bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitric Oxide Synthesis and Regional Cerebral Blood Flow Responses to Hypercapnia and Hypoxia in the Rat
Authors: Pelligrino D. A. , Koenig H. M. , Albrecht R. F.
Published: April 2011

The role of nitric oxide (NO) synthesis in the cerebral hyperemic responses to hypercapnia and hypoxia was investigated in anesthetized rats. Regional CBF (rCBF) measurements were obtained in the cortex (CX), subcortex (SC), brainstem (BS), and cerebellum (CE) using radiolabeled microspheres. The rCBF responses to either hypercapnia (Paco2 = 70–80 mm Hg) or hypoxia (Paco2 = 40–45 mm Hg) were compared in rat groups studied in the presence and absence of NO synthase inhibition induced via the intravenous infusion of nitro-l-arginine methyl ester (l-NAME, 3 mg kg−1 min−1). Administration of l-NAME under normocapnic/normoxic conditions produced a 40–60% reduction in baseline rCBF values, indicating the presence of a NO “tone” in the cerebral vasculature. Infusion of l-NAME resulted in a substantial attenuation, in all regions measured, of the rCBF increases that normally accompany hypercapnia. In comparing saline-infused to l-NAME-infused rats, the percentage increases in rCBF (from normocapnic baseline values) were 351% versus 166% (CX), 446% versus 199% (SC), 443% versus 206% (BS), and 483% versus 174% (CE), respectively. The rCBF changes from baseline (ΔrCBF in ml 100 g−1 min−1) were 488 versus 57 (CX), 570 versus 60 (SC), 434 versus 72 (BS), and 393 versus 45 (CE), respectively. These differences were all statistically significant ( p < 0.05). During hypoxia, when compared to rats not given l-NAME, inhibition of NO synthase activity resulted in significantly greater ( p < 0.05) percentage increases in rCBF (from normoxic baseline values) in most regions. The changes in non-l-NAME- vs. l-NAME-infused rats were 156% versus 262% (CX), 181% versus 309% (SC), and 210% versus 462% (BS), respectively. When the ΔrCBF values (from normoxic baseline levels) were compared, the changes were greater in the l-NAME group, but the differences were statistically insignificant. The results of this study indicated that NO synthesis is critically involved in the cerebral hyperemic response to hypercapnia but not hypoxia. In fact, the data obtained in the hypoxic groups suggested that reductions in O2 supply may inhibit the NO-generating capacity in the brain.
Developmental Changes in Intracellular Calcium Regulation in Rat Cerebral Cortex during Hypoxia
Authors: Bickler Philip E. , Gallego Steven M. , Hansen Bonnie M.
Published: April 2011

During the first weeks of life, injury to the central nervous system caused by brief periods of oxygen deprivation greatly increases. To investigate possible causes for this change, the effects of hypoxia or application of the excitatory neurotransmitter glutamate on intracellular calcium ([Ca2+]i) and ATP were studied in rat cerebrocortical brain slices. [Ca2+]i was measured fluo-rometrically with the indicator Fura-2. Hypoxia (95% N2/ 5% CO2) or 100 μ M sodium cyanide produced gradual elevations in [Ca2+]i and ATP depletion in slices from rats <2 weeks old, but rapid changes in older rats. After 20 min, [Ca2+]i in adult slices exposed to cyanide was 1,980 ± 310 n M; in day 1–14 animals, it was 796 ± 181 n M (p < 0.05). Combination of cyanide and a glycolytic inhibitor (iodoacetate) rapidly elevated [Ca2+]i and depleted ATP in all age groups. Energy utilization during anoxia, assessed by measuring ATP fall in cyanide/ iodoacetate-treated brain slices, increased with age. Elevations in [Ca2+]i caused by application of 500 μ M glutamate increased 240% from days 1–2 to day 28, but ATP loss caused by glutamate did not change with age. The N-methyl-d-aspartate antagonist MK-801 delayed calcium entry during the initial 5–7 min of hypoxia or cyanide in rats <2 weeks old. We conclude that anaerobic ATP production, conservation of energy by reduced ATP consumption, and reduced sensitivity to glutamate contribute to delaying elevation in [Ca2+]i in neonatal rat brain during hypoxia.
MK-801 (Dizocilpine) Protects the Brain from Repeated Normothermic Global Ischemic Insults in the Rat
Authors: Lin Baowan , Dietrich W. Dalton , Ginsberg Myron D. , Globus Mordecai Y.-T. , Busto Raul
Published: April 2011

We investigated the neuroprotective potential of MK-801 (dizocilpine), a noncompetitive N-methyl-d-aspartate (NMDA) antagonist, in the setting of three 5-min periods of global cerebral ischemia separated by 1-h intervals in halothane-anesthetized rats. Each ischemic insult was produced by bilateral carotid artery occlusions plus hypotension (50 mm Hg). Brain temperature was maintained at normothermic levels (36.5–37.0°C) throughout the experiment. MK-801 (3 mg/kg) (n = 6) or saline (n = 6) was injected intraperitoneally 45 min following the end of the first ischemic insult. Following 7-day survival, quantitative neuronal counts of perfusion-fixed brains revealed severe ischemic damage in hippocampal CA1 area, neocortex, ventrolateral thalamus, and striatum of untreated rats. By contrast, significant protection was observed in MK-801-treated rats. In area CA1 of the hippocampus, numbers of normal neurons were increased 11- to 14-fold by MK-801 treatment (p < 0.01). The ventrolateral thalamus of MK-801-treated rats showed almost complete histologic protection, and neocortical damage was reduced by 71% (p < 0.01). The degree of MK-801 protection of striatal neurons was less complete than that seen in other vulnerable structures, amounting to 63% for central striatum (p = 0.02, Mann–Whitney U test) and 48% in the dorsolateral striatum (NS). A repeated-measures analysis of variance demonstrated a highly significant overall protective effect of MK-801 treatment ( F1,10 = 37.2, p = 0.0001). These findings indicate that excitotoxic mechanisms play a major role in neuronal damage produced by repeated ischemic insults and that striking cerebroprotection is conferred by MK-801 administered following the first insult in animals with cerebral normothermia. NMDA antagonists may prove useful in patients at risk of repeated episodes of cerebral ischemia.
Increased Ca2+ Influx in the Resting State Maintains the Myogenic Tone and Activates Charybdotoxin-Sensitive K+ Channels in Dog Basilar Artery
Authors: Asano Masahisa , Masuzawa-Ito Kaoru , Matsuda Tomohiro , Suzuki Yoshio , Oyama Hirofumi , Shibuya Masato , Sugita Kenichiro
Published: April 2011

