. The mechanisms of neuroprotection are still debated because, (i) inhalation of 100% O2 does not significantly increase total blood O2 content; (ii) it is not known whether normobaric hyperoxia increases O2 delivery to the severely ischaemic cortex because of its short diffusion distance; and (iii) hyperoxia may reduce collateral cerebral blood flow (CBF) to ischaemic penumbra because it can cause vasoconstriction. We addressed these issues using real-time two-dimensional multispectral reflectance imaging and laser speckle flowmetry to simultaneously and non-invasively determine the impact of normobaric hyperoxia on CBF and oxygenation in ischaemic cortex. Ischaemia was induced by distal middle cerebral artery occlusion (dMCAO) in normoxic (30% inhaled O2, arterial pO2 134 +/- 9 mmHg), or hyperoxic mice (100% inhaled O2 starting 15 min after dMCAO, arterial pO2 312 +/- 10 mmHg). Post-ischaemic normobaric hyperoxia caused an immediate and progressive increase in oxyhaemoglobin (oxyHb) concentration, nearly doubling it in ischaemic core within 60 min. In addition, hyperoxia improved CBF so that the area of cortex with < or =20% residual CBF was decreased by 45% 60 min after dMCAO. Furthermore, hyperoxia reduced the frequency of peri-infarct depolarizations (PIDs) by more than 60%, and diminished their deleterious effects on CBF and metabolic load. Consistent with these findings, infarct size was reduced by 45% in the hyperoxia group 2 days after 75 min transient dMCAO. Our data show that normobaric hyperoxia increases tissue O2 delivery, and that novel mechanisms such as CBF augmentation, and suppression of PIDs may afford neuroprotection during hyperoxia.

title: Effect of the NMDA Antagonist MK-801 on Local Cerebral Blood Flow in Focal Cerebral Ischaemia in the Rat
abstract: The effects of MK-801 upon local CBF after permanent middle cerebral artery (MCA) occlusion have been examined using [14C]iodoantipyrine autoradiography in halothane-anaesthetised rats. MK-801 (0.5 mg kg-1 i.v.) or saline was administered 30 min before MCA occlusion and CBF measured ∼40 min after occlusion. In the hemisphere contralateral to the occluded MCA, MK-801 significantly reduced local CBF in 19 of the 22 regions examined from the levels in saline-treated rats. In the contralateral hemisphere, after treatment with MK-801, blood flow was reduced by an average of 37% with little variation in the magnitude of the reductions in different regions. In the hemisphere ipsilateral to MCA occlusion, MK-801 reduced CBF in almost every region located outside the territory of the occluded MCA. Within the territory of the occluded MCA, blood flow in the MK-801–treated rat did not significantly differ from values in vehicle-treated rats in any of the five cortical areas examined, although in the caudate nucleus there was a tendency for CBF to be lower in rats pretreated with MK-801. MK-801 had no effect on the amount of hypoperfused cerebral tissue (CBF <30 ml 100 g−1 min−1) in the ipsilateral hemisphere at any coronal plane examined; e.g., at coronal plane anterior 7.2 mm, 51 ± 5% of the hemisphere displayed CBF of <30 ml 100 g−1 min−1 in saline-treated rats with MCA occlusion compared with 52 ± 8% of the hemisphere in rats treated with MK-801 prior to MCA occlusion. Thus, the reported antiischaemic effects of MK-801 in this model cannot be attributed to improvement of blood flow to the hypoperfused cerebral tissue.

title: Extracellular potassium and blood flow in the post-ischemic rat brain
abstract: The concentration of extracellular potassium, [K+]e, was measured in parietal cortex and basal ganglia of rats during and after ten minutes of complete cerebral ischemia. The post-ischemic normalization of [K+]e was considerably delayed in parietal cortex compared to basal ganglia, but in both regions, [K+]e reached its normal concentration within 4 min of the end of the ischemia. Also, in both regions blood flow was elevated at the time of maximal [K+]3 decrease. Our findings suggest that the normalization of [K+]e and cerebrovascular resistance after ischemia are related by positive feed-back, possibly via the stimulation of Na+−K+-ATPase.

title: Cerebrovascular resistance in ischemia
abstract: The cerebrovascular resistance (CVR) of rat, and its dependence on stagnant blood or endothelial capillary swelling, was studied after 10 min of total ischemia by 10 s single carotid infusion of [14C]butanol in saline. The regional saline flow (CPR) was calculated from the uptake of [14C]butanol. CVR was estimated at infusion pressures ranging from 8–25 kPa (60–190 mm Hg).At 14.7 kPa (110 mm Hg) infusion pressure, the regional CVR of the non-ischemic group varied between 0.21 and 0.40 kPa 100 g min ml−1. After 10 min of complete global cerebral ischemia, it increased to values between 0.82 and 1.95.Removal of blood from the brain by rinsing prior to ischemia did not change the CVR in ischemia. Increasing the plasma osmolality by 8% with mannitol before ischemia attenuated the CVR increase in ischemia. Thus, although osmotic swelling of endothelial cells contributed, the main cause of the CVR increase in ischemia was constriction of arterioles.

title: No-flow state following cerebral ischemia. Role of increase in potassium concentration in brain interstitial fluid.
abstract: Rats were subjected to total cerebral ischemia by occluding outflow from the heart. In control experiments and following different periods of ischemia, potassium concentration was measured in cisternal cerebrospinal fluid (CSF). It rose to 19.4 mEq/liter following 16 minutes of ischemia. Changes in cerebrovascular resistance (CVR) were also assessed by measuring the cerebral perfusion rate (CPR). Following two minutes of ischemia, CVR was decreased to half control value. After 8 and 16 minutes of ischemia, CVR was markedly increased, and "no-flow" state was approached after 16 minutes of ischemia. The CVR increased concomitantly with increase in potassium concentration in cisternal CSF. We suggest that the increase in CVR following cerebral ischemia is due to increase in potassium concentration in brain extracellular fluid and is part of a vicious circle that leads to brain death.

title: Hyperacute stroke: simultaneous measurement of relative cerebral blood volume, relative cerebral blood flow, and mean tissue transit time.
abstract: To investigate additional information provided by maps of relative cerebral blood flow in functional magnetic resonance (MR) imaging of human hyperacute cerebral ischemic stroke.



Diffusion-weighted and hemodynamic MR imaging were performed in 23 patients less than 12 hours after the onset of symptoms. Maps of relative cerebral blood flow and tracer mean tissue transit time were computed, as were maps of apparent diffusion and relative cerebral blood volume. Acute lesion volumes on the maps were compared with follow-up imaging findings.



In 15 of 23 subjects (65%), blood flow maps revealed hemodynamic abnormalities not visible on blood volume maps. A mismatch between initial blood flow and diffusion findings predicted growth of infarct more often (12 of 15 subjects with infarcts that grew) than did a mismatch between initial blood volume and diffusion findings (eight of 15). However, lesion volumes on blood volume and diffusion maps correlated better with eventual infarct volumes (r > 0.90) than did those on blood flow and tracer mean transit time maps (r approximately 0.6), likely as a result of threshold effects. In eight patients, blood volume was elevated around the diffusion abnormality, suggesting a compensatory hemodynamic response.



