bluuebunny/crossref_metadata_2025 huggingface dataset:
The CBF Threshold and Dynamics for Focal Cerebral Infarction in Spontaneously Hypertensive Rats
Authors: Jacewicz Michael , Tanabe Jody , Pulsinelli William A.
Published: April 2011

Two strategies were used to estimate the blood flow threshold for focal cerebral infarction in spontaneously hypertensive rats (SHRs) subjected to permanent middle cerebral artery and common carotid artery occlusion (MCA/CCAO). The first compared the volume of cortical infarction (24 h after ischemia onset) to the volumes of ischemic cortex (image analysis of [14C]iodoantipyrine CBF autoradiographs) perfused below CBF values <50 (VIC50) and <25 ml 100 g−1 min−1 (VIC25) at serial intervals during the first 3 h of ischemia. The infarct process becomes irreversible within 3 h in this model. In the second, measurements of CBF at the border separating normal from infarcted cortex at 24 h after ischemia onset were used as an index of the threshold. During the first 3 h of ischemia, VIC50 increased slightly to reach a maximum size at 3 h that closely matched the 24 h infarct volume. VIC25, in contrast, consistently underestimated the infarct volume by a factor of 2–3. CBF at the 24 h infarct border averaged 50 ml 100 g−1 min−1. Taken together, the results indicate that the CBF threshold for infarction in SHRs approaches 50 ml 100 g−1 min−1 when ischemia persists for ≥3 h. This threshold value is approximately three times higher than in primates. Since cortical neuronal density is also threefold greater in rats than in primates, the higher injury threshold in the rat may reflect a neuronal primacy in determining the brain's susceptibility to partial ischemia.
Reduction in Focal Cerebral Ischemia by Agents Acting at Imidazole Receptors
Authors: Maiese Kenneth , Pek Laszlo , Berger Scott B. , Reis Donald J.
Published: April 2011

Treatment with the α2-adrenergic antagonist idazoxan (IDA) can provide protection from global cerebral ischemia. However, IDA also recognizes another class of receptors, termed imidazole (IM) receptors, which differ from α2-adrenergic receptors and are responsible for the hypotensive actions of some centrally acting agents such as the oxazole rilmenidine (RIL). We therefore sought to determine whether RIL, an agent highly selective for IM receptors, offered protection from focal cerebral ischemia elicited in rat by ligation of the middle cerebral artery (MCA). We compared the effects of RIL with the effects of IDA and the selective non-IM α2-antagonist SKF 86466 (SKF). In addition, we examined whether the neuroprotective effects of RIL and IDA could be attributed to changes in local CBF (LCBF). The MCA was occluded and animals either received immediate administration of drug while arterial pressure was maintained for 1 h or had local CBF increased to 200% of control for 1 h by hypercapnia or hypertension. RIL elicited a significant dose-dependent preservation of tissue to 33% of control at optimal dose (0.75 mg/kg). IDA (3 mg/kg) significantly reduced the size of ischemic infarction by 22%. In contrast, SKF (15 mg/kg) as well as doubling of LCBF did not preserve ischemic tissue. We conclude that both RIL and IDA can reduce focal ischemic infarction but that the mechanism does not appear secondary to antagonism of α2-adrenergic receptors or elevation of LCBF. Occupation of IM receptors, either in the ischemic zone or at remote brain sites, may be responsible for neuroprotection of RIL and IDA.
Perivascular Microapplication of Endothelin-1: A New Model of Focal Cerebral Ischaemia in the Rat
Authors: Sharkey John
Published: April 2011

In the present study, we describe the effects of perivascular microapplication of the potent vasoconstrictor peptide endothelin-1 (Et-1; (120 pmol in 3 μl), delivered via a guide cannula stereotaxically positioned above the left cerebral artery (MCA) of the conscious male Sprague–Dawley rat. Ten minutes after the administration of Et-1, mean arterial blood pressure had increased by 20% and profound reductions in local cerebral blood flow (up to 93%) were observed within those brain areas supplied by the MCA. In addition, significant increases in local cerebral blood flow were observed within the globus pallidus (100%), substantia nigra pars reticulata (48%), ventrolateral thalamus (65%), and dorsal hippocampus (74%) ipsilateral to the insult. Twenty-four hours following the insult, the pattern of ischaemic damage was similar to that reported previously following permanent occlusion of the rat MCA. It is suggested that perivascular microapplication of Et-1 may provide a useful model for the study of the functional disturbances associated with focal cerebral ischaemia in the conscious rat.
Inhibition of Nitric Oxide Synthesis: Effects on Cerebral Blood Flow and Glucose Utilisation in the Rat
Authors: Macrae I. M. , Dawson D. A. , Norrie J. D. , McCulloch J.
Published: April 2011

The consequences of inhibition of nitric oxide synthesis on local CBF and glucose utilisation have been studied in the conscious rat using the specific nitric oxide synthase inhibitor Ng-nitro-l-arginine methyl ester (l-NAME; 30 mg kg−1 i.v.). Local CBF and glucose utilisation were assessed with the [14C]iodoantipyrine and the 2-deoxy-d-[14C]glucose autoradiographic techniques, respectively. l-NAME induced prolonged (>3 h) reductions in local CBF throughout the CNS with concomitant increases in arterial blood pressure. For example, 1 h post l-NAME, CBF dropped from 79 ± 4 to 45 ± 1 ml 100 g−1 min−1 in cerebellum, from 76 ± 4 to 47 ± 2 ml 100 g−1 min−1 in medulla oblongata, and from 117 ± 6 to 72 ± 2 ml 100 g−1 min−1 in cortex. l-NAME produced sustained elevations (e.g., 46 ± 2 mm Hg at 1 h after bolus administration) in mean arterial blood pressure throughout the period evaluated. Despite evidence implicating nitric oxide in neuronal signalling, l-NAME did not significantly influence CNS functional activity, as measured by local rates of glucose utilisation, in any neuroanatomical region examined. Consequently, the normal ratio of blood flow to glucose use throughout the brain was significantly reduced in the presence of l-NAME, although the hierarchy of blood flow levels in different neuroanatomical regions was preserved. These results are consistent with the involvement of nitric oxide in the tonic control of cerebral tissue perfusion.
Creatine Kinase-Catalyzed Reaction Rate in the Cyanide-Poisoned Mouse Brain
Authors: Holtzman David , Offutt Martin , Tsuji Miles , Neuringer Leo J. , Jacobs Danny
Published: April 2011