We examined whether Ca2+ channel function in the resting state alters the resting tone and Ca2+ -activated K+ (KCa) channel function in dog basilar artery: data were compared with findings in the mesenteric artery. Isolated dog basilar artery maintained a myogenic tone; that is, the resting tone decreased when either the Krebs solution was replaced with a Ca2+ -free solution or nifedipine was added. The basal 45Ca influx in the resting state of the basilar artery was significantly increased compared with that in the mesenteric artery, and this increase in the basilar artery was reduced by nifedipine. The addition of charybdotoxin (ChTX), a blocker of large-conductance KCa channels, to the resting strips caused a concentration-dependent contraction in the basilar artery but not in the mesenteric artery. The ChTX-induced contraction in the basilar artery was abolished by nifedipine. In resting strips preloaded with 86Rb, the basal 86Rb efflux rate constant was significantly greater in the basilar artery than in the mesenteric artery. The addition of nifedipine to the resting strips decreased the basal 86Rb efflux rate constant only in the basilar artery. These results suggest that the transmembrane Ca2+ influx via L-type voltage-dependent Ca2+ channels was significantly increased in the resting state of the basilar artery and that the myogenic tone was therefore maintained and the ChTX-sensitive KCa channels were highly activated.
Does Ischemia with Reperfusion Lead to Oxidative Damage to Proteins in the Brain?
Authors: Folbergrová Jaroslava , Kiyota Yoshihiro , Pahlmark Kerstin , Memezawa Hajime , Smith Maj-Lis , Siesjö Bo K.
Published: April 2011

Recent results suggest that even relatively brief periods of ischemia in gerbils (10 min) lead to oxidative damage to brain proteins, reflected in an increased carbonyl content in the soluble protein fraction and a decreased glutamine synthetase (GS) activity. Since we failed to reproduce these findings in rats subjected to 15 min of transient ischemia, we explored whether oxidative damage to proteins could be observed after longer ischemic periods. To that end, one middle cerebral artery was occluded in rats for either 1 or 3 h, with recirculation periods of 0 min, 15 min, 1 h, and 6 h. Protein carbonyl content and GS activity were determined in focal and perifocal tissues and compared with values obtained in the same areas on the contralateral side. Ischemia, particularly of 3-h duration, followed by various reperfusion periods was accompanied by a significant (16–35%) decrease in the concentration of proteins of the soluble protein fraction. However, in no group was there an increased carbonyl content of the remaining proteins in this fraction. When expressed per milligram of protein, GS activity remained unchanged or rose somewhat. An inconsistent (and moderate) decrease in GS activity was present only if GS activity was expressed per milligram of wet tissue. The present findings, which fail to document oxidative damage to proteins following focal ischemia of 1- or 3-h duration, are thus radically different from those obtained in gerbils. The results suggest that appreciable species differences exist and raise the question of whether free radical–mediated oxidation of proteins is an invariable component of ischemic brain damage.
Influence of Plasma Glucose Concentration on Rat Brain Extracellular Calcium Transients during Spreading Depression
Authors: Gidö Gunilla , Katsura Kenichiro , Kristian Tibor , Siesjö Bo K.
Published: April 2011

The objective of this study was to establish whether tissues that are energy compromised, but not energy depleted, demonstrate exaggerated calcium transients when subjected to membrane depolarizations of the spreading depression (SD) type. Anesthetized and artificially ventilated rats were given insulin in order to induce progressively lower plasma glucose concentrations. Spreading depression was elicited by local application of KCl; extracellular calcium concentration (Ca2+e) as well as direct current (DC) potential were recorded. When plasma glucose concentration fell below ∼3 m M, the duration of the Ca2+e transient gradually increased to values exceeding 500% of control. The increase was associated with a corresponding increase in the duration of the DC potential shift, but the amplitude of the Ca2+e transient did not change. It is concluded that a restriction of glucose (or oxygen) supply, as occurs in hypoglycemia (or hypoxia), prolongs the calcium transient associated with depolarization of the SD type, even though tissue phosphocreatine and ATP concentrations are normal. The results support the contention that repeated depolarizations, occurring in the penumbral zone of a focal ischemic lesion, could lead to calcium-related damage.
Attenuation of Ischemia-Induced Extracellular Adenosine Accumulation by Homocysteine
Authors: Sciotti Veronica M. , Van Wylen David G. L.
Published: April 2011

