bluuebunny/crossref_metadata_2025 huggingface dataset:
Neurotransmission in the Sheep Middle Cerebral Artery: Modulation of Responses by 5-HT and Haemolysate
Authors: Gaw Alasdair J. , Wadsworth Roger M. , Humphrey Patrick P. A.
Published: April 2011

In ring sections of the sheep middle cerebral artery, electrical field stimulation elicits a complex response due to the simultaneous release of vasodilator and vasoconstrictor neurotransmitters. Haemolysate abolishes the relaxant effects of the vasodilator neurotransmitter and causes a marked augmentation of the contractile response in both the presence (448 ± 191%) and absence (409 ± 134%) of an intact endothelium. The haemolysate also reverses relaxation induced by sodium nitroprusside or sodium nitrite but has no effect on relaxation induced by 8-Br-cGMP. The vasodilator neurotransmitter therefore appears to act directly on the smooth muscle to cause relaxation by the stimulation of guanylate cyclase. The vasoconstrictor neurotransmitters that are released are antagonised by prazosin (100 n M), ketanserin (100 n M) and atropine (100 n M), which suggests that the transmitters involved are noradrenaline, 5-hydroxytryptamine (5-HT), and acetylcholine, respectively. In the presence of these three antagonists at 10 μ M, there was 86.9 ± 4.8% inhibition. Incubation with 5-HT (10 μ M) causes a marked augmentation of the contractile response (267 ± 56%) to field stimulation that can be reduced by pretreatment with either desipramine or citalopram, inhibitors of noradrenergic and serotoninergic uptake mechanisms, respectively. The 5-HT appears to be taken up into noradrenergic nerves and released as an alternative neurotransmitter upon subsequent stimulation. These actions of haemolysate and 5-HT may be involved in the cerebral vasospasm observed following subarachnoid haemorrhage.
Delayed Onset of Neurologic Deterioration following Anoxia/Ischemia Coincides with Appearance of Impaired Brain Mitochondrial Respiration and Decreased Cytochrome Oxidase Activity
Authors: Wagner Kenneth R. , Kleinholz Marla , Myers Ronald E.
Published: April 2011

We previously demonstrated markedly inhibited brain mitochondrial respiration only in cats that (a) were hyperglycemic at anoxia and (b) had neurologic signs, i.e., fasciculations in tongue or facial muscles or focal seizures following reoxygenation. However, since the relationship between time of onset of mitochondrial dysfunction and neurologic signs was unclear, in the present study we killed postanoxic cats immediately when signs first appeared. Cerebrocortical homogenates and isolated brain mitochondria only from symptomatic cats showed markedly inhibited substrate-, ADP-, and uncoupler-stimulated respiration rates. Cytochrome oxidase activity and cytochrome aa3 concentrations were also markedly reduced in these mitochondria. Since brain mitochondrial function was impaired when neurologic signs first appeared, mitochondrial alterations are an important early organellar change correlated with development of neurologic deterioration following anoxia.
Actions of Platelet-Activating Factor on Isolated Feline and Human Cerebral Arteries
Authors: Uski Tore K. , Reinstrup Peter
Published: April 2011

The effects of platelet-activating factor (PAF) were studied on isolated feline basilar arteries (BAs) and human pial arteries (PAs). PAF contracted the BAs by 67% of the contraction induced by 124 m M K+ and the PAs by 80%. The contraction in BAs was unaffected by both indomethacin and the thromboxane receptor antagonist AH23848. PAF relaxed prostaglandin F2α-contracted arteries. In BAs 10−6 M PAF reduced the contraction by 17% and in PAs by 47%. The relaxant effects in both arteries were unaffected by indomethacin. In conclusion, PAF can act both as a constrictor and as a dilator of isolated feline and human cerebral arteries. The effects are seemingly unrelated to vascular prostanoid production.
Comparison of [11C]Diprenorphine and [11C]Carfentanil Binding to Opiate Receptors in Humans by Positron Emission Tomography
Authors: Frost J. James , Mayberg Helen S. , Sadzot Bernard , Dannals Robert F. , Lever John R. , Ravert Hayden T. , Wilson Alan A. , Wagner Henry N. , Links Jonathan M.
Published: April 2011

The kinetics and regional distribution of [11C]carfentanil, a μ-selective opiate receptor agonist, and [11C]diprenorphine, a nonselective opiate receptor antagonist, were compared using paired positron emission tomography studies in two normal volunteers. Kinetics of total radioactivity (counts/mCi/pixel) was greater for [11C]diprenorphine than [11C]carfentanil in all regions. [11C]Carfentanil binding (expressed as the total/nonspecific ratio) reached near equilibrium at ∼40 min, whereas [11C]diprenorphine showed a linear increase until ∼60 min. Kinetics of specific binding demonstrated significant dissociation of [11C]carfentanil from opiate receptors, whereas little dissociation of [11C]diprenorphine was observed during the 90-min scan session. Regional distributions of [11C]carfentanil and [11C]diprenorphine were qualitatively and quantitatively different: Relative to the thalamus (a region with known predominance of μ-receptors), [11C]diprenorphine displayed greater binding in the striatum and cingulate and frontal cortex compared to [11C]carfentanil, consistent with labeling of additional, non-μ sites by [11C]diprenorphine. We conclude from these studies that [11C]diprenorphine labels other opiate receptor subtypes in addition to the μ sites selectively labeled by [11C]carfentanil. The nonselective nature of diprenorphine potentially limits its usefulness in defining abnormalities of specific opiate receptor subtypes in various diseases. Development of selective tracers for the δ- and κ-opiate receptor sites, or alternatively use of unlabeled inhibitors to differentially displace μ, δ, and κ subtypes, will help offset these limitations.
Mild Hypothermia Prevents Ischemic Injury in Gerbil Hippocampus
Authors: Welsh Frank A. , Sims Reneé E. , Harris Valerie A.
Published: April 2011

