bluuebunny/crossref_metadata_2025 huggingface dataset:
Blood Viscoelasticity Response during Carotid Endarterectomy
Authors: Hold Michael , Merrelaar Johann J. , Hollaus Peter , Bull Phillipe G. , Denck Helmuth
Published: April 2011

As demonstrated in many studies ischemic brain injury causes microcirculatory disturbances which is reflected in changes in the rheological behavior of blood. This is caused by multifactorial interaction between blood cells and damaged endothelium in the capillary network with release of tissue metabolites and byproducts of cellular injury with resulting increased cellular permeability producing a volume shift into the interstitium and, subsequently, a rise in the hematocrit density. Drop in perfusion pressure produces an increase in whole blood viscosity. By means of an oscillating capillary rheometer and densimeter, the viscous and elastic parts of the complex viscosity of whole blood and plasma were measured from the ipsilateral internal jugular vein in 17 patients with unilateral occlusive carotid lesions during different stages of carotid endarterectomy. Our results show that fluid characteristics deteriorated significantly during carotid clamping with increase in whole blood viscoelasticity and plasma density, although collateral circulation was judged sufficient in the angiogram and cerebral perfusion pressure. These parameters not only returned to their initial value, but a significant amelioration was observed after installation of an intraluminal indwelling shunt as a response to improved orthograde flow and an enhanced shear velocity. We conclude that an increase in whole blood viscosity does correlate with decreased cerebral blood flow. This response is immediate. Hematocrit density increases significantly as a result of fluid shift into the interstitium. These changes are reversible if blood flow is promptly restored.
Neuroprotective Effects of L-Kynurenine on Hypoxia—Ischemia and NMDA Lesions in Neonatal Rats
Authors: Nozaki Kazuhiko , Beal M. Flint
Published: April 2011

Kynurenic acid is the only known endogenous excitatory amino acid receptor antagonist in the central nervous system. In the present study, we examined whether increasing brain concentrations of kynurenic acid by loading with its precursor l-kynurenine, or blocking its excretion with probenecid, could exert neuroprotective effects. Neuroprotective effects were examined in a neonatal model of hypoxia–ischemia, and following intrastriatal injection of N-methyl-d-aspartate (NMDA). Seven-day-old rats underwent unilateral ligation of the carotid artery, followed by exposure to 8% oxygen for 1.5 h. l-kynurenine administered 1 h before the hypoxia–ischemia showed a dose-dependent significant neuroprotective effect, with complete protection at a dose of 300 mg kg−1. The induction of c-fos immunoreactivity in cerebral cortex was also blocked by this dose of l-kynurenine. Probenecid alone had moderate neuroprotective effects, while a combination of a low dose of probenecid with doses of 50–200 mg kg−1 of l-kynurenine showed significant dose-dependent neuroprotection. Kynurenine dose-dependently protected against NMDA neurotoxicity in 7-day-old rats. Neurochemical analysis confirmed that l-kynurenine with or without probenecid markedly increased concentrations of kynurenic acid in cerebral cortex of 7-day-old rats. These results show for the first time that pharmacologic manipulation of endogenous concentrations of kynurenic acid can exert neuroprotective effects.
Effect of Sumatriptan, a Selective 5-HT1-like Receptor Agonist, on Pial Vessel Diameter in Anaesthetised Cats
Authors: Connor Helen E. , Stubbs Carole M. , Feniuk Wasyl , Humphrey Patrick P. A.
Published: April 2011

The action of sumatriptan, a selective 5-HT1-like receptor agonist that is effective for the acute treatment of migraine, was compared on pial vessel diameter following perivascular or intravenous administration to anaesthetised cats. Sumatriptan (0.01–10 μ M), when microinjected perivascularly, caused a decrease in pial artery diameter (maximum change of –19 ± 9%; mean ± SD) but had no effect on the diameter of pial veins. Sumatriptan (1 μ M)-induced pial artery vasoconstriction was unaffected by coadministration of ketanserin (1 μ M) or ondansetron (1 μ M) but was significantly (p < 0.01) attenuated by methiothepin (1 μ M). Intravenous infusion of a clinically effective dose of sumatriptan (64 μg/kg/10 min) caused selective carotid vasoconstriction (22 ± 6% increase in carotid vascular resistance with little or no change in blood pressure or heart rate) and no change in pial artery diameter, although sumatriptan (1 μ M) administered perivascularly in these animals before and after the infusion caused pial artery vasoconstriction. These results demonstrate that perivascularly administered sumatriptan causes pial artery vasoconstriction via activation of 5-HT1-like receptors. However, intravenously administered sumatriptan does not cause pial artery vasoconstriction, which suggests that sumatriptan does not readily penetrate the cerebrovascular intima.
Measurement of Radiotracer Concentration in Brain Gray Matter Using Positron Emission Tomography: MRI-Based Correction for Partial Volume Effects
Authors: Müller-Gärtner Hans W. , Links Jonathan M. , Prince Jerry L. , Bryan R. Nick , McVeigh Elliot , Leal Jeffrey P. , Davatzikos Christos , Frost J. James
Published: April 2011

