bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous Recording of Cerebral Blood Oxygenation Changes during Human Brain Activation by Magnetic Resonance Imaging and Near-Infrared Spectroscopy
Authors: Kleinschmidt Andreas , Obrig Hellmuth , Requardt Martin , Merboldt Klaus-Dietmar , Dirnagl Ulrich , Villringer Arno , Frahm Jens
Published: November 2003

Changes in cerebral blood oxygenation due to functional activation of the primary sensorimotor cortex during a unilateral finger opposition task were simultaneously mapped by deoxyhemoglobin-sensitive magnetic resonance imaging (MRI) and monitored by near-infrared spectroscopy (NIRS). Activation foci along the contralateral central sulcus displayed task-associated increases in MRI signal intensity, indicating a concomitant decrease of the focal concentration of deoxyhemoglobin. This interpretation was confirmed by simultaneous reductions in deoxyhemoglobin measured optically. Since observation of the latter effect required exact spatial matching of the MRI-detected activation foci and position of the fiber optic bundles (“optodes”) used for transmitting and receiving light, it may be concluded that optical recordings of changes in deoxyhemoglobin during functional challenge probe only a restricted brain tissue region. While deoxyhemoglobin responses seen by NIRS were smaller for ipsi- than for contralateral finger movements, task-related increases in oxyhemoglobin were rather similar between both conditions and, thus, seem to be less specific. Furthermore, no consistent changes were obtained for total hemoglobin during task performance, possibly due to the short timing of the repetitive protocol. In general, results underline, in humans, the hitherto assumed signal physiology for functional brain mapping by oxygenation-sensitive MRI and allow assessment of both constraints and practicability of functional studies by NIRS.
Distribution Volume Ratios without Blood Sampling from Graphical Analysis of PET Data
Authors: Logan Jean , Fowler Joanna S. , Volkow Nora D. , Wang Gene-Jack , Ding Yu-Shin , Alexoff David L.
Published: November 2003

The distribution volume ratio (DVR), which is a linear function of receptor availability, is widely used as a model parameter in imaging studies. The DVR corresponds to the ratio of the DV of a receptor-containing region to a nonreceptor region and generally requires the measurement of an arterial input function. Here we propose a graphical method for determining the DVR that does not require blood sampling. This method uses data from a nonreceptor region with an average tissue-to-plasma efflux constant k2 to approximate the plasma integral. Data from positron emission tomography studies with [15C]raclopride (n = 20) and [11C] d-threo-methylphenidate ([11C]dMP) (n = 8) in which plasma data were taken and used to compare results from two graphical methods, one that uses plasma data and one that does not. k2 was 0.163 and 0.051 min−1 for [11C]raclopride and [11C]dMP, respectively. Results from both methods were very similar, and the average percentage difference between the methods was −0.11% for [11C]raclopride and 0.46% for [11C]dMP for DVR of basal ganglia (BG) to cerebellum (CB). Good agreement between the two methods was also achieved for DVR images created by both methods. This technique provides an alternative method of analysis not requiring blood sampling that gives equivalent results for the two ligands studied. It requires initial studies with blood sampling to determine the average kinetic constant and to test applicability. In some cases, it may be possible to neglect the b̅2 term if the BG/CB ratio becomes reasonably constant for a sufficiently long period of time over the course of the experiment.
Comparison of Two Compartmental Models for Describing Receptor Ligand Kinetics and Receptor Availability in Multiple Injection PET Studies
Authors: Morris Evan D. , Alpert Nathaniel M. , Fischman Alan J.
Published: November 2003

The goal of research with receptor ligands and PET is the characterization of an in vivo system that measures rates of association and dissociation of a ligand-receptor complex and the density of available binding sites. It has been suggested that multiple injection studies of radioactive ligand are more likely to identify model parameters than are single injection studies. Typically, at least one of the late injections is at a low specific activity (SA), so that part of the positron emission tomography (PET) curve reflects ligand dissociation. Low SA injections and the attendant reductions in receptor availability, however, may violate tracer kinetic assumptions, namely, tracer may no longer be in steady state with the total (labeled and unlabeled) ligand. Tissue response becomes critically dependent on the dose of total ligand, and an accurate description of the cold ligand in the tissue is needed to properly model the system. Two alternative models have been applied to the receptor modeling problem, which reduces to describing the time-varying number of available receptor sites. The first ( Huang et al., 1989 ) contains only compartments for the hot ligand, ‘hot only’ (HO), but indirectly accounts for the action of cold ligand at receptor sites via SA. The second stipulates separate compartments for the hot and cold ligands, ‘hot and cold’ (HC), thus explicitly calculating available number of receptors. We examined these models and contrasted their abilities to predict PET activity, receptor availability, and SA in each tissue compartment. For multiple injection studies, the models consistently predicted different PET activities—especially following the third injection. Only for very high rate constants were the models identical for multiple injections. In one case, simulated PET curves were quite similar, but discrepancies appeared in predictions of receptor availability. The HO model predicted nonphysiological changes in the availability of receptor sites and introduced errors of 30–60% into estimates of B′max for test data. We, therefore, strongly recommend the use of the HC model for all analyses of multiple injection PET studies.
Fluorodopa Positron Emission Tomography with an Inhibitor of Catechol-O-Methyltransferase: Effect of the Plasma 3-O-Methyldopa Fraction on Data Analysis
Authors: Ishikawa Tatsuya , Dhawan Vijay , Chaly Thomas , Robeson William , Belakhlef Abdelfatihe , Mandel Francine , Dahl Robert , Margouleff Claude , Eidelberg David
Published: November 2003