The objective of this study was to define the degree of hypothermia required to diminish ischemic injury to CA1 hippocampal neurons following 5-min bilateral ischemia in the gerbil. The temperature of the body and head was regulated in three groups of animals at 37.5, 35.5, or 32.5°C during 5-min bilateral carotid artery occlusion. Upon recirculation, normothermia was restored in all animals, and recovery was permitted for 1 week. Ischemic injury to CA1 hippocampus was determined using three endpoints: histologic injury, ATP content, and adenylate kinase activity. Reduction of head temperature to 35.5 and 32.5°C during ischemia diminished histologic injury and improved CA1 levels of ATP and adenylate kinase activity in a dose-dependent manner. Indeed, 32.5°C completely abolished ischemic injury to CA1 hippocampus, judging from each of the three endpoints. Reduction of head temperature to 32.5°C delayed but did not prevent the depletion of ATP throughout the hippocampus during the 5-min ischemic insult. These results demonstrate that a decrease in head temperature of only 2°C reduces the degree of CA1 injury in the gerbil model of 5-min bilateral ischemia. Thus, it is imperative to maintain strict normothermia in pharmacologic studies of ischemic protection. Finally, administration of nicardipine to normothermic gerbils failed to diminish ischemic injury in the CA1 hippocampus.
Bradykinin Receptors of Cerebral Microvessels Stimulate Phosphoinositide Turnover
Authors: Homayoun Parvin , Harik Sami I.
Published: April 2011

We examined by ligand binding methods whether bradykinin (BK) receptors exist in rat and pig cerebral microvessels, and in the cerebral cortex from which the microvessels were isolated. We found a high-affinity and saturable BK receptor site in both rat and pig cerebral microvessels, but not in their cerebral cortex. The maximal density of binding and the dissociation constant were 8.0 ± 4.1 and 6.8 ± 1.5 fmol/mg of protein and 47 ± 24 and 150 ± 8 p M (mean ± SD) in cerebral microvessels of the pig and rat, respectively. The high-affinity specific binding of BK was effectively displaced by des-Arg0[Hyp3-Thi5–8,D-Phe7]BK, a specific B2 receptor antagonist, but not by des-Arg9[Leu8]BK, a specific B1 antagonist. We also demonstrated that BK increases phosphatidylinositol hydrolysis in cerebral microvessels of the rat and pig. This effect was also blocked by the B2, but not by the B1, antagonist. Increased phosphatidylinositol hydrolysis was manifested by a rapid transient increase in inositol trisphosphate and the later slow accumulation of inositol bisphosphate and inositol monophosphate. Preincubation of microvessels with phorbol ester, stable GTP analogs, pertussis toxin, or in Ca2+-free buffer did not influence BK activation of phosphatidylinositol hydrolysis. These results demonstrate the existence of BK receptors of the B2 subtype in brain microvessels, which may play an important role in modulation of the brain microcirculation, probably via increased phosphoinositide turnover.
Autoradiographic Measurement of Cerebral Lactate Transport Rate Constants in Normal and Activated Conditions
Authors: Lear James L. , Kasliwal Ravindra K.
Published: April 2011

We used quantitative autoradiography to measure the regional rate constants of blood-to-brain transport of lactate in normal rats and rats treated with kainic acid. Mean cerebral values of lactate transport rate constants were not significantly different between the normal and treated rats, being 0.13 and 0.14 min−1 (ml/g), respectively. Regional values were also generally similar between the groups, but structures that are known to be activated by kainic acid showed increased values in the treated rats compared with rates in the controls. Our measured values of lactate transport rate constants are ∼50% as great as those published for glucose, indicating that blood–brain transfer of lactate can be significant. This observation supports the hypothesis that radiolabel derived from glucose can leave the brain as radiolabeled lactate in conditions in which intracerebral lactate concentration rises, a hypothesis that has previously been presented to explain differences between rates of accumulation of radiolabel derived from deoxyglucose and glucose in such conditions.
The Effects of Hyponatraemia and Subarachnoid Haemorrhage on the Cerebral Vasomotor Responses of the Rabbit
Authors: Nelson R. J. , Perry S. , Burns A. C. R. , Roberts J. , Pickard J. D.
Published: April 2011

Impairment of cerebral autoregulation and development of hyponatraemia are both implicated in the pathogenesis of delayed cerebral ischaemia and infarction following subarachnoid haemorrhage (SAH) but the pathophysiology and interactions involved are not fully understood. We have studied the effects of hyponatraemia and SAH on the cerebral vasomotor responses of the rabbit. Cerebrovascular reactivity to hypercapnia and cerebral autoregulation to trimetaphan-induced hypotension were determined in normal and hyponatraemic rabbits before and 6 days after experimental SAH produced by two intracisternal injections of autologous blood. Hyponatraemia (mean plasma sodium of 119 m M) was induced gradually over 48 h by administration of Desmopressin and intraperitoneal 5% dextrose. Sham animals received normal saline. The cerebrovascular reactivity (% change ±SD in cortical CBF/mm Hg PaCO2, measured by hydrogen clearance) of hyponatraemic (4.8 ± 3.0%) and SAH (1.3 ± 2.0%) animals was significantly less ( p < 0.05) than control (11.6 ± 4.0%) and sham (8 ± 2.0%) animals, whereas the reactivity of hyponatraemic-SAH animals was preserved (9.8 ± 6.0%). Hyponatraemia and SAH alone each significantly impaired CBF autoregulation but their combined effects were not additive. Systemic hyponatraemia impairs normal cerebral vasomotor responses but does not augment the effects of experimental SAH in the rabbit.
Postischemic Neuronal Damage Causes Astroglial Activation and Increase in Local Cerebral Glucose Utilization of Rat Hippocampus
Authors: Rischke R. , Krieglstein J.
Published: April 2011