The purpose of this study was to determine the effects of homocysteine, which consumes intracellular adenosine via formation of S-adenosylhomocysteine, on interstitial fluid (ISF) adeonsine and cerebral blood flow (CBF) before, during, and after cerebral ischemia. Microdialysis probes, used to measure local CBF (H2 clearance) and to sample ISF, were implanted bilaterally into the caudate nucleus of halothane-anesthetized rats ( n = 8). l-Homocysteine thiolactone was administered locally via one of the probes. Animals were exposed to 20 min of ischemia, induced by bilateral carotid occlusion plus hemorrhage to an arterial blood pressure of 50 mm Hg, followed by 60 min of reperfusion. Before ischemia, CBF and dialysate adenosine were decreased with homocysteine. During ischemia and early reperfusion, dialysate purine metabolites increased on both sides of the brain; however, the ischemia-induced increase in adenosine was attenuated on the side of local homocysteine. CBF was lower on the side of homocysteine throughout reperfusion. These data demonstrate that homocysteine (a) decreases basal ISF adenosine and CBF, (b) attenuates the increase in dialysate adenosine during ischemia, and (c) reduces hyperemia during early reperfusion.
Hilar Somatostatin Neurons are More Vulnerable to an Ischemic Insult Than CA1 Pyramidal Neurons
Authors: Matsuyama Tomohiro , Tsuchiyama Masato , Nakamura Hitoshi , Matsumoto Masayasu , Sugita Minoru
Published: April 2011

The effects of a very short ischemic insult on hilar somatostatin (SS) neurons were investigated in the gerbil hippocampus by means of immunocytochemistry and in situ hybridization histochemistry. A selective and significant loss of 40% of hilar SS neurons took place after 1 day, and a 60% loss after 7 days following 2 min of ischemia, while no SS neurons were lost during recirculation after 1 min of ischemia. Repeated 2-min periods of ischemia, which induced ischemic tolerance by vulnerable CA1 neurons, caused almost complete loss of hilar SS neurons. This study clearly demonstrates that hilar SS neurons are more vulnerable to ischemic insult than CA1 pyramidal neurons. Ischemic tolerance may be induced during the progressive loss of SS neurons in the hilus by changes in their synaptic connections to CA1 pyramidal neurons.
PACAP, a VIP-like Peptide: Immunohistochemical Localization and Effect upon Cat Pial Arteries and Cerebral Blood Flow
Authors: Uddman R. , Goadsby P. J. , Jansen I. , Edvinsson L.
Published: April 2011

Pituitary adenylate cyclase activating peptide (PACAP) is a vasoactive intestinal polypeptide (VIP)–like peptide recently isolated from ovine hypothalami. Nerve fibers containing PACAP immunoreactivity were present in the adventitia and the adventitia-media border of cat cerebral arteries. Double immunostaining revealed that PACAP-immunoreactive nerve fibers constituted a sub-population of the VIP-containing fibers. PACAP effected a concentration-dependent relaxation of feline middle cerebral arteries that had been precontracted with prostaglandin F2α. The maximum relaxation, 24 and 34% of precontraction, was achieved with PACAP-38 and PACAP-27, respectively, at a concentration of 10−6 M. In cats anesthetized with α-chloralose, intracerebral microinjection of PACAP effected a moderate increase in cerebral blood flow. The maximal increase (18.6 ± 6%) was observed following the injection of 5 μg PACAP.
Metabolites of 2-Deoxy-[14C]Glucose in Plasma and Brain: Influence on Rate of Glucose Utilization Determined with Deoxyglucose Method in Rat Brain
Authors: Dienel Gerald A. , Cruz Nancy F. , Sokoloff Louis
Published: April 2011

The [14]deoxyglucose ([14C]DG) method depends upon quantitative trapping of metabolites in brain at the site of phosphorylation, and in the usual procedure it is assumed that all the label in plasma is in free DG. Our previous finding of labeled nonacidic derivatives of DG in plasma raised the possibility that some metabolites of DG might not be fully retained in body tissues and therefore cause overestimation of the integrated specific activity of the precursor pool determined from assay of label in plasma and/or underestimation of the true size of the metabolite fraction in brain. In the present study, metabolism of DG in rat tissues by secondary pathways was examined and found to be more extensive than previously recognized. When 14C-labeled compounds in ethanol extracts of either plasma or brain were separated by anion exchange HPLC, eight fractions were obtained. 14C-labeled metabolites in plasma were detected after a 35-min lag and gradually increased in amount with time after an intravenous pulse. In brain, deoxyglucose-6-phosphate was further metabolized, mainly to deoxyglucose-1-phosphate and deoxyglucose-1,6-phosphate. These are acid-labile compounds and accounted for ∼20% of the 14C in the metabolite pool in brain. The rate constants for net loss of 14C from the metabolite pool between 45 and 180 min after a pulse were similar (0.4–0.5%/min) in vivo and in intact postmortem brain. The rate constant for loss of deoxyglucose-6-phosphate (DG-6-P) in vivo (∼0.7%/min) was, however, about twice that for postmortem brain, suggesting that a significant fraction of the DG-6-P lost in vivo is due to its further metabolism by energy-dependent reactions. 14C-labeled metabolites of [14C]DG in plasma and brain do not interfere with determination of local rates of glucose utilization in brain in normal, conscious rats by the autoradiographic method if the prescribed procedures and a 45-min experimental period are used.
Dexmedetomidine Decreases Cerebral Blood Flow Velocity in Humans
Authors: Zornow Mark H. , Maze Mervyn , Dyck J. Barry , Shafer Steven L.
Published: April 2011