Brain creatine kinase (CK)-catalyzed phosphorus flux from phosphocreatine (PC) to ATP was measured in vivo in young adult mice made reversibly hypoxic by injection of cyanide. Phosphorus spectra and saturation transfer measurements of CK-catalyzed flux were acquired using a high-field (8.45 T) nuclear magnetic resonance (NMR) spectrometer. After low cyanide doses (1–3 mg/kg of body weight), there were no measurable changes in brain pH or in concentrations of PC, the nucleoside triphosphates (including ATP), and Pi, The CK-catalyzed phosphorus flux increased about 75% after the low cyanide dose. Higher doses (4–6 mg/kg) produced a transient 30–40% decrease in PC concentration, doubling of Pi, and a 0.2 unit decrease in pH. The CK-catalyzed phosphorus flux decreased 50–80% after the higher cyanide doses. This decrease in phosphorus flux was present long after reactant concentrations returned to precyanide values. It is proposed that the increase in brain CK-catalyzed phosphorus flux with the lower cyanide doses is due to an increase in ADP concentration. The large, prolonged decrease in CK-catalyzed reaction rate in the moderately poisoned brain may be due to loss of activity of the mitochondrial CK isoform.
Glial Glycogen Stores Affect Neuronal Survival during Glucose Deprivation in vitro
Authors: Swanson Raymond A. , Choi Dennis W.
Published: April 2011

Glia perform several energy-dependent functions that may aid neuronal survival under pathological conditions. Glycogen is the major energy reserve in brain, and it is localized almost exclusively to astrocytes. Using murine cortical cell cultures containing both glia and neurons, we examined the effect of altered glial glycogen stores on neuronal survival following glucose deprivation. As previously reported, cultures exposed for several hours to media lacking glucose developed widespread neuronal degeneration without glial degeneration. If glial astrocyte glycogen content was increased to 2–3 times control levels by a 24-h pretreatment with 1 μ M insulin or 0.5 m M methionine sulfoximine (MSO), glucose deprivation-induced neuronal degeneration was attenuated. These protective effects were blocked if glycogen levels were reduced back to control levels by a 30-min exposure to 1 m M dibutyryl cyclic AMP or 20 μ M norepinephrine prior to glucose deprivation. Astrocyte glycogen stores may be an important factor influencing neuronal survival under conditions of energy substrate limitation.
Selective Vulnerability of White Matter during Spinal Cord Ischemia
Authors: Follis F. , Scremin O. U. , Blisard K. S. , Scremin A. M. E. , Pett S. B. , Scott W. J. , Kessler R. M. , Wernly J. A.
Published: April 2011

The long-term effects of spinal cord ischemia were studied in 21 rats by lesion scores (LS, n = 21), somatosensory evoked potentials (SEP, n = 16), electromyographic measurements (EMG, n = 12) and histology of the spinal cord ( n = 21) 48.5 ± 57.2 days after 10- to 12-min occlusion of the thoracic aorta and subclavian arteries. All the animals were initially paraplegic with a spastic presentation but seven recovered within 2 days (group A), demonstrating low LS (3.4 ± 1.05) normal EMGs ( n = 3) and unremarkable histology. The 14 paraplegic animals presented relevant findings of the lumbar cord consisting of white matter lesions only (group B, n = 7) or white and gray matter lesions (group C, n = 7). Group B animals showed severe deficit (LS = 11.8 ± 2.93) without denervation on EMG ( n = 5) or muscle atrophy on histology. Group C animals displayed equal impairment (LS = 14.4 ± 0.71), denervation on EMG ( n = 4), and muscle atrophy. Resting motor unit activity of groups B and C were significantly different from group A ( p < 0.001), while LS of groups B and C did not differ ( p = 0.083). These data underscore the nature and the extent of white matter lesions during spinal cord ischemia, a finding which has generally been eclipsed by emphasis on gray matter lesions in previous studies.
Coupling of Energy Failure and Dissipative K+ Flux during Ischemia: Role of Preischemic Plasma Glucose Concentration
Authors: Ekholm Anders , Katsura Ken-Ichiro , Siesjö Bo K.
Published: April 2011