Fluorodopa (FDOPA) is an analogue of L-dihydroxyphenylalanine (L-dopa) used to assess the nigrostriatal dopamine system in vivo with positron emission tomography (PET). However, FDOPA/PET quantitation is complicated by the presence of the 3- O-methyl-FDOPA (30MFD) fraction in brain and plasma. Pretreatment with entacapone (OR-611), a peripheral catechol O-methyltransferase (COMT) inhibitor, greatly reduces the plasma 30MFD fraction and provides an ideal situation to evaluate the contribution of the plasma 30MFD fraction in several kinetic models of FDOPA uptake. We performed FDOPA/PET with and without the OR-611 preadministration in six Parkinson's disease (PD) patients. We measured the time-course of the plasma FDOPA and 30MFD fractions using high-pressure liquid chromatography (HPLC). We calculated striato-occipital ratios (SOR), and estimated the striatal FDOPA uptake rate constant graphically using the plasma FDOPA and occipital tissue time activity curves (KiFD and KiOCC, respectively). We also estimated striatal dopa decarboxylase (DDC) activity (k3D) using a model incorporating independent measurements of 30MFD transport kinetic rate constants. With the preadministration of OR-611, the pharmacological efficiency in plasma was prolonged significantly (21.1–37.7%; p < 0.01). We also observed significant mean elevations in SOR and KiOCC by 21.8 and 53.5%, respectively ( p < 0.05). KiFD and k3D did not show significant change. We conclude that OR-611 prolongs the circulation time of FDOPA in the plasma but does not alter rate constants for striatal FDOPA uptake or decarboxylation.
Simplified Brain Slice Glucose Utilization
Authors: Newman George C. , Hospod Frank E. , Maghsoudlou Behzad , Patlak Clifford S.
Published: November 2003

Brain slice glucose utilization (SGU) can be measured by methods analogous to those used for in vivo cerebral glucose utilization. In order to make this technique more accessible and applicable to a broad range of experimental conditions, we have derived a simplified operational rate equation and generated the table of apparent rate coefficients necessary to apply the equation under different experimental situations. Calculations of the apparent rate coefficients were based upon an eight-parameter kinetic model combined with Michaelis–Menten theory to account for changes in the rate constants as a function of buffer glucose concentration. The theory was tested with a series of experiments using rat brain slices, [14C]-2-deoxyglucose (2DG) and [14C]-3– O-methylglucose (3OMG). The errors involved in the simplified technique were estimated by a variety of techniques and found to be acceptable over a broad range of conditions. A detailed, practical protocol for the simplified method is presented.
Correlation of the Average Water Diffusion Constant with Cerebral Blood Flow and Ischemic Damage after Transient Middle Cerebral Artery Occlusion in Cats
Authors: Miyabe Masayuki , Mori Susumu , van Zijl Peter C. M. , Kirsch Jeffrey R. , Eleff Scott M. , Koehler Raymond C. , Traystman Richard J.
Published: November 2003

Magnetic resonance water diffusion imaging can detect early ischemic changes in stroke. Using a middle cerebral artery occlusion model, we examined which range of values of the orientation-independent diffusion quantity [Formula: see text] is an early noninvasive indicator of reduced cerebral perfusion and focal brain injury. Cats underwent either a 30-min occlusion followed by 3.5 h reperfusion (n = 7) or a 60-min occlusion followed by 4-h reperfusion (n = 6). Repeated measurements of CBF were made with radiolabeled microspheres, and acute focal injury was measured with triphenyltetrazolium chloride (TTC) staining. During occlusion, the decrease in Dav correlated with CBF for caudate [30-min occlusion (n = 13): p < 0.0001; 60-min occlusion (n = 6): p < 0.02] and for cortex [30-min occlusion (n = 12): p < 0.0001; 60-min occlusion (n = 5): p < 0.04]. Variable caudate and hemispheric injury levels were found among cats in both groups. The area of tissue injury demarcated by TTC began to correlate with the area of reduced Dav by 30 min of occlusion (p < 0.02), and this correlation improved (p < 0.0001) at 1, 1.5, and 2.0 h after the onset of occlusion. The time necessary to reach a one-to-one correspondence between the percent of hemisphere injured and the percent of hemispheric area with Dav < 0.65 × 10−9 m2/s was 2 h after occlusion. Thus, the absolute value of Dav is a good indicator of the risk of tissue injury, whereas the combination of Dav and the length of time of Dav reduction is an excellent predictor of acute focal tissue injury demarcated by TTC staining.
Evidence against High Extracellular Glutamate Promoting the Elicitation of Spreading Depression by Potassium
Authors: Obrenovitch Tihomir P. , Zilkha Elias , Urenjak Jutta
Published: November 2003