This study was designed to determine the effects of dexmedetomidine on CBF velocity as measured by transcranial Doppler sonography in human volunteers. Dexmedetomidine, a potent α-2 adrenergic agonist, was administered by computer-driven infusion pump to six male volunteers. Serial measurements of middle cerebral artery blood flow velocity at four steady-state plasma concentrations of dexmedetomidine were made with a 2-MHz transcranial Doppler transducer via the temporal window. The targeted plasma concentrations were 0.49, 0.65, 0.81, and 0.97 ng/ml. These represent 60, 80, 100, and 120%, respectively, of the mean peak concentration following the intramuscular administration of 2 μg/kg of dexmedetomidine. Subjects experienced a significant degree of sedation at the highest infusion rates. Mean CBF velocity decreased with each increase in plasma concentration of dexmedetomidine and then began to return to basal levels after termination of the infusion. A trend toward an increase in the pulsatility index at the higher levels of dexmedetomidine suggests that the observed decrement in CBF velocity was due to an increase in cerebral vascular resistance. Upon initiation of the drug infusion, mean arterial pressure decreased from ∼95 mm Hg to 78 mm Hg. There were no further decreases in arterial pressure with subsequent increases in plasma concentrations of dexmedetomidine. Arterial carbon dioxide tension increased to a maximum of 45 mm Hg during the drug infusion, but this increase from baseline was not statistically significant. These studies are in agreement with previous animal studies which demonstrate a decrease in CBF after administration of dexmedetomidine.
Spectral Analysis of Dynamic PET Studies
Authors: Cunningham Vincent J. , Jones Terry
Published: April 2011

We describe a new technique for the analysis of dynamic positron emission tomography (PET) studies in humans, where data consist of the time courses of label in tissue regions of interest and in arterial blood, following the administration of radiolabeled tracers. The technique produces a simple spectrum of the kinetic components which relate the tissue's response to the blood activity curve. From this summary of the kinetic components, the tissue's unit impulse response can be derived. The convolution of the arterial input function with the derived unit impulse response function gives the curve of best fit to the observed tissue data. The analysis makes no a priori assumptions regarding the number of compartments or components required to describe the time course of label in the tissue. Rather, it is based on a general linear model, presented here in a formulation compatible with its solution using standard computer algorithms. Its application is illustrated with reference to cerebral blood flow, glucose utilization, and ligand binding. The interpretation of the spectra, and of the tissue unit impulse response functions, are discussed in terms of vascular components, unidirectional clearance of tracer by the tissue, and reversible and irreversible phenomena. The significance of the number of components which can be identified within a given datum set is also discussed. The technique facilitates the interpretation of dynamic PET data and simplifies comparisons between regions and between subjects.
Comparison of Bolus and Infusion Methods for Receptor Quantitation: Application to [18F]Cyclofoxy and Positron Emission Tomography
Authors: Carson Richard E. , Channing Michael A. , Blasberg Ronald G. , Dunn Bonnie B. , Cohen Robert M. , Rice Kenner C. , Herscovitch Peter
Published: April 2011

Positron emission tomography studies with the opiate antagonist [18F]cyclofoxy ([18F]CF) were performed in baboons. Bolus injection studies demonstrated initial uptake dependent on blood flow. The late uptake showed highest binding in caudate nuclei, amygdala, thalamus, and brainstem and the least accumulation in cerebellum. By 60 min postinjection, regional brain radioactivity cleared at the same rate as metabolite-corrected plasma, i.e., transient equilibrium was achieved. Compartmental modeling methods were applied to time-activity curves from brain and metabolite-corrected plasma. Individual rate constants were estimated with poor precision. The model estimate of the total volume of distribution ( VT), representing the ratio of tissue radioactivity to metabolite-corrected plasma at equilibrium, was reliably determined. The apparent volume of distribution ( Va), the concentration ratio of tissue to metabolite-corrected plasma during transient equilibrium, was compared with the fitted VT values to determine if single-scan methods could provide accurate receptor measurements. Va significantly overestimated VT and produced artificially high image contrast. These differences were predicted by compartment model theory and were caused by a plasma clearance rate that was close to the slowest tissue clearance rate. To develop a simple method to measure VT, an infusion protocol consisting of bolus plus continuous infusion (B/I) of CF was designed and applied in a separate set of studies. The Va values from the B/I studies agreed with the VT values from both B/I and bolus studies. This infusion approach can produce accurate receptor measurements and has the potential to shorten scan time and simplify the acquisition and processing of scan and blood data.
Detection of Thirty-Second Cognitive Activations in Single Subjects with Positron Emission Tomography: A New Low-Dose H215O Regional Cerebral Blood Flow Three-Dimensional Imaging Technique
Authors: Silbersweig David A. , Stern Emily , Frith Christopher D. , Cahill Connie , Schnorr Leonard , Grootoonk Sylke , Spinks Terry , Clark John , Frackowiak Richard , Jones Terry
Published: April 2011

Positron emission tomography regional CBF (rCBF) studies of cognitive processes have traditionally required 30–60 mCi of H215O per scan and intersubject averaging to achieve statistical significance. However, intersubject anatomical, functional, and disease variability can make such an approach problematic. A new method that produces significant results in single subjects is presented. It is based upon high-sensitivity three-dimensional imaging and a “slow” bolus administration of >15 mCi of H215O per scan. The method is validated in four normal volunteers using control and auditory-language activation tasks with four scans per condition and statistical parametric mapping analysis. It is demonstrated that the rCBF distribution associated with the cognitive state is detected during the arrival of radiotracer in the brain. This occurs over 30 s and constitutes a critical temporal window during which stimulation should be performed. A 90-s acquisition time is found to produce results of greater significance than a 60-s acquisition time. The implications of the results and the functional neuroanatomical findings are discussed. This method is suitable for the study of individual functional neuroanatomy in many neuropsychological, pharmacologic, and symptom states in normal subjects and in patients with psychiatric and neurologic disorders.
Improved Detection of Focal Cerebral Blood Flow Changes Using Three-Dimensional Positron Emission Tomography
Authors: Cherry Simon R. , Woods Roger P. , Hoffman Edward J. , Mazziotta John C.
Published: April 2011