The purpose of the present study was to determine the consequences of postischemic neuronal damage on CMRglc. Forebrain ischemia of 10 min duration was induced in male Wistar rats. The extent of neuronal damage and the numbers of immunocytochemically detected astrocytes in the hippocampal CA1 subfield as well as CMRglc were determined 2, 5, 7, and 14 days after ischemia. CBF was additionally measured 7 days postischemia. CMRglc was decreased in cortical and thalamic structures up to 5 days postischemia, and was normalized again on day 7 after ischemia. In the hippocampal areas, CMRglc was decreased only on day 2 after ischemia, was normalized after 5 days, and increased in the stratum oriens and pyramidale of the CA1 subfield from postischemic day 7 onward. Neuronal damage was clearly demonstrable 5 days after ischemia and further increased up to day 7. The number of GFAP-reactive astrocytes increased markedly at day 7 postischemia. It is assumed that the activation of astrocytes is induced by neuronal damage, and that the astroglial metabolism is responsible for the increase in CMRglc of the CA1 subfield 7 days after ischemia. The decrease in CBF of the CA1 subfield 7 days after ischemia could be caused by a reduced density of perfused capillaries.
Lack of Sympathetic and Cholinergic Influences on Cerebral Vasodilation Caused by Sciatic Nerve Stimulation in the Rat
Authors: Ibayashi Setsuro , Ngai Al C. , Howard Matthew A. , Meno Joseph R. , Mayberg Marc R. , Winn H. Richard
Published: April 2011

We studied the influences of sympathetic and cholinergic mechanisms on pial arteriolar responses during cortical activation in the rat. Adult male Sprague-Dawley rats were anesthetized with α-chloralose and urethane and mechanically ventilated. Pial arterioles on the somatosensory cortex were visualized on a video monitor through a closed cranial window. Changes in arteriolar diameter induced by sciatic nerve stimulation (0.2 V, 5 Hz, 5 ms, for 20 s) were measured before and after (a) ipsilateral superior cervical ganglionectomy (n = 5), (b) intravenous (0.5 mg/kg) administration and topical (10−5 M) application of atropine ( n = 5), and (c) lesion of the nucleus basalis magnocellularis (the major source of intracerebral acetylcholine neurons, n = 7). Unilateral nucleus basalis magnocellularis lesions were performed stereotactically by injection of ibotenic acid (25 nmol/μl). Sensory cortex cholinergic denervation was confirmed histologically. These treatments had no significant effect on arteriolar responses to sciatic nerve stimulation. Thus, the present results suggest that neither sympathetic nor cholinergic mechanisms play a significant role in somatosensory evoked cerebral vasodilation.
Comparing Functional (PET) Images: The Assessment of Significant Change
Authors: Friston K. J. , Frith C. D. , Liddle P. F. , Frackowiak R. S. J.
Published: April 2011

Statistical parametric maps (SPMs) are potentially powerful ways of localizing differences in regional cerebral activity. This potential is limited by uncertainties in assessing the significance of these maps. In this report, we describe an approach that may partially resolve this issue. A distinction is made between using SPMs as images of change significance and using them to identify foci of significant change. In the first case, the SPM can be reported nonselectively as a single mathematical object with its omnibus significance. Alternatively, the SPM constitutes a large number of repeated measures over the brain. To reject the null hypothesis, that no change has occurred at a specific location, a threshold adjustment must be made that accounts for the large number of comparisons made. This adjustment is shown to depend on the SPM's smoothness. Smoothness can be determined empirically and be used to calculate a threshold required to identify significant foci. The approach models the SPM as a stationary stochastic process. The theory and applications are illustrated using uniform phantom images and data from a verbal fluency activation study of four normal subjects.
CBF Measured by Xe-CT: Approach to Analysis and Normal Values
Authors: Yonas Howard , Darby Joseph M. , Marks Elizabeth C. , Durham Susan R. , Maxwell Cheryl
Published: April 2011

Normal reference values and a practical approach to CBF analysis are needed for routine clinical analysis and interpretation of xenon-enhanced computed tomography (CT) CBF studies. We measured CBF in 67 normal individuals with the GE 9800 CT scanner adapted for CBF imaging with stable Xe. CBF values for vascular territories were systematically analyzed using the clustering of contiguous 2-cm circular regions of interest (ROIs) placed within the cortical mantle and basal ganglia. Mixed cortical flows averaged 51 ± 10 ml · 100 g−1 · min−1. High and low flow compartments, sampled by placing 5-mm circular ROIs in regions containing the highest and lowest flow values in each hemisphere, averaged 84 ± 14 and 20 ± 5 ml · 100 g−1 · min−1, respectively. Mixed cortical flow values as well as values within the high flow compartment demonstrated significant decline with age; however, there were no significant age-related changes in the low flow compartment. The clustering of systematically placed cortical and subcortical ROIs has provided a normative data base for Xe-CT CBF and a flexible and uncomplicated method for the analysis of CBF maps generated by Xe-enhanced CT.
Differentiation of Radioligand Delivery and Binding in the Brain: Validation of a Two-Compartment Model for [11C]Flumazenil
Authors: Holthoff Vjera A. , Koeppe Robert A. , Frey Kirk A. , Paradise Avram H. , Kuhl David E.
Published: April 2011