MR imaging can delineate areas of altered blood flow, blood volume, and water mobility in hyperacute human stroke. Predictive models of tissue outcome may benefit by including computation of both relative cerebral blood flow and blood volume.

title: Relationships between glutamate release, blood flow and spreading depression: real-time monitoring using an electroenzymatic dialysis electrode
abstract: Spreading depression (SD) in a flow-restricted area of the brain may be prolonged and may become potentially harmful by releasing glutamate. We induced SD in an oligemia model and examined the subsequent glutamate release. In 18 anesthetized male Fischer rats, a laser Doppler flowmeter, an electroenzymatic electrode for continuous measurement of glutamate, and a calomel electrode for measuring DC potential were placed through a cranial window positioned 3 mm away from a second window where KCl-soaked cotton was placed to initiate SD. The left carotid artery or both the common carotid arteries were ligated to suppress reactive hyperemia of SD. SD produced an increase in glutamate from 24.8 +/- 13.8 to 33.5 +/- 25.3 microM (peak value) (P < 0.0001). After ligation of both carotid arteries, the duration of SD increased from 1.5 +/- 0.6 min (before ligation) to 6.4 +/- 5.1 min (P < 0.05). Glutamate reached a peak level of 63.9 +/- 72.3 microM, then quickly returned to the control value. However, there was no positive correlation between the duration of SD and glutamate concentration. It is concluded that prolonged SD is not accompanied by a progressive increase in glutamate. Therefore, glutamate release induced by SD may not exert harmful effects on neurons.

title: Effects of Cortical Spreading Depression on Cortical Blood Flow, Impedance, DC Potential, and Infarct Size in a Rat Venous Infarct Model
abstract: A cortical venous infarction model has been evaluated as to the degree of regional flow reduction and by studying effects of cortical spreading depression (CSD). Two adjacent cortical veins were occluded photochemically with rose bengal and fiberoptic illumination. Seven rats served to demonstrate effects on regional cortical blood flow using laser Doppler scanning. In 36 rats local CBF, DC potential, and brain tissue impedance were measured continuously for 75 min after vein occlusion. No, 3, or 10 CSD waves were induced by potassium chloride injection during the initial 75 min. Rats were compared for spontaneous CSDs; baseline local CBF, CBF, and impedance response to CSD; and infarct volume. Seventy-five minutes after vein occlusion regional cortical flow in a 3.5x7-mm window was reduced to 34.3+/-13.2%. At 45% of the 840 measured locations in 7 rats flow was <40% baseline and at 27.3% <30%, indicating a widespread penumbra territory. During the initial 75 min 2.1+/-1.1 spontaneous CSDs were observed. There was a positive correlation between the number of spontaneous CSDs seen acutely and infarction volume after 5 days. Moreover, brain injury was significantly increased in the group with 10 KCl-induced CSDs. A reduced 1CBF response and an overshooting tissue impedance change during CSD were predictors of ischemic damage. This study demonstrates a CSD-related growth of the venous infarct. Second, the data indicate that flow after two-vein occlusion resembles that seen under penumbra conditions, allowing for studies of damage mechanisms responsible for infarct growth.

title: Products of hemolysis in the subarachnoid space inducing spreading ischemia in the cortex and focal necrosis in rats: a model for delayed ischemic neurological deficits after subarachnoid hemorrhage?
abstract: OBJECT
The pathogenesis of delayed ischemic neurological deficits after subarachnoid hemorrhage has been related to products of hemolysis. Topical brain superfusion of artificial cerebrospinal fluid (ACSF) containing the hemolysis products K+ and hemoglobin (Hb) was previously shown to induce ischemia in rats. Superimposed on a slow vasospastic reaction, the ischemic events represent spreading depolarizations of the neuronal-glial network that trigger acute vasoconstriction. The purpose of the present study was to investigate whether such spreading ischemias in the cortex lead to brain damage.



A cranial window was implanted in 31 rats. Cerebral blood flow (CBF) was measured using laser Doppler flowmetry, and direct current (DC) potentials were recorded. The ACSF was superfused topically over the brain. Rats were assigned to five groups representing different ACSF compositions. Analyses included classic histochemical and immunohistochemical studies (glial fibrillary acidic protein and ionized calcium binding adaptor molecule) as well as a terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay. Superfusion of ACSF containing Hb combined with either a high concentration of K+ (35 mmol/L, 16 animals) or a low concentration of glucose (0.8 mmol/L, four animals) reduced CBF gradually. Spreading ischemia in the cortex appeared when CBF reached 40 to 70% compared with baseline (which was deemed 100%). This spreading ischemia was characterized by a sharp negative shift in DC, which preceded a steep CBF decrease that was followed by a slow recovery (average duration 60 minutes). In 12 of the surviving 14 animals widespread cortical infarction was observed at the site of the cranial window and neighboring areas in contrast to findings in the three control groups (11 animals).



The authors conclude that subarachnoid Hb combined with either a high K+ or a low glucose concentration leads to widespread necrosis of the cortex.

title: Ischemia triggered by spreading neuronal activation is induced by endothelin‐1 and hemoglobin in the subarachnoid space
abstract: Delayed cerebral vasospasm has a major impact on the outcome of subarachnoid hemorrhage. Two important candidates to cause the arterial spasm are the red blood cell product oxyhemoglobin and the vasoconstrictor endothelin‐1, although oxyhemoglobin alone is not sufficient to induce cerebral ischemia and endothelin‐1 leads to ischemia only at relatively high concentrations. In this study, we demonstrated that the combination of oxyhemoglobin and endothelin‐1 triggered spreading neuronal activation in rat cortex in vivo. In contrast with the expected transient increase of regional cerebral blood flow during spreading depression, however, cerebral blood flow decreased profoundly and was long‐lasting, paralleled by delayed repolarization of the steady (direct current) potential. These changes are characteristic of cortical spreading ischemia. Replacing oxyhemoglobin for the nitric oxide synthase inhibitor Nω‐nitro‐L‐arginine mimicked these effects, implicating nitric oxide scavenging functions of oxyhemoglobin. Furthermore, the effect of endothelin‐1 was related to a reduction of Na+‐/K+‐ATPase activity rather than solely to its vasoconstrictive properties. In conclusion, the threshold concentration of endothelin‐1 that induces cerebral ischemia is profoundly reduced via a complex interaction between the neuronal/astroglial network and the cortical microcirculation if nitric oxide availability declines. The results may have implications for the understanding of subarachnoid hemorrhage–related cortical lesions.

title: Partial antagonistic effect of adenosine on inverse coupling between spreading neuronal activation and cerebral blood flow in rats
abstract: Fundamental principles in the central nervous system are that primary depolarization of neurons causes hyperemia, whereas focal cerebral ischemia causes secondary neuronal depolarization. In rats, an exception to these rules was discovered recently in which primary neuronal depolarization led to focal cerebral ischemia via inverse coupling between neuronal metabolism and cerebral blood flow (CBF). Adenosine is one of the classical candidate factors to mediate the coupling between neuronal metabolism and CBF. Therefore, the effect of topically applied adenosine on cortical spreading ischemia was studied. A cranial window was implanted in 10 rats. At the window, CBF (laser Doppler flowmetry) and the subarachnoid direct current potential were recorded; the cortical surface was superfused with artificial cerebrospinal fluid (ACSF). A spreading neuronal/astroglial depolarization wave was triggered at a remote site, from which it propagated to the cranial window. In all rats, the depolarization wave triggered a hyperemic event under physiological conditions. When ACSF containing the nitric oxide (NO)-synthase inhibitor NG-nitro-l-arginine (l-NNA) at 10−3M and K+ at 20×10−3M was subsequently superfused, the depolarization wave triggered an ischemic event. In 5 of 10 animals, a second depolarization wave under l-NNA and elevated K+ also triggered an ischemic event. In contrast, in the remaining five animals, the depolarization wave triggered a significantly smaller and shorter hypoperfusion when adenosine at 100 µM was coapplied with l-NNA and elevated K+.Conclusion: The results of this study suggest that adenosine, like other vasodilators, is unable to antagonize the initial hypoperfusion in response to a spreading neuronal/astroglial depolarization wave when the NO concentration is reduced and K+ is elevated but shortens the hypoperfusion phase significantly.