Removal of the interplane septa and configuration of a typical multislice PET scanner to accept all possible coincidence lines of response leads to a fivefold increase in sensitivity. This can be of value in regional CBF studies using bolus 15O-labeled water injections, allowing the injected dose to be reduced by a factor of 4, while maintaining the same number of noise equivalent counts. Thus, for a given cumulative dose limit, four times as many studies can be performed in a single subject. Data from the three-dimensional Hoffman brain phantom, closely matched to count rates seen in human studies, show that for an identical cumulative dose, the noise in subtraction (stimulus minus baseline) images can be reduced by a factor of 2 using three-dimensional data acquisition, with appropriate fractionation of the dose. This improvement is dependent on axial position due to the sensitivity characteristics of three-dimensional scans; however, there is a significant gain in the signal-to-noise ratio (S/N) in all image planes. Studies performed in a human subject demonstrate how the factor of 2 gain in S/N leads to improved detectability of activation sites in PET subtraction images.
Effect of Side and Rate of Stimulation on Cerebral Blood Flow Changes in Motor Areas during Finger Movements in Humans
Authors: Sabatini Umberto , Chollet François , Rascol Olivier , Celsis Pierre , Rascol André , Lenzi Gian Luigi , Marc-Vergnes Jean-Pierre
Published: April 2011

We measured, using single photon emission computed tomography, the regional CBF (rCBF) changes in the motor areas of 24 right-handed normal volunteers during the performance of a motor task consisting of sequential finger-to-thumb opposition. Twelve of them performed the task with their right and their left hands consecutively with a fast frequency and large amplitude. The other 12 subjects performed the task with their right hand only at a slow frequency and small amplitude. The contralateral primary sensorimotor area (S1/M1), supplementary motor area (SMA), and ipsilateral cerebellum were significantly activated during right and left finger movements performed at fast frequency and large amplitude. No significant difference was found between the rCBF changes induced by the right dominant and left nondominant hands. When the task was performed with a slow rate and small amplitude, the SMA was significantly activated while no significant changes were observed in the contralateral S1/M1 or in the ipsilateral cerebellum. These results demonstrate (a) that hand dominance evokes no differences in the activation of the main motor areas and (b) that the frequency and amplitude of the movement have a major effect on the quantitative and qualitative aspect of activation of motor areas in humans.
Average Blood Flow and Oxygen Uptake in the Human Brain during Resting Wakefulness: A Critical Appraisal of the Kety—Schmidt Technique
Authors: Madsen Peter Lund , Holm Søren , Herning Margrethe , Lassen Niels A.
Published: April 2011

The Kety–Schmidt technique can be regarded as the reference method for measurement of global average cerebral blood flow (average CBF) and global average cerebral metabolic rate of oxygen (average CMRO2). However, in the practical application of the method, diffusion equilibrium for inert gas tracer between the brain and its venous blood is not reached. As a consequence, normal values for CBF and CMRO2 of 54 ml 100 g−1 min−1 and 3.5 ml 100 g−1 min−1 obtained with the Kety–Schmidt technique are an overestimation of the true values. Using the Kety–Schmidt technique we have performed 57 measurements of CBF and CMRO2 during EEG-verified wakeful rest in young normal adults. In order to estimate the equilibrium values for CBF and CMRO2, a simple computer-based simulation model was employed to quantitate the systematic overestimation caused by incomplete tracer equilibrium. When correcting the measured data, we find that the true average values for CBF and CMRO2 in the healthy young adult are ∼46 ml 100 g−1 min−1 and ∼3.0 ml 100 g−1 min−1. Previous studies have suggested that some of the variation in CMRO2 values could be ascribed to differences in cerebral venous anatomy. However in the present study, no correlation between CMRO2 and cerebral venous anatomy as imaged by magnetic resonance angiography could be established. Our data show that the interindividual variation of CMRO2 is 11% (coefficient of variation).
Possible Origins and Distribution of Immunoreactive Nitric Oxide Synthase-Containing Nerve Fibers in Cerebral Arteries
Authors: Nozaki Kazuhiko , Moskowitz Michael A. , Maynard Kenneth I. , Koketsu Naoki , Dawson Ted M. , Bredt David S. , Snyder Solomon H.
Published: April 2011

The distribution of perivascular nerve fibers expressing nitric oxide synthase (NOS)-immunoreactivity was examined in Sprague–Dawley and Long–Evans rats using affinity-purified rabbit antisera raised against NOS from rat cerebellum. NOS immunoreactivity was expressed within the endothelium and adventitial nerve fibers in both rat strains. Labeled axons were abundant and dense in the proximal anterior and middle cerebral arteries, but were less numerous in the caudal circle of Willis and in small pial arteries. The sphenopalatine ganglia were the major source of positive fibers in these vessels. Sectioning postganglionic parasympathetic fibers from both sphenopalatine ganglia reduced the density of NOS-immunoreactive (IR) nerve fibers by >75% in the rostral circle of Willis. Moreover, NOS-IR was present in 70–80% of sphenopalatine ganglion cells. Twenty percent of these neurons also contained vasoactive intestinal polypeptide (VlP)-immunoreactivity. By contrast, the superior cervical ganglia did not contain NOS-IR cells. In the trigeminal ganglion, NO-IR neurons were found chiefly within the ophthalmic division; ∼10–15% of neurons were positively labeled. Colocalization with calcitonin gene-related peptide (CGRP) was not observed. Sectioning the major trigeminal branch innervating the circle of Willis decreased positive fibers by ≤25% in the ipsilateral vessels. In the nodose ganglion, 20–30% of neurons contained NOS-immunoreactivity, whereas less than 1% were in the C2 and C3 dorsal root ganglia. Three human circles of Willis obtained at autopsy showed sparse immunoreactive fibers, chiefly within vessels of the posterior circulation. Postmortem delay accounted for some of the reduced density. Our findings indicate that nerve fibers innervating cerebral arteries may serve as a nonendothelial source of the vasodilator nitric oxide (NO). The coexistence of NOS and VIP within sphenopalatine ganglion cells raises the possibility that two vasodilatory agents, one, a highly diffusable short-lived, low-molecular-weight molecule, and the other, a polar 28 amino acid-containing peptide, may serve as coneuromediators within the cerebral circulation.
Correlational Imaging of Thalamocortical Coupling in the Primary Visual Pathway of the Human Brain
Authors: Kleinschmidt Andreas , Merboldt Klaus-Dietmar , Hänicke Wolfgang , Steinmetz Helmuth , Frahm Jens
Published: April 2011