Accuracy in in vivo quantitation of brain function with positron emission tomography (PET) has often been limited by partial volume effects. This limitation becomes prominent in studies of aging and degenerative brain diseases where partial volume effects vary with different degrees of atrophy. The present study describes how the actual gray matter (GM) tracer concentration can be estimated using an algorithm that relates the regional fraction of GM to partial volume effects. The regional fraction of GM was determined by magnetic resonance imaging (MRI). The procedure is designated as GM PET. In computer simulations and phantom studies, the GM PET algorithm permitted a 100% recovery of the actual tracer concentration in neocortical GM and hippocampus, irrespective of the GM volume. GM PET was applied in a test case of temporal lobe epilepsy revealing an increase in radiotracer activity in GM that was undetected in the PET image before correction for partial volume effects. In computer simulations, errors in the segmentation of GM and errors in registration of PET and MRI images resulted in less than 15% inaccuracy in the GM PET image. In conclusion, GM PET permits accurate determination of the actual radiotracer concentration in human brain GM in vivo. The method differentiates whether a change in the apparent radiotracer concentration reflects solely an alteration in GM volume or rather a change in radiotracer concentration per unit volume of GM.
Chronic Parasympathetic Sectioning Decreases Regional Cerebral Blood Flow during Hemorrhagic Hypotension and Increases Infarct Size after Middle Cerebral Artery Occlusion in Spontaneously Hypertensive Rats
Authors: Koketsu Naoki , Moskowitz Michael A. , Kontos Hermes A. , Yokota Masayuki , Shimizu Takeo
Published: April 2011

Regional cerebral blood flow (rCBF) during controlled hemorrhagic hypotension (140–20 mm Hg) was assessed 10–14 days after chronic unilateral sectioning of parasympathetic and/or sensory fibers innervating pial vessels in spontaneously hypertensive rats (SHR). rCBF was measured in the cortical barrel fields bilaterally by laser Doppler blood flowmetry. Immunohistochemistry of middle cerebral artery (MCA) whole mount preparations was used to verify the surgical lesion. During hemorrhagic hypotension, rCBF was equivalent on the two sides in shams, after selective sensory denervation, or in parasympathetically sectioned animals exhibiting small decreases (≤30%) in immunoreactive vasoactive intestinal peptide (VIP)-containing fibers. After chronic parasympathetic denervation, decreases in perfusion pressure were accompanied by greater reductions in rCBF on the lesioned side; changes in vascular resistance were also attenuated on that side. The rCBF response to hypercapnia (Paco2 50 mm Hg), however, was symmetrical and robust. To examine the effects of impaired neurogenic vasodilation on the pathophysiology of cerebral ischemia, infarct size was measured 24 h following tandem MCA occlusion in denervated animals. Infarction volume was larger after selective parasympathetic sectioning (sham, 156 ± 27 vs. 196 ± 32 mm3, respectively) but only in those denervated animals demonstrating ≥40% decrease in immunoreactive VIP-containing fibers within the ipsilateral MCA. Lower than expected blood flow/perfusion pressure in the cortex distal to an occluded blood vessel may relate the observed blood flow responses to the occurrence of larger cortical infarcts in parasympathetically denervated animals. If true, the findings suggest a novel role for neurogenic vasodilation in the pathophysiology of cerebral ischemia and in rCBF regulation within the peri-infarction zone.
The Endothelium-Dependent Effects of Thimerosal on Mouse Pial Arterioles in vivo: Evidence for Control of Microvascular Events by EDRF as Well as Prostaglandins
Authors: Rosenblum William I. , Nishimura Hiroyuki , Ellis Earl F. , Nelson Guy H.
Published: April 2011

Thimerosal causes synthesis and/or release of both endothelium-derived relaxing factor (EDRF) and prostaglandins from conductance vessels in vitro. We tested its effects and mechanism of action on mouse pial arterioles in vivo using intravital microscopic techniques. Topical thimerosal dilated pial arterioles. This effect was eliminated by endothelial injury produced by a laser/Evans blue technique. Dilation was also eliminated by topical l-NMMA, a reported inhibitor of EDRF synthesis. Topical thimerosal also reduced the incidence of platelet adhesion/aggregation (“capture”) at a site of minimal endothelial damage. This effect was eliminated by l-NMMA pretreatment. The ability of thimerosal to dilate arterioles was eliminated not only by treatments thought to eliminate synthesis/release of EDRF, but also by cyclooxygenase inhibitors. However, inhibition of platelet adhesion/aggregation was not affected by cyclooxygenase inhibition. Thimerosal significantly increased production of prostaglandin E2 recovered from a closed cranial window. We conclude that the dilating effects of thimerosal on diameter require two endothelium-derived agents: EDRF and one or more prostaglandins acting in concert. However, the inhibiting effect of thimerosal on local platelet adhesion/aggregation appears to be caused only by an increase in EDRF at the injured site.
Biphasic Striatal Acetylcholine Release during and after Transient Cerebral Ischemia in Gerbils
Authors: Bertrand N. , Ishii H. , Beley A. , Spatz M.
Published: April 2011

Acetylcholine (ACh) release into the extracellular space was measured by HPLC with electrochemical detection after in vivo intracerebral microdialysis in the striatum of gerbils subjected to 15 min of bilateral carotid artery occlusion followed by 5 h of recirculation. Tissue ACh and choline (Ch) contents were also determined during ischemia and after 5, 30, 60, and 120 min of reflow. Fifteen minutes of ischemia led to a significant transient increase in extracellular ACh concentration (threefold after 7.5 min of ischemia) concomitant with a reduced endogenous ACh level (–62%) and increased tissue Ch content (ninefold). Recirculation significantly reduced the ACh release during the early period of reflow (–50% vs. basal level), followed by a significant increase in ACh release between 1 and 3 h of reflow (45–55% vs. basal level) and subsequent normalization. Simultaneously, a “rebound” of tissue ACh level occurred in the early period of reflow (fourfold vs. ischemic value), followed by gradual normalization after 2 h of reperfusion, whereas a rapid decrease in tissue Ch levels was found after 30 min of reflow. These findings represent the first demonstration of a biphasic release of ACh during ischemia and reperfusion, as assessed by intracerebral microdialysis in gerbils.
Hypothermia Attenuates the Loss of Hippocampal Microtubule-Associated Protein 2 (MAP2) following Traumatic Brain Injury
Authors: Taft William C. , Yang Keyi , Dixon C. Edward , Clifton Guy L. , Hayes Ronald L.
Published: April 2011