This study ascertains whether high extracellular glutamate contributes to the initiation of spreading depression (SD) by K+. Two microdialysis probes, each incorporating an electrode to record the extracellular direct current (DC) potential at the elicitation site, were implanted symmetrically in the cortex of anesthetized rats. Recurrent SD was triggered by perfusion of 130 m M K+ through the microdialysis probe for 20 min. On one side, this medium was supplemented with increasing concentrations of glutamate (0.1–1 m M) or of the selective glutamate uptake inhibitor L- trans-pyrrolidine-2,4-dicarboxylate (L-trans-PDC; 1–10 m M). The effects of L- trans-PDC on extracellular glutamate and basal DC potential were studied in separate experiments. Application of K+ for 20 min consistently elicited five to seven waves of SD. Increasing the concentration of glutamate in the perfusion medium did not alter SD elicitation. Application of L- trans-PDC concentration dependently increased the dialysate levels of glutamate (by ∼ 19-fold with 10 m M L- trans-PDC) but, unexpectedly, reduced SD elicitation. These data do not support the hypothesis that SD is elicited because high extracellular glutamate resulting from exocytosis and/or reversal of glutamate uptake depolarizes adjacent neurons. As SD elicitation requires activation of N-methyl-D-aspartate (NMDA) receptors, these results also illustrate that sensitivity of a pathological or experimental event to NMDA receptor antagonists does not necessarily imply involvement of increased extracellular glutamate. This does not rule out a selective action of glutamate, transiently released from presynaptic vesicles, on immediately juxtaposed postsynaptic receptors.
The AMPA Antagonist LY293558 Improves Functional Neurological Outcome following Reversible Spinal Cord Ischemia in Rabbits
Authors: Bowes Mark P. , Swanson Steven , Zivin Justin A.
Published: November 2003

Glutamate (Glu) neurotoxicity is an important element of a number of neurological disorders including central nervous system (CNS) ischemia. We evaluated the effects of the novel AMPA Glu antagonist LY293558 on functional neurological outcome in two rabbit stroke models. In the reversible spinal cord ischemia model, ischemia of the caudal lumbar spinal cord was produced by temporary occlusion of the abdominal aorta. LY293558 was administered 5 min after recirculation as a 16 mg/kg i.v. bolus followed by 2.2 mg/kg infused over 1 h. Control animals received saline. LY293558 significantly increased the duration of ischemia required to produce paraplegia, from 30.5 ± 15.8 min (mean ± SD) controls to 50.1 ± 11.5 in treated animals ( p < 0.01). In an irreversible model of cerebral ischemia, 50 μm plastic microspheres were injected into the carotid artery and lodged in the cerebral microvasculature. LY293558 did not significantly reduce neurological damage in this model. These data suggest that LY293558 may have therapeutic benefit following some types of ischemic injury.
Enlarged Infarcts in Endothelial Nitric Oxide Synthase Knockout Mice are Attenuated by Nitro-L-Arginine
Authors: Huang Zhihong , Huang Paul L. , Ma Jianya , Meng Wei , Ayata Cenk , Fishman Mark C. , Moskowitz Michael A.
Published: November 2003

Infarct size and vascular hemodynamics were measured 24 h after middle cerebral artery (MCA) occlusion in mice genetically deficient in the endothelial nitric oxide synthase (eNOS) isoform. eNOS mutant mice developed larger infarcts (21%) than the wild-type strain when assessed 24 h after intraluminal filament occlusion. Moreover, regional CBF values recorded in the MCA territory by laser-Doppler flowmetry were more severely reduced after occlusion and were disproportionately reduced during controlled hemorrhagic hypotension in autoregulation experiments. Unlike the situation in wild-type mice, nitro-L-arginine superfusion (1 m M) dilated pial arterioles of eNOS knockout mice in a closed cranial window preparation. As noted previously, eNOS mutant mice were hypertensive. However, infarct size remained increased despite lowering blood pressure to normotensive levels by hydralazine treatment. Systemic administration of nitro-L-arginine decreased infarct size in eNOS mutant mice (24%) but not in the wild-type strain. This finding complements published data showing that nitro-L-arginine increases infarct size in knockout mice expressing the eNOS but not the neuronal NOS isoform (i.e., neuronal NOS knockout mice). We conclude that NO production within endothelium may protect brain tissue, perhaps by hemodynamic mechanisms, whereas neuronal NO overproduction may lead to neurotoxicity.
Hypercapnia Relaxes Cerebral Arteries and Potentiates Neurally-Induced Relaxation
Authors: Toda Noboru , Ayajiki Kazuhide , Okamura Tomio
Published: November 2003

