bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct Evidence for Acute and Massive Norepinephrine Release in the Hippocampus during Transient Ischemia
Authors: Globus Mordecai Y.-T. , Busto Raul , Dietrich W. Dalton , Martinez Elena , Valdés Isabel , Ginsberg Myron D.
Published: April 2011

Recent studies suggest the norepinephrine (NE) may play a regulatory role in neuronal cell death in the hippocampus after transient ischemia. However, ischemia-induced changes in extracellular NE release have not been demonstrated. In the present study, we utilized the microdialysis technique to measure extracellular NE levels in the hippocampus before, during, and after 20 min of global ischemia induced by two-vessel occlusion combined with systemic hypotension in the rat. Stable basal concentrations of extracellular NE were detected in three consecutive samples collected prior to ischemia (1.86 ± 1.21 pmol/ml of perfusate mean ± SEM). During ischemia, NE levels increased to 30.1 ± 5.5 pmol/ml, representing an 18-fold increase. The levels gradually returned to baseline by 40 min of reperfusion. These results are the first to demonstrate that acute and massive extracellular release of NE occurs in the hippocampus during ischemia and early recirculation. These results support the hypothesis that the activation of the noradrenergic system may play a significant role in modulating the development of ischemic neuronal damage.
A Highly Accurate Method of Localizing Regions of Neuronal Activation in the Human Brain with Positron Emission Tomography
Authors: Mintun Mark A. , Fox Peter T. , Raichle Marcus E.
Published: April 2011

Functional mapping of the human brain with positron emission tomography (PET) can best be performed by obtaining multiple short measurements of cerebral blood flow in a single sitting. In this manner regional changes in blood flow accompanying the increased neuronal activity from a movement, sensation, or even cognition task, have been identified. However, localizing a functional region with PET has been severely limited by the poor resolving properties of PET devices. Using a new method of data analysis we recently reported the mapping of visual field stimuli on human visual cortex with surprisingly high reliability as measured by the low standard deviation in positions across different subjects (as low as 1 mm). In this work the analysis technique enabling such high-resolution functional brain mapping is fully described. Additionally, simulations are presented to illustrate its advantages and limitations.
Hypoxia-Induced Dysfunctions and Injury of Astrocytes in Primary Cell Cultures
Authors: Yu Albert C. H. , Gregory George A. , Chan Pak H.
Published: April 2011

The effects of severe hypoxia were studied in a primary culture of astrocytes prepared from newborn rat cerebral cortex. Hypoxia was created by placing cultures in an airtight chamber that was flushed with 95% N2/5% CO2 for 15 min before being sealed. The hypoxic environment was maintained constant for up to 24 h. During the first 12 h of hypoxia, astrocytes showed no morphological changes by phase-contrast microscopy. After 18 h of hypoxia, some astrocytes in culture became swollen and started to detach from the culture dish. All cells in the culture were destroyed after 24 h of hypoxia. The lactate dehydrogenase level in the culture medium increased more than tenfold between 12 and 24 h of hypoxia. Glutamate uptake was inhibited 80% by similar hypoxic conditions. The cell volume of astrocytes, as measured by 3-O-methyl-[14C]-D-glucose uptake, was increased. These observations suggested cell membrane dysfunction. The malondialdehyde level of hypoxic cultures increased twofold after 24 h of hypoxia. Verapamil (0.5 m M), furosemide (1 m M), indomethacin (1 m M), MgCl2 (10 m M), and mannitol (10 m M) reduced but never completely abolished the release of lactate dehydrogenase from hypoxic astrocytes. These data suggest multifactorial causes for severe injury in hypoxic astrocytes.
Effects of Dopamine on Pial Arteriolar Diameter and CSF Prostanoid Levels in Piglets
Authors: Busija David W. , Leffler Charles W.
Published: April 2011

We examined effects of topically applied dopamine on pial arteriolar diameter and CSF prostanoid levels in newborn pigs. Vascular responses were determined using the closed cranial window technique and intravital microscopy, and prostanoids were determined by radioimmunoassay. Topical application of dopamine did not change arteriolar diameter at 10−7–10−5 M, but constricted arterioles at 10−4 (16%) and 10−3 M (30%). Intravenous administration of indomethacin (5 mg/kg) did not alter this constriction. In addition, CSF prostanoid levels did not increase in response to application of dopamine except for a modest increase of prostaglandin E2 at 10−3 M. We conclude that dopamine is a constrictor at high doses of piglet pial arterioles and that this response is not modified by endogenous prostanoids.
Effects of Neuropeptide Y and Calcitonin Gene-Related Peptide on Local Cerebral Blood Flow in Rat Striatum
Authors: Suzuki Yoshio , Satoh Shin-Ichi , Ikegaki Ichiro , Okada Tomohisa , Shibuya Masato , Sugita Kenichiro , Asano Toshio
Published: April 2011

The effects of neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) on local cerebral blood flow (LCBF) were studied in vivo in rat striatum. Administration of 1 and 5 nmol NPY as a bolus into the internal carotid artery caused a dose-dependent decrease in the ipsilateral striatal LCBF. This decrease developed slowly and persisted for at least 2 h, without affecting mean blood pressure. In contrast, CGRP, at a concentration of 10 pmol, increased striatal LCBF by about 30%, and the duration of the increase was about 1 h. However, at higher doses of CGRP no increase in LCBF was observed. These results suggest that NPY and CGRP released from nerve fibers innervating blood vessels can function as long-acting modulators of CBF.
Effects of Moderate Hypoxemia and Unilateral Carotid Ligation on Cerebral Glucose Metabolism and Acid-Base Balance in the Rat
Authors: Lockwood Alan H. , Peek Kathryn E. , Izumiyama Masahiro , Yap Eddy W. H. , Labove Jocelyn
Published: April 2011