Traumatic brain injury (TBI) produces a tissue-specific decrease in protein levels of microtubule-associated protein 2 (MAP2), an important cross-linking component of the neuronal cytoskeleton. Because moderate brain hypothermia (30°C) reduces certain neurobehavioral deficits produced by TBI, we examined the efficacy of moderate hypothermia (30°C) in reversing the TBI-induced loss of MAP2 protein. Naive, sham-injured, and moderate (2.1 atm) fluid percussion-injured rats were assessed for MAP2 protein content 3 h post injury using quantitative immunoreactivity measurements. Parallel groups of sham-injured and fluid percussion-injured animals were maintained in moderate hypothermia (30°C), as measured by temporalis muscle temperature, for MAP2 quantitation 3 h post injury. No difference in MAP2 levels was observed between naive and sham-injured normothermic animals. Hypothermia alone had no effect on soluble MAP2 levels in sham-injured animals compared with normothermic sham-injured controls (88.0 ± 7.3%; p > 0.10). Fluid percussion injury dramatically reduced MAP2 levels in he normothermic group (44.3 ± 5.9%; p < 0.0005) compared with normothermic sham-injured controls. No significant reduction of MAP2 was seen in the hypothermic injured group (95.2 ± 4.6%; compared with hypothermic sham-injured controls, p > 0.20). Although it is premature to infer any causal link, the data suggest that the attenuation of injury-induced MAP2 loss by hypothermia may contribute to its overall neuroprotective action.
Regulation of Intracellular pH in Single Rat Cortical Neurons in vitro: A Microspectrofluorometric Study
Authors: Ou-Yang Yibing , Mellergård Pekka , Siesjö Bo K.
Published: April 2011

Intracellular pH (pHi) and the mechanisms of pHi regulation in cultured rat cortical neurons were studied with microspectrofluorometry and the pH-sensitive fluorophore 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein. Steady-state pHi was 7.00 ± 0.17 (mean ± SD) and 7.09 ± 0.14 in nominally HCO3− -free and HCO3−-containing solutions, respectively, and was dependent on extracellular Na+ and Cl−. Following an acid transient, induced by an NH1 prepulse or an increase in CO2 tension, pHi decreased and then rapidly returned to baseline, with an average net acid extrusion rate of 2.6 and 2.8 mmol/L/min, in nominally HCO3− -free and HCO3− -containing solutions, respectively. The recovery was completely blocked by removal of extracellular Na+ and was partially inhibited by amiloride or 5- N-methyl- N-isobutylamiloride. In most cells pHi recovery was completely blocked in the presence of harmaline. The recovery of pHi was not influenced by addition of 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) or removal of Cl−. The rapid regulation of pHi seen following a transient alkalinization was not inhibited by amiloride or by removal of extracellular Na+, but was partially inhibited by DIDS and by removal of extracellular Cl−. The results are compatible with the presence of at least two different pHi-regulating mechanisms: an acid-extruding Na+/H+ antiporter, possibly consisting of different subtypes, and a passive Cl−/HCO3− exchanger, mediating loss of HCO3− from the cell.
A Model of Brain Arteriolar Oxygen and Carbon Dioxide Transport during Anemia
Authors: Schacterle Richard S. , Ribando Robert J. , Adams J. Milton
Published: April 2011

Existing experimental and theoretical evidence suggests that precapillary diffusion of O2 and CO2 occurs between arterioles and tissue under normal physiologic conditions. However, limited information is available on arteriolar gas transport during anemia. With use of a mathematical model of an arteriolar network in brain tissue, anemic hematocrits of 35, 25, and 15% were modeled to determine the effect of anemia on the exchange, the change in the equilibrium tissue O2 and CO2 tensions, and the increase in blood flow needed to restore tissue oxygenation. We found that the blood Po2 exiting the network fell from 66 mm Hg normally to 48 mm Hg during the severest anemia. Concurrently, the equilibrium tissue O2 tensions dropped from 44 to 23 mm Hg. For CO2 the exit blood Pco2 was 58 mm Hg for a 15% hematocrit, an increase of 4 mm Hg from the normal value, and equilibrium tissue Pco2 increased from 56 to 61 mm Hg. Blood flow increases from normal values necessary to offset the effects of the decreased O2 delivery to the tissue were 26, 86, and 222%, respectively, for hematocrits of 35, 25, and 15%. We compared our model results with recent experimental studies that have suggested that the amount of O2 diffusion is much higher than predicted values. We found that these experimental O2 gradients are three to four times larger than theoretical.
Changes in Insulin-like Growth Factor 1 Receptor Density after Transient Cerebral Ischemia in the Rat. Lack of Protection against Ischemic Brain Damage following Injection of Insulin-Like Growth Factor 1
Authors: Bergstedt Kerstin , Wieloch Tadeusz
Published: April 2011

Binding of 125I-insulin-like growth factor-1 (125I-IGF-1) to rat brain slices was studied after 15 min of two-vessel occlusion ischemia and 1 h to 4 days of recirculation. Ligand binding in the hippocampus increased at 6 h post ischemia in the CA1 and CA3 regions and the dentate gyrus, suggesting that the IGF-1 receptors were up-regulated, while no change was seen in neocortex and striatum. Intracerebroventricular injections of IGF-1 (2 μg) prior to and after transient cerebral ischemia did not reduce neuronal damage. The increased up-regulation on IGF-1 receptors and the absence of neuroprotection by IGF-1 suggest that the intracellular signal transduction chain activated by the IGF-1 receptor may be interrupted.
Differential Transcription and Translation of Immediate Early Genes in the Gerbil Hippocampus after Transient Global Ischemia
Authors: Kiessling Marika , Stumm Gabriele , Xie Yaxia , Herdegen Thomas , Aguzzi Adriano , Bravo Rodrigo , Gass Peter
Published: April 2011