We recently developed a two-compartment, two-parameter tracer kinetic model to estimate the in vivo ligand transport rate ( K1) and distribution volume (DV) for the benzodiazepine antagonist [11C]flumazenil (FMZ) as measured by positron emission tomography (PET). The aim of the present study was to validate that this simplified model provides a stable measure of regional benzodiazepine receptor availability even when ligand delivery is altered. Six young normal volunteers underwent two PET studies subsequent to intravenous injections of [11C]FMZ. Each FMZ study was immediately preceded by measurements of CBF following injection of [15O]water. One set of scans (water/FMZ) was acquired under resting conditions and the other set during audiovisual stimulation. Six additional volunteers underwent two FMZ studies under identical resting conditions. Parametric images were analyzed and a comparison of test-retest studies in the stimulation group revealed a significant increase of CBF and K1 of FMZ in the occipital cortex evoked by visual activation, whereas no regional changes were noted for the DV of FMZ. No significant changes were noted for either K1 or DV of FMZ when comparing studies in the rest-rest setting. The results indicate that the use of a simple two-compartment model for the tracer kinetic analysis of [11C]FMZ makes it possible to separate high-affinity binding from altered radioligand delivery to the human brain.
Changes in Pyruvate Dehydrogenase Complex Activity during and following Severe Insulin-Induced Hypoglycemia
Authors: Cardell Monika , Siesjö Bo K. , Wieloch Tadeusz
Published: April 2011

The effect of severe insulin-induced hypoglycemia on the activity of the pyruvate dehydrogenase enzyme complex (PDHC) was investigated in homogenates of frozen rat cerebral cortex during burst suppression EEG, after 10, 30, and 60 min of isoelectric EEG, and after 30 and 180 min and 24 h of recovery following 30 min of hypoglycemic coma. Changes in PDHC activity were correlated to levels of labile organic phosphates and glycolytic metabolites. In cortex from control animals, the rate of [1-14C]pyruvate decarboxylation was 7.1 ± 1.3 U/mg of protein, or 35% of the total PDHC activity. The activity was unchanged during burst suppression EEG whereas the active fraction increased to 81–87% during hypoglycemic coma. Thirty minutes after glucose-induced recovery, the PDHC activity had decreased by 33% compared to control levels, and remained significantly depressed after 3 h of recovery. This decrease in activity was not due to a decrease in the total PDHC activity. At 24 h of recovery, PDHC activity had returned to control levels. We conclude that the activation of PDHC during hypoglycemic coma is probably the result of an increased PDH phosphatase activity following depolarization and calcium influx, and allosteric inhibition of PDH kinase due to increased ADP/ATP ratio. The depression of PDHC activity following hypoglycemic coma is probably due to an increased phosphorylation of the enzyme, as a consequence of an imbalance between PDH phosphatase and kinase activities. Since some reduction of the ATP/ADP ratio persisted and since the lactate/pyruvate ratio had normalized by 3 h of recovery, the depression of PDHC most likely reflects a decrease in PDH phosphatase activity, probably due to a decrease in intramitochondrial Ca2+.
Ischemia-Reperfusion Does Not Affect Reactivity of Isolated Canine Basilar Artery
Authors: Katušić Zvonimir S. , Michenfelder John D. , Milde James H.
Published: April 2011

The effect of ischemia-reperfusion on endothelium-dependent relaxations and reactivity of vascular smooth-muscle cells was studied in rings of basilar arteries obtained from six dogs exposed to 12 min of complete global cerebral ischemia followed by 100 min of reperfusion. Three sham-operated control dogs served as controls. Ischemia was induced either by an increase in intracranial pressure or by aortic occlusion. The rings were suspended for isometric tension recording in physiological salt solution. Ischemia-reperfusion did not affect endothelium-dependent relaxations to vasopressin and bradykinin. In rings without endothelium relaxations to sodium nitroprusside, molsidomine (SIN-1), and papaverine as well as contractions to 5-hydroxytryptamine and KCl were preserved. These results demonstrate that in large canine cerebral arteries, ischemia-reperfusion of these durations does not affect relaxations mediated by activation of endothelium or direct relaxations and contractions of vascular smooth-muscle cells.
Reduction of Infarct Volume by Magnesium after Middle Cerebral Artery Occlusion in Rats
Authors: Izumi Yoshio , Roussel Simon , Pinard Elisabeth , Seylaz Jacques
Published: April 2011