title: Prevention and Treatment of Delayed Ischemic Dysfunction in Patients With Aneurysmal Subarachnoid Hemorrhage
abstract: Subarachnoid hemorrhage (SAH) is a rare, life-threatening condition that is caused by the rupture of an intracranial aneurysm in approximately two thirds of the cases. These aneurysms are small outpouchings from the cerebral arteries on the base of the brain that develop during a lifetime and rarely give rise to any signs or symptoms until they rupture "like a bolt from the blue." In many cases, the hemorrhage is so severe that the patient dies immediately. In other cases, the bleeding results in focal signs such as hemiparesis, aphasia, or disturbances of consciousness. Patients who recover from the initial effect of the bleed often deteriorate secondarily a few days later because of arterial narrowing associated with delayed ischemic dysfunction. The incidence of angiographic vasospasm has been reported to be as high as 50-70% with 20-30% of these patients developing clinical ischemic symptoms ("symptomatic vasospasm"), and approximately 15% of patients dying or becoming permanently disabled. The exact pathophysiology of this phenomenon has not been elucidated. Many vasoactive substances in the posthemorrhagic cerebrospinal fluid from patients with aneurysm rupture have been incriminated, including epinephrine, serotonin, prostanoids, hemoglobin, and potassium. The experimental finding that nimodipine prevents vasoconstriction of isolated animal or human cerebral arteries induced by almost all contractile agents has led to clinical studies in the prevention or treatment of delayed ischemic dysfunction. This review discusses the clinical experiences with nimodipine.

title: Inversion of neurovascular coupling by subarachnoid blood depends on large-conductance Ca2+-activated K+ (BK) channels
abstract: The cellular events that cause ischemic neurological damage following aneurysmal subarachnoid hemorrhage (SAH) have remained elusive. We report that subarachnoid blood profoundly impacts communication within the neurovascular unit—neurons, astrocytes, and arterioles—causing inversion of neurovascular coupling. Elevation of astrocytic endfoot Ca2+ to ∼400 nM by neuronal stimulation or to ∼300 nM by Ca2+ uncaging dilated parenchymal arterioles in control brain slices but caused vasoconstriction in post-SAH brain slices. Inhibition of K+ efflux via astrocytic endfoot large-conductance Ca2+-activated K+ (BK) channels prevented both neurally evoked vasodilation (control) and vasoconstriction (SAH). Consistent with the dual vasodilator/vasoconstrictor action of extracellular K+ ([K+]o), [K+]o <10 mM dilated and [K+]o >20 mM constricted isolated brain cortex parenchymal arterioles with or without SAH. Notably, elevation of external K+ to 10 mM caused vasodilation in brain slices from control animals but caused a modest constriction in brain slices from SAH model rats; this latter effect was reversed by BK channel inhibition, which restored K+-induced dilations. Importantly, the amplitude of spontaneous astrocytic Ca2+ oscillations was increased after SAH, with peak Ca2+ reaching ∼490 nM. Our data support a model in which SAH increases the amplitude of spontaneous astrocytic Ca2+ oscillations sufficiently to activate endfoot BK channels and elevate [K+]o in the restricted perivascular space. Abnormally elevated basal [K+]o combined with further K+ efflux stimulated by neuronal activity elevates [K+]o above the dilation/constriction threshold, switching the polarity of arteriolar responses to vasoconstriction. Inversion of neurovascular coupling may contribute to the decreased cerebral blood flow and development of neurological deficits that commonly follow SAH.

title: Role of Cortical Spreading Depressions for Secondary Brain Damage after Traumatic Brain Injury in Mice
abstract: In recent years, several studies have unequivocally shown the occurrence of cortical spreading depressions (CSDs) after stroke and traumatic brain injury (TBI) in humans. The fundamental question, however, is whether CSDs cause or result from secondary brain damage. The aim of the current study was, therefore, to investigate the role of CSDs for secondary brain damage in an experimental model of TBI. C57/BL6 mice were traumatized by controlled cortical impact. Immediately after trauma, each animal showed one heterogeneous direct current (DC) potential shift accompanied by a profound depression of electroencephalogram (EEG) amplitude, and a temporary decrease of ipsi- and contralateral regional cerebral blood flow (rCBF) suggesting bilateral CSDs. Within the next 3 h after TBI, CSDs occurred at a low frequency (0.38 CSD/h per animal, n = 7) and were accompanied by rCBF changes confined to the ipsilateral hemisphere. No significant relationship between the number of SDs and lesion size or intracranial pressure (ICP) could be detected. Even increasing the number of posttraumatic CSDs by application of KCl by more than six times did not increase ICP or contusion volume. We therefore conclude that CSDs may not contribute to posttraumatic secondary brain damage in the normally perfused and oxygenated brain.

title: PATTERNS OF CEREBRAL INTEGRATION INDICATED BY THE SCOTOMAS OF MIGRAINE
abstract: The scotomas characteristic of ophthalmic migraine have been described by a number of investigators.1The visual disturbance precedes or accompanies other symptoms of migraine and is usually of short duration. It is generally restricted to one half of the visual field, the right or the left, and ranges in size from a scarcely noticeable blind-spot to total hemianopia. A great variety of forms have been mentioned in the literature, but those which have been described in detail are of much the same type. The scotoma starts as a disturbance of vision limited to the neighborhood of the macula and spreads rapidly toward the temporal field. With increase in size the disturbed area moves or "drifts" across the visual field, so that its central margin withdraws from the macular region as its peripheral margin invades the temporal. Spread from the temporal toward the macular region has also been described and

title: Pathophysiology of the migraine aura. The spreading depression theory.
abstract: The characteristic form and development of sensory disturbances during migraine auras suggests that the underlying mechanism is a disturbance of the cerebral cortex, probably the cortical spreading depression (CSD) of Leão. The demonstration of unique changes of brain blood flow during attacks of migraine with aura, which have been replicated in animal experiments during CSD, constitutes another important line of support for the 'spreading depression' theory, which may be a key to an understanding of the migraine attack. Cortical spreading depression is a short-lasting depolarization wave that moves across the cortex at a rate of 3-5 mm/min. A brief phase of excitation heralds the reaction which is immediately followed by prolonged nerve cell depression synchronously with a dramatic failure of brain ion homeostasis, efflux of excitatory amino acids from nerve cells and enhanced energy metabolism. Recent experimental work has shown that CSD in the neocortex of a variety of species including man is dependent on activation of a single receptor, the N-methyl-D-aspartate receptor, one of the three subtypes of glutamate receptors. The combined experimental and clinical studies point to fruitful areas in which to look for migraine treatments of the future and provide a framework within which important aspects of the migraine attack can be modelled.