Excitotoxic activation of glutamate receptors is thought to be a key event for the molecular pathogenesis of postischemic delayed neuronal death of CA-1 neurons in the gerbil hippocampus. Glutamate receptor stimulation also causes induction of transcription factors that belong to the class of immediate early genes. We examined the expression of six different immediate early genes in the gerbil hippocampus after transient global ischemia. Comparative analysis of c-fos and Krox-24 expression was carried out in the same animals at the transcriptional and translational level by in situ hybridization and immunocytochemistry. Postischemic synthesis of four additional immediate early gene (IEG)–encoded proteins (FOS-B, c-JUN, JUN-B, and JUN-D) was investigated by immunocytochemistry at recirculation intervals between 1 and 48 h. After 5 min of ischemia, transcription of c-fos and Krox-24 mRNA was induced in all hippocampal subpopulations with peak expression at 1 h after recirculation. In vulnerable CA-1 neurons, increased transcription of c-fos and Krox-24 was not followed by translation into protein. Induction of immediate early gene-encoded proteins was restricted to neuronal populations less vulnerable to brief ischemia and identified neurons that are targets of glutamate receptor-mediated neurotoxicity but that are destined to survive. Our data indicate an asynchronous synthesis and persistence of individual IEG-encoded proteins in these neurons. The staggered induction implies that combinatorial changes of transcription factors allow a differential postischemic regulation of target gene expression both spatially and over time.
Changes in Brain Capillary Diameter during Hypocapnia and Hypercapnia
Authors: Duelli Roman , Kuschinsky Wolfgang
Published: April 2011

Since changes in the surface area of capillaries may be relevant to capillary exchange, the distensibility of brain capillaries was investigated. Brain capillary diameters were measured after perfusion fixation of brain tissue at a constant perfusion pressure during hypo- or hypercapnia. Sections were embedded, stained, and analyzed by light microscopy. The results showed significant differences in mean capillary diameter between the hypocapnic and the hypercapnic group. In the eight brain structures analyzed, capillary diameters were always larger in the hypercapnic group. Mean capillary diameter was 4.93 ± 0.29 μm in the hypocapnic group and 5.91 ± 0.10 μm in the hypercapnic group (means ± SD). We conclude that brain capillaries exhibit a moderate degree of distensibility. Variations in the precapillary pressure of microvessels may therefore influence both capillary flow and capillary surface area.
Induction of 70-kDa Heat Shock Protein and hsp70 mRNA following Transient Focal Cerebral Ischemia in the Rat
Authors: Kinouchi Hiroyuki , Sharp Frank R. , Hill Mary P. , Koistinaho Jari , Sagar Stephen M. , Chan Pak H.
Published: April 2011

Induction of the 70-kDa heat shock protein (HSP70) was demonstrated immunocytochemically in adult rats 4 h to 7 days following temporary middle cerebral artery (MCA) occlusions lasting 30, 60, or 90 min. Maximal HSP70 induction occurred ∼24 h following ischemia. Thirty minutes of ischemia induced HSP70 in neurons throughout the cortex in the MCA distribution, whereas 90 min of ischemia induced HSP70 in neurons in the penumbra. HSP70 protein was induced in endothelial cells in infarcted neocortex following 60–90 min of MCA occlusion, and HSP70 was induced in endothelial cells in infarcted regions of lateral striatum following 30–90 min of MCA occlusion. hsp70 mRNA was induced in the MCA distribution in cortex and to a lesser extent in striatum at 2 h to 3 days following 60 min of ischemia. It is proposed that brief ischemia induces hsp70 mRNA and HSP70 protein in the cells most vulnerable to ischemia—the neurons. HSP70 protein is not induced in most neurons and glia following 60–90 min of ischemia in areas destined to infarct, whereas it is induced in vascular endothelial cells.
Regional Changes in Interstitial K+ and Ca2+ Levels following Cortical Compression Contusion Trauma in Rats
Authors: Nilsson P. , Hillered L. , Olsson Y. , Sheardown M. J. , Hansen A. J.
Published: April 2011

Brain trauma is associated with acute functional impairment and neuronal injury. At present, it is unclear to what extent disturbances in ion homeostasis are involved in these changes. We used ion-selective microelectrodes to register interstitial potassium ([K+]e) and calcium ([Ca2+]e) concentrations in the brain cortex following cerebral compression contusion in the rat. The trauma was produced by dropping a 21 g weight from a height of 35 cm onto a piston that compressed the cortex 1.5 mm. Ion measurements were made in two different locations of the contused region: in the perimeter, i.e., the shear stress zone (region A), and in the center (region B). The trauma resulted in an immediate increase in [K+]e from a control level of 3 m M to a level >60 m M in both regions, and a concomitant negative shift in DC potential. In both regions, there was a simultaneous, dramatic decrease in [Ca2+]e from a baseline of 1.1 m M to 0.3–0.1 m M. Interstitial [K+] and the DC potential normalized within 3 min after trauma. In region B, [Ca2+]e recovered to near control levels within 5 min after ictus. In region A, however, recovery of [Ca2+]e was significantly slower, with a return to near baseline values within 50 min after trauma. The prolonged lowering of [Ca2+]e in region A was associated with an inability to propagate cortical spreading depression, suggesting a profound functional disturbance. Histologic evaluation 72 h after trauma revealed that neuronal injury was confined exclusively to region A. The results indicate that compression contusion trauma produces a transient membrane depolarization associated with a pronounced cellular release of K+ and a massive Ca2+ entry into the intracellular compartment. We suggest that the acute functional impairment and the subsequent neuronal injury in region A is caused by the prolonged disturbance of cellular calcium homeostasis mediated by leaky membranes exposed to shear stress.
Energy Reserves and Utilization Rates in Developing Brain Measured in vivo by 31P and 1H Nuclear Magnetic Resonance Spectroscopy
Authors: Corbett Ronald J. T. , Laptook Abbot R. , Garcia Damian , Ruley Joan I.
Published: April 2011