The effects of magnesium, an endogenous inhibitor of calcium entry into neurons, upon ischemic brain damage were investigated using a well-characterized model of focal cerebral ischemia in rats. Infarct volumes were determined by 2,3,5-triphenyltetrazolium chloride transcardiac perfusion 48 h after middle cerebral artery (MCA) occlusion. The area of ischemic damage was quantified by image analysis in coronal sections taken every 0.5 mm. MgCl2 (1 mmol/kg) was injected intraperitoneally just after MCA occlusion and again 1 h later. Posttreatment with MgCl2 (16 control and 16 treated rats) significantly reduced the cortical infarct volume. Compensation for the hyperglycemic effect of MgCl2 with insulin (17 rats) further reduced the infarct volume in the neocortex. No systemic effects of either treatment could account for the observed neuroprotection.
Model of Kinetic Behavior of Deoxyglucose in Heterogeneous Tissues in Brain: A Reinterpretation of the Significance of Parameters Fitted to Homogeneous Tissue Models
Authors: Schmidt K. , Mies G. , Sokoloff L.
Published: April 2011

Effects of tissue heterogeneity on regional CMRglc (rCMRglc) calculated by use of the deoxyglucose (DG) method at 45 min following the pulse of DG were evaluated in simulation studies. A theoretical model was developed to describe the kinetics of DG uptake and metabolism in heterogeneous brain tissues. Rate constants were fitted to simulation data for mixed tissue and rCMRglc computed on the basis of this tissue heterogeneity model. The results were compared with those obtained by use of the original model of the DG method for homogeneous tissue, both without (3K model) and with (4K model) a term to describe an apparent loss of deoxyglucose-6-phosphate (DG-6-P). As a direct consequence of tissue heterogeneity, the effective rate constant for phosphorylation of DG, k*3, declined with time. To compensate for the time-changing k*3, estimates of the dephosphorylation rate constant, k*4, were artifactually high when the 4K model was used, even though no dephosphorylation of DG-6-P actually occurred. The present study demonstrates that the finding of a significant k*4, at least within 45 min following a pulse of DG, may not represent dephosphorylation at all, but rather the consequence of measuring radioactivity in a heterogeneous tissue and applying a model designed for a homogeneous tissue. Furthermore, the high estimates of k*4 resulted in significant overestimation of rCMRglc. When rCMRglc was computed with the conventional single-scan or autoradiographic method at 45 min after a pulse of DG, the 3K and tissue heterogeneity models yielded values that were within 5% of the true weighted average value for the heterogeneous tissue as a whole. We conclude that the effects of tissue heterogeneity alone can give the appearance of product loss, even when none occurs, and that the use of the 4K model with the assumption of product loss in the 45-min experimental period recommended for the DG method may lead to overestimation of the rates of glucose utilization.
Precision and Accuracy Considerations of Physiological Quantitation in PET
Authors: Carson Richard E.
Published: April 2011

The ability to differentiate regional patterns of flow and metabolism between various patient populations depends upon the signal-to-noise characteristics of the data. The approach chosen for producing quantitative data will affect the detection sensitivity of a method. Methods based on mathematical models can reduce intersubject variability by accounting for factors unrelated to the physiological measure of interest, in particular, differences in the input function. However, errors in the model and in the implementation of a model-based method can increase variability compared to simpler, empirical methods. Normalization of physiological measures can significantly reduce intersubject variation; however, interpretation of normalized results can be more complex. The advantages and disadvantages of various approaches for physiological quantitation are considered.
Cerebral Blood Flow with the Indicator Fractionation of [14C]Iodoantipyrine: Effect of Paco2 on Cerebral Venous Appearance Time
Authors: Jones Stephen C. , Korfali Ender , Marshall Sam A.
Published: April 2011

The indicator fractionation technique using a diffusible indicator as a tracer for the determination of CBF has been used for numerous investigations of the cerebral circulation and its pathophysiology. The diffusible tracer is “trapped” in the brain based on the proper delay between tracer injection and cessation of the cerebral circulation by decapitation before the appearance of the tracer in the cerebral venous circulation. If this delay is too long, the quantitative assumption of the indicator fractionation technique will not be met, and CBF values will be underestimated. In 13 Sprague-Dawley rats anesthetized with pentobarbital, the appearance of [14C]iodoantipyrine at the torcular was assessed as a function of Paco2. An inverse linear relationship between Paco2 (in millimeters of mercury) and cerebral venous appearance, Ta (in seconds), was established with the regression equation Ta = −0.0842 · Paco2 + 12.3 ( R2 = 0.70, slope significantly different from zero, p < 0.001). Ta varied between 5 and 12 s and Paco2 varied between 84 and 18 mm Hg, respectively. Thus, in low-flow states, the decapitation time may be lengthened to 12 s, whereas in high-flow states, the time must be 5 s to eliminate the possibility of backflux of tracer out of the brain.
Acetylcholine Levels and Choline Acetyltransferase Activity in Rat Cerebrovascular Bed after Uni- or Bilateral Sphenopalatine Ganglionectomy
Authors: Dauphin François , Richard Jean W. , Seylaz Jacques , Quirion Rémi , Hamel Edith
Published: April 2011

Endogenous acetylcholine (ACh) levels and choline acetyltransferase (ChAT) activity were measured in several vascular segments (major cerebral arteries, cortical pial vessels, and peripheral arteries) and nervous tissues [including the sphenopalatine ganglion (SPG)] in the rat. The effects of uni- or bilateral surgical ablation of the SPG, a putative origin of the cholinergic cerebrovascular innervation, were investigated on these two specific cholinergic markers at various postoperative times. ChAT activity and ACh levels were enriched in the cerebral as compared to the peripheral arteries. Among the cerebrovascular tissues tested, ACh levels were particularly high in the circle of Willis and the vertebrobasilar segments and, to a lesser extent, in the middle cerebral artery. Lower levels were found in the small pial vessels and choroid plexus. Overall, ChAT activity measured in different arterial beds paralleled the distribution of ACh. Following uni- or bilateral removal of the SPG, slight reductions (18–36%, statistically not significant) were observed in ChAT activity in rostral cerebral arteries and pial vessels overlying the frontal cortex. Similarly, bilateral ganglionectomy resulted in minor decreases (11–22%, not significant) in the cerebrovascular contents of ACh in these same vascular segments. These results clearly show that the SPG does not or only partly contributes to the cholinergic fibers that supply the cerebrovascular bed.
Regional Density of Perfused Capillaries and Cerebral Blood Flow in Untreated Short-Term and Long-Term Streptozotocin Diabetes
Authors: Knudsen Gitte Moos , Göbel Ulrich , Paulson Olaf B. , Kuschinsky Wolfgang
Published: April 2011