title: Regional cerebral blood flow during migraine attacks by Xenon-133 inhalation and emission tomography.
abstract: Regional cerebral blood flow (rCBF) was measured by single photon emission tomography, using Xenon-133 inhalation during migraine attacks. The method yields images of three brain slices, depicting rCBF with a spatial resolution of 1.7 cm. Twelve patients with common migraine showed a normal cerebral blood flow pattern during an attack. Of 11 patients with classical migraine, 8 displayed a unilateral region of hypoperfusion, while 3 had a normal flow pattern. The focal decrease of blood flow average 17 per cent as compared with the symmetrical contralateral region. The localization of the blood flow reduction corresponded to the tomographic representation of the lateral aspect of the cortex in 8 patients, while in one patient the mesial aspect also appeared to be involved. The low-flow regions were always on the side opposite to the focal neurological symptoms. The hypoperfusion remained through the headache period for four to six hours. Regions of relative or absolute hyperaemia were not observed during headache of either form of migraine. Between attacks, rCBF was normal except in one patient who had a minor low-flow region in the insula. The cortical distribution of the vasomotor changes in classical migraine appeared unrelated to the distribution of major cerebral arteries and may represent a manifestation of disturbed cerebral metabolism, possibly the spreading depression of Leão. Since classical migraine in most cases was associated with intracranial blood flow changes while common migraine was not, the study was taken to support that these two forms of migraine may differ, not only on a clinical basis, but also on pathophysiological grounds.

title: Transient hyperemia succeeds oligemia in the wake of cortical spreading depression
abstract: Regional cerebral blood flow (rCBF) was examined following single episodes of cortical spreading depression (CSD) in rat brain after an intravenous bolus injection of [14C]iodoantipyrine. Cortical rCBF decreased to approximately 75% of control values during the first 60 min after CSD. This change was succeeded at 90-105 min by a small, transient flow increase. rCBF returned to normal at 120 min after CSD, and remained normal for the following 2 h. The same sequence of rCBF changes has been recorded in patients during migraine attacks. This study therefore supports the notion that CSD may serve as an animal model of migraine.

title: Focal hyperemia followed by spreading oligemia and impaired activation of rcbf in classic migraine
abstract: Regional cerebral blood flow (rCBF) was measured in 254 areas of a hemisphere with the xenon 133 intraarterial injection method. Six cases of classic migraine were followed from the normal state into the prodromal phase, and in 3 cases further into the headache phase. One patient with common migraine was similarly followed during his only classic attack. The attacks were initiated by focal hyperemia in 3 patients. During prodromes all patients displayed occipitoparietal rCBF reduction (oligemia), but in only 1 case did the reduction approach critical values. Oligemia gradually spread anteriorly in the course of 15 to 45 minutes. In 4 patients a global oligemia was observed. In 4 patients severe headache was present concomitantly with oligemia and with no sign of hyperemia or nonhomogeneous brain perfusion. The normal rCBF increase during cortical activity (hand movement, speech, and similar activities) was impaired in 6 patients. The results indicate that the vasospastic model of the migraine attack is too simplistic.

title: Cerebrovascular dynamics in patients with migraine: Near-infrared spectroscopy study
abstract: Migraine is hypothesized to be a neurovascular coupling disorder where the cerebral vascular reactivity is malfunctioning and measuring hemodynamic changes during migraine without causing more disturbance has always been a challenge. Functional near infrared spectroscopy system (fNIRS) is being proposed as an inexpensive, rapid, safe and accurate alternative to fMRI, transcranial doppler sonography (TCD). We have developed NIROXCOPE 201, a novel device for fNIRS which offers 16 source-detector pairs distributed on a probe that is placed on the forehead. Measuring hemodynamic changes during migraine without causing more disturbance has always been a challenge. Using NIROXCOPE 201, we have attempted to investigate the cerebrovascular reactivity of migraine patients to a breath hold task which produces a metabolic perturbation. Six normals and six migraine patients performed four consecutive breath holding task. We calculated the peak and latencies of the initial dip and recovery phases for [Hb], [HbO(2)], [tHb], and [OXY] signals. [Hb], [tHb], and [OXY] ID and R amplitudes of normals are approximately a magnitude higher than migraine patients (P<0.01), while latencies showed no significant differences. Data suggests an altered neurovascular coupling in frontal cortex of migraine patients interictally. The application of NIROXCOPE 201 to patients suffering from other primary headache disorders will reveal diagnostic as well as therapeutic implications of the presented study.

title: Changes in regional cerebral blood flow during the course of classic migraine attacks
abstract: Regional cerebral blood flow (rCBF) following carotid arteriography was studied in thirteen patients with classic migraine. Using the 133xenon intraarterial injection method, rCBF was measured in 254 areas in one hemisphere. Nine patients developed a characteristic attack following arteriography and were examined by a series of rCBF studies, spaced by intervals of 5 to 10 minutes. A wave of reduced blood flow originating in the posterior part of the brain and progressing anteriorly was observed in eight of the nine patients. The oligemia advanced at a speed of 2 mm per minute over the hemisphere, progressing anteriorly but not crossing the rolandic or sylvian sulcus. Typically, the spreading oligemia reached the primary sensorimotor area after symptoms from that area had begun and persisted there long after the focal symptoms had disappeared. The observed time course suggests that the focal symptoms are not secondary to the oligemia. We suggest that focal symptoms and blood flow changes may be secondary to spreading depression of Leao.

title: Cerebral vasomotor paralysis during migraine attack.
abstract: Regional cerebral blood flow (rCBF) was studied using the xenon Xe 133 intra-arterial injection method during a long-lasting preheadache phase of a migraine attack. The patient was hyperventilating moderately, rCBF was markedly reduced, and the reduction was uniform throughout the hemisphere. (Hyperventilation could not account for the rCBF reduction.) Increase of arterial carbon dioxide pressure by the inhalation of a carbon dioxide mixture did not change rCBF.  At the end of the study, papaverine was injected into the internal carotid artery; flow increase was observed, but the patient's preheadache phase now seemed to end gradually. Whether papaverine had a vasodilator effect in the preheadache phase remains unknown. The patient was restudied when asymptomatic, and rCBF and its regulation were normal.

title: Focal ischaemia caused by instability of cerebrovascular tone during attacks of hemiplegic migraine. A regional cerebral blood flow study.
abstract: During the course of hemiplegic migraine in 3 patients, changes in regional cerebral blood flow (rCBF) were recorded by the intracarotid 133Xe method and a 254 multidetector camera covering one hemisphere. The rCBF measurements were performed in conjunction with cerebral angiography. During repeated rCBF measurements all 3 patients developed focal hypoperfusion originating in the frontal lobe, subsequently spreading posteriorly to involve the precentral and postcentral regions. In 2 cases focal hyperperfusion appeared to precede the hypoperfusion. In association with the rCBF changes the patients developed transient motor and/or sensory deficits and subsequently severe headache. No signs of arterial occlusion were found. In the over and underperfused regions blood flow fluctuated rapidly because of instability of cerebrovascular tone, defined as transient constriction of the smallest cerebral vessels (arterioles) alternating with a normal calibre for these vessels and/or short periods of vasodilatation. It is considered to be a primary pathological condition of the vessels. When vasoconstriction was present the blood flow decreased to values consistent with ischaemia, which was probably the cause of the neurological deficits. On the basis of these observations and previous work from our laboratory we conclude that instability of cerebrovascular tone may cause focal ischaemia during the course of attacks of classical and hemiplegic migraine.