We used our recently developed method for the simultaneous measurement of the local CMRglc (LCMRglc) and composite tissue pH to evaluate the response to unilateral carotid ligation and moderate hypoxia [40.1 ± 4.8 (SD) mm Hg]. The LCMRglc and tissue pH were measured simultaneously in brain slices using [14C]2-deoxy-d-glucose and [14C]5,5-dimethyl-2,4-oxazolidinedione. The ipsilateral LCMRglc was increased significantly in the caudate-putamen and medial thalamus and was surrounded by a much more extensive zone of acidosis, as shown by significant reductions in the tissue pH, which was affected in parietal cortex, caudate-putamen, lateral septal nucleus, medial geniculate, Ammon's horn, and nucleus reticularis of substantia nigra. In regions with an elevated LCMRglc and acidosis, anaerobic glycolysis combined with ATP hydrolysis are likely to co-exist. In regions characterized by normal glucose metabolism and acidosis, we hypothesize that a direct effect of hypoxia on the sodium/hydrogen ion antiporter may lead to secondary acidosis. Disturbed acid-base balance during hypoxia may have an adverse effect on cerebral function and cause clinical symptoms.
Dynamics of Extracellular Metabolites in the Striatum after Middle Cerebral Artery Occlusion in the Rat Monitored by Intracerebral Microdialysis
Authors: Hillered L. , Hallström A. , Segersvärd S. , Persson L. , Ungerstedt U.
Published: April 2011

The aim of this study was to measure changes in the extracellular fluid (ECF) concentration of lactate, pyruvate, purines, amino acids, dopamine, and dopamine metabolites in the striatum of rats subjected to focal cerebral ischemia, using intracerebral microdialysis as the sampling technique. Microdialysis probes were inserted into the lateral part of the caudate-putamen bilaterally 2 h before the experiment. Ischemia was induced by permanent middle cerebral artery occlusion (MCAO) on the left side. Microdialysis samples were analyzed by high performance liquid chromatography. Following MCAO, the concentration of lactate, adenosine, inosine, and hypoxanthine rose markedly in the ECF on the occluded side, while there was no significant change in pyruvate. These changes were accompanied by dramatically elevated levels of aspartate, glutamate, taurine, γ-aminobutyric acid, and dopamine. There was also a marked increase in alanine/tyrosine, while minor or no changes occurred with other amino acids. Concomitantly, the ECF level of the dopamine metabolites 3,4–dihydroxyphenylacetate and homovanillic acid decreased. There was no significant increase in any of the metabolites measured on the right, nonoccluded side. In relation to the concept of excitotoxicity in brain ischemia, it is concluded that during the acute stage of focal cerebral ischemia, the ECF is flooded with both potentially harmful (e.g., aspartate, glutamate, and DA) and protective (e.g., taurine, GABA, and adenosine) agents. The relative importance of these events for the development of cell death in the ischemic penumbra needs to be elucidated. In addition, lactate, inosine, and hypoxanthine, measured in the ECF by intracerebral microdialysis, may prove to have diagnostic and/or prognostic value in neurometabolic monitoring of the ischemic brain.
Functional, Behavioral, and Histological Changes Induced by Transient Global Cerebral Ischemia in Rats: Effects of Cinnarizine and Flunarizine
Authors: Poignet H. , Beaughard M. , Lecoin G. , Massingham R.
Published: April 2011

Temporary cerebral ischemia (15 min) produced by “four-vessel occlusion” in the rat causes neurological disorders, changes in behavior (locomotor hyperactivity), and neuronal damage in the neocortex, striatum, and especially the CA1 zone of the hippocampus. We have studied the effects of two calcium overload blockers, flunarizine (50 mg/kg p.o. twice a day) and cinnarizine (100 mg/kg p.o. twice a day), on these alterations. Cinnarizine markedly improved the functional abnormalities of ischemia but had little or no effect upon the neuronal damage. In contrast, flunarizine provided far greater neuronal protection but with less obvious effects upon behavioral parameters. However, there was evidence of sedation 2 h after treating animals with this dose of flunarizine that might have masked any positive effect of the drug on behavior. We conclude that under the present experimental conditions, there is no correlation between the early and late behavioral changes observed following a temporary cerebral ischemic episode and the histological damage observed in certain vulnerable neurons, particularly in the hippocampus, 72 h after the insult.
Alterations in the N-Methyl-D-Aspartate Receptor Complex following Focal Cerebral Ischemia
Authors: Dewar D. , Wallace M. C. , Kurumaji A. , McCulloch J.
Published: April 2011

The functional integrity of the N-methyl-d-aspartate receptor complex following focal cerebral ischemia in the rat has been examined at a time when brain tissue is irreversibly damaged. Twelve hours after unilateral permanent middle cerebral artery occlusion, [3H]-MK-801 binding was not significantly altered in the ischemic cerebral cortex compared to sham-operated animals. Moreover, the enhancement of [3H]MK-801 binding by exogenous glutamate was preserved in an area of the brain that was permanently damaged by the ischemic insult.
Neuropeptide Y and the Cerebral Circulation
Authors: Tuor U. I. , Kelly P. A. T. , Edvinsson L. , McCulloch J.
Published: April 2011