The present experiments were undertaken to assess the influence of preischemic hypo- or hyperglycemia on the coupling among changes in extracellular K+ concentration (K+e) and in cellular energy state, as the latter is reflected in the tissue concentrations of phosphocreatine (PCr), Cr, ATP, ADP, and AMP, and in the calculated free ADP (ADPf) concentrations. The questions posed were whether the final release of K+ was delayed because the extra glucose accumulated by hyperglycemic animals produced enough ATP to continue supporting Na+–K+-driven ATPase activity, and whether the additional acidosis altered the ionic transients. As expected, preischemic hypoglycemia shortened and hyperglycemia prolonged the phase before K+e rapidly increased. This was reflected in corresponding changes in tissue ATP content. Thus, hypoglycemia shortened and hyperglycemia prolonged the time before the fall in ATP concentration accelerated. When tissue was frozen at the moment of depolarization, the tissue contents of ATP were similar in hypo-, normo-, and hyperglycemic groups, ∼ 30% of control. This suggests that hyperglycemia retards loss of ion homeostasis by leading to production of additional ATP. However, hyperglycemia did not reduce the rate at which the PCr concentration fell, and the ATP/ADPf ratio decreased. There were marked differences in the amount of lactate accumulated between the groups. Thus, massive depolarization in hypoglycemic groups occurred at a tissue lactate content of ∼4 m M kg−1. This corresponds to a decrease in intracellular pH (pHi) from ∼7.0 to ∼6.9. In the hyperglycemic groups, depolarization occurred at a lactate content of about 12 mm kg−1, corresponding to a pHi of ∼6.4. This fall in pHi, or the accompanying fall in extracellular pH (pHe), did not affect the maximal rate of efflux of K+. Measurements of ischemic depolarization at constant tissue temperature (37°C) suggest that the influence of the plasma glucose concentration on the terminal depolarization time is restricted. Thus, the time to depolarization varied between 30 s (hypoglycemia) and 90 s (moderate to severe hyperglycemia). Previous results obtained without temperature control may well have reflected a combination between hyperglycemia and a fall in tissue temperature.
Increases in Interstitial Adenosine and Cerebral Blood Flow with Inhibition of Adenosine Kinase and Adenosine Deaminase
Authors: Sciotti Veronica M. , Van Wylen David G. L.
Published: April 2011

The purpose of this study was to determine the changes in interstitial fluid (ISF) adenosine and cerebral blood flow (CBF) during inhibition of adenosine kinase or adenosine deaminase. Brain microdialysis was used to (a) measure CBF (H2 clearance), (b) sample cerebral ISF, and (c) deliver drugs locally to the brain. Microdialysis probes were implanted bilaterally in the caudate nucleus of halothane-anesthetized rats ( n = 11). One probe was perfused with artificial cerebrospinal fluid (CSF) containing iodotubercidin (IODO), an adenosine kinase inhibitor, while the other probe was perfused with erythro-2-(2-hydroxy-3-nonyl)adenine (EHNA), an adenosine deaminase inhibitor. Both probes were subsequently perfused with EHNA + IODO. Finally, 8-( p-sulfophenyl)theophylline (SPT), an adenosine receptor antagonist, was added to EHNA + IODO in one probe, while the other probe continued to receive only EHNA + IODO. CBF and dialysate adenosine levels increased with either EHNA or IODO; however, the increases were greater with IODO. EHNA + IODO further increased CBF and dialysate adenosine. The hyperemia observed with EHNA + IODO was abolished by adenosine receptor blockade. These data suggest that basal adenosine levels are influenced to a greater extent by adenosine kinase than by adenosine deaminase. In addition, the increased CBF observed with inhibition of adenosine metabolism and the attenuation of this vasodilatory response with adenosine receptor blockade support a role for adenosine in CBF regulation.
Phospholipase C Activity in Cerebrospinal Fluid following Subarachnoid Hemorrhage Related to Brain Damage
Authors: Nakashima Toshihiko , Takenaka Katsunobu , Nishimura Yasuaki , Andoh Takashi , Sakai Noboru , Yamada Hiromu , Banno Yoshiko , Okano Yukio , Nozawa Yoshinori
Published: April 2011

Phosphoinositide-specific phospholipase C (PLC) activities were measured in CSF from patients after subarachnoid hemorrhage (SAH). Their PLC activities were significantly higher than those in control CSF. Moreover, there was an obvious correlation between the PLC activity in CSF collected on day 3 and the preoperative clinical grade. The PLC activity was also closely correlated with the level of neuron-specific enolase as a marker of brain damage. Furthermore, the PLC activities were partially purified from CSF of patients after SAH and were immunologically identified to be PLCβ, PLCγ, and PLCδ. These results suggest that PLCs are released into the CSF from brain tissue in conjunction with the initial hemorrhage and that their activity may reflect the extent of brain damage.
Cerebral Vascular Autoregulation and CO2 Reactivity following Onset of the Delayed Postischemic Hypoperfusion State in Dogs
Authors: Christopherson Thomas J. , Milde James H. , Michenfelder John D.
Published: April 2011

A small number of animal studies have suggested that during the delayed postischemic hypoperfusion state, CO2 reactivity of the cerebral vasculature is lost whereas autoregulation is retained. These findings, however, are inconsistent with the bulk of experimental evidence which demonstrates that CO2 reactivity is more robust and may be retained in pathologic circumstances which abolish autoregulation. These opposing viewpoints were therefore further evaluated in 18 dogs in which complete global ischemia was induced by cerebrospinal fluid (CSF) compression for periods of 12 ( n = 12) and 18 ( n = 6) min. Following 45 min of reperfusion and with onset of the delayed postischemic hypoperfusion state, autoregulation and CO2 reactivity were evaluated using a continuous measurement of CBF (by sagittal sinus outflow). CO2 reactivity was tested over a Paco2 range of 20 to 60 mm Hg; autoregulation was tested over a blood pressure range of 60 to 140 mm Hg. Results demonstrated that after both 12 and 18 min of complete global ischemia, autoregulation and CO2 reactivity of the cerebral vasculature were both present, but attenuated. In the case of CO2 reactivity, the slope of the CBF response was decreased approximately 75%. In the case of autoregulation, the response in some dogs was incomplete as compared with their preischemic response.
Role of Nitric Oxide in the Cerebral Vasodilatory Responses to Vasopressin and Oxytocin in Dogs
Authors: Oyama Hirofumi , Suzuki Yoshio , Satoh Shin-Ichi , Kajita Yasukazu , Takayasu Masakazu , Shibuya Masato , Sugita Kenichiro
Published: April 2011