title: Neurovascular changes in prolonged migraine aura in FHM with a novel ATP1A2 gene mutation
abstract: To report cerebral blood flow changes during attacks of hemiplegic migraine with prolonged aura (HMPA) longer than 24 h in patients with familial hemiplegic migraine (FHM) with a novel gene mutation.  The authors performed serial neuroimaging studies during acute stage and after recovery of aura symptoms in eight HMPA attacks in two affected individuals of the Japanese family of FHM during a 10-year-observational period. The authors also performed a mutational analysis for all exons of the CACNA1A, ATP1A2 and SCN1A genes in three individuals of this family.  Each patient had an individual ‘predominantly affected hemisphere,’ that is, susceptible to hemiplegia during an HMPA attack. Migraine aura lasted 4 to 12 days. Neuroimaging studies performed on days 1 to 4 showed hyperperfusion in the affected hemisphere contralateral to hemiplegia in five attacks, hypoperfusion in three, middle cerebral artery vasodilation in five and augmented vasogenic leakage with cortical oedema in one. Hyperperfusion developed more frequently than hypoperfusion in the ‘predominantly affected hemisphere,’ whereas only hypoperfusion developed in the ‘non-predominantly affected hemisphere.’ All changes were fully reversible. The authors identified a novel heterozygous p.H916L mutation in the ATP1A2 gene in all three individuals.  Although the perfusion state could be different depending on the time course of migraine or the timing of scans in relation to cortical spreading depression, prolonged aura symptoms in this family were frequently associated with hyperperfusion and middle cerebral artery vasodilation. Hyperperfusion tended to occur in the ‘predominantly affected hemisphere,’ but the mechanism of HMPA awaits further investigations on additional cases of FHM2.

title: Migraine Mutations Increase Stroke Vulnerability by Facilitating Ischemic Depolarizations
abstract: Migraine is an independent risk factor for stroke. Mechanisms underlying this association are unclear. Familial hemiplegic migraine (FHM), a migraine subtype that also carries an increased stroke risk, is a useful model for common migraine phenotypes because of shared aura and headache features, trigger factors, and underlying glutamatergic mechanisms.  Here, we show that FHM type 1 (FHM1) mutations in CaV2.1 voltage-gated Ca2+ channels render the brain more vulnerable to ischemic stroke. Compared with wild-type mice, 2 FHM1 mutant mouse strains developed earlier onset of anoxic depolarization and more frequent peri-infarct depolarizations associated with rapid expansion of infarct core on diffusion-weighted magnetic resonance imaging and larger perfusion deficits on laser speckle flowmetry. Cerebral blood flow required for tissue survival was higher in the mutants, leading to infarction with milder ischemia. As a result, mutants developed larger infarcts and worse neurological outcomes after stroke, which were selectively attenuated by a glutamate receptor antagonist.  We propose that enhanced susceptibility to ischemic depolarizations akin to spreading depression predisposes migraineurs to infarction during mild ischemic events, thereby increasing the stroke risk.

title: Enhanced Subcortical Spreading Depression in Familial Hemiplegic Migraine Type 1 Mutant Mice
abstract: Familial hemiplegic migraine type 1, a monogenic migraine variant with aura, is linked to gain-of-function mutations in the CACNA1A gene encoding CaV2.1 channels. The S218L mutation causes severe channel dysfunction, and paroxysmal migraine attacks can be accompanied by seizures, coma, and hemiplegia; patients expressing the R192Q mutation exhibit hemiplegia only. Familial hemiplegic migraine knock-in mice expressing the S218L or R192Q mutation are highly susceptible to cortical spreading depression, the electrophysiological surrogate for migraine aura, and develop severe and prolonged motor deficits after spreading depression. The S218L mutants also develop coma and seizures and sometimes die. To investigate underlying mechanisms for these symptoms, we used multielectrode electrophysiological recordings, diffusion-weighted magnetic resonance imaging, and c-fos immunohistochemistry to trace spreading depression propagation into subcortical structures. We showed that unlike the wild type, cortical spreading depression readily propagated into subcortical structures in both familial hemiplegic migraine type 1 mutants. Whereas the facilitated subcortical spread appeared limited to the striatum in R192Q, hippocampal and thalamic spread was detected in the S218L mutants with an allele-dosage effect. Both strains exhibited increased susceptibility to subcortical spreading depression and reverberating spreading depression waves. Altogether, these data show that spreading depression propagates between cortex, basal ganglia, diencephalon, and hippocampus in genetically susceptible brains, which could explain the prolonged hemiplegia, coma, and seizure phenotype in this variant of migraine with aura.

title: A Cacna1a Knockin Migraine Mouse Model with Increased Susceptibility to Cortical Spreading Depression
abstract: Migraine is a common, disabling, multifactorial, episodic neurovascular disorder of unknown etiology. Familial hemiplegic migraine type 1 (FHM-1) is a Mendelian subtype of migraine with aura that is caused by missense mutations in the CACNA1A gene that encodes the alpha(1) subunit of neuronal Ca(v)2.1 Ca(2+) channels. We generated a knockin mouse model carrying the human pure FHM-1 R192Q mutation and found multiple gain-of-function effects. These include increased Ca(v)2.1 current density in cerebellar neurons, enhanced neurotransmission at the neuromuscular junction, and, in the intact animal, a reduced threshold and increased velocity of cortical spreading depression (CSD; the likely mechanism for the migraine aura). Our data show that the increased susceptibility for CSD and aura in migraine may be due to cortical hyperexcitability. The R192Q FHM-1 mouse is a promising animal model to study migraine mechanisms and treatments.

title: High cortical spreading depression susceptibility and migraine‐associated symptoms in Cav2.1 S218L mice
abstract: The CACNA1A gene encodes the pore‐forming subunit of neuronal CaV2.1 Ca2+ channels. In patients, the S218L CACNA1A mutation causes a dramatic hemiplegic migraine syndrome that is associated with ataxia, seizures, and severe, sometimes fatal, brain edema often triggered by only a mild head trauma.

title: Active Dilation of Penetrating Arterioles Restores Red Blood Cell Flux to Penumbral Neocortex after Focal Stroke
abstract: Pial arterioles actively change diameter to regulate blood flow to the cortex. However, it is unclear whether arteriole reactivity and its homeostatic role of conserving red blood cell (RBC) flux remains intact after a transient period of ischemia. To examine this issue, we measured vasodynamics in pial arteriole networks that overlie the stroke penumbra during transient middle cerebral artery occlusion in rat. In vivo two-photon laser-scanning microscopy was used to obtain direct and repeated measurements of RBC velocity and lumen diameter of individual arterioles, from which the flux of RBCs was calculated. We observed that occlusion altered surface arteriole flow patterns in a manner that ensured undisrupted flow to penetrating arterioles throughout the imaging field. Small-diameter arterioles (< 23 µm), which included 88% of all penetrating arterioles, exhibited robust vasodilation over a 90-min occlusion period. Critically, persistent vasodilation compensated for an incomplete recovery of RBC velocity during reperfusion to enable a complete restoration of postischemic RBC flux. Further, histologic examination of tissue hypoxia suggested re-oxygenation through all cortical layers of the penumbra. These findings indicate that selective reactivity of small pial arterioles is preserved in the stroke penumbra and acts to conserve RBC flux during reperfusion.

title: Penetrating arterioles are a bottleneck in the perfusion of neocortex
abstract: Penetrating arterioles bridge the mesh of communicating arterioles on the surface of cortex with the subsurface microvascular bed that feeds the underlying neural tissue. We tested the conjecture that penetrating arterioles, which are positioned to regulate the delivery of blood, are loci of severe ischemia in the event of occlusion. Focal photothrombosis was used to occlude single penetrating arterioles in rat parietal cortex, and the resultant changes in flow of red blood cells were measured with two-photon laser-scanning microscopy in individual subsurface microvessels that surround the occlusion. We observed that the average flow of red blood cells nearly stalls adjacent to the occlusion and remains within 30% of its baseline value in vessels as far as 10 branch points downstream from the occlusion. Preservation of average flow emerges 350 μm away; this length scale is consistent with the spatial distribution of penetrating arterioles. We conclude that penetrating arterioles are a bottleneck in the supply of blood to neocortex, at least to superficial layers.