While the anatomy of the human brain is well defined, the functional connectivity of its structures is far less understood. Modern neuroimaging techniques offer the unique opportunity of visualizing physiologic activation in central nervous structures and of identifying the elements underlying distributed networks for information processing. Following improved spatial resolution of deoxyhemoglobin-sensitive magnetic resonance imaging, we were able to detect simultaneous signal changes in the lateral geniculate nucleus and primary visual cortex during periodic photic stimulation. Visualization of coupled activation by cross-correlation analysis resulted in the first demonstration of thalamocortical interaction in the primary visual pathway of the intact human brain.
The Functional Anatomy of Attention in Humans: Cerebral Blood Flow Changes Induced by Reading, Naming, and the Stroop Effect
Authors: Larrue Vincent , Celsis Pierre , Bès André , Marc-Vergnes Jean Pierre
Published: April 2011

We measured changes in regional cerebral blood flow (rCBF) induced by reading, naming, and the Stroop effect in 12 right-handed normal volunteers. rCBF was quantified with a single-photon emission computerized tomograph after intravenous injection of 133Xe. Data were analyzed using predetermined regions of interest and a linear model. A significant relative activation was revealed in the right superior mesial frontal region during the Stroop effect.
Increased Densities of Binding Sites for the “Peripheral-Type” Benzodiazepine Receptor Ligand [3H]PK11195 in Vulnerable Regions of the Rat Brain in Thiamine Deficiency Encephalopathy
Authors: Leong Dorothy K. , Le Oanh , Oliva Luis , Butterworth Roger F.
Published: April 2011

Quantitative receptor autoradiography was used to evaluate the density of high-affinity binding sites for the “peripheral-type” benzodiazepine receptor (PTBR) ligand [3H]PK11195 in brain regions of the rat at different stages of pyrithiamine-induced thiamine deficiency encephalopathy, an experimental model of the Wernicke-Korsakoff syndrome (WKS). Assessment of the density of [3H]PK11195 binding sites in thiamine-deficient animals showing no neurologic signs of thiamine deficiency encephalopathy, and revealed no significant alterations compared with pair-fed control animals in any brain region studied. Densities of [3H]PK11195 binding sites were, however, significantly increased in brain regions of the rat at the symptomatic stage, where increased densities were seen in the inferior colliculus (233% increase, p < 0.001), inferior olivary nucleus (154% increase, p < 0.001) and thalamus (up to 107% increase, p < 0.001). Histologic studies of these same brain regions revealed evidence of neuronal cell loss and concomitant gliosis. Densities of [3H]PK11195 binding sites in nonvulnerable brain regions that showed no histologic evidence of neuronal loss, such as the cerebral cortex, hippocampus, and caudate-putamen, were not significantly different from those in control animals. Increased densities of binding sites for the PTBR ligand probably reflect glial proliferation and are consistent with an excitotoxic mechanism in the pathogenesis of neuronal cell loss in thiamine deficiency encephalopathy. Positron emission tomography (PET) using [11C]PK11195 could offer a potentially useful diagnostic tool in WKS in humans.
Functional Metabolic Mapping of the Rat Brain during Unilateral Electrical Stimulation of the Subthalamic Nucleus
Authors: Tzagournissakis Minas , Dermon Catherine R. , Savaki Helen E.
Published: April 2011

The alterations in local metabolic activity of several anatomically distinct brain areas were investigated by means of the quantitative autoradiographic 2-deoxy-D-[1-14C]glucose method in awake rats during unilateral electrical stimulation of the subthalamic nucleus (STH). Unilateral electrical stimulation of the STH induced local metabolic activation (by 70% as compared with the control group), as well as distal metabolic activations in the substantia nigra reticulata (by 34%), globus pallidus (by 19%), entopeduncular nucleus (by 18%), deep layers of the superior colliculi (by 15%), and parafascicular thalamic nucleus (by 18%), ipsilaterally to the stimulated side. The ventrolateral motor thalamic nucleus as well as the limbic components, posterior cingulate cortex, and anteroventral thalamic nucleus displayed bilateral metabolic activations (by 20–28%). These results indicate that, in addition to its known ipsilateral motor connections, each STH is functionally related to the limbic system bilaterally. It is suggested that the STH is a site where the central motor information is accessible to the limbic system. Quantitative image analysis of individual serial sections in the STH, substantia nigra, and globus pallidus revealed a consistent dorsoventral pattern of topographic interrelations. Stimulation of either the dorsal or the ventral subdivision of the STH induced always stronger activation in the dorsal compartment of the substantia nigra and in the ventral compartment of the globus pallidus. These results suggest that the earlier-described inversion of the dorsoventral functional correspondence between the substantia nigra and globus pallidus may be partly mediated via the subthalamic nerve cells projecting collateral axons to both these areas.
Intraventricular Administration of Insulin and IGF-1 in Transient Forebrain Ischemia
Authors: Zhu C. Z. , Auer R. N.
Published: April 2011