The significance of neuropeptide Y (NPY) in the cerebral circulation has been examined in the rat using immunocytochemistry, isolated cerebral artery preparations, and quantitative autoradiographic techniques for determining local CBF and glucose utilisation. In the rat the middle cerebral artery and the lenticulostriate artery from which blood is supplied to the caudate nucleus were found to be invested with numerous perivascular NPY immunoreactive nerve fibres. NPY (3–300 n M) contracted rat middle cerebral artery segments in a concentration-dependent manner. Intracerebral microinjections of NPY (200 pmol) or vehicle (1 μl) were performed in rats after full recovery from anaesthesia via previously implanted guide cannulae. Following injection of NPY into the striatum, local blood flow was markedly decreased by 36% throughout the ipsilateral caudate nucleus (e.g., from 104 ± 25 to 67 ± 15 ml 100 g−1 min −1; mean ± SD), whereas glucose use in this region was not altered significantly (e.g., 73 ± 8 and 74 ± 10 μmol 100 g−1 min−1 with vehicle and NPY, respectively). Intrastriatal NPY did not alter CBF or glucose use in the majority of other brain areas, including all of the 40 contralateral regions examined and almost all regions within the ipsilateral hemisphere. In a small number of highly discrete brain areas remote from the injection site (e.g., amygdala), there were significant reductions in blood flow with minimal changes in glucose use. Since NPY is present around rat cerebral blood vessels, is capable of evoking their contraction, and has the ability to produce reductions in blood flow independently of oxidative metabolism, this neuropeptide may be of major importance in cerebrovascular regulation.
The Novel Dihydronaphthyridine Ca2+ Channel Blocker CI-951 Improves CBF, Brain pHi, and EEG Recovery in Focal Cerebral Ischemia
Authors: Meyer Fredric B. , Anderson Robert E. , Sundt Thoralf M.
Published: April 2011

The effects of the novel dihydronaphthyridine Ca2+ antagonist CI-951 on focal cerebral ischemia were assessed during MCA occlusion in 30 white New Zealand rabbits under 1.0% halothane anesthesia. In vivo brain pHi and focal CBF were measured with umbelliferone fluorescense. Baseline normocapnic brain pHi and CBF were 7.02 ± 0.02 and 48.4 ± 2.9 ml/100 g/min, respectively. In the severe ischemic regions, 15 min postocclusion brain pHi, and CBF were 6.62 ± 0.04 and 14.4 ± 0.7 ml/100 g/min in controls vs. 6.60 ± 0.02 and 12.9 ± 2.3 ml/100 g/min, respectively, in animals destined to receive CI-951. Twenty minutes after MCA occlusion, CI-951 was administered at 0.5 μg/kg/min and brain pHi and CBF were determined in both regions of severe and moderate ischemia for 4 h postocclusion. Control severe ischemic sites demonstrated no significant improvement in brain pHi and only mild increases in CBF over the next 4 h. CI-951 caused significant improvement in both of these parameters. Postocclusion 4 h brain pHi and CBF measured 6.69 ± 0.04 and 18.5 ± 3.2 ml/100 g/min in controls vs. 7.01 ± 0.04 and 41.7 ± 5.3 ml/100 g/min, respectively, in CI-951 animals ( p < 0.001). Similar improvements were observed in moderate ischemic sites. In animals that demonstrated postocclusion EEG attenuation, 75% of CI-951 animals had EEG recovery as compared to 18% in controls. CI-951 may be a useful therapeutic agent for focal cerebral ischemia if histological and outcome studies verify these data.
Kinetic Analysis of 3-Quinuclidinyl 4-[125I]Iodobenzilate Transport and Specific Binding to Muscarinic Acetylcholine Receptor in Rat Brain in vivo: Implications for Human Studies
Authors: Sawada Y. , Hiraga S. , Francis B. , Patlak C. , Pettigrew K. , Ito K. , Owens E. , Gibson R. , Reba R. , Eckelman W. , Larson S. , Blasberg R. G.
Published: April 2011

Radioiodinated R- and S-Quinuclidinyl derivatives of RS-benzilate (R- and S-125IQNB) have been synthesized for quantitative evaluation of muscarinic acetylcholine receptor binding in vivo. Two sets of experiments were performed in rats. The first involved determining the metabolite-corrected blood concentration and tissue distribution of tracer R-IQNB (active enantiomer) and S-IQNB (inactive enantiomer) in brain 1 min to 26 h after intravenous injection. The second involved the measurement of brain tissue washout over a 2-min period after loading the brain by an intracarotid artery injection of the ligands. Various pharmacokinetic models were tested, which included transport across the blood–brain barrier (BBB), nonspecific binding, low-affinity binding, and high-affinity binding. Our analysis demonstrated that the assumptions of rapid equilibrium across the BBB and rapid nonspecific binding are incorrect and result in erroneous estimates of the forward rate constant for binding at the high-affinity receptor sites ( k3). The estimated values for influx across the BBB ( K1), the steady-state accumulation rate in cerebrum ( K), and the dissociation rate constant at the high-affinity site ( k4) of R-IQNB were independent of the specific compartmental model used to analyze these data ( K1 ≈ 0.23 ml/min/g, K ≈ 0.13 ml/ min/g, and k4 ≈ 0.0019 min− 1 for caudate). In contrast, the estimated values of k3 and the efflux rate constant ( k2) varied over a 10-fold range between different compartmental models ( k3 ≈ 2.3–22 min− 1 and k2 ≈ 1.6–16 min− 1 in caudate), but their ratios were constant ( k3/ k2 ≈ 1.4). Our analysis demonstrates that the estimates of k3 (and derived values such as the binding potential) are model dependent, that the rate of R-IQNB accumulation in cerebrum depends on transport across the BBB as well as the rate of binding, and that uptake in cerebrum is essentially irreversible during the first 360 min after intravenous administration. Graphical analysis was consistent with compartmental analysis of the data and indicated that steady-state uptake of R-IQNB in cerebrum is established within 1–5 min after intravenous injection. We propose a new approach to the analysis of R-IQNB time-activity data that yields reliable quantitative estimates of k3, k4, and the nonspecific binding equilibrium constant ( Keq) by either compartmental or graphical analysis. The approach is based on determining the free unbound fraction of radiolabeled ligand in blood and an estimate of K1. The analysis can be applied to time-activity data obtained in a clinical setting using either positron emission tomography or single photon emission computed tomography and has general application for other highly lipophilic ligands.
Peptidergic Innervation in the Cerebral Blood Vessels of the Guinea Pig: An Immunohistochemical Study
Authors: Nakakita Kazuo
Published: April 2011