Age-related changes in cerebral energy utilization were examined in swine, a species whose maximal rate of development is known to occur in the perinatal period. Interleaved in vivo 31P and 1H nuclear magnetic resonance spectroscopy was used to measure the rates of change in cerebral concentrations of phosphocreatine (PCr), nucleoside triphosphates, and lactate following complete ischemia, induced via cardiac arrest, in a total of 19 newborn, 10-day-old, and 1-month-old piglets. Preischemic concentrations of these three metabolites plus glucose and glycogen were determined in a separate experiment on 12 piglets whose brains were funnel-frozen in situ. The rate constants for the PCr and ATP decline and lactate increase were determined by nonlinear regression fits to the experimental data, assuming first-order kinetics. The rate constants and preischemic metabolite concentrations were used to calculate the initial flux of high-energy phosphate equivalents (∼P), which was used as an estimate of cerebral energy utilization at the point when ischemia was initiated. Cerebral energy utilization equaled 6.5 ± 1.9, 9.5 ± 3.2, and 15.1 ± 3.2 μmol ∼P/g/min in newborn, 10-day-old, and 1-month-old piglets, respectively. Within each age group the energy utilization rate was not altered by hyperglycemia-induced increases in cerebral energy reserves, but during hypoglycemia cerebral energy utilization rates decrease. The slope of ∼P versus time decreased with the duration of ischemia, indicating that cerebral energy utilization rates decrease after the first few minutes of ischemia. Newborn piglets had higher cerebral energy utilization rates compared with literature values for newborn rats and mice. This is consistent with the concept that newborns from a species with a perinatal stage of maximal growth and development will have higher cerebral energy demands compared with newborns from a species such as rodents, whose maximal growth occurs postnatally. However, this conclusion remains tentative because literature cerebral utilization rates estimated from the initial slope of ∼P-versus-time plots tend to underestimate the true rate, since the assumption of continued linearity may not be valid for the interval chosen.
Triphasic Response of Rat Intracerebral Arterioles to Increasing Concentrations of Vasopressin in vitro
Authors: Takayasu Masakazu , Kajita Yasukazu , Suzuki Yoshio , Shibuya Masato , Sugita Kenichiro , Ishikawa Tomohiko , Hidaka Hiroyoshi
Published: April 2011

To determine how vasopressin affects the vascular tone of the smaller cerebral arterioles, we carried out an in vitro study of isolated and cannulated intracerebral arterioles of rats. We found that increasing concentrations of vasopressin induced a triphasic response of vasodilation (10−12–10−11 M), vasoconstriction (10−10–10−8 M), and vasodilation stabilizing to control diameter (10−7–10−6 M) and that the maximum constriction was twice the maximum dilation in these smaller arterioles [21.2 ± 13.1% (mean ± SD) decrease in diameter vs. 11.2 ± 5.7% increase]. Pretreatment of the arterioles with NG-monomethyl-l-arginine (10−4 M), a specific inhibitor of endothelium-derived relaxing factor, abolished the vasopressin-induced vasodilation and significantly increased the vasoconstriction. These results suggest that these arterioles were maintained in a dilated state by an endothelium-derived relaxing factor activated by vasopressin. Both vasodilation and vasoconstriction were found to be mediated through vasopressin V1 receptors in a study of arterioles pretreated with d(CH2)5Tyr(Me)arginine vasopressin (10−6 M), a vasopressin V1 receptor antagonist. These results support the hypothesis that vasopressin may constrict smaller cerebral arterioles while simultaneously dilating larger cerebral arteries. Our results also suggest that vasopressin may aggravate cerebral ischemia in pathological conditions, such as subarachnoid hemorrhage, when the arteriolar response to vasopressin shifts from vasodilation to vasoconstriction due to increased vasopressin levels in plasma and CSF and impaired endothelium-derived relaxation.
Glucose Transporter Isoforms in Brain: Absence of GLUT3 from the Blood—Brain Barrier
Authors: Maher Frances , Vannucci Susan J. , Simpson Ian A.
Published: April 2011

Two glucose transporter (GLUT) isoforms have been identified in brain. The GLUT1 isoform is abundant in cerebral microvessels and may be present in glia and neurons, whereas GLUT3 is probably the major neuronal glucose transporter. This study investigates whether GLUT3 is also present in microvessels from rat, human, and canine brain, by means of antisera directed against the divergent C-terminal sequences of mouse and human GLUT3. GLUT1 was detected in whole brain as two molecular mass forms: 55 kDa in microvessels and 45 kDa in cortical neuronal/glial membranes. With the aid of the appropriate antisera to the species-specific sequences, GLUT3 was detected in rat and human cortical membranes but not in isolated rat or human microvessels. These antisera failed to detect GLUT3 in either canine cortical membranes or canine microvessels, implying additional species specificity in the C-terminal sequence.
Investigation of Postmortem Functional Changes in Human Cerebral Arteries
Authors: Onoue Hisashi , Kaito Nobuyoshi , Tokudome Shogo , Abe Toshiaki , Tashibu Koichi , Nagashima Hiroyasu , Nakamura Norio
Published: April 2011

This study demonstrated the time-dependent changes in postmortem responses of isolated human middle cerebral artery strips to vasodilators. The relaxation induced by prostaglandin (PG) I2 or nitroglycerin remained stable for 24 h postmortem. In arterial strips precontracted with PGF2α, substance P and bradykinin both elicited relaxation that was almost completely abolished by removal of the endothelium. The endothelium-dependent response to both peptides was significantly degraded in strips obtained >12 h postmortem. These results indicate a selective functional or anatomical vulnerability of the vascular endothelium compared with that of the vasodilator mechanisms of the smooth muscle in the postmortem period. However, cerebral arteries isolated from human cadavers within 12 h postmortem should be adequate for studies of both smooth muscle and endothelial reactivity to vasodilators.
Pharmacokinetics of Plasma 6-[18F]Fluoro-l-3,4-Dihydroxyphenylalanine ([18F]FDOPA) in Humans
Authors: Cumming Paul , Léger Gabriel C. , Kuwabara Hiroto , Gjedde Albert
Published: April 2011