A beneficial effect of insulin in reducing cerebral ischemic damage has been recently demonstrated, and a direct central mechanism of insulin action in cerebral ischemia has been proposed. To test the hypothesis that one of the neuroprotective mechanisms of insulin action involves a direct interaction with CNS tissue via a growth factor effect, a continuous intraventricular infusion of two doses of insulin and of insulin-like growth factor 1 (IGF-1) was given to fed Wistar rats subjected to 10 min, 15 s of transient forebrain ischemia. Quantitative neuropathology after 1-week survival showed that low-dose insulin (7 IU/rat/day; n = 10) reduced selective necrosis in the striatum (p = 0.015) and one level of the hippocampus (p = 0.023) as compared with animals infused with phosphate-buffered saline (200 μl/rat/day; n = 8). IGF-1 (50 μg/rat/day; n = 8) significantly ameliorated hippocampal damage in four of the six hippocampal levels (p < 0.05). High-dose insulin infusion (23 IU/rat/day; n = 8) produced a robust reduction in cortical (p = 0.0108), striatal (p = 0.003), and hippocampal (p < 0.05) necrosis at all coronal levels. However, this high-dose insulin reduced the blood sugar significantly (p < 0.01), from 11.8 to 7.8 m M, probably by virtue of centrally administered insulin reaching the periphery. We conclude that insulin and IGF-1 offer a moderate, centrally mediated, neuroprotective effect, likely mediated at least in part via a growth factor mechanism. In addition, we confirm our earlier findings that higher doses of insulin, accompanied by lowering of peripheral blood glucose levels even within the physiologic range, yield the greatest protective effect.
Delayed Treatment with AMPA, but Not NMDA, Antagonists Reduces Neocortical Infarction
Authors: Xue Dong , Huang Zhi-Gao , Barnes Kimberley , Lesiuk Howard J. , Smith Karen E. , Buchan Alastair M.
Published: April 2011

We tested the abilities of two potent non- N-methyl-d-aspartate (non-NMDA) glutamate antagonists [2,3-dihydroxy-6-nitro-7-sulfamoylbenzo( F)quinoxaline (NBQX)] and [1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5 H-2,3-benzodiazepine hydrochloride (GYKI 52466)] to reduce neocortical infarction following 2 h of transient middle cerebral artery occlusion in a hypertensive stroke model in the rat and compared these effects against, and in combination with, a potent NMDA antagonist [(+)-5-methyl-10,11-dihydro-5 H-dibenzo-[ a,d]cyclohepten-5,10-amine maleate (MK-801)]. In Expt. 1, an already established cytoprotective dose of Na+-NBQX (30 mg/kg i.p. × 3) was compared with saline (1 ml), the NMDA antagonist MK-801 (1 mg/kg i.p. × 3), and a combination of the same doses of both NBQX and MK-801. Initial doses were delayed to 90 min following occlusion with subsequent injections at the time of reperfusion and 30 min following reperfusion. Saline-treated rats sustained 181 ± 32 mm3 (n = 15) of neocortical infarction (mean ± SD). This was significantly reduced by NBQX to 137 ± 25 mm3 (n = 15, p < 0.05) of damage. Neither MK-801 (170 ± 33 mm3; n = 11) nor the combination of MK-801 and NBQX (169 ± 20 mm3; n = 6) proved to be cytoprotective when given with a 90-min delay. In Expt. 2, NBQX (30 mg/kg) was dissolved (6 mg/ml) in 5% dextrose and compared with both saline and dextrose (1.2 ml) i.v. infusions given over a 4-h period starting 1 h after occlusion. Saline-treated rats had a mean infarct of 183 ± 27 mm3 (n = 6), dextrose-treated had 200 ± 30 mm3 (n = 9), while for NBQX-treated rats it was reduced to 129 ± 60 mm3 (n = 10, p < 0.05). Intravenous NBQX precipitated into the renal tubules, causing nephrotoxicity. In Expt. 3, rats were given either saline (1 ml i.p.) or GYKI 52466 (10 mg/kg i.p.) at 30 and 90 min following occlusion and at 30, 90, and 150 min following reperfusion. Saline-treated rats sustained 187 ± 27 mm3 of neocortical infarction (n = 7), while those treated with GYKI 52466 were protected, with 139 ± 38 mm3 of infarction (n = 7, p < 0.05). A clinically useful role for α-amino-3-hydroxy-5-methyl-4-isoxazole propionate antagonists in embolic stroke is envisaged if nontoxic drugs can be developed, since cerebroprotection was achieved with delayed treatment with both of these lead compounds.
Motor Performance, Histologic Damage, and Calcium Influx in Rats Treated with NBQX after Focal Ischemia
Authors: DeGraba T. J. , Ostrow P. , Hanson S. , Grotta J. C.
Published: April 2011

2,3-Dihydroxy-6-nitro-7-sulfamoylbenzo( F)-quinoxaline (NBQX), an α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonist, has been reported to provide neuronal protection after global ischemia. The objectives of this study were to evaluate the neuroprotective effects of NBQX initiated after focal cortical ischemia and to validate a method for measuring functional outcome in this model. Male spontaneously hypertensive rats (SHRs) were exposed to various durations of transient or permanent tandem middle cerebral artery (MCA) occlusion. Studies compared motor performance using balance beam and prehensile-traction tests, calcium–calmodulin (Ca–CaM) binding by immunohistochemistry, and infarct volume between NBQX-treated animals [intravenous (i.v.) 5 mg/kg/h × 6 h or intraperitoneal (i.p.) 30 mg/kg q 30 min × 3 begun postischemia] and controls. All ischemic groups performed less well than sham-operated controls on the motor performance tasks in proportion to the severity of ischemia. No significant improvement in motor performance was noted in the NBQX-treated versus the control animals after 1 h or permanent MCA/CCA occlusion. Treatment with NBQX (i.v. or i.p. dosing) did not reduce Ca–CaM binding after 1 h of occlusion with 1 h of reperfusion or after 2 h of occlusion. Similarly, there was no reduction in infarct size between NBQX-treated and control animals after 24 h of permanent MCA/CCA occlusion (74.6 ±7.1 vs. 80.1 ± 6.0 ml; ns) or after 1 h of occlusion with 23 h of reperfusion (55.1 ± 4.4 vs. 47.4 ± 6.2 ml; ns). We conclude that therapy with NBQX alone has no protective effect in this model of ischemia, which may be related in part to its inability to prevent a postischemic increase in intracellular Ca in cortical neurons, and that our method of measuring motor performance is a useful indicator of functional outcome in this model.
Diffusion-Weighted Magnetic Resonance Imaging of Acute Focal Cerebral Ischemia: Comparison of Signal Intensity with Changes in Brain Water and Na+,K+ -ATPase Activity
Authors: Mintorovitch Jan , Yang G. Y. , Shimizu Hiroaki , Kucharczyk John , Chan Pak H. , Weinstein Philip R.
Published: April 2011