The distribution of peptidergic nerve fibers containing substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in the cerebral arteries and veins of the guinea pig was studied using immunohistochemical techniques. The ultrastructure of these immunoreactive nerve terminals was also compared. The cerebral arteries were innervated by abundant peptidergic nerve fibers with characteristic running patterns, i.e., SP fibers in a meshwork, VIP and NPY fibers in a spiral fashion. Only CGRP fibers showed both meshwork and spiral patterns. In the cerebral veins, the abundant SP fibers innervated the cortical veins, deep cerebral veins, and dural sinuses. However, CGRP, VIP, and NPY fibers in extremely low density were noted merely in the cortical veins. Electron microscopic observations demonstrated that SP-immunoreactive nerve terminals existed apart from the arterial smooth muscle cells, while VIP- and NPY-immunoreactive nerve terminals adjoined them. As for CGRP nerve terminals, some existed close to the arterial smooth muscle cells, and others were found some distance from them. These morphological characteristics observed by light and electron microscopy suggest that SP fibers are not related directly to the vasomotor function, but VIP and NPY fibers are, and that CGRP fibers have a more complicated function. The distribution patterns of the peptidergic nerve fibers are consistent with the suggestion that vasomotor peptidergic fibers may function actively on cerebral arteries and passively on cerebral veins and that SP fibers regarded as sensory fibers may provide information regarding cerebral vascular conditions, innervating every part of both cerebral arteries and veins.
Microvascular Changes during the Early Phase of Experimental Bacterial Meningitis
Authors: Pfister H.-W. , Koedel U. , Haberl R. L. , Dirnagl U. , Feiden W. , Ruckdeschel G. , Einhäupl K. M.
Published: April 2011

We investigated the temporal profile of the changes in regional CBF (rCBF) and intracranial pressure (ICP) during the early phase of pneumococcal meningitis in the rat. rCBF, as measured by laser-Doppler flowmetry, and ICP were continuously monitored during 6 h post infection (p.i.). Brain edema formation was assessed by brain water content determinations. Meningitis was induced by intracisternal injection of 75 μl of 107 colony-forming units/ml pneumococci (n = 7). In control animals (n = 6), saline was injected. There was no change in the rCBF or ICP of controls throughout the experiment. However, there was a dramatic increase in rCBF and ICP associated with brain edema formation in untreated meningitis animals. rCBF increased to 135.3 ± 33.8% (mean ± SD) in the untreated animals at 1 h p.i, and reached 211.1 ± 40.5% at 6 h p.i. (p < 0.05 compared with controls). ICP increased from 2.9 ± 1.4 to 10.4 ± 4.7 mm Hg at 6 h p.i. (p < 0.05 compared with controls). Brain water content was significantly elevated (79.69 ± 0.24 compared with 78.94 ± 0.16% in the control group, p < 0.05). We investigated the effect of dexamethasone (3 mg/kg i.p.), which was given prior to the induction of meningitis (n = 3) or at 2 h after pneumococcal injection (n = 5), indomethacin (10 mg/kg i.V., n = 5), and superoxide dismutase (SOD; 132,000 U/kg i.v. per 6 h, n = 6). The increases in rCBF and ICP were prevented by the pretreatment with dexamethasone and the administration of SOD, delayed and attenuated by pretreatment with indomethacin, and reversed by administration of dexamethasone 2 h p.i. These findings suggest that oxygen-derived free radicals are involved as mediators in the increases of rCBF and ICP and brain edema formation during the early phase of experimental bacterial meningitis. Arachidonic acid metabolites of the cyclooxygenase pathway are partially involved in the observed changes and are one possible source for the generation of oxygen-derived free radicals in bacterial meningitis.
Brain Eicosanoid Formation following Acute Penetration Injury as Studied by in vivo Microdialysis
Authors: Yergey James A. , Heyes Melvyn P.
Published: April 2011

Formation of eicosanoids has been implicated in the pathological changes that follow brain injuries. In the present study, we used a microdialysis probe to both induce acute penetration injury and also sample extracellular fluid concentrations of eicosanoids. Formation of prostaglandin (PG) D2, PGF2 a, and thromboxane B2 was highest in the first hour following introduction of the probe into rat striatum. In contrast, the level of PGE2 was highest during the sixth hour of collection, while 6-keto-PGF1 a remained stable throughout the sampling period. We conclude that in vivo microdialysis may be useful in the evaluation of the time course of the effects of acute penetration injury of the brain on the local production of eicosanoids.
Model for Drug Uptake by Brain Tumors: Effects of Osmotic Treatment and of Diffusion in Brain
Authors: Robinson P. J. , Rapoport S. I.
Published: April 2011

A mathematical model describing drug uptake into brain tumors, directly from blood and indirectly from neighboring tissue, is presented. The model quantitatively describes uptake into tumor, brain surrounding tumor (BST), and normal brain and uptake following reversible osmotic blood–brain barrier (BBB) and blood–tumor barrier disruption. It employs published data on the time course for reclosure of the BBB following osmotic treatment and on the brain and tumor uptake of [14C]α-aminoisobutyric acid by Walker 256 carcinomas and C6 gliomas implanted into the rat brain. Constant infusion and bolus injection infusion schedules are considered. In untreated brain, the BST acts as a sink, reducing the integrated exposure of the adjacent tumor to the drug, whereas following osmotic treatment, tumor exposure to drug is enhanced, not only by increased delivery from blood but also by diffusion (and bulk flow) from neighboring brain. The model provides a quantitative framework for examining the efficacy of osmotic treatment to enhance chemotherapy of brain tumors.
Measurement of Free Intracellular and Transfer RNA Amino Acid Specific Activity and Protein Synthesis in Rat Brain in vivo
Authors: Hargreaves-Wall Katharine M. , Buciak Jody L. , Pardridge William M.
Published: April 2011