title: Raised Plasma Endothelin During Acute Migraine Attack
abstract: Endothelins are the most potent vasoconstrictor peptides known. Plasma endothelin (ET-1) concentrations were measured in eight migraine patients (mean age 44.5 years), two during an acute migraine attack with aura and six during an attack without aura. The mean ET-1 values were elevated in all migraine patients above the range of normal subjects, and were 10.6 (range 6.0–16.0) pg/ml in migraine patients and 3.8 (range 0.7–5.8) pg/ml in controls. We hypothesize that ET-1 may constrict cerebral vessels during the initial stage of the migraine attack.

title: Endothelin 1 in migraine and tension‐type headache
abstract: We determined the plasma levels of ET1, both interictally and ictally, in 50 migraine patients, 20 with aura (MPA) and 30 without aura (MPWA), comparing them with the levels of 40 age‐matched tension‐type headache patients (20 episodic and 20 chronic) (ETTHP and CTTHP) and the levels of a group of 20 healthy control subjects (CS). No statistically significant difference was evident between the mean ET1 plasma levels of MPA and those of MPWA, assessed in headache‐free periods. The mean ET1 plasma levels of MPA and MPWA, assessed interictally, were significantly higher than those of CS. However, the values of plasma ET1 in ETTP and in CTTHP did not differ statistically from those of CS. MPA and MPWA ET1 plasma levels increased significantly within 2 h from the onset of attacks (p<0.0001) and remained significantly higher between 4 and 6 h from the onset. The ET1 plasma levels of ETTHP and CTTHP assessed during attacks did not differ statistically from those of the same patients assessed in the headache‐free periods. The increase in ET1 levels in MPA and MPWA patients when assessed ictally, suggests that this peptide is involved in the haemodynamic changes and vascular tone modifications observed during migraine attacks, particularly in the first phase of the ictal period.

title: Spreading depolarizations occur in human ischemic stroke with high incidence
abstract: Cortical spreading depression (CSD) and periinfarct depolarization (PID) have been shown in various experimental models of stroke to cause secondary neuronal damage and infarct expansion. For decades it has been questioned whether CSD or PID occur in human ischemic stroke. Here, we describe CSD and PID in patients with malignant middle cerebral artery infarction detected by subdural electrocorticography (ECoG).

title: Characterization of periinfarct flow transients with laser speckle and Doppler after middle cerebral artery occlusion in the rat
abstract: Little information exists on the role and the characteristics of perfusion changes related to periinfarct depolarization. Our aim was to visualize and monitor periinfarct flow transients (PIFTs) in Sprague‐Dawley rats (n = 10) with two different laser methods in a closed‐skull model of filament middle cerebral artery occlusion. A laser Doppler probe was placed over the ischemic cortex 5 mm lateral to Bregma, and a 5 × 5 mm area centered 5 mm posterior and 4 mm lateral to Bregma was thinned for laser speckle imaging. Both neurological and histological evaluations were performed at 72 hr postinjury. Mean flow during 90‐min ischemia was 29% of baseline measured by laser Doppler and 36–54% by laser speckle. Flow transients occurred in all rats, the number of PIFTs being 4.6 ± 1.8/90 min. By both methods, 95.6% of them occurred with temporal correlation. The average duration of PIFTs was also identical (162 ± 24 and 162 ± 34 sec, respectively). Five different morphologies of flow transients ranging from hypoperfusive to hyperemic were identified by laser speckle. The PIFTs changed their morphology dynamically over certain regions. All of the animals showed an infarct (178.5 ± 26 mm3) in the middle cerebral artery territory. Laser Doppler in itself can be a reliable method for counting/detecting PIFTs, but laser speckle is capable of monitoring the dynamic changes in PIFT morphology over the penumbral and periischemic cortex.

title: Cortical spreading ischaemia is a novel process involved in ischaemic damage in patients with aneurysmal subarachnoid haemorrhage
abstract: The term cortical spreading depolarization (CSD) describes a wave of mass neuronal depolarization associated with net influx of cations and water. Clusters of prolonged CSDs were measured time-locked to progressive ischaemic damage in human cortex. CSD induces tone alterations in resistance vessels, causing either transient hyperperfusion (physiological haemodynamic response) in healthy tissue; or hypoperfusion [inverse haemodynamic response = cortical spreading ischaemia (CSI)] in tissue at risk for progressive damage, which has so far only been shown experimentally. Here, we performed a prospective, multicentre study in 13 patients with aneurysmal subarachnoid haemorrhage, using novel subdural opto-electrode technology for simultaneous laser-Doppler flowmetry (LDF) and direct current-electrocorticography, combined with measurements of tissue partial pressure of oxygen (ptiO2). Regional cerebral blood flow and electrocorticography were simultaneously recorded in 417 CSDs. Isolated CSDs occurred in 12 patients and were associated with either physiological, absent or inverse haemodynamic responses. Whereas the physiological haemodynamic response caused tissue hyperoxia, the inverse response led to tissue hypoxia. Clusters of prolonged CSDs were measured in five patients in close proximity to structural brain damage as assessed by neuroimaging. Clusters were associated with CSD-induced spreading hypoperfusions, which were significantly longer in duration (up to 144 min) than those of isolated CSDs. Thus, oxygen depletion caused by the inverse haemodynamic response may contribute to the establishment of clusters of prolonged CSDs and lesion progression. Combined electrocorticography and perfusion monitoring also revealed a characteristic vascular signature that might be used for non-invasive detection of CSD. Low-frequency vascular fluctuations (LF-VF) (f < 0.1 Hz), detectable by functional imaging methods, are determined by the brain's resting neuronal activity. CSD provides a depolarization block of the resting activity, recorded electrophysiologically as spreading depression of high-frequency-electrocorticography activity. Accordingly, we observed a spreading suppression of LF-VF, which accompanied spreading depression of high-frequency-electrocorticography activity, independently of whether CSD was associated with a physiological, absent or inverse haemodynamic response. Spreading suppressions of LF-VF thus allow the differentiation of progressive ischaemia and repair phases in a fashion similar to that shown previously for spreading depressions of high-frequency-electrocorticography activity. In conclusion, it is suggested that (i) CSI is a novel human disease mechanism associated with lesion development and a potential target for therapeutic intervention in stroke; and that (ii) prolonged spreading suppressions of LF-VF are a novel ‘functional marker’ for progressive ischaemia.

title: Focal laminar cortical MR signal abnormalities after subarachnoid hemorrhage
abstract: In the autopsy studies of patients with delayed ischemic neurological deficits after subarachnoid hemorrhage, a predominance of cortical lesions has been observed. Similar to the autopsy descriptions in the literature, we present magnetic resonance images visualizing focal laminar cortical lesions around a fissure or sulcus in two patients, who initially did not undergo surgery, with delayed ischemic neurological deficits. This magnetic resonance imaging pattern may provide a clue to the diagnosis if the patient does not present to the emergency room with the acute hemorrhage but with delayed ischemic neurological deficits.