We angiographically assessed the vasodilatory effects of vasopressin and oxytocin on the basilar arteries in dogs. Intracisternal bolus injections of vasopressin (100 pmol and 1 nmol) and oxytocin (1 and 10 nmol) produced dose-dependent increases in the internal diameter of the basilar arteries without affecting mean arterial blood pressure. The maximal dilatations of the basilar arteries induced by 1 nmol vasopressin and 10 nmol oxytocin were 142.3 ± 19.9 and 136.8 ± 25.5% of the baseline, respectively. When the same peptides were injected into the vertebral artery, the maximal dilatations were similar, but the duration of response was shorter. Pretreatment with intracisternal injection of 10 μmol NG-monomethyl-l-arginine (l-NMMA), which inhibits the synthesis of nitric oxide from l-arginine, suppressed the vasodilatory responses induced by intracisternal injection of vasopressin and oxytocin and by intraarterial injection of vasopressin. Calcitonin gene-related peptide also caused dilatation of the basilar artery when injected into the cisterna magna, but its effect was not blocked by l-NMMA. l-NMMA reduced the basal diameter of the basilar artery in a dose-dependent manner; l-arginine produced dose-dependent increases in diameter. The vasoconstriction induced by l-NMMA was reversed by high concentrations of l-arginine. These results suggest that vasopressin and oxytocin dilate the basilar arteries via the release of nitric oxide from both the intraluminal and the extraluminal sides and that synthesis and release of nitric oxide in the vascular wall contribute to maintenance of basal vascular tonus.
Nonpeptide Angiotensin AT1 and AT2 Receptor Ligands Modulate the Upper Limit of Cerebral Blood Flow Autoregulation in Rats
Authors: Strömberg Christer , Näveri Liisa , Saavedra Juan M.
Published: April 2011

We investigated the effect of angiotensin AT1 and AT2 receptor blockade on the upper limit of CBF autoregulation in pentobarbital-anesthetized rats. CBF was measured by laser-Doppler flowmetry from the parietal cortex and MABP was increased by intravenous phenylephrine infusion. Neither the AT1 antagonist losartan nor the AT2 ligand PD 123319 nor angiotensin II (ANG II) in the presence of losartan affected baseline CBF. When the blood pressure was increased in the control group, CBF remained fairly constant up to 145 mm Hg and increased steeply after 150 mm Hg. Both PD 123319(7–10 mg/kg) and losartan (1–10mg/kg) shifted the upper limit of CBF autoregulation toward higher pressures. Intravenous infusion of PD 123319 was more effective than bolus injection. The losartan effect was dose dependent. Selective stimulation of AT2 receptors with an intravenous ANG II infusion (0.54 μg/min) in the presence of losartan did not reverse the effect of losartan on CBF autoregulation, but, on the contrary, appeared to further shift the upper limit of autoregulation toward higher pressures. The results implicate a role for both AT1 and AT2 angiotensin receptors in the regulation of CBF.
Decrease in Human Striatal Dopamine D2 Receptor Density with Age: A PET Study with [11C]Raclopride
Authors: Rinne Juha O. , Hietala Jarmo , Ruotsalainen Ulla , Säkö Erkki , Laihinen Arto , Någren Kjell , Lehikoinen Pertti , Oikonen Vesa , Syvälahti Erkka
Published: April 2011

The effect of age on human striatal dopamine D2 receptors was investigated with positron emission tomography (PET) using [11C]raclopride as a radioligand. Twenty-one healthy volunteers aged from 20 to 81 years were studied. An equilibrium method was applied and two separate PET scans with different specific activities of [11C]raclopride were performed. The maximal number of receptors ( Bmax) and their dissociation constant ( Kd) were calculated using Scatchard analysis. There was an age-dependent decline in the Bmax ( r = 0.49; p = 0.02) of striatal D2 receptors while the Kd remained unchanged. The results show that there is an age-related loss of striatal D2 receptors, which, together with other changes in the brain nigrostriatal dopaminergic system, may contribute to extrapyramidal symptoms associated with aging.
Human Striatal l-DOPA Decarboxylase Activity Estimated in vivo Using 6-[18F]fluoro-DOPA and Positron Emission Tomography: Error Analysis and Application to Normal Subjects
Authors: Kuwabara Hiroto , Cumming Paul , Reith Jakob , Léger Gabriel , Diksic Mirko , Evans Alan C. , Gjedde Albert
Published: April 2011

DOPA decarboxylase is the enzyme directly responsible for the synthesis of the neurotransmitters dopamine and serotonin, and indirectly of noradrenaline, in brain. We used the decarboxylation coefficient ( kD3) of 6-[18F]fluoro-DOPA (FDOPA) to denote the relative activity of l-DOPA decarboxylase in vivo in the human brain. To determine the relative enzyme activity with positron emission tomography (PET), we evaluated the model that separates the metabolism into compartments of nondiffusible and diffusible (i.e., transient) tracer metabolites. Error analysis indicated that the least-squares optimization alone was not sufficient to yield accurate estimates of kD3 in the presence of the inherent error of PET. To improve the accuracy of the kD3 estimates by optimizing the number of parameters, we introduced biological constraints which included a tracer partition volume ( Ve) common to frontal cortex and striatum, and a fixed ratio ( q) between the blood–brain barrier transport coefficients of O-methyl-[18F]fluoro-DOPA and FDOPA, the two sources of radioactivity in plasma. We found that a two-step analysis yielded sufficiently accurate estimates of kD3. The two steps include the initial estimation of the partition volume in frontal cortex and the subsequent use of this value to determine kD3 in striatum and other structures. We studied twelve healthy controls (age 45 ± 15 years). The average kD3 value was 0.081 ± 0.024 min−1 (coefficient of variation (COV) 30%) for caudate nucleus, 0.074 ± 0.013 min“1 (COV 18%) for putamen, and 0.010 ± 0.005 min−1 (COV 50%) for cerebral cortex.
Neuronal Protection and Preservation of Calcium/Calmodulin-Dependent Protein Kinase II and Protein Kinase C Activity by Dextrorphan Treatment in Global Ischemia
Authors: Aronowski Jaroslaw , Waxham M. Neal , Grotta James C.
Published: April 2011