Brain protein synthesis was measured in anesthetized adult, male Sprague–Dawley rats by an in situ internal carotid arterial perfusion technique using [3H]leucine. The specific activity of free intracellular leucine and of tRNA leucine were determined by HPLC separation of phenylisothiocyanate (PITC) derivatives of amino acids. The specific activity of the leucyl-tRNA pool rapidly equilibrated with the free intracellular leucine pool within 2 min. The specific activity of the tRNA and free leucine pools in brain reached equilibrium by 10 min. Plasma amino acid specific activity, however, remained threefold higher than the specific activity of tRNA and free leucine pools. Estimates of protein synthesis were 0.62 ± 0.06 nmol/min/g and were constant between 10 and 30 min of perfusion. The in situ perfusion model for protein synthesis described is a controlled system suited to measurements of protein synthesis in brain that can be applied to the study of brain metabolism under changing physiological conditions.
Michaelis-Menten Constraints Improved Cerebral Glucose Metabolism and Regional Lumped Constant Measurements with [18F]Fluorodeoxyglucose
Authors: Kuwabara Hiroto , Evans Alan C. , Gjedde Albert
Published: April 2011

In the three-compartment model of transfer of native glucose and [18F]fluorodeoxyglucose (FDG) into brain, both transport across the blood–brain barrier and phosphorylation by hexokinase can be described by the Michaelis-Menten equation. This permits the use of fixed transport (τ = K*1/ K1) and phosphorylation (φ = k*3/ k3) ratios and a common partition volume ( Ve = K1/ k2) for tracer and glucose. By substituting transfer constants of FDG for those of glucose, using τ and φ, the lumped constant was determined directly by positron tomography. The same constraints also eliminated k*2 and k*3 from the model, thus limiting the parameters to K* [equivalent to K*1 k*3/( k*2 + k*3)], K*1, and the cerebral vascular volume ( Vo). In six healthy elderly men (aged 61 ± 5 years), time-activity records of cerebral cortical regions were analyzed with τ = 1.1 and φ = 0.3. The results were compared with those of the conventional FDG method. At 20 min, the goodness of fit by the new equation was as good as that of the conventional method at 45 min. The estimates obtained by the constrained method had stable coefficients of variation. After 20 min, regional differences between the estimates were independent of time, although we observed steady decreases of K* and ( k*3). The decrease strongly suggested dephosphorylation of FDG-6-phosphate, particularly after 20 min. All estimates of variables with the constrained method were more accurate than those of the conventional method, including the cerebral glucose metabolic rate itself, as well as physiologically more meaningful, particularly with respect to k*2 and k*3.
Characterization of Cerebral Energetics and Brain pH by 31P Spectroscopy after Graded Canine Cardiac Arrest and Bypass Reperfusion
Authors: Martin Gerard B. , Nowak Richard M. , Paradis Norman , Rosenberg Jack , Walton Dean , Smith Michael , Eisiminger Roy , Welch K. M. A.
Published: April 2011

Recovery of cerebral energy metabolism is used to indicate CNS viability after ischemia. This study utilized 31P nuclear magnetic resonance (NMR) spectroscopy to measure cerebral energy state and intracellular pH in dogs subjected to 8, 12, or 16 min of cardiac arrest and reperfusion using cardiopulmonary bypass. Spectra were obtained throughout ischemia and initial reperfusion and repeated at 30 and 144 h post ischemia. Neurologic deficit scoring was performed at 12 and 24 h post insult and then daily. High-energy phosphates were depleted by the end of all ischemic intervals. Recovery occurred within 60 min of reperfusion and persisted with no differences in the rate of return between groups (p > 0.05). Brain pH (pHb) decreased by the end of ischemia in all groups (p < 0.0001). Neither the pHb nadir nor its recovery differed between groups (p > 0.05). Although long-term neurologic outcome differed between groups, the spectra were similar. Assessment of cerebral energy state using 31P NMR spectroscopy does not appear to be a sensitive indicator of neurologic outcome after global ischemia in dogs. Return of high-energy phosphates may be a necessary but not sufficient condition for cerebral recovery after ischemia. The return of high-energy phosphates after a 16-min cardiac arrest, however, indicates a potential for neurological recovery.
Cholinergic and VIPergic Innervation in Cerebral Arteries: A Sequential Double-Labeling Immunohistochemical Study
Authors: Miao Frederick Jia-Pei , Lee Tony Jer-Fu
Published: April 2011