title: The gamut of blood flow responses coupled to spreading depolarization in rat and human brain: from hyperemia to prolonged ischemia.
abstract: Cortical spreading depolarizations (SD) have been shown to occur frequently in patients with aneurysmal subarachnoid hemorrhage (SAH) and are associated with delayed ischemic brain damage. In animal models the link between SD and cell damage is the microvascular spasm coupled to the passage of SDs, resulting in spreading ischemia. Here we compared the hemodynamic changes induced by SD between human and rat cerebral cortex. Specifically, we addressed the question, whether the full spectrum of regional cerebral blood flow (rCBF) responses to SD is found in the human brain in a similar fashion to animal models. SDs were identified by slow potential changes in electrocorticographic recordings and the rCBF response profiles and magnitudes were analyzed. We found a large variability of rCBF changes concomitant to SDs in rat and in human recordings. The spectrum ranged from normal hyperemic responses to prolonged cortical spreading ischemia with intermediate forms characterized by biphasic (hypoemic-hyperemic) responses. The bandwidths of rCBF responses were comparable and the relative response magnitudes of hypo- and hyperperfusion phases did not differ significantly between rats and humans. The correspondence of the rCBF response spectrum to SD between human and animal brain underscores the importance of animal models to learn more about the mechanisms underlying the early and delayed pathological sequelae of SAH.

title: Regional and species differences in vascular reactivity to extracellular potassium.
abstract: In-vitro vasoreactivity to extracellular potassium (Ko+) was tested in isolated human pial and mesenteric arteries as well as basilar and mesenteric arteries from rabbits and rats. Contractions were induced by stepwise increases in [K+]o and were measured isometrically with a force-displacement transducer, in small-volume organ baths. Significant differences between species as well as between regions were found. The threshold of [K+]o for eliciting contraction in human cerebral arteries in hyperosmotic solutions was 10 mM, in rabbit cerebral arteries 17 mM and in rat cerebral arteries 27 mM. The threshold concentration for contraction in mesenteric arteries was significantly higher compared to cerebral arteries in humans and rabbits, but lower in rats: 20 mM in humans, 26 mM in rabbits and 25 mM in rats. In all species the contractile amplitudes were significantly higher in both cerebral and mesenteric arteries when [K+]o was increased under isotonic conditions in the buffer solution than when hyperosomolality was created. This difference increased with increasing hyperosmolality. In hyperosmotic solutions, the EC50 for [K+]o was lower in cerebral and mesenteric arteries from man than in vessels from rabbit and rat. When the solutions were isotonic, this pattern was seen only in mesenteric arteries. It is concluded that significant species and regional differences in vascular responses to [K+]o exist. Considering that [K+]o is increased in cerebral ischaemia, the observed significantly lower threshold for K+-induced contractions in human cerebral arteries may be of importance, especially in human cerebral ischaemic events.

title: Cortical spreading depression: an adverse but treatable factor in intensive care?
abstract: Purpose of reviewThe aetiology and management of secondary deterioration in patients with acute traumatic or ischaemic brain injury remain serious challenges for clinicians and also for basic neuroscientists. The occurrence of spreading depolarization events and some of their features in the cerebral cortex in patients with traumatic brain injury and aneurysmal subarachnoid haemorrhage, as documented in recent papers, represent a novel pathophysiological mechanism in this setting. Recent findingsThe history and definitions of two critically different patterns of depolarization are reviewed on the basis of their physiology and pathophysiology, particularly the responses of the cerebral microcirculation to depolarization as seen in the laboratory. It is now becoming possible to conduct similar assessments in the brain-injured patient. Currently the recorded incidence of depolarization events in patients undergoing craniotomy for traumatic contusions is in the region of 50–60%, rising to 72% following major subarachnoid haemorrhage. SummaryRealization of the therapeutic potential of the new findings will depend on clear knowledge of the impact of the different patterns of depolarization on outcome. Meantime, current results call for even stricter attention during clinical management of acute brain injury to secondary factors such as body temperature and plasma glucose.

title: Microemboli may link spreading depression, migraine aura, and patent foramen ovale
abstract: Patent foramen ovale and pulmonary arteriovenous shunts are associated with serious complications such as cerebral emboli, stroke, and migraine with aura. The pathophysiological mechanisms that link these conditions are unknown. We aimed to establish a mechanism linking microembolization to migraine aura in an experimental animal model.

title: Paradoxical Air Microembolism Induces Cerebral Bioelectrical Abnormalities and Occasionally Headache in Patent Foramen Ovale Patients With Migraine
abstract: Although controversial, paradoxical embolism via patent foramen ovale (PFO) may account for some of the migraine attacks in a subset of migraine with aura (MA) patients. Induction of MA attacks with air bubble injection during transcranial Doppler ultrasound in MA patients with PFO supports this view. It is likely that cerebral embolism in patients with right-to-left shunt induces bioelectrical abnormalities to initiate MA under some conditions.  We investigated changes in cerebral bioelectrical activity after intravenous microbubble injection in 10 MA patients with large PFO and right-to-left cardiac shunt. Eight PFO patients without migraine but with large right-to-left shunt and 12 MA patients without PFO served as controls. Four MA patients with PFO were reexamined with sham injections of saline without microbubbles. Bioelectrical activity was evaluated using spectral electroencephalography and, passage of microbubbles through cerebral arteries was monitored with transcranial Doppler ultrasound. Microbubble embolism caused significant electroencephalographic power increase in MA+PFO patients but not in control groups including the sham-injected MA+PFO patients. Headache developed in 2 MA with PFO patients after microbubble injection.  These findings demonstrate that air microembolism through large PFOs may cause cerebral bioelectrical disturbances and, occasionally, headache in MA patients, which may reflect an increased reactivity of their brain to transient subclinical hypoxia–ischemia, and suggest that paradoxical embolism is not a common cause of migraine but may induce headache in the presence of a large PFO and facilitating conditions.

title: Transient neurological symptoms during contrast transcranial Doppler right-to-left shunt testing in patients with cryptogenic neurological disease.
abstract: Paradoxical embolization from right-to-left shunt (RLS) resulting in neurological events is well described and patients with cryptogenic neurological disease are commonly evaluated for this condition. In the course of testing for RLS by bubble contrast transcranial Doppler (TCD), we observed that some patients developed transient neurological symptoms. This report describes our findings.



We performed diagnostic TCD on 445 consecutive patients with cryptogenic neurological disease (cerebral vascular accident, 21%; transient ischemic attack, 30%; migraine, 48%; and abnormal magnetic resonance brain imaging, 68%). Immediately following the procedure, patients were questioned about neurological symptoms.



One hundred and sixty-three (37%) of the 445 patients had absent or minimal shunting (Spencer grades 0-1) and 233 of 445 (52%) had severe RLS (Spencer grades 4-5+). One or more TCD-associated neurological symptoms (TCD-SX) developed in 95 of 445 (21%) of the patients. Compared to patients with absent or minimal shunting, patients with shunt grades 2-5+ were two and one half times more likely to develop TCD-SX (18/164 [11%] vs. 77/283 [27%], P < 0.001). TCD-SX were fourfold more common among patients with a history of migraine compared to history-negative subjects (35 vs. 8.7%, P < 0.0001).