This study analyzed the ability of the N-methyl-d-aspartate receptor antagonist dextrorphan (DX) to prevent neuronal degeneration (analyzed by light microscopy), calmodulin (CaM) redistribution (analyzed by immunocytochemistry) and changes in activity of two major Ca2+-dependent protein kinases—calcium/calmodulin-dependent protein kinase II (CaM-KII) and protein kinase C (PKC) (analyzed by specific substrate phosphorylation) after 20 min of global ischemia (four-vessel occlusion model) in rats. DX treatment before and after ischemia significantly protected hippocampal and cortical neurons from neurodegeneration whereas DX posttreatment alone did not have any effect on preservation of neuronal morphology as compared with placebo treatment analyzed 72 h after 20 min of ischemia. Similarly to histological changes, DX exhibited protection against redistribution of CaM observed after ischemia. These changes were detected both in hippocampus as well as in cerebral cortex. Finally, DX administered before ligation of the carotid arteries reduced loss in both CaM-KII and PKC activity evoked by ischemia.
Characterization of Cortical Depolarizations Evoked in Focal Cerebral Ischemia
Authors: Nedergaard Maiken , Hansen Anker Jon
Published: April 2011

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 m M. One-third of these transient increases in [K+]e were biphasic, consisting of a slow initial increase to 10–12 m M, 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.
Changes in Amino Acid Neurotransmitters and Cerebral Blood Flow in the Ischemic Penumbral Region following Middle Cerebral Artery Occlusion in the Rat: Correlation with Histopathology
Authors: Takagi Kiyoshi , Ginsberg Myron D. , Globus Mordecai Y.-T. , Dietrich W. Dalton , Martinez Elena , Kraydieh Susan , Busto Raul
Published: April 2011

We simultaneously measured neurotransmitter amino acids by the microdialysis technique and cortical CBF by laser-Doppler flowmetry in the ischemic penumbral cortex of rats subjected to 2-h normothermic (36.5–37.5°C) transient middle cerebral artery (MCA) clipocclusion. Brains were perfusion-fixed 3 days later and infarct volume measured. CBF (% of preischemic values) fell to 32 ± 2% (mean ± SD) during ischemia and rose to 157 ± 68% during recirculation. Extracellular glutamate levels increased from a baseline value of 7 ± 3 μ M to a peak value of 180 ± 247 μ M 20–30 min following onset of ischemia but subsequently returned to near baseline levels after 70 min of ischemia despite ongoing MCA occlusion. The threshold CBF for moderate glutamate release was 48%. Massive glutamate release was seen during the first 60 min of MCA occlusion in the two animals showing the largest infarcts and occurred at CBF values ≤20% of control levels. Mean CBF during ischemia exhibited an inverse relationship with infarct volume, and the magnitude of glutamate release during ischemia was positively correlated with infarct volume. Extracellular γ-aminobutyrate and glycine changes were similar to those of glutamate but showed no significant correlation with infarct volume. These results suggest that (a) accumulation of extracellular glutamate is an important determinant of injury in the setting of reversible MCA occlusion and (b) reuptake systems for neurotransmitter amino acids may be functional in the penumbra during transient focal ischemia.

We have shown that during temporary MCA occlusion, penumbral levels of amino acid neurotransmitter initially rise but subsequently decline to baseline despite ongoing ischemia and that moderate extracellular glutamate release and massive release of GABA and glycine occur at a CBF threshold of 48%. It was suggested that massive glutamate release might require a lower ischemic threshold of 20%. The magnitude of glutamate release is correlated to the size of the resultant cortical infarct. These results are consistent with the impressions of previous investigations that have implicated glutamatergic mechanisms in focal ischemic injury. It is well known that MK-801 and other glutamate-related receptor antagonists are effective in reducing infarct size in focal ischemia models (Ozyurt et al., 1988; Park et al., 1988 b; Simon and Shiraishi, 1990; Buchan et al., 1991; Smith and Meldrum, 1992). While glutamate is a contributory factor, it is nonetheless unlikely to be the sole cause of infarction during transient focal ischemia, and other neurotransmitter systems as well as nonneuronal events may also participate in infarct formation (Plum, 1983; Dietrich et al., 1991; Globus et al., 1991).
Elevation of Neuroactive Substances in the Cortex of Cats during Prolonged Focal Ischemia
Authors: Matsumoto Katsumi , Graf Rudolf , Rosner Gerhard , Taguchi Junji , Heiss Wolf-Dieter
Published: April 2011