The possible co-localization of choline acetyltransferase (ChAT) and vasoactive intestinal polypeptide (VIP) in the nerve fibers of cat cerebral arteries was examined by a sequential double-labeling immunohistochemical method. Diaminobenzidine and tetramethylbenzidine were used as chromogens to distinguish ChAT (protein) and VIP (peptide) immunoreactivities. Since available fixatives often did not provide simultaneous preservation of optimal protein and peptide immunoreactivities, a new fixative, buffered periodate-paraformal-dehyde-picric acid-formaldehyde-lysine (PPPFL), was formulated and tested. PPPFL fixative is more reliable for simultaneously preserving ChAT and VIP immunoreactivities than were periodate-lysine-paraformaldehyde (PLP) fixative, Zamboni's fixative, or 2% paraformaldehyde solution alone. Using PPPFL as fixative, both ChAT immunoreactive (ChAT-I) and VIP-immunoreactive (VIP-I) fibers in cerebral arteries appeared as bundle and fine fibers. Most ChAT-I and VIP-I fibers were separate. Portions of ChAT-I and VIP-I fibers often ran closely in parallel or across each other. Overlaying of VIP-I on ChAT-I fibers and relay connections between them were also observed. These morphological data suggest the potential functional interactions between cholinergic and VIPergic innervations. In <5% of the fibers examined did ChAT and VIP immunoreactivities appear to be co-localized. These data therefore do not support the hypothesis that acetylcholine and VIP are co-localized in most fibers innervating the cerebral arterial wall.
Extracellular pH in the Rat Brain during Hypoglycemic Coma and Recovery
Authors: Bengtsson Finn , Boris-Möller Fredrik , Hansen Anker J. , Siesjö Bo K.
Published: April 2011

It has previously been shown that hypoglycemic coma is accompanied by marked energy failure and by loss of cellular ionic homeostasis. The general proposal is that shortage of carbohydrate substrate prevents lactic acid formation and thereby acidosis during hypoglycemic coma. The objective of the present study was to explore whether rapid downhill ion fluxes, known to occur during coma, are accompanied by changes in extra-and/or intracellular pH (pHe and/or pHi), and how these relate to the de- and repolarization of cellular membranes. Cortical pHe was recorded by microelectrodes in insulin-injected rats subjected to 30 min of hypoglycemic coma, with cellular membrane depolarization. Some rats were allowed up to 180 min of recovery after glucose infusion and membrane repolarization. Arterial blood gases and physiological parameters were monitored to maintain normotension, normoxia, normocapnia, and normal plasma pH. Following depolarization during hypoglycemia, a prompt, rapidly reversible alkaline pHe shift of about 0.1 units was observed in 37/43 rats. Immediately thereafter, all rats showed an acid pH shift of about 0.2 units. This shift developed during the first minute, and pHe remained at that level until repolarization was induced. Following repolarization, there was an additional, rapid, further lowering of pHe by about 0.05 units, followed by a more prolonged decrease in pHe that was maximal at 90 min of recovery (ΔpHe of approximately −0.4 units). The pHe then slowly normalized but was still decreased (−0.18 pH units) after 180 min when the experiment was terminated. The calculated pHi showed no major alterations during hypoglycemic coma or after membrane repolarization following glucose administration. The results demonstrate that hypoglycemic coma is accompanied by a decrease in pHe of almost the same magnitude as observed in status epilepticus, and that a lingering extracellular acidosis is observed during recovery from hypoglycemia. It is proposed that, at least in part, the initial extracellular alkaline/acid shift is caused by H+ influx or HCO3− outflux (alkaline shift) followed by H+ efflux or HCO3− influx (acid shift) through conductance channels that are opened during depolarization. The alkaline shift appears before the depolarization has occurred and the acid shift after the depolarization, when mainly the chemical gradient provides the driving force. It is speculated that Na+/H+ exchange contributes to the further extracellular acidification seen during repolarization.
In vivo Binding of Spiperone and N-Methylspiperone to Dopaminergic and Serotonergic Sites in the Rat Brain: Multiple Modeling and Implications for PET Scanning
Authors: Swart Jacobus A. A. , van der Werf Jan F. , Wiegman Tonnie , Paans Anne M. J. , Vaalburg Willem , Korf Jakob
Published: April 2011

Equilibrium models are derived and applied to in vivo binding of spiperone in the rat brain. The models express the concentration of the ligand in the striatum and frontal cortex as a function of the accumulation in the cerebellum. The models differ with respect to the description of specific binding. Nonlinear regression analysis shows that the in vivo specific binding of 3H-labeled spiperone in the frontal cortex (mainly serotonergic) can be described by a noninteracting sites model, whereas the specific binding in the striatum (mainly dopaminergic) can best be described by models that lead to sigmoid saturation curves. These results were tested and partly confirmed by determining the region-of-interest/cerebellar radioactivity ratio of 11C-labeled N-methylspiperone, with and without pretreatment with haloperidol. The estimated Bmax was 32 fmol/mg wet tissue in the frontal cortex and ∼90 fmol/mg wet tissue in the striatum. The free plus nonspecific binding of spiperone was similar in the frontal cortex but lower in the striatum than in the cerebellum. The occurrence of sigmoidicity can be best explained by the existence of high-affinity/low-capacity sites in the cerebellum rather than mutual interactions of striatal sites. The consequence of the present analysis for positron emission tomography is that the striatal/cerebellar activity ratio is not an accurate parameter of specific binding features at tracer doses of spiperone or N-methylspiperone.
Glucose Deprivation Neuronal Injury in vitro is Modified by Withdrawal of Extracellular Glutamine
Authors: Monyer Hannelore , Choi Dennis W.
Published: April 2011

Cultured cortical neurons deprived of glucose in a defined solution containing 2 m M glutamine became acutely swollen and went on to degenerate over the next day; this neuronal loss could be substantially attenuated by an N-methyl-D-aspartate (NMDA) antagonist. Removal of extracellular glutamine produced two effects: an increase in overall neuronal injury and a decrease in the protective effect of an NMDA antagonist. Both effects of glutamine removal were glutamine concentration dependent (EC50 for both ∼300 μ M) and not reversed by substitution of equimolar concentrations of alanine or arginine. These observations suggest that glucose deprivation neuronal injury may be tonically regulated by the presence of extracellular glutamine. We speculate that glutamine may reduce overall injury by serving as an energy substrate in the absence of glucose, but may increase NMDA receptor-mediated injury by serving as a precursor for transmitter excitatory amino acids.
Dissociation by Chloralose of the Cardiovascular and Cerebrovascular Responses Evoked from the Cerebellar Fastigial Nucleus
Authors: Iadecola Costantino , Springston Mary E. , Reis Donald J.
Published: April 2011