Diagnostic bubble-contrast TCD provoked transient neurological symptoms. The symptoms correlated with the severity of RLS and were more common in migraine patients, suggesting that migraine patients are sensitized to chemical and/or microembolic shunt factors. There was no significant residual morbidity, and bubble-contrast echocardiograph continues to be a safe and valuable diagnostic procedure.

title: Migraine Intervention With STARFlex Technology (MIST) Trial: A Prospective, Multicenter, Double-Blind, Sham-Controlled Trial to Evaluate the Effectiveness of Patent Foramen Ovale Closure With STARFlex Septal Repair Implant to Resolve Refractory Migraine Headache
abstract: Patent foramen ovale (PFO) is prevalent in patients with migraine with aura. Observational studies show that PFO closure resulted in migraine cessation or improvement in ≈80% of such patients. We investigated the effects of PFO closure for migraine in a randomized, double-blind, sham-controlled trial.  Patients who suffered from migraine with aura, experienced frequent migraine attacks, had previously failed ≥2 classes of prophylactic treatments, and had moderate or large right-to-left shunts consistent with the presence of a PFO were randomized to transcatheter PFO closure with the STARFlex implant or to a sham procedure. Patients were followed up for 6 months. The primary efficacy end point was cessation of migraine headache 91 to 180 days after the procedure. In total, 163 of 432 patients (38%) had right-to-left shunts consistent with a moderate or large PFO. One hundred forty-seven patients were randomized. No significant difference was observed in the primary end point of migraine headache cessation between implant and sham groups (3 of 74 versus 3 of 73, respectively; P=0.51). Secondary end points also were not achieved. On exploratory analysis, excluding 2 outliers, the implant group demonstrated a greater reduction in total migraine headache days (P=0.027). As expected, the implant arm experienced more procedural serious adverse events. All events were transient.  This trial confirmed the high prevalence of right-to-left shunts in patients with migraine with aura. Although no significant effect was found for primary or secondary end points, the exploratory analysis supports further investigation. The robust design of this study has served as the model for larger trials that are currently underway in the United States and Europe.

title: Patent Foramen Ovale and Migraine: A Cross-Sectional Study From the Northern Manhattan Study (NOMAS)
abstract: A causal relationship between patent foramen ovale (PFO) and migraine has been hypothesized, and improvement of migraine frequency and severity after percutaneous PFO closure has been reported. Population-based data on the relationship between PFO and migraine are sparse, however. The objective of this study was to examine the association between PFO and migraine among stroke-free individuals in an urban, population-based, multiethnic cohort.  As a part of the ongoing Northern Manhattan Study (NOMAS), 1101 stroke-free subjects were assessed for self-reported history of migraine. The presence of PFO was assessed by transthoracic echocardiography. The mean age of the group was 69±10 years; 58% were women. Forty-eight percent were Caribbean Hispanic, 24% were white, 26% were black, and 2% were another race/ethnicity. The prevalence of self-reported migraine was 16% (13% migraine with aura). The prevalence of PFO was 15%. Migraine was significantly more frequent among younger subjects, women, and Hispanics. The prevalence of PFO was not significantly different between subjects who had migraine (26/178, or 14.6%) and those who did not (138/923, or 15.0%; P=0.9). In an adjusted multivariate logistic regression model, the presence of PFO was not associated with increased prevalence of migraine (odds ratio 1.01, 95% confidence interval 0.63 to 1.61). Increasing age was associated with lower prevalence of migraine in both subjects with a PFO (odds ratio 0.94, 95% confidence interval 0.90 to 0.99 per year) and those without PFO (odds ratio 0.97, 95% confidence interval 0.95 to 0.99 per year). The observed lack of association between PFO and migraine (with or without aura) was not modified by diabetes mellitus, hypertension, cigarette smoking, or dyslipidemia.  In this multiethnic, elderly, population-based cohort, PFO detected with transthoracic echocardiography and agitated saline was not associated with self-reported migraine. The causal relationship between PFO and migraine remains uncertain, and the role of PFO closure among unselected patients with migraine remains questionable.

title: Endothelin-1 potently induces Leão's cortical spreading depression in vivo in the rat: a model for an endothelial trigger of migrainous aura?
abstract: According to the 'neuronal' theory, cortical spreading depression (CSD) is the pathophysiological correlate of migrainous aura. However, the 'vascular' theory has implicated altered vascular function in the induction of aura symptoms. The possibility of a vascular origin of aura symptoms is supported, e.g. by the clinical observation that cerebral angiography frequently provokes migrainous aura. This suggests that endothelial irritation may somehow initiate one of the pathways resulting in migrainous aura. Up to now, an endothelium-derived factor has never been shown to trigger CSD. Here, for the first time, we demonstrate and characterize the ability of the vasoconstrictor and astroglial/neuronal modulator endothelin-1 to trigger Leão's 'spreading depression of activity' in vivo in rats. At a concentration range between 10 nM and 1 microM, endothelin-1 induced changes characteristic of CSD with regard to the rate of propagation, steady (direct current) potential and extracellular K(+)-concentration. A spreading hyperaemia followed by oligaemia was observed similar to those in K(+)-induced CSD. Endothelin-1 did not provoke changes characteristic of a terminal depolarization. The mechanism by which endothelin-1 generated CSD involved the N-methyl-D-asparate receptor. Cerebral blood flow decreased slightly, but significantly, before endothelin-1 generated CSD. A vasodilator (NO*-donor) shifted the threshold for CSD induction to higher concentrations of endothelin-1. Endothelin-1, in contrast to K(+), did not induce CSD in rat brain slices suggesting indirectly that endothelin-1 may require intact perfusion to exert its effects. In conclusion, endothelin-1 was found in the experiment to be the most potent inducer of CSD currently known. We propose endothelin-1 as a possible candidate for the yet enigmatic link between endothelial irritation and migrainous aura.

title: ET-1 induces cortical spreading depression via activation of the ETA receptor/phospholipase C pathway in vivo.
abstract: Recently, it has been shown that brain topical superfusion of endothelin (ET)-1 at concentrations around 100 nM induces repetitive cortical spreading depressions (CSDs) in vivo. It has remained unclear whether this effect of ET-1 is related to a primary neuronal/astroglial effect, such as an increase in neuronal excitability or induction of interastroglial calcium waves, or a penumbra-like condition after vasoconstriction. In vitro, ET-1 regulates interastroglial communication via combined activation of ET(A) and ET(B) receptors, whereas it induces vasoconstriction via single activation of ET(A) receptors. We have determined the ET receptor profile and intracellular signaling pathway of ET-1-induced CSDs in vivo. In contrast to the ET(B) receptor antagonist BQ-788 and concentration dependently, the ET(A) receptor antagonist BQ-123 completely blocked the occurrence of ET-1-induced CSDs. The ET(B) receptor antagonist did not increase the efficacy of the ET(A) receptor antagonist. Direct stimulation of ET(B) receptors with the selective ET(B) agonist BQ-3020 did not trigger CSDs. The phospholipase C (PLC) antagonist U-73122 inhibited CSD occurrence in contrast to the protein kinase C inhibitor Gö-6983. Our findings indicate that ET-1 induces CSDs through ET(A) receptor and PLC activation. We conclude that the induction of interastroglial calcium waves is unlikely the primary cause of ET-1-induced CSDs. On the basis of the receptor profile, likely primary targets of ET-1 mediating CSD are either neurons or vascular smooth muscle cells.

title: Pediatric Stroke in the United States and the Impact of Risk Factors
abstract: One approach to studying pediatric stroke is to analyze a national database that contains data on a significant number of children. We examined an administrative dataset of hospital discharges from the United States, Kids' Inpatient Database 2003 (KID2003), for ICD-9 codes associated with hemorrhagic or ischemic stroke in children aged >30 days to 20 years. 3156 children were discharged with a diagnosis of ischemic stroke and 2022 with hemorrhagic stroke after statistical weighting. The odds for a male discharged with hemorrhagic stroke was 1.5 (CI: 1.35-1.68) and for ischemic stroke was 1.37 (CI: 1.24-1.51) compared with a female. The odds for males discharged with a stroke were greatest for ages 16 to 20 years and least for 4 years. This study confirms a male predominance for stroke. The odds for hospitalization with a stroke diagnosis are greatest in very young and older adolescent males. Hemorrhage is an important stroke subtype in children.