Sustained accumulation of excitatory amino acids and other neuroactive substances may contribute to the delayed progression of infarction in focal ischemia. Following occlusion of the left middle cerebral artery (MCAO), extracellular amino acid and purine catabolite concentrations as well as local CBF were repeatedly monitored for up to 15 h in auditory (A) and somatosensory (SF) cortices of seven halothane-anesthetized cats using microdialysis/HPLC and hydrogen clearance. MCAO resulted in persistent reduction of local CBF, which was more severe in A (n = 6) than in SF (n = 6). Accordingly, higher transmitter amino acid and purine catabolite concentrations were found in A than in SF during ischemia. Aspartate, glutamate, and γ-aminobutyrate (GABA) as well as hypoxanthine and inosine reached maximum levels 1–2 h after onset of ischemia (15-, 7-, 31-, 8-, and 14-fold increases, respectively). Maximum levels remained almost constant, with the exception of inosine, which decreased subsequently. Glycine seemed to increase with prolonged ischemia and reached maximum levels (10-fold) 15 h after occlusion. Adenosine peaked 30 min after occlusion (54-fold) and decreased thereafter to control levels within 1–2 h. One hour after occlusion, CBF thresholds for amino acid elevation were lower (glutamate and GABA ∼20 ml 100 g−1 min−1 and glycine ∼10 ml 100 g−1 min−1) than 6 and 15 h after occlusion (thresholds for all amino acids at ∼30 ml 100 g−1 min−1). These results indicate that in prolonged ischemia, excitotoxicity is an important factor, particularly in border zones of ischemic foci. It may be enhanced by an increase of glycine and the early disappearance of adenosine, which are considered to facilitate and inhibit, respectively, the deleterious effects of excitatory amino acids.
The Effects of IGF-1 Treatment after Hypoxic-Ischemic Brain Injury in Adult Rats
Authors: Guan Jian , Williams Chris , Gunning Mark , Mallard Carina , Gluckman Peter
Published: April 2011

Intraventricular injection of insulin-like growth factor 1 (IGF-1) 2 h after hypoxic–ischemic injury reduces neuronal loss. To clarify the mode of action, we compared histological outcome between treatment groups in the following three studies: 0, 0.5, 5, and 50 μg IGF-1 given 2 h after injury; 0 and 20 μg IGF-1 given 1 h before; and 20 μg IGF-1 and insulin or vehicle alone given 2 h after. Unilateral hypoxic-ischemic injury was induced in adult rats by ligation of the right carotid and exposure to 6% O2 for 10 min. Histological outcome was evaluated in the cortex, striatum, and hippocampus 5 days later. Five to 50 μg IGF-1 reduced the incidence of infarction and neuronal loss in a dose-dependent manner in all regions (p < 0.05), and 50 μg reduced the infarction rate from 87 to 26% (p < 0.01). Pretreatment did not alter outcome. IGF-1 improved outcome compared with equimolar doses of insulin (p < 0.05) and did not affect systemic glucose concentrations or cortical temperature. The results indicate that the neuronal protective effects of IGF-1 are specific and are not mediated via insulin receptors, hypothermia, or hypoglycemic mechanisms. Centrally administered IGF-1 appears to provide worthwhile trophic support to cells within most cerebral structures after transient hypoxic-ischemic injury.
Effects of Nitric Oxide Synthase Inhibition on Cerebral Blood Flow following Bilateral Carotid Artery Occlusion and Recirculation in the Rat
Authors: Prado Ricardo , Watson Brant D. , Wester Per
Published: April 2011

The effects of bilateral carotid artery occlusion/recirculation on cortical CBF (cCBF) were studied in rats following the intravenous administration of either the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester hydrochloride (l-NAME; 30 mg/kg) or an equivalent volume of saline (500 μl). Induction of bilateral carotid occlusion (BCO) in l-NAME-treated animals resulted in a reduction of cCBF to 30% of baseline. During recirculation subsequent to 20 min of BCO, cCBF in l-NAME-infused animals remained at 30% of baseline. In contrast, cCBF in saline-treated control animals returned to the original baseline level following a similar reduction to 30–40% of baseline during BCO. These results indicate that inhibition of nitric oxide generation limits normalization of regional cortical perfusion following occlusion of proximal large cerebral vessels.
Endothelin-Induced Contraction and Relaxation of Rat Isolated Basilar Artery: Effect of BQ-123
Authors: Feger G. I. , Schilling L. , Ehrenreich H. , Wahl M.
Published: April 2011

In ring segments from rat basilar artery (BA) the endothelin (ET) peptides ET-1, ET-2, and ET-3 induced concentration-related contractions. The order of potency was ET-1 = ET-2 > ET-3, while no differences occurred in the maximum contraction. The selective ETA receptor antagonist, BQ-123 (10−10-10−4 M) alone elicited a small contraction only at 10−4 M. In the presence of BQ-123 (10−7-10−5 M), the concentration-response curve for ET-1 was shifted to the right without any decrease in maximum contraction, indicating competitive inhibition of ET-1 binding to the ETA receptor by BQ-123. The pA2 value calculated for BQ-123 was 6.935; the slope of the regression curve was 0.734. In contrast to ET-1, the contractile action of ET-3 was abolished by 10−5 M BQ-123. In segments precontracted with 10−6 M serotonin, ET-3, but not ET-1, induced relaxation at low concentrations (10−11-10−8 M), with maximum relaxation amounting to 17.8 ± 14.7% of precontraction (mean ± SD; n = 16). The relaxant action of ET-3 was abolished in vessels incubated with NG-nitro-l-arginine (10−5 M), an inhibitor of nitric oxide synthase. These results indicate that the ET-induced contraction of the isolated rat BA involves activation of the ETA receptor. The ET-3-induced relaxation of precontracted rat BA is apparently mediated by release of nitric oxide from the endothelium.
Time Course of Anoxia-Induced Increase in Cerebral Blood Flow Rate in Turtles: Evidence for a Role of Adenosine
Authors: Hylland Patrick , Nilsson Göran E. , Lutz Peter L.
Published: April 2011