The present study was designed to determine whether relaxations induced by hypercapnia depend upon nitric oxide (NO) derived from the endothelium, and whether NO-mediated relaxant response to electrical and chemical stimulation of vasodilator nerves is modulated by hypercapnia. In canine and monkey cerebral arterial strips contracted with K+, raising the level of CO2 of the aerating gas in the bathing media from 5 to 10% produced a moderate relaxation, together with an increased Pco2 (from 29.8 to 59.3 mm Hg) and a decreased pH (from 7.43 to 7.15). Relaxation was not influenced by endothelium denudation and treatment with NG-nitro-L-arginine. Contractions elicited by the NO synthase inhibitor were attenuated by the removal of the endothelium. Relaxations, caused by transmural electrical stimulation and nicotine, of canine cerebral arterial strips contracted with prostaglandin F2α were potentiated only slightly by hypercapnia, but the potentiation of the response to exogenous NO (acidified NaNO2) was clearly greater. It is concluded that as far as the arteries used are concerned, hypercapnia does not seem to liberate NO from the endothelium but does potentiate the effect of NO. The reason for lesser potentiation, by hypercapnia, of the response to nitroxidergic nerve stimulation than to NO action may be associated with an impairment by intracellular acidosis of NO synthase activation.
Selective Distribution of Lactate Dehydrogenase Isoenzymes in Neurons and Astrocytes of Human Brain
Authors: Bittar Philippe G. , Charnay Yves , Pellerin Luc , Bouras Constantin , Magistretti Pierre J.
Published: November 2003

In vertebrates, the interconversion of lactate and pyruvate is catalyzed by the enzyme lactate dehydrogenase. Two distinct subunits combine to form the five tetrameric isoenzymes of lactate dehydrogenase. The LDH-5 subunit (muscle type) has higher maximal velocity ( Vmax) and is present in glycolytic tissues, favoring the formation of lactate from pyruvate. The LDH-1 subunit (heart type) is inhibited by pyruvate and therefore preferentially drives the reaction toward the production of pyruvate. There is mounting evidence indicating that during activation the brain resorts to the transient glycolytic processing of glucose. Indeed, transient lactate formation during physiological stimulation has been shown by 1H-magnetic resonance spectroscopy. However, since whole-brain arteriovenous studies under basal conditions indicate a virtually complete oxidation of glucose, the vast proportion of the lactate transiently formed during activation is likely to be oxidized. These in vivo data suggest that lactate may be formed in certain cells and oxidized in others. We therefore set out to determine whether the two isoforms of lactate dehydrogenase are localized to selective cell types in the human brain. We report here the production and characterization of two rat antisera, specific for the LDH-5 and LDH-1 subunits of lactate dehydrogenase, respectively. Immunohistochemical, immunodot, and western-blot analyses show that these antisera specifically recognize their homologous antigens. Immunohistochemistry on 10 control cases demonstrated a differential cellular distribution between both subunits in the hippocampus and occipital cortex: neurons are exclusively stained with the anti-LDH1 subunit while astrocytes are stained by both antibodies. These observations support the notion of a regulated lactate flux between astrocytes and neurons.
Potassium-Induced Cortical Spreading Depressions during Focal Cerebral Ischemia in Rats: Contribution to Lesion Growth Assessed by Diffusion-Weighted NMR and Biochemical Imaging
Authors: Busch Elmar , Gyngell Michael L. , Eis Manfred , Hoehn-Berlage Mathias , Hossmann Konstantin-Alexander
Published: November 2003

In focal ischemia of rats, the volume of ischemic lesion correlates with the number of peri-infarct depolarizations. To test the hypothesis that depolarizations accelerate infarct growth, we combined focal ischemia with externally evoked spreading depression (SD) waves. Ischemic brain infarcts were produced in halothane-anaesthetized rats by intraluminal thread occlusion of the middle cerebral artery (MCA). In one group of animals, repeated SDs were evoked at 15-min intervals by microinjections of potassium acetate into the frontal cortex. In another group, the spread of the potassium-evoked depolarizations was prevented by application of the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801). The volume of ischemic lesion was monitored for 2 h by diffusion-weighted imaging (DWI) and correlated with electrophysiological recordings and biochemical imaging techniques. In untreated rats, each microinjection produced an SD wave and a stepwise rise of the volume and signal intensity of the DWI-visible cortical lesion. The volume of this lesion increased between 15 min and 2 h of MCA occlusion from 19 ± 15% to 66 ± 16% of ipsilateral cortex. In dizocilpine-treated animals, microinjections of potassium did not evoke SDs, nor did the volume and signal intensity of the DWI-visible cortical lesion change. At 15 min after MCA occlusion, the DWI-visible lesion was larger than in untreated animals—43 ± 16% of the ipsilateral cortex; however, after 2 h, it increased only slightly further to 49 ± 21%. Slower lesion growth in the absence of SDs was also reflected by the volume of ATP-depleted tissue, which, after 2 h of MCA occlusion, involved 26 ± 12% of the ipsilateral cortex in treated and 49 ± 9% in untreated animals ( p < 0.01). These observations support the hypothesis that peri-infarct depolarizations accelerate cerebral infarct growth.
Experimental Antileukocyte Interventions in Cerebral Ischemia
Authors: Härtl Roger , Schürer Ludwig , Schmid-Schönbein Geert W. , del Zoppo Gregory J.
Published: November 2003