Like native DOPA, [18F]-6-fluoro-l-3,4-dihydroxyphenylalanine ([18F]FDOPA) is subject to methylation and decarboxylation. To determine the rates of formation and elimination of [18F]FDOPA metabolites, plasma from human subjects undergoing positron emission tomographic (PET) studies was analyzed by high-performance liquid chromatography (HPLC). In addition to the principal metabolite O-methyl-[18F]FDOPA (OMe-[18F]FDOPA), two decarboxylated metabolites were detected in plasma from carbidopa pretreated subjects. The concentrations of each metabolite during 90 min following tracer injection could be described as a function of the concentration of [18F]FDOPA, and two rate constants; k0, the rate of formation, and k–1, the rate of clearance. Plasma metabolite time series generated from total plasma activity curves and measured rate constants were in close agreement with the actual concentrations determined by HPLC fractionation. Population means for k0 (0.011 ± 0.002 min−1) and k–1, (0.010 ± 0.003 min−1) were used to generate “simulated” plasma curves. The measured and generated plasma curves were used as inputs for estimation of partition and decarboxylation coefficients of [18F]FDOPA in brain. The use of generated input functions from normal population means of transfer coefficients did not introduce a systematic error into the estimate of the enzyme activity. However, the high variability of these estimates in patients precludes the use of this technique as an alterative to individual HPLC measurements.
Reproducibility of Resting Cerebral Blood Flow Measurements with H215O Positron Emission Tomography in Humans
Authors: Matthew Elizabeth , Andreason Paul , Carson Richard E. , Herscovitch Peter , Pettigrew Karen , Cohen Robert , King Catherine , Johanson Chris-Ellyn , Paul Steven M.
Published: April 2011

Two consecutive measurements of resting CBF were carried out in normal volunteers (n = 25) using H215O positron emission tomography. Absolute whole-brain blood flow (WBBF; ml 100 g−1 min−1, mean ± SD) for the first (40.3 ± 6.4) and second (39.3 ± 6.5) measurements was not significantly different (mean % difference 2.3 ± 8.7). Analysis of regions of interest showed no significant differences in absolute regional CBF (rCBF) and normalized (rCBF/WBBF) rCBF. Left-right differences were also not significant. These data demonstrate the reproducibility of resting CBF measurements in normal humans.
Local Cerebral Blood Flow Measured by Xenon-Enhanced CT during Cryogenic Brain Edema and Intracranial Hypertension in Monkeys
Authors: Darby Joseph M. , Nemoto Edwin M. , Yonas Howard , Yao Liping , Melick John A. , Boston J. Robert
Published: April 2011

We developed a closed-skull model of freeze injury-induced brain edema, a model classically thought to produce vasogenic edema, and observed the natural course of changes in edema and blood flow using xenon-enhanced computed tomography (CT) in five rhesus monkeys before and for up to 6 h post insult. Intracranial pressure (ICP) gradually rose throughout the duration of the experiment. CT scans and CBF images permitted direct observation of the evolution of the lesion and revealed early ischemia in the periphery of the injury zone that progressed over time in association with edema. Frequency histogram analysis of local CBF (lCBF) demonstrated subtle but potentially important changes in distribution of lCBF between and within hemispheres at various times post insult. Changes in lCBF distribution were phasic and dissociated from increases in ICP in the latter stages of injury. The Xe/CT CBF method can be used to evaluate the effects of injury and therapy on CBF in this and other models of acute brain injury.
Glucose Can Fuel Glutamate Uptake in Ischemic Brain
Authors: Swanson Raymond A. , Chen Jun , Graham Steven H.
Published: April 2011

Astrocytes in culture can maintain glutamate uptake during hypoxia if glucose is available. To determine whether this capacity is shared by brain in situ, extracellular glutamate levels were measured in ischemic brain under conditions of continued glucose delivery. Microdialysis probes were placed bilaterally in caudate nuclei of rats and perfused with artificial cerebrospinal fluid (CSF) containing either 30 or 0 m M glucose. Global cerebral ischemia was induced by cardiac arrest. Dialysate collected from probes not perfused with glucose showed a 50-fold increase in glutamate levels over the 60 min following cardiac arrest. Addition of glucose to the perfusate reduced the glutamate rise to <20% of the levels attained in the glucose-free probes. The glucose effect was negated by the addition of 0.5 m M of the glutamate uptake blocker threo-β-hydroxyaspartate to the artificial CSF. These results show that oxygen is not required to maintain efficient uptake of extracellular glutamate in brain and suggest that elevations in extracellular glutamate levels during ischemia result from metabolic perturbations other than hypoxia.
Intravital Microreflectometry of Individual Pial Vessels and Capillary Region of Rat
Authors: Watanabe Manabu , Harada Noboru , Kosaka Hiroaki , Shiga Takeshi
Published: April 2011