The exceptional ability of the turtle brain to survive prolonged anoxia makes it a unique model for studying anoxic survival mechanisms. We have used epiillumination microscopy to record blood flow rate in venules on the cortical surface of turtles ( Trachemys scripta). During anoxia, blood flow rate increased 1.7 times after 45–75 min, whereupon it fell back, reaching preanoxic values after 115 min of anoxia. Topical super-fusion with adenosine (50 μ M) during normoxia caused a 3.8-fold increase in flow rate. Superfusing the brain with the adenosine receptor blocker aminophylline (250 μ M) totally inhibited the effects of both adenosine and anoxia, while aminophylline had no effect on normoxic flow rate. None of the treatments affected systemic blood pressure. These results indicate an initial adenosine-mediated increase in cerebral blood flow rate during anoxia, probably representing an emergency response before deep metabolic depression sets in.
Brain Glucose Levels in Portacaval-Shunted Rats with Chronic, Moderate Hyperammonemia: Implications for Determination of Local Cerebral Glucose Utilization
Authors: Cruz Nancy F. , Dienel Gerald A.
Published: April 2011

Rates of glucose utilization (lCMRglc) in many structures of the brain of fed, portacaval-shunted rats, when assayed with the [14C]deoxyglucose (DG) method in our laboratory, were previously found to be unchanged (30 of 36 structures) or depressed (6 structures) during the first 4 weeks after shunting, but to rise progressively to higher than normal values in 25 of 36 structures from 4–12 weeks. In contrast, lCMRglc, when assayed with the [14C]glucose method in another laboratory, was depressed in most structures of brains of 4–8-week shunted rats that had relatively high brain ammonia levels. There was a possibility that the increases in lCMRglc obtained with the [14C]DG method may have been artifactual, due, in part, to a change in brain glucose content which could alter the value of the lumped constant of the DG method. Brain glucose levels of shunted rats were, therefore, assayed by both direct chemical measurement in freeze-blown samples and by determination of steady-state brain:plasma distribution ratios for [14C]methylglucose; the methylglucose distribution ratio varies as a function of plasma and tissue glucose contents. Within a week after shunting, ammonia levels in blood and brain rose to 0.25–0.30 m M and 0.35–0.70 μmol/g, respectively, and mean plasma glucose levels fell from 9–10 m M to 7.4–8.5 m M, and then remained nearly constant. Brains of fedshunted rats had normal glycogen levels and stable but moderately reduced glucose contents between 1 and 12 weeks (i.e., 1.9–2.2 μmol/g). [14C]Methylglucose distribution ratios were essentially the same as those in controls in 22 brain structures at 2 and 8 weeks after shunting. Because brain glucose levels remained stable from 1 to 12 weeks after shunting, there is no evidence to support the hypothesis that the value of the lumped constant would have changed and caused an artifactual rise in lCMRglc.
Effects of MK-801 and NBQX on Acute Recovery of Piglet Cerebral Metabolism after Hypothermic Circulatory Arrest
Authors: Aoki Mitsuru , Nomura Fumikazu , Stromski Michael E. , Tsuji Miles K. , Fackler James C. , Hickey Paul R. , Holtzman David , Jonas Richard A.
Published: April 2011

Brain protection during open heart surgery in the neonate and infant remains inadequate. Effects of the excitatory neurotransmitter antagonists MK-801 and NBQX on recovery of brain cellular energy state and metabolic rates were evaluated in 34 4-week-old piglets (10 MK-801, 10 NBQX, 14 controls) undergoing cardiopulmonary bypass and hypothermic circulatory arrest at 15°C nasopharyngeal temperature for 1 h, as is used clinically for repair of congenital heart defects. MK-801 (dizocilpine) (0.75 mg/kg) or NBQX [2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo( F)quinoxaline] (25 mg/kg) was given intravenously before cardiopulmonary bypass. Equivalent doses were placed in the cardiopulmonary bypass prime plus continuous infusions after reperfusion (0.15 mg kg−1h−1 and 5 mg kg−1h−1). Changes in high-energy phosphate concentrations and pH were analyzed by magnetic resonance spectroscopy in 17 animals until 225 min after reperfusion. Cerebral blood flow determined by radioactive microspheres as well as cerebral oxygen and glucose consumption were studied in 17 other animals. Cerebral blood flow and oxygen consumption were depressed relative to control by both MK-801 and NBQX at baseline. Recovery of phosphocreatine (p = 0.010), ATP (p = 0.030), and intracellular pH (p = 0.004) was accelerated by MK-801 and retarded by NBQX over the 45 min of rewarming reperfusion and the first hour of normothermic reperfusion. The final recovery of ATP at 3 h and 45 min reperfusion was significantly reduced by NBQX (46 ± 26% baseline, mean ± SD) versus control (81 ± 19%) and MK-801 (75 ± 8%) (p = 0.030). Cerebral oxygen consumption recovered to 105 ± 30% baseline in group MK-801 and 94 ± 31% in control but only to 61 ± 22% in group NBQX (p = 0.070). Cerebral blood flow stayed significantly lower in group NBQX relative to control. Thus, MK-801 accelerates recovery of cerebral high-energy phosphates and metabolic rate after cardiopulmonary bypass and hypothermic circulatory arrest in the immature animal. At the dosage used NBQX exerts an adverse effect.
Cerebral Glucose and Energy Utilization during the Evolution of Hypoxic—Ischemic Brain Damage in the Immature Rat
Authors: Vannucci Robert C. , Yager Jermone Y. , Vannucci Susan J.
Published: April 2011