White blood cells (WBCs) play vital roles in host defense. Recently, increasing interest has been directed toward the question of whether WBCs, particularly polymorphonuclear leukocytes, could also act as mediators of secondary brain damage in the setting of focal and global cerebral ischemia with and without reperfusion. Considerable insight into the importance of WBC-mediated tissue injury has been gained from studies employing antileukocyte interventions in experimental cerebral ischemia. The purpose of this article is to survey the different approaches taken to interfere with WBC inflammatory function. Emphasis is laid on a discussion of the efficacy of these interventions, their effects and side effects on cerebral and systemic parameters, and the power of evidence they provide for identification of WBCs as important factors in cerebral ischemia. The role of WBCs has been investigated in a great variety of global and focal cerebral ischemia models with and without reperfusion, leading to spmetimes contradictory results. In the light of currently available data, it seems likely that WBCs contribute to secondary brain damage in the scenario of experimental transient focal cerebral ischemia, if the insult is not too severe.
Interaction between ATP-Sensitive K+ Channels and Nitric Oxide on Pial Arterioles in Piglets
Authors: Bari Ferenc , Errico Robert A. , Louis Thomas M. , Busija David W.
Published: November 2003

The interaction between ATP-sensitive K+ channels (KATP) and nitric oxide (NO) was studied in pial arterioles of piglets. We examined the effects of N-nitro-l-arginine methyl ester (l-NAME), a general inhibitor of nitric oxide synthase (NOS), and 7-nitroindazole (7-NI), a selective inhibitor of neuronal NOS, on aprikalim-induced cerebral vasodilation. Topically applied, aprikalim, a selective activator of KATP, dilated arterioles by 11 ± 7% at 10−8 M and 17 ± 6% at 10−6 M. After l-NAME treatment (15 mg/kg, i.v.), the response was reduced (4 ± 4% and 12 ± 7%, respectively; n = 8, p < 0.05). Administration of 7-NI (50 mg/kg, i.p.) did not change pial arteriolar responsiveness to aprikalim. However, both l-NAME and 7-NI reduced the vasodilator responses to 10−4 M N-methyl-d-aspartate (NMDA) (by 73% and by 36%, respectively). Furthermore, 7-NI treatment abolished the glutamate-induced dilatation of pial arterioles. Administration of l-NAME reduced the NOS activity in the cerebral cortex by 88%, whereas the reduction after the 7-NI treatment was 44%. Pretreatment and coadministration of 10−5 M glibenclaminde, a specific inhibitor of KATP or l-NAME administration, did not change the dilatory response to sodium nitroprusside. We conclude that NO may be involved in aprikalim-induced dilation of pial arterioles.
DNA Fragmentation and HSP70 Protein Induction in Hippocampus and Cortex Occurs in Separate Neurons following Permanent Middle Cerebral Artery Occlusions
Authors: States Bradley A. , Honkaniemi Jari , Weinstein Philip R. , Sharp Frank R.
Published: November 2003

DNA nick end-labeling (TUNEL) and heat shock protein (HSP)70 immunocytochemistry were performed on the same brain sections 1 (n = 6), 3 (n = 12), and 7 (n = 7) days following permanent middle cerebral artery (MCA) occlusions produced in adult rats using the endovascular carotid suture method. In the cortex at 1 and 3 days following MCA occlusions, HSP70 immunoreactive neurons were located outside areas of infarction and showed little evidence of DNA fragmentation. HSP70-stained cortical neurons were intermingled with TUNEL cells near the infarct, but extended for greater distances away from the infarct. DNA fragmentation occurred in CA1 hippocampal neurons in 39% of the animals at 1 and 3 days following ipsilateral MCA occlusion. Bilateral DNA fragmentation occurred in CA1 neurons in one subject. HSP70 protein was expressed in CA1 hippocampal neurons in nine of 18 (50%) animals at 1 and 3 days following MCA occlusions, including all animals that exhibited hippocampal DNA fragmentation. Three animals had bilateral expression of HSP70 in CA1 neurons. Cells that stained for either HSP70 protein or DNA fragmentation existed in close proximity to one another. Approximately 5–7% of HSP70-stained cells were TUNEL stained and 3% of TUNEL-positive cells also stained for HSP70. There was no HSP70 staining or DNA fragmentation in the brains of sham-operated controls (n = 4) or in the brains of animals 7 days following MCA occlusions. These data suggest that ischemic cells capable of translating HSP70 protein generally do not undergo DNA fragmentation. These data support the concept that most HSP70 protein-containing neurons in the cortical “penumbra” and hippocampus survive ischemic injury and are “reversibly injured.” It is shown that CA1 hippocampal pyramidal neurons die or are reversibly injured in ˜50% of animals following permanent MCA occlusions. Although the mechanism of this hippocampal injury is unknown, it could relate to transynaptic activation of N-methyl-d-aspartate (NMDA) receptors that mediate induction of early genes in hippocampus.
Microtubular Proteolysis in Focal Cerebral Ischemia
Authors: Pettigrew L. Creed , Holtz Mary L. , Craddock Susan D. , Minger Stephen L. , Hall Nathan , Geddes James W.
Published: November 2003