We studied the effects of chloralose anesthesia on the elevation in arterial pressure (AP), heart rate (HR), and regional CBF (rCBF) elicited by stimulation of the cerebellar fastigial nucleus (FN). Rats were anesthetized with an initial dose of chloralose (40 mg/kg s.c), paralyzed, and artificially ventilated. The FN was stimulated (50–100 μA, 50 Hz, 1 s on/1 s off) with microelectrodes stereotaxically implanted. During the stimulation AP was carefully maintained within cerebrovascular autoregulation. CBF was measured by the [14C]iodoantipyrine technique with regional dissection. In rats that received only the initial dose of chloralose, FN stimulation elevated rCBF in brain and spinal cord, up to 209 ± 13% of control in frontal cortex (n = 5; p < 0.01, analysis of variance). Administration of additional chloralose (10 mg/kg i.v., 30 min prior to measurement of CBF) did not affect resting rCBF (n = 5), the EEG, or the elevation in AP and HR elicited by FN stimulation (n = 4). However, the additional chloralose abolished the elevations in rCBF (n = 5; p > 0.05). Thus, the cerebrovasodilation elicited from the FN is more susceptible to the effects of additional anesthesia than the elevation in AP and HR. These results indicate that the cerebrovascular and cardiovascular responses elicited from the FN are functionally distinct and provide additional evidence for the notion that these responses are mediated by different neural pathways and transmitters.
Effect of Dipyridamole on Cerebral Extracellular Adenosine Level in vivo
Authors: Park T. S. , Gidday Jeffrey M.
Published: April 2011

The effect of dipyridamole, an adenosine transport inhibitor, on cerebral extracellular adenosine concentration remains to be determined. To examine this issue, bilateral brain dialysis samples were obtained from piglet frontal cortex before, during, and after 5 min of cerebral ischemia; 10−4 M dipyridamole was administered through one dialysis probe. On the control side, dialysate adenosine concentration increased 5.7-fold during ischemia and 15-fold during the first 5 min of reperfusion; it returned to control levels after 15 min of reperfusion. Relative to the control side, dipyridamole caused a twofold increase in basal dialysate adenosine concentration and increased dialysate adenosine concentration at 10 and 15 min of reperfusion, but no increase in dialysate adenosine occurred during and immediately after ischemia. The results indicate that, in the piglet brain, cerebral ischemia markedly elevates intracerebral extracellular adenosine concentration and that dipyridamole increases extracellular adenosine levels.
Mild Cerebral Hypothermia during and after Cardiac Arrest Improves Neurologic Outcome in Dogs
Authors: Leonov Yuval , Sterz Fritz , Safar Peter , Radovsky Ann , Oku Ken-Ichi , Tisherman Samuel , Stezoski S. William
Published: April 2011

We previously found mild hypothermia (34–36°C), induced before cardiac arrest, to improve neurologic outcome. In this study we used a reproducible dog model to evaluate mild hypothermia by head cooling during arrest, continued with systemic cooling (34°C) during recirculation and for 1 h after arrest. In four groups of dogs, ventricular fibrillation (no flow) of 12.5 min at 37.5°C was reversed with cardiopulmonary bypass and defibrillation in ≤5 min, and followed by controlled ventilation to 20 h and intensive care to 96 h. In Study A we resuscitated with normotension and normal hematocrit; Control Group A-I (n = 12) was maintained normothermic, while Treatment Group A-II (n = 10) was treated with hypothermia. In Study B we resuscitated with hypertension and hemodilution. Control Group B-I (n = 12) was maintained no rmo thermic (6 of 12 were not hemodiluted), while Treatment Group B-II (n = 10) was treated with hypothermia. Best overall performance categories (OPCs) achieved between 24 and 96 h postarrest were in Group A-I: OPC 1 (normal) in 0 of 12 dogs, OPC 2 (moderate disability) in 2, OPC 3 (severe disability) in 7, and OPC 4 (coma) in 3 dogs. In Group A-II, OPC 1 was achieved in 5 of 10 dogs (p < 0.01), OPC 2 in 4 (p < 0.001), OPC 3 in 1, and OPC 4 in 0 dogs. In Group B-I, OPC 1 was achieved in 0 of 12 dogs, OPC 2 in 6, OPC 3 in 5, and OPC 4 in 1 dog. In Group B-II, OPC 1 was achieved in 6 of 10 dogs (p < 0.01), OPC 2 in 4 (p < 0.05), and OPC 3 or 4 in 0 dogs. Mean neurologic deficit and brain histopathologic damage scores showed similar significant group differences. Morphologic myocardial damage scores were the same in all four groups. We conclude that mild brain cooling during and after insult improves neurologic outcome after cardiac arrest.
Parasympathetic Denervation of Rat Pial Vessels Significantly Increases Infarction Volume following Middle Cerebral Artery Occlusion
Authors: Kano Michihisa , Moskowitz Michael A. , Yokota Masayuki
Published: April 2011