The regional density of perfused cerebral capillaries (rDPC) and regional cerebral blood flow (rCBF) were measured in 12 selected brain regions in rats after 3 and 20 weeks of streptozotocin-induced diabetes and in control groups. After 3 weeks of diabetes, both rCBF and rDPC were unchanged in the diabetic group compared to the control group. A diabetes duration of 20 weeks causing bilateral cataracts induced a significant (p < 0.05) reduction in rCBF in two structures in the visual system compared to the control group (visual cortex: 105 versus 129 ml 100 g−1 min−1; lateral geniculate body: 106 versus 128 ml 100 g−1 min−1) and in the pontine reticular nucleus (82 versus 128 ml 100 g−1 min−1), whereas rDPC remained unchanged. A highly significant correlation between rCBF and rDPC was found in both control groups ( r = 0.8, p < 0.005) whereas the correlation was more scattered in the diabetic groups ( r = 0.6, p < 0.05). The present results show that during chronic diabetes, a reduction of rCBF does not affect the number of perfused capillaries.
Evaluation of Cerebral Vasomotor Reactivity by Various Vasodilating Stimuli: Comparison of CO2 to Acetazolamide
Authors: Ringelstein Erich Bernd , Van Eyck Sabine , Mertens Irene
Published: April 2011

To evaluate the role of different vasomotor stimuli for the measurement of cerebrovascular vasomotor reactivity (VMR), 47 patients (i.e., 93 hemispheres) with various degrees of internal carotid artery (ICA) occlusive disease were studied. Patients were divided into clinical [asymptomatic, transient ischemic attack (TIA) or completed stroke] as well as angiological subgroups. Low-grade or high-grade unilateral ICA lesions were compared to bilateral ICA occlusive disease. Relative flow velocity changes within the middle cerebral artery were measured by means of transcranial Doppler during hyper- and hypocapnia (VMRTOT), during hypercapnia alone, and after injection of 1 g acetazolamide (VMRACE). VMR was expressed as the percentage change in flow velocity after stimulus application as compared with flow velocity at rest. There was a close and statistically highly significant correlation of CO2-induced with acetazolamide-induced VMR ( r = 0.69 in VMRTOT versus VMRACE and 0.79 in versus VMRACE; p < 0.0001; linear regression), indicating a strong similarity of the vasodilatative effects of CO2 and acetazolamide on cerebral arteries. Both stimulation techniques highly significantly differentiated between asymptomatic patients and those with TIA or completed stroke. Angiological subgroups were separated best by the acetazolamide test. Reclassification of patients into angiological subgroups by linear discriminant analysis was equally good with all three methods. We conclude that both acetazolamide- and CO2-induced stimulation of the cerebral vasomotors are valid techniques to measure reduction in perfusion reserve due to extracranial cerebrovascular occlusive disease. Acetazolamide has the advantage of being independent of the patient's cooperation. However, it has the disadvantage of increasing the intracranial pressure and not permitting evaluation of the vasoconstrictor capabilities of the cerebral vasculature.
The Role of Electrode Size on the Incidence of Spreading Depression and on Cortical Cerebral Blood Flow as Measured by H2 Clearance
Authors: Verhaegen Marleen J. , Todd Michael M. , Warner David S. , James Bruce , Weeks Julie B.
Published: April 2011

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.
The Significance of Brain Temperature in Focal Cerebral Ischemia: Histopathological Consequences of Middle Cerebral Artery Occlusion in the Rat
Authors: Morikawa Eiharu , Ginsberg Myron D. , Dietrich W. Dalton , Duncan Robert C. , Kraydieh Susan , Globus Mordecai Y.-T. , Busto Raul
Published: April 2011

The purpose of this study was to determine the effect of selective modulation of brain temperature in the experimental settings of permanent and reversible middle cerebral artery (MCA) occlusion in Sprague–Dawley rats. Three models of proximal MCA occlusion were used, in which the effect of brain-temperature modulations could be studied. These included (a) permanent MCA occlusion with an initial 30-min period of hypotension (30 or 36°C × 4 h), (b) permanent MCA occlusion alone (30, 36, or 39°C × 2 h), and (c) 2 h of reversible MCA occlusion (30, 36, or 39°C × 2 h). In the transient MCA occlusion series, intra- and postischemic cortical blood flow was assessed using a laser–Doppler flowmeter placed over the dorsolateral cortex. After a 3-day survival, all rats were perfusion fixed for histopathological analysis and the determination of infarct volume. In animals with permanent MCA occlusion plus hypotension, no significant difference in infarct volume was demonstrated between the 30 and 36°C groups. In rats with permanent MCA occlusion without hypotension, significant differences in infarct volume were again not demonstrable, but an interaction between infarct area and temperature class was shown by repeated-measures analysis, indicating that hypothermia altered the topographic pattern of the cortical infarct. With 2 h of reversible MCA occlusion, there was a statistically significant reduction in infarct volume in the 30°C group compared to 39°C rats. Although intra- and postischemic CBF were not significantly different among the three temperature groups, the cortical infarct volume was positively correlated with postischemic CBF. The postischemic CBF, in turn, was positively correlated to the intraischemic brain temperature and was negatively correlated to CBF during the ischemic period. These findings demonstrate that moderate manipulations of brain temperature have a greater influence on the resulting cortical infarction in the setting of transient focal ischemia than in the context of permanent vascular occlusion.
Disturbance of Membrane Function Preceding Ischemic Delayed Neuronal Death in the Gerbil Hippocampus
Authors: Kirino Takaaki , Robinson Hugh P. C. , Miwa Akiko , Tamura Akira , Kawai Nobufumi
Published: April 2011