Calpain, a neutral protease activated by calcium, may promote microtubular proteolysis in ischemic brain. We tested this hypothesis in an animal model of focal cerebral ischemia without reperfusion. The earliest sign of tissue injury was observed after no more than 15 min of ischemia, with coiling of apical dendrites immunolabeled to show microtubule-associated protein 2 (MAP2). After 6 h of ischemia, MAP2 immunoreactivity was markedly diminished in the infarct zone. Quantitative Western analysis demonstrated that MAP2 was almost unmeasurable after 24 h of ischemia. An increase in calpain activity, shown by an antibody recognizing calpain-cleaved spectrin fragments, paralleled the loss of MAP2 immunostaining. Double-labeled immunofluorescent studies showed that intraneuronal calpain activity preceded evidence of MAP2 proteolysis. Perikaryal immunolabeling of τ protein became increasingly prominent between 1 and 6 h in neurons located within the transition zone between ischemic and unaffected tissue. Western blot experiments confirmed that dephosphorylation of τ protein occurred during 24 h of ischemia, but was not associated with significant loss of τ antigen. We conclude that focal cerebral ischemia is associated with early microtubular proteolysis caused by calpain.
Induction of Na+/Myo-Inositol Cotransporter mRNA after Focal Cerebral Ischemia: Evidence for Extensive Osmotic Stress in Remote Areas
Authors: Yamashita Toshihide , Kohmura Eiji , Yamauchi Atsushi , Shimada Shoichi , Yuguchi Takamichi , Sakaki Takayuki , Miyai Akiko , Tohyama Masaya , Hayakawa Toru
Published: November 2003

Myo-inositol is one of the major organic osmolytes in the brain. It is accumulated into cells through an Na+/myo-inositol cotransporter (SMIT) that is regulated by extracellular tonicity. To investigate the role of SMIT in the brain after cerebral ischemia, we examined expression of SMIT mRNA in the rat brain after middle cerebral artery occlusion, which would reflect alteration of extracellular tonicity. The expression of SMIT mRNA was markedly increased 12 h after surgery in the cortex of the affected side and lasted until the second day. Increased expression was also found in the contralateral cingulate cortex. Up-regulated expression was found predominantly in the neurons in remote areas, although nonneuronal cells adjacent to the ischemic core also expressed this mRNA. These results suggest that cerebral ischemia causes extensive osmotic stress in brain and that the neuronal cells respond to this stress by increasing SMIT expression.
Duration Threshold of Induced Hypertension on Cerebral Blood Flow, Energy Metabolism, and Edema after Transient Forebrain Ischemia in Gerbils
Authors: Hosomi Naohisa , Tsuda Yoshiyasu , Ichihara Shin-Ichiro , Kitadai Masaya , Ohyama Hideo , Matsuo Hirohide
Published: November 2003

We have investigated whether there is a duration threshold for the effects of phenylephrine-induced hypertension on CBF, brain energy metabolism, and cerebral parenchymal specific gravity (SG) following transient forebrain ischemia in gerbils. Sixty gerbils were randomly assigned to one of the four treatment groups: one control group and three groups subjected to an increase of 25 mm Hg in MABP induced by treatment, 30 min after reperfusion, with phenylephrine for 15 min, 30 min, or 60 min. The local CBF was measured continuously, and the SG was evaluated 120 min after reperfusion. Sequential changes in brain energy metabolism, as shown by the ratio of phosphocreatine to inorganic phosphate (Pi), the β-ATP/Pi ratio, and intracellular pH, were also measured. The 15-min induced hypertension regimen was most suited to the recovery of brain energy metabolism, which was associated with an increase in local CBF and a decrease in cerebral edema. These results demonstrate that a suitable duration can be chosen to optimize the beneficial effects of phenylephrine-induced hypertension on ischemic brain injury following transient forebrain ischemia.
Reduced Transit-Time Sensitivity in Noninvasive Magnetic Resonance Imaging of Human Cerebral Blood Flow
Authors: Alsop D. C. , Detre J. A.
Published: November 2003