A microscopic reflectance spectrophotometer was constructed to obtain the spectra of single pial vessels and of a region containing only capillaries (capillary region). The difference in the oxygen saturation (So2) of hemoglobin between the regional arteriole and venule [R(A – V)] and that between the regional arteriole or capillaries [R(A – C)] were calculated. The reduction of cytochrome aa3 was also estimated in the capillary region. This method was applied to the brain surface of spontaneously breathing rats subjected to hypoxic and anemic hypoxia. On decreasing the inhaled O2 from 100 to 15%, elevation of R(A – V) and R(A – C) with slight arteriolar dilatation (though statistically not significant) was observed. Below 10% O2 (especially at 4 and 3% O2), the R(A – V) and R(A – C) decreased in spite of significant arteriolar dilatation with progressive reduction of cytochrome aa3, indicating suppression of oxygen transport to mitochondria. In the case of hemodilution down to 37% hematocrit (Ht), elevation of R(A – V) and R(A – C) occurred with a slight tendency toward arteriolar dilatation. Below 32% Ht, the R(A – V) decreased but the R(A – C) remained steady, while reduction of cytochrome aa3 progressed. Altogether, the So2 in the capillary region decreased and the reduction of cytochrome aa3 progressed with the decline of arteriolar O2 supply in both hypoxic and anemic hypoxia.
A Selective N-Type Ca2+-Channel Blocker Prevents CA1 Injury 24 h following Severe Forebrain Ischemia and Reduces Infarction following Focal Ischemia
Authors: Buchan Alastair M. , Gertler Stan Z. , Li Hui , Xue Dong , Huang Zhi-Gao , Chaundy Karen E. , Barnes Kimberley , Lesiuk Howard J.
Published: April 2011

SNX-111 (NEUREX Corporation, Menlo Park, CA, U.S.A.) an ω-conopeptide, was tested for cytoprotection following normothermic ischemia using both a four-vessel occlusion model of severe forebrain ischemia and a model of transient middle cerebral artery occlusion focal ischemia. Adult male Wistar rats were subjected to 10 min of forebrain ischemia followed by 7 days of reperfusion. A single dose of SNX-111 (5 mg/kg) was injected intravenously following delays of either 6 or 24 h after reperfusion. For 11 rats treated with saline, there was 78 ± 13% CA1 neuronal injury (mean ± SD); for 11 given SNX-111 delayed by 6 h, injury was reduced to 35 ± 30% ( p < 0.01); and remarkably, treatment delayed by 24 h ( n = 10), still resulted in protection, with only 50 ± 29% injury ( p < 0.05). Adult male spontaneously hypertensive rats had transient occlusion of the right middle cerebral artery of 1.5- or 2-h duration followed by 22.5 or 22 h of reperfusion, respectively. Rats were randomly assigned to receive either saline or SNX-111 (5 mg/kg i.v.), with treatment starting immediately after reperfusion (1.5-h ischemic group) or at 1 h following the onset of ischemia (2-h ischemic group). In the 1.5-h ischemic group, saline-treated animals sustained 138 ± 32 mm3 of neocortical infarction ( n = 9), and SNX-111 treatment resulted in an infarct reduction to 76 ± 25 mm3 ( n = 9; p < 0.001). In the 2-h ischemic group, saline-treated controls sustained 211 ± 51 mm3 ( n = 6) of infarction, and SNX-111 infusion attenuated the infarct size to 126 ± 50 mm3 ( n = 5; p < 0.05). Because of the hypotensive effects of SNX-111, an additional SNX-111-treated group with intravenous norepinephrine blood pressure support was studied, using 2 h of focal ischemia and 22 h of reperfusion. In this group, combined treatment resulted in 141 ± 22 mm3 of infarction ( n = 5; p < 0.05). These data suggest that Ca2+ fluxes through ω-conopeptide-sensitive N-type Ca2+ channels are critically involved in the pathogenesis of selective neuronal death up to 24 h after ischemia in the hippocampus and that this conopeptide protection extends, even when given late, to neocortical infarct reduction.
Mechanism of Action and Persistence of Neuroprotection by Cell-Permeant Ca2+ Chelators
Authors: Tymianski Michael , Spigelman Igor , Zhang Liang , Carlen Peter L. , Tator Charles H. , Charlton Milton P. , Wallace M. Christopher
Published: April 2011

Cell-permeant Ca2+ chelators such as 1,2-bis-(2-aminophenoxy)ethane- N,N,N′,N′-tetraacetic acid acetoxymethyl ester (BAPTA-AM) have been reported to protect neurons in experimental focal cerebral ischemia. However, their in vivo actions are uncertain, and their protective efficacy is proven only in brief cerebral ischemia paradigms. Here we examine their mechanism of action in vitro and duration of efficacy in vivo. Electrophysiological studies were made in CA1 neurons in rat hippocampal slices. When superfused with BAPTA-AM (30–50 μ M), CA1 somatic field potential recordings showed attenuation of the population spike amplitude, and intracellular recordings showed reduced excitatory postsynaptic potentials, indicating inhibition of excitatory synaptic transmission. Also, Ca2+ -dependent accommodation and post-spike-train hyperpolarizations were reduced, indicating Ca2+ chelation hear the internal cell membrane surface. To determine whether Ca2+ chelators reduce the size of cerebral infarction rather than simply delaying its evolution, we studied the effects of BAPTA-AM treatment on infarction size 24 h after permanent middle cerebral artery occlusion. Fischer rats ( n = 8 per group) were pretreated with saline, BAPTA-AM (20 mg/kg), or MK-801 (0.5 mg/kg). Infarction volumes in animals treated with BAPTA-AM were reduced by 50.5% compared with controls ( p = 0.018), whereas animals treated with MK-801 experienced a statistically insignificant infarct volume reduction (26%; p = 0.27). These data show a persistence of neuroprotection by the Ca2+ chelator at 24 h and indicate that it may act by attenuating synaptic transmission and subplasma membrane Ca2+ excess.
The NOS Inhibitor, 7-Nitroindazole, Decreases Focal Infarct Volume but Not the Response to Topical Acetylcholine in Pial Vessels
Authors: Yoshida Tazuka , Limmroth Volker , Irikura Katsumi , Moskowitz Michael A.
Published: April 2011