Slice preparations were made from the hippocampus of gerbils after 5 min of ischemia by carotid artery occlusion and the membrane properties of pyramidal neurons were examined. A majority of CA1 neurons lost the capacity for long-term potentiation following tetanic stimulation of the input fibers. CA3 pyramidal neurons, in contrast, preserved responses similar to those in the normal gerbil. Following ischemia, CA1 pyramidal neurons showed increased spontaneous firing that was highly voltage dependent and was blocked by intracellular injection of the Ca2+ chelator, EGTA. Thirty-five percent of CA1 neurons showed an abnormal slow oscillation of the membrane potential after 24 h following ischemia. Intracellular injection of GTPγS or IP3 produced facilitation of the oscillations followed by irreversible depolarization. Our results indicate that ischemia-damaged CA1 neurons suffer from abnormal Ca2+ homeostasis, involving IP3-induced liberation of Ca2+ from internal stores.
NMR Determination of Intracerebral Glucose Concentration and Transport Kinetics in Rat Brain
Authors: Mason Graeme F. , Behar Kevin L. , Rothman Douglas L. , Shulman Robert G.
Published: April 2011

The concentration of intracerebral glucose as a function of plasma glucose concentration was measured in rats by 13C NMR spectroscopy. Measurements were made in 20–60 min periods during the infusion of [1-13C]d-glucose, when intracerebral and plasma glucose levels were at steady state. Intracerebral glucose was found to vary from 0.7 to 19 μmol g−1 wet weight as the steady-state plasma glucose concentration was varied from 3 to 62 m M. A symmetric Michaelis–Menten model was fit to the brain and plasma glucose data with and without an unsaturable component, yielding the transport parameters Km, Vmax, and Kd. If it is assumed that all transport is saturable ( Kd = 0), then Km = 13.9 ± 2.7 m M and Vmax/ Vgly = 5.8 ± 0.8, where Vgly is the rate of brain glucose consumption. If an unsaturable component of transport is included, the transport parameters are Km = 9.2 ± 4.7 m M, Vmax/ Vgly = 5.3 ± 1.5, and Kd/ Vgly = 0.0088 ± 0.0075 ml μmol−1. It was not possible to distinguish between the cases of Kd = 0 and Kd > 0, because the goodness of fit was similar for both. However, the results in both cases indicate that the unidirectional rate of glucose influx exceeds the glycolytic rate in the basal state by 2.4-fold and as a result should not be rate limiting for normal glucose utilization.
Effect of 2-Chloroadenosine on Cerebrovascular Reactivity to Hypercapnia in Newborn Pig
Authors: Gidday Jeffrey M. , Park T. S.
Published: April 2011

The effect of local administration of vasodilative concentrations of the adenosine receptor agonist 2-chloroadenosine (2-CADO) on the hyperemic responses of the pial and parenchymal microcirculations to graded hypercapnia was determined. The cranial window and brain microdialysis–hydrogen clearance techniques were utilized in two groups of isoflurane-anesthetized newborn pigs to measure changes in pial diameters and local CBF, respectively, in response to graded hypercapnia in the absence and presence of 2-CADO. Progressive size-dependent dilations of pial arterioles [small = 41 ± 7 μm (mean ± SD), intermediate = 78 ± 13 μm, and large = 176 ± 57 μm in diameter] occurred in response to graded hypercapnia alone (Paco2 = 58 and 98 mm Hg) and to superfusions of 2-CADO (10−5 M) during normocapnia; the magnitude of the dilative response to each of these stimuli was inversely proportional to vessel size. When hypercapnia was induced concomitantly with 2-CADO superfusion, the dilative effects of each stimulus were directly additive. Similarly, local microdialysis infusion of 10−5 M 2-CADO, which doubled CBF during normocapnia, did not affect the hyperemic response of the parenchymal circulation to graded hypercapnia (Paco2 = 69 and 101 mm Hg). Our findings are consistent with the participation of adenosine in the mediation of cerebral hypercapnic hyperemia. If, however, adenosine is not involved in this dilative response, our results indicate that concomitant vascular and neuromodulatory actions induced by adenosine receptor stimulation do not affect the mechanism responsible for the hypercapnic hyperemic response.
Limiting Ischemic Injury by Inhibition of Excitatory Amino Acid Release
Authors: Graham Steven H. , Chen Jun , Sharp Frank R. , Simon Roger P.
Published: April 2011