Herein, we present a theoretical framework and experimental methods to more accurately account for transit effects in quantitative human perfusion imaging using endogenous magnetic resonance imaging (MRI) contrast. The theoretical transit time sensitivities of both continuous and pulsed inversion spin tagging experiments are demonstrated. We propose introducing a delay following continuous labeling, and demonstrate theoretically that introduction of a delay dramatically reduces the transit time sensitivity of perfusion imaging. The effects of magnetization transfer saturation on this modified continuous labeling experiment are also derived, and the assumption that the perfusion signal resides entirely within tissue rather than the arterial microvasculature is examined. We present results demonstrating the implementation of the continuous tagging experiment with delay on an echoplanar scanner for measuring cerebral blood flow (CBF) in normal volunteers. By varying the delay, we estimate transit times in the arterial system, values that are necessary for assessing the accuracy of our quantification. The effect of uncertainties in the transit time from the tagging plane to the arterial microvasculature and the transit time to the tissue itself on the accuracy of perfusion quantification is discussed and found to be small in gray matter but still potentially significant in white matter. A novel method for measuring T1, which is fast, insensitive to contamination by cerebrospinal fluid, and compatible with the application of magnetization transfer saturation, is also presented. The methods are combined to produce quantitative maps of resting and hypercarbic CBF.
Relationship between Finger Movement Rate and Functional Magnetic Resonance Signal Change in Human Primary Motor Cortex
Authors: Rao S. M. , Bandettini P. A. , Binder J. R. , Bobholz J. A. , Hammeke T. A. , Stein E. A. , Hyde J. S.
Published: November 2003

Functional magnetic resonance imaging (FMRI) is a noninvasive technique for mapping regional brain changes in response to sensory, motor, or cognitive activation tasks. Interpretation of these activation experiments may be confounded by more elementary task parameters, such as stimulus presentation or movement rates. We examined the effect of movement rate on the FMRI response recorded from the contralateral primary motor cortex. Four right-handed healthy subjects performed flexion-extension movements of digits 2–5 of the right hand at rates of 1, 2, 3, 4, or 5 Hz. Results of this study indicated a positive linear relationship between movement rate and FMRI signal change. Additionally, the number of voxels demonstrating functional activity increased significantly with faster movement rates. The magnitude of the signal change at each movement rate remained constant over the course of three 8-min scanning series. These findings are similar to those of previous rate studies of the visual and auditory system performed with positron emission tomography (PET) and FMRI.
Relationship of 133Xe Cerebral Blood Flow to Middle Cerebral Arterial Flow Velocity in Men at Rest
Authors: Clark James M. , Skolnick Brett E. , Gelfand Robert , Farber Roger E. , Stierheim Maria , Stevens W. Craig , Beck George , Lambertsen Christian J.
Published: November 2003

Cerebral blood flow (CBF) was measured by 133Xe clearance simultaneously with the velocity of blood flow through the left middle cerebral artery (MCA) over a wide range of arterial PCO2 in eight normal men. Average arterial PCO2, which was varied by giving 4% and 6% CO2 in O2 and by controlled hyperventilation on O2, ranged from 25.3 to 49.9 mm Hg. Corresponding average values of global CBF15 were 27.2 and 65.0 ml 100 g min−1, respectively, whereas MCA blood-flow velocity ranged from 42.8 to 94.2 cm/s. The relationship of CBF to MCA blood-flow velocity over the imposed range of arterial PCO2 was described analytically by a parabola with the equation: [Formula: see text]

The observed data indicate that MCA blood-flow velocity is a useful index of CBF response to change in arterial PCO2 during O2 breathing at rest. With respect to baseline values measured while breathing 100% O2 spontaneously, percent changes in velocity were significantly smaller than corresponding percent changes in CBF at increased levels of arterial PCO2 and larger than CBF changes at the lower arterial PCO2. These observed relative changes are consistent with MCA vasodilation at the site of measurement during exposure to progressive hypercapnia and also during extreme hyperventilation hypocapnia.
Brief Hypercapnia Enhances Somatosensory Activation of Blood Flow in Rat
Authors: Schmitz Bernd , Böttiger Bernd W. , Hossmann Konstantin-Alexander
Published: November 2003

Activation of CBF by hypercapnia or functional stimulation has been attributed to multiple mediators, most of which are thought to interfere with cerebrovascular reactivity in a closely time-related manner. Here we describe that brief hypercapnia produces marked up-regulation of somatosensory activation of blood flow that outlasts carbon dioxide exposure for at least 60 min. In chloralose-anesthetized, mechanically ventilated rats, somatosensory activation was carried out by electrical stimulation of the forepaw. Blood flow was measured in the contralateral primary somatosensory cortex by laser-Doppler flowmetry (LDF). Under control conditions, somatosensory stimulation increased LDF by 38.8 ± 11.0%. Ventilation with 6% CO2 for 3 min caused a rise of LDF by 28.0 ± 8.7%. Baseline CBF and Paco2 returned to control values within 20 min. Repetition of somatosensory stimulation after hypercapnia revealed a long-lasting up-regulation of the flow response: 25 min after hypercapnia, functional stimulation increased LDF by 86.0 ± 18.1%, and 60 min after hypercapnia even by 96.0 ± 26.0%. This is the first demonstration of CO2-induced up-regulation of functional activation of blood flow and an example of the importance of general physiological variables for the modulation of the coupling process.
Brain Capillary Perfusion during Sleep
Authors: Zoccoli Giovanna , Lucchi Maria Luisa , Andreoli Emanuela , Bach Veronique , Cianci Tullia , Lenzi Pierluigi , Franzini Carlo
Published: November 2003