We examined whether 7-nitroindazole (7-NI), a putative inhibitor of neuronal nitric oxide synthase (nNOS), decreases cerebral infarction 24 h after proximal middle cerebral artery (MCA) occlusion. In preliminary experiments, we determined that 7-NI (25, 50, and 100 mg/kg i.p.) decreased nitric oxide synthase (NOS) activity within cerebral cortex by 40–60% when measured up to 120 min, but not 240 min after administration. At 25 or 50 mg/kg, 7-NI did not alter the systemic arterial blood pressure or the dilation of pial arterioles after topical acetylcholine (10 and 100 μ M). To examine the effect of 7-NI on infarct size, 55 Sprague–Dawley halothaneanesthetized rats were subjected to proximal MCA occlusion (modified Tamura method). Five minutes after occlusion, 7-NI (25 or 50 mg/kg i.p.) or vehicle was injected. Animals treated with 25 or 50 mg/kg showed 25 and 27% reductions in infarct volume, respectively. Coadministration of l-arginine (300 mg/kg i.p.) plus 7-NI (25 mg/kg i.p.) reversed the effect. If, indeed, the effects of 7-NI are mediated by inhibition of nNOS activity, these results suggest that enzymatic products of the neuronal isoform promote ischemic injury and that they do so at least within the first few hours after permanent occlusion. The results also emphasize the importance of developing strategies to selectively inhibit the neuronal isoform inasmuch as we observed previously that administering the less selective NOS inhibitor, Nω-nitro-l-arginine (L-NA), in the same model either caused no change or increased the volume of ischemic injury.
The Role of Endothelium and Nitric Oxide in Rat Pial Arteriolar Dilatory Responses to CO2 in vivo
Authors: Wang Qiong , Pelligrino Dale A. , Koenig Heidi M. , Albrecht Ronald F.
Published: April 2011

Using a closed cranial window system and intravital microscopy/videometry, we studied the rat pial arteriolar (30–60 μm) responses to CO2 before and following a light/dye (L/D) endothelial injury or topical application of the nitric oxide synthase (NOS) inhibitor, nitro-l-arginine (L-NA) or its inactive form, D-NA. L/D treatment consisted of intravenous injection of sodium fluorescein and the illumination (for 90 s) of arteriolar discrete segments on the cortical surface with light from a mercury lamp. Functional changes in pial arteriolar endothelium were characterized by evaluating responses to topical application of acetylcholine (Ach, 5 × 10−4 M) and to intravenous (i.v.) oxotremorine (OXO, a stable blood–brain barrier permeant muscarinic agonist, 1 μg kg−1 min−1). After the L/D injury, dilation to Ach was absent whereas dilations to the NO donor, S-nitrosoacetyl-penicillamine (SNAP, 10−5 M) and to CO2 (5%) were unchanged (Paco2 = 70 mm Hg). Loss of Ach response but intact SNAP response confirmed functional endothelial injury and intact smooth-muscle function. The global endothelium-dependent vasodilation induced by i.v. OXO was markedly attenuated when expanding the L/D injury field from 300 μm to 6 mm in diameter. However, the global vasodilation induced by inhalation of CO2 was still unaffected by this increase in the area of light exposure. This provides evidence that the expanded exposure was capable of impairing global vasodilation resulting from endothelium-dependent stimuli but not from inhalation of CO2. The intact CO2 response despite an endothelial dysfunction suggests that the reported NO dependence of hypercapnia-induced cerebral hyperemia in rats cannot be attributed to an endothelial NO source. Topical suffusion of L-NA (1 m M) for 45–60 min in our preparation blocked the pial arteriolar response to Ach, whereas CO2 and SNAP responses were unaffected. An attenuation (by 50%) of the response to CO2 was achieved if suffusion of L-NA was given for ≥2 h. Suffusion of D-NA, applied in the same manner, did not influence responses to any of the above applications. This demonstrates that there is a NO-dependent component for hypercapnic cerebral vasodilation even at the pial arteriolar level. The strikingly different time-related effect of topical L-NA on the Ach and CO2 responses, together with the lack of effect of endothelial injury on CO2-induced dilation, strongly suggest a nonendothelial source of NO in hypercapnic cerebrovascular dilation.
Graphical, Kinetic, and Equilibrium Analyses of in vivo [123I]β-CIT Binding to Dopamine Transporters in Healthy Human Subjects
Authors: Laruelle Marc , Wallace Elizabeth , Seibyl John P. , Baldwin Ronald M. , Zea-Ponce Yolanda , Zoghbi Sami S. , Neumeyer John L. , Charney Dennis S. , Hoffer Paul B. , Innis Robert B.
Published: April 2011

The in vivo kinetics of the dopamine (DA) transporter probe 123I-labeled 2β-carboxymethoxy-3β-(4-iodophenyl)tropane ([123I]β-CIT) in striatum was investigated with single-photon emission computerized tomography (SPECT) in five healthy human subjects. The aim of this study was to derive an adequate measure of the DA transporter density that would not be affected by regional cerebral blood flow or peripheral clearance of the tracer. SPECT data were acquired on the day of injection (day 1) from 0 to 7 h and on the following day (day 2) from 19 to 25 h. Arterial sampling on day 1 was used to measure the input function. Graphical, kinetic, and equilibrium analyses were evaluated. Graphical analysis of day 1 data, with the assumption of negligible dissociation of the tracer–receptor complex ( k4 = 0), was found to be blood flow-dependent. A three-compartment kinetic analysis of day 1 data were performed using a three ( k4 = 0)- and a four ( k4 > 0)-parameter model. The three-parameter model estimated the kon Bmax product at 0.886 ± 0.087 min−1. The four-parameter model gave a binding potential (BP) of 476 ml g−1, a value consistent with in vitro measurements. The stability of the regional uptake on day 2 allowed direct measurement of the specific to nonspecific equilibrium partition coefficient (V3″ = k3/ k4 = 6.66 ± 1.54). Results of day 1 kinetic analysis and day 2 equilibrium analysis were well correlated among subjects. Simulations indicated that the error associated with the day 2 equilibrium analysis was acceptable for plasma tracer terminal half-lives >10 h. We propose the equilibrium analysis on day 2 as the method of choice for clinical studies since it does not require multiple scans or the measurement of the arterial plasma tracer concentrations.