Diffusion-weighted magnetic resonance (MR) images from rats during acute cerebral ischemia induced by middle cerebral artery occlusion were analyzed for correspondence with changes in brain water, cation concentrations, and Na+,K+-ATPase activity measured in vitro after 30 or 60 min of ischemia. In the ischemic hemisphere, signal intensity was increased at 30 min (p < 0.05 vs contralateral hemisphere) and further increased at 60 min. Na+,K+-ATPase activity was 34% lower in ischemic cortex and 40% lower in ischemic basal ganglia after 30 min (p < 0.05), but water content and Na+ and K+ concentrations were not significantly different between hemispheres. After 60 min, water content and Na+ concentration were increased, and both Na+,K+-ATPase activity and K+ concentration were decreased in the ischemic hemisphere (p < 0.05). These findings are consistent with the hypothesis that the early onset of signal hyperintensity in diffusion-weighted MR images may reflect cellular edema associated with impaired membrane pump function. Early in vivo detection and localization of potentially reversible ischemic cerebral edema may have important research and clinical applications.
Endothelin Levels Increase in Rat Focal and Global Ischemia
Authors: Barone F. C. , Globus M. Y.-T. , Price W. J. , White R. F. , Storer B. L. , Feuerstein G. Z. , Busto R. , Ohlstein E. H.
Published: April 2011

Endothelin-1, a peptide exhibiting extremely potent cerebral vasoactive properties, is elevated in the cerebrospinal fluid after hemorrhagic stroke and implicated in cerebral vasospasm. The purpose of this study was to determine changes in endothelin in ischemic rat brain by assaying endothelin tissue and extracellular levels. Immunoreactive endothelin levels in ischemic brain tissue following permanent or transient focal ischemia produced by middle cerebral artery occlusion was determined. In addition, endothelin levels were assayed in striatal extracellular fluid collected by microdialysis before, during, and after global ischemia produced by two-vessel occlusion combined with hypotension. Twenty-four hours after the onset of permanent middle cerebral artery occlusion, the ischemic cortex level (0.58 ± 0.27 fmol/mg protein) of immunoreactive endothelin was significantly (p < 0.05) increased, by 100%, over that in the nonischemic cortex (0.29 ± 0.13 fmol/mg protein). Transient artery occlusion for 80 min with reperfusion for 24 h also resulted in a similar significant (p < 0.05) increase, 78%, in immunoreactive endothelin in the ischemic zone. Global forebrain ischemia significantly (p < 0.05) increased the level of immunoreactive endothelin collected in striatal microdialysis perfusate, from a basal level of 14.6 ± 6.7 to 26.5 ± 7.7 and 26.2 ± 7.4 amol/μl (i.e. 82 and 79%). These changes reflect the relative picomolar extracellular concentration increases during ischemia and following reperfusion, respectively. This is the first demonstration of elevated levels of endothelin in focal ischemic tissue and in the extracellular fluid in global ischemia and suggests a role of the peptide in ischemic and postischemic derangements of cerebral vascular function and tissue injury.
Quantitation of Perivascular Monocytes and Macrophages around Cerebral Blood Vessels of Hypertensive and Aged Rats
Authors: Liu Yong , Jacobowitz David M. , Barone Frank , McCarron Richard , Spatz Maria , Feuerstein Giora , Hallenbeck John M. , Sirén Anna-Leena
Published: April 2011

The numbers of monocytes and macrophages in the walls of cerebral blood vessels were counted on perfusion-fixed frozen brain sections (16 μm) of spontaneously hypertensive rats (SHR), stroke-prone SHR (SHR-SP), normotensive Wistar-Kyoto (WKY) rats, and young (16-week-old) and old (2-year-old) normotensive Sprague-Dawley rats (SD-16w and SD-2y, respectively) using monoclonal antibodies against rat macrophages (ED2). The staining was visualized with fluorescein-labeled second antibodies. The ED2-specific staining in brain sections was restricted to macrophages in a perivascular location. The number of perivascular cells per square millimeter of high-power field was significantly greater in SHR-SP (8.6 ± 2.1; n = 4) and SHR (6.7 ± 0.9; n = 6) than in normotensive WKY (4.0 ± 0.5; n = 6; p < 0.01). The number of perivascular macrophages was also greater in SD-2y (7.5 ± 2.7; n = 9) than in SD-16w (2.9 ± 1.8; n = 8; p < 0.01). No ED2 staining was found in the resident microglia or in the endothelial cells, which were identified by double staining with rhodamine-labeled anti-factor VIII-related antigen antibodies. The results suggest that the stroke risk factors hypertension and advanced age are associated with increased subendothelial accumulation of monocytes and macrophages. This accumulation could increase the tendency for the endothelium to convert from an anticoagulant to a procoagulant surface in response to mediators released from these subendothelial cells.