Brain capillary perfusion was evaluated in the different states of the wake–sleep cycle—quiet wakefulness (QW), quiet sleep (QS), and active sleep (AS)—in rats. The extent of the perfused capillary network was determined by intravascular distribution of a fluorescent marker, Evans blue (EB); it remained unchanged across the three behavioral conditions, QW, QS, and AS. The anatomical network was assessed by alkaline phosphatase (AP) endothelial staining, which is known to underestimate the number of existing capillaries. The resulting number of AP profiles were, therefore, significantly lower than the number of EB profiles, but the percentage of AP-stained capillaries that were perfused (96%) was also unchanged across the behavioral conditions. The results indicate that no capillary recruitment accompanies the wake–sleep cycle. Capillary surface area is a relevant factor in determining exchanges across the blood–brain barrier. In the absence of capillary recruitment (relative constancy of the surface area), the CBF changes during sleep should preferentially affect flow-limited with respect to diffusion-limited transport.
Protein Synthesis and Immunoreactivities of Contraction-Related Proteins in Smooth Muscle Cells of Canine Basilar Artery after Experimental Subarachnoid Hemorrhage
Authors: Oka Yoshihisa , Ohta Shinsuke , Todo Hirooki , Kohno Kanehisa , Kumon Yoshiaki , Sakaki Saburo
Published: November 2003

We examined time-dependent changes in protein synthesis and in the immunoreactivities of representative contraction-related structural proteins in smooth muscle cells of canine basilar arteries after experimental subarachnoid hemorrhage (SAH). Protein synthesis was assessed by the percentage of polyribosome-forming ribosomes to total ribosomes (aggregation rate), a morphological index of the activity of protein synthesis. The aggregation rates in prostaglandin F2α- (PGF2α) and 12- O-tetradecanoyl-phorbol-13-acetate (TPA)-induced contracted basilar arteries were 70.0 ± 7.0% and 71.4 ± 8.7%, respectively, quite similar to the value in normal basilar artery (73.0 ± 8.0%). In the single-SAH group with little delayed histological changes in the basilar arteries, the aggregation rate was significantly decreased to 30.5 ± 6.4% by 24 h after the SAH, and recovered to 52.3 ± 9.0% and 70.2 ± 7.6% at 7 and 14 days postSAH, respectively, when the vasospasm was moderately and completely ameliorated. In contrast, in the double-SAH group in which the basilar arteries developed delayed smooth muscle cell death and long-lasting arterial contraction, a significant decrease in the aggregation rate (25.0 ± 5.0% on day 4) persisted for 14 days. The in vitro incorporation of [3H]-leucine in the basilar arterial cells was also significantly suppressed 4 and 7 days after the initial SAH (1.2 ± 0.4 and 1.4 ± 0.3 × 103 dpm/mg protein) in the double-SAH group, as opposed to no significant decrease in the basilar artery at 7 days postSAH in the single-SAH group (1.9 ± 0.6 × 103 dpm/mg protein). The immunoreactivity of α-smooth muscle actin, a contractile protein, demonstrated by immunohistochemistry and immunoblots, was not altered for up to 14 days even in the double-SAH group, but that of calponin and of h-caldesmon, contraction-inhibiting proteins, was markedly reduced 4–14 days after the initial SAH. Persistent impairment of protein synthesis and relative reduction of immunoreactivities of the contraction-inhibiting proteins were observed in arteries with severe vasospasm and loss of smooth muscle cells, as noted in the double-SAH subjects. These abnormalities may cooperate to cause cerebral arterial narrowing accompanied by degeneration of smooth muscle cells after SAH.
Hemorrhagic Transformation and Microvascular Integrity during Focal Cerebral Ischemia/Reperfusion
Authors: Hamann Gerhard F. , Okada Yasushi , del Zoppo Gregory J.
Published: November 2003

Hemorrhagic transformation after cerebral ischemia is a well known clinical concern. The frequency of intact basal lamina (BL), identified by laminin antigen, in hemorrhagic and nonhemorrhagic zones after middle cerebral artery occlusion (MCA:O) and 3-h MCA:O with reperfusion in adolescent male baboons was assessed. Parenchymal hemoglobin was not detected prior to 24-h reperfusion. A significant decrease in the density of laminin (BL) in hemorrhagic zones (6.2 ± 2.4) compared with nonhemorrhagic ischemic zones (10.5 ± 2.4) (p < 0.05) and nonischemic basal ganglia (17.0 ± 2.7) (p < 0.01) was observed. Time-dependent changes in BL integrity appear linked to the extravasation of blood components.
Reactive Astrocytosis from Excitotoxic Injury in