Studies were undertaken in Long Evans rats to examine the hypothesis that chronic unilateral sectioning of vasodilating nerve fibers (parasympathetic and/or sensory) innervating the circle of Willis increases infarction volume following unilateral branch occlusion of the middle cerebral artery (MCA) combined with temporary (45 min) bilateral common carotid occlusion. Infarct size was measured 24 h after surgical occlusion from seven coronal slices. Infarction volume (mean ± SD) in sham animals (group A) and surgically naive animals (group B) measured 153 ± 43 and 131 ± 38 mm3, respectively. After lesions of both sensory (nasociliary nerve) and parasympathetic efferents at the ethmoidal foramen (group C, combined lesion) or selective lesions of parasympathetic efferents (group D), infarction volume increased [214 ± 47 mm3 (p < 0.01) and 209 ± 46 mm3 (p < 0.05), respectively]. No increases were detected after cutting the nasociliary nerve alone (group E) or occluding the external ethmoidal artery (group F) [145 ± 39 mm3 (p > 0.05) and 124 ± 63 mm3 (p > 0.05), respectively]. The infarct was predominantly located within cortical gray matter and became enlarged on its superior and inferior aspects after parasympathectomy. Large infarcts were noted whether animals breathed spontaneously (all of the above) or were artificially respired or whether animals were anesthetized with xylazine and ketamine or chloral hydrate. Taken together, these studies suggest a previously unrecognized protective role for autonomic parasympathetic fibers in the pathophysiology of focal cerebral ischemia that is not shared by sensory fibers. The importance of autonomic vasodilating fibers to blood flow in ischemic brain merits further study.
Decreases in Regional Cerebral Blood Flow with Normal Aging
Authors: Martin Andrew J. , Friston Karl J. , Colebatch James G. , Frackowiak Richard S. J.
Published: April 2011

Positron emission tomographic (PET) images of regional cerebral blood flow (rCBF) from 30 normal, resting volunteers aged 30 to 85 years were analysed to identify areas where rCBF fell with age. Images were anatomically normalised, and a pixel-by-pixel linear regression was performed to remove differences in global CBF between subjects. Pixels at which rCBF then showed a significant ( p < 0.01) negative correlation with age were identified. They were displayed as a statistical parametric map (SPM) of correlations. We demonstrate an age-related decrease in adjusted rCBF in the cingulate, parahippocampal, superior temporal, medial frontal, and posterior parietal cortices bilaterally, and in the left insular and left posterior prefrontal cortices (omnibus significance, χ2 = 2,291, p < 0.0001, df = 1). Decreases in rCBF suggest a regionally specific loss of cerebral function with age. The affected areas were all limbic, or association, cortices. Therefore, these decreases may constitute the cerebral substrate of the cognitive changes that occur during normal aging.
Marked Protection by Moderate Hypothermia after Experimental Traumatic Brain Injury
Authors: Clifton Guy L. , Jiang Ji Y. , Lyeth Bruce G. , Jenkins Larry W. , Hamm Robert J. , Hayes Ronald L.
Published: April 2011

These experiments examined the effects of moderate hypothermia on mortality and neurological deficits observed after experimental traumatic brain injury (TBI) in the rat. Brain temperature was measured continuously in all experiments by intraparenchymal probes. Brain cooling was induced by partial immersion (skin protected by a plastic barrier) in a water bath (0°C) under general anesthesia (1.5% halothane/70% nitrous oxide/30% oxygen). In experiment I, we examined the effects of moderate hypothermia induced prior to injury on mortality following fluid percussion TBI. Rats were cooled to 36°C ( n = 16), 33°C ( n = 17), or 30°C ( n = 11) prior to injury and maintained at their target temperature for 1 h after injury. There was a significant (p < 0.04) reduction in mortality by a brain temperature of 30°C. The mortality rate at 36°C was 37.5%, at 33°C was 41%, and at 30°C was 9.1%. In experiment II, we examined the effects of mod erate hypothermia or hyperthermia initiated after TBI or long-term behavioral deficits. Rats were cooled to 36°C ( n = 10), 33°C ( n = 10), or 30°C ( n = 10) or warmed to 38°C ( n = 10) or 40°C ( n = 12) starting at 5 min after injury and maintained at their target temperatures for 1 h. Hypothermia-treated rats had significantly less beam-walking beam-balance, and body weight loss deficits compared to normothermic (38°C) rats. The greatest protection was observed in the 30°C hypothermia group. Since a temperature of 30°C can be induced in humans by surface cooling without coagulopathy or ventricular fibrillation, hypothermia to 30°C may have potential clinical value for treatment of human brain injury.
Compartmental Analysis of [11C]Flumazenil Kinetics for the Estimation of Ligand Transport Rate and Receptor Distribution Using Positron Emission Tomography
Authors: Koeppe R. A. , Holthoff V. A. , Frey K. A. , Kilbourn M. R. , Kuhl D. E.
Published: April 2011

The in vivo kinetic behavior of [11C]flumazenil ([11C]FMZ), a non-subtype-specific central benzodiazepine antagonist, is characterized using compartmental analysis with the aim of producing an optimized data acquisition protocol and tracer kinetic model configuration for the assessment of [11C]FMZ binding to benzodiazepine receptors (BZRs) in human brain. The approach presented is simple, requiring only a single radioligand injection. Dynamic positron emission tomography data were acquired on 18 normal volunteers using a 60- to 90-min sequence of scans and were analyzed with model configurations that included a three-compartment, four-parameter model, a three-compartment, three-parameter model, with a fixed value for free plus nonspecific binding; and a two-compartment, two-parameter model. Statistical analysis indicated that a four-parameter model did not yield significantly better fits than a three-parameter model. Goodness of fit was improved for three- versus two-parameter configurations in regions with low receptor density, but not in regions with moderate to high receptor density. Thus, a two-compartment, two-parameter configuration was found to adequately describe the kinetic behavior of [11C]FMZ in human brain, with stable estimates of the model parameters obtainable from as little as 20–30 min of data. Pixel-by-pixel analysis yields functional images of transport rate ( K1) and ligand distribution volume ( DV“), and thus provides independent estimates of ligand delivery and BZR binding.