The cerebral metabolic rate for glucose (CMRg1) and cerebral energy utilization (CEU) were assessed in immature rats during recovery from cerebral hypoxia–ischemia. CMRg1 was determined using a modification of the Sokoloff technique with 2-deoxy-[14C]glucose (2-DG) as the radioactive tracer. CEU was determined using the Lowry decapitation technique. Seven-day postnatal rats underwent unilateral common carotid artery ligation, followed 4 h thereafter by exposure to 8% oxygen at 37°C for 3 h. At 1, 4, or 24 h of recovery, the rat pups underwent those procedures necessary for the measurement of either CMRg1 or CEU. At 1 h of recovery, the CMRg1 of the cerebral hemisphere ipsilateral to the carotid artery occlusion was 97% of the control rate (8.7 μmol 100 g−1 min−1) but was only 48% of the control in the contralateral hemisphere. At 4 h of recovery, the CMRg1 was increased 49% above baseline in the ipsilateral hemisphere, decreasing thereafter to 84% of the control at 24 h. The CMRg1 of the contralateral hemisphere normalized by 4 h of recovery. An inverse correlation between endogenous concentrations of ATP or phosphocreatine and CMRg1 in the ipsilateral hemisphere was apparent at 4 h of recovery. CEU in the ipsilateral cerebral hemisphere was 64 and 46% of the control (3.47 mmol ∼P/kg/min) at 1 and 24 h, respectively (p < 0.05) and 77% of the control at 4 h of recovery. CEU in the contralateral hemisphere was unchanged from the control at all measured intervals. Correlation of the alterations in CMRg1 with those in CEU at the same intervals indicated that substrate supply exceeds energy utilization during early recovery from hypoxia-ischemia. The discrepancy combined with a persistent disruption of the cerebral energy state implies the existence of an uncoupling of mitochondrial oxidative phosphorylation as one mechanism for the occurrence of perinatal hypoxic-ischemic brain damage.
Cerebral Sinus and Venous Thrombosis in Rats Induces Long-Term Deficits in Brain Function and Morphology—Evidence for a Cytotoxic Genesis
Authors: Frerichs Kai U. , Deckert Maria , Kempski Oliver , Schürer Ludwig , Einhäupl Karl , Baethmann Alexander
Published: April 2011

The pathophysiology of cerebral venous infarctions is poorly understood, due partially to the lack of a suitable experimental model. Therefore, we developed a model in rats to study acute and long-term changes of brain function and morphology following thrombosis of the superior sagittal sinus. The superior sagittal sinus of rats was exposed, ligated, and injected with thrombogenic material. Thrombosis of the longitudinal sinus and ascending cortical veins was monitored by intravital fluorescence angiography. Histology was studied at 24 h and 4 weeks after thrombosis and changes in intracranial pressure, electroencephalogram (EEG), and tissue impedance were noted. Spontaneous locomotor activity was followed for 4 weeks after thrombosis. The effect of heparin treatment on tissue impedance was evaluated. Thrombosis of the superior sagittal sinus could be regularly induced, although pathological sequelae developed only if ascending veins were affected. Sinus and venous thrombosis was histologically characterized by bilateral, parasagittal infarctions. Thrombosis induction was followed by an increase in intracranial pressure from 4.7 ± 1.6 to 12.8 ± 2.4 mm Hg (n = 4) at 1 h after thrombosis, associated with an exponential rise in tissue impedance to 165 ± 14% (n = 8) of the control. EEG changes were similar to those following global cerebral ischemia and remained pathological for up to 6 months after thrombosis (n = 6). As a permanent behavioral deficit spontaneous locomotor activity was reduced to 60 ± 10% (n = 6) of the control. Finally, the administration of heparin (1 IU/g body weight) after thrombosis induction was found to reverse the pathological tissue impedance response of the brain. In conclusion, involvement of ascending cortical veins following sinus thrombosis appears to be critical for the development of irreversible tissue damage, such as infarction. Changes in intracranial pressure and tissue impedance suggest that the venous thrombosis was followed by brain edema of a predominantly cytotoxic nature. Venous thrombosis led to long-term changes of brain function, as demonstrated by persistent disturbances of the EEG or of the spontaneous locomotor drive. These deficits may be amenable to treatment with heparin.
Photothrombotic Infarction Triggers Multiple Episodes of Cortical Spreading Depression in Distant Brain Regions
Authors: Dietrich W. Dalton , Feng Zi-Cai , Leistra Hans , Watson Brant D. , Rosenthal Myron
Published: April 2011

The purposes of this study were to determine whether cortical spreading depression occurs outside of the infarct produced by photothrombotic vascular occlusion, and also the direction of spreading. Focal cerebral thrombotic infarction was produced by irradiating the exposed skull of anesthetized rats with green light (560 nm) following systemic injection of rose bengal dye. At proximal sites (∼2 mm anterior to the infarct border), transient, severe hyperemic episodes (THEs) lasting 1–2 min were intermittently recorded. THE frequency was greatest in the first hour and declined over a 3-h period. THEs were accompanied (and usually preceded) by a precipitous rise in [K+]0 (from ∼3 to >40 m M) and were associated with increases in local tissue oxygen tension (tPO2). Following the rise in [K+]0, clearance of [K+]0 to its pre-THE baseline preceded baseline recovery of CBF. These data indicate that THEs were reactive to physiologic events resembling cortical spreading depression (CSD), which provoked increased demand for oxygen and blood flow, and which spread from proximal sites to areas more distal (∼4 mm) from the rim of the evolving infarct. MK-801 (1 mg/kg, i.v.) inhibited subsequent CSD-like episodes. We conclude that photothrombosis-induced ischemia provoked CSD which was triggered either within the infarct core or in the infarct rim and spread to more distal sites. Whether multiple episodes of CSD during infarct generation are responsible for the remote consequences of focal brain injury remains to be determined.