Excitatory amino acids (EAAs) are important mediators of ischemic injury in stroke. N-Methyl-d-aspartate (NMDA) receptor antagonists have been shown to be very effective neuroprotective agents in animal models of stroke, but may have unacceptable toxicity for human use. An alternative approach is to inhibit the release of EAAs during stroke. BW1003C87 [5-(2,3,5-trichlorophenyl)-2,4-diaminopyrimidine], a drug that inhibits veratrine-induced release of the EAA glutamate in vitro, was tested in a rat model of proximal middle cerebral artery (MCA) occlusion. BW1003C87 significantly decreased ischemia-induced glutamate release in brain when given either 5 min before or 15 min following permanent MCA occlusion. Pretreated and posttreated rats had smaller infarct volumes and preserved glucose metabolism in the ischemic cortex at 24 h after MCA occlusion. BW1003C87 did not induce heat shock protein in the cingulate or retrosplenial cortex, suggesting that it does not injure neurons in these regions as do NMDA antagonists. These results demonstrate that drugs that inhibit glutamate release in ischemia may be nontoxic and show promise for the treatment of stroke.
High-Speed MR Imaging of Ischemic Brain Injury following Stenosis of the Middle Cerebral Artery
Authors: Roberts T. P. L. , Vexler Z. , Derugin N. , Moseley M. E. , Kucharczyk J.
Published: April 2011

Magnetic susceptibility contrast-enhanced and diffusion-weighted echo planar magnetic resonance (MR) imaging was performed using a cat model of acute regional cerebral ischemia induced by partial stenosis of the right middle cerebral artery (MCA). The imaging data were correlated with triphenyltetrazolium chloride (TTC)-stained histopathologic coronal brain sections to determine the prognostic efficacy of high-speed MR imaging techniques in differentiating mild, moderate, and severe cerebral hypoperfusion. Brains of animals without cortical injury on TTC staining were found to have a reduction in peak contrast enhancement of 32 ± 6% (mean ± SD) below control values with no significant change in the apparent diffusion coefficient (ADC), determined from the diffusion-weighted MR images. In cases where moderate ischemic injury was observed in the TTC-stained sections, a 10–20% drop in the ADC was found over the 6-h study period, accompanied by a much wider variation in peak contrast enhancement. Finally, where TTC staining showed severe ischemic brain damage, a 40–50% drop in ADC and a reduction in peak contrast enhancement effect of >95% were observed as early as 1 h following MCA stenosis. The significant correlation between imaging observations and histologically confirmed cerebral ischemia indicates that magnetic susceptibility contrast-enhanced echo planar MR imaging is sensitive to slight reductions in cerebral perfusion that fall below the threshold for reliably detectable ischemia-induced alterations in ADC. First-pass perfusion-sensitive imaging may thus be diagnostically useful in differentiating severely hypoperfused permanently injured tissue from the mildly hypoperfused ischemic penumbra.
Ketamine Alters Calcium and Magnesium in Brain Tissue following Experimental Head Trauma in Rats
Authors: Shapira Yoram , Lam Arthur M. , Artru Alan A. , Eng Calvin , Soltow Louise
Published: April 2011

We previously reported that the N-methyl-d-aspartate receptor antagonists dizocilpine maleate and ketamine improved the neurological severity score (NSS) after head trauma in rats. Other investigators have reported increased calcium and decreased magnesium following head trauma in untreated rats. The present study was designed to determine whether ketamine influences the concentrations of calcium and magnesium in brain tissue following head trauma. Eighty-six male Sprague–Dawley rats (180 ± 15 g) were divided into eight groups. Groups A (no head injury) and C (head injury) received no treatment. Groups B (no head injury) and D–H (head injury) received ketamine. In groups D, E, and F, ketamine, 180 mg/kg i.p., was given 1, 2, and 4 h after head trauma, respectively. In groups G and H, ketamine, 120 and 60 mg/kg, respectively, was given 1 h after head trauma. After we killed the rats at 48 h, cortical slices were taken to measure tissue calcium and magnesium content by the inductively coupled plasma atomic emission spectroscopy method. In the contused hemispheres, calcium increased and magnesium decreased (p < 0.0001). Among the head-injured groups, the increase in brain tissue calcium was smaller in groups receiving 60 mg/kg of ketamine at 1 h or 180 mg/kg of ketamine at 1, 2, or 4 h than in the group not receiving ketamine. The decrease in brain tissue magnesium was smaller in the groups receiving 180 mg/kg of ketamine at 1 and 2 h than in the group not receiving ketamine. Temporalis muscle and rectal temperatures at 1, 2, 4, 24, and 48 h after head trauma were not significantly different between treated and untreated groups. It is concluded that, in this model of closed cranial impact, 180 mg/kg of ketamine given 1 or 2 h after injury reduced both the increase in brain tissue calcium and the decrease in brain tissue magnesium at 48 h following head trauma.
DFMO Reduces Cortical Infarct Volume after Middle Cerebral Artery Occlusion in the Rat
Authors: Muszynski Cheryl A. , Robertson Claudia S. , Goodman J. Clay , Henley Charles M.
Published: April 2011

Ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, is induced in ischemic tissue and may mediate vasogenic edema and delayed neuronal death. We determined the effects of α-difluoromethylornithine (DFMO), a specific inhibitor of ODC, on infarct size and ODC activity in a rat model of transient focal ischemia. DFMO blocked the ischemia-induced increase in ODC and significantly reduced infarct volumes by 57–45%, depending upon the treatment regimen. These studies suggest that polyamine metabolism plays a role in the development of cerebral infarction after focal ischemia and that DFMO may be useful in limiting injury after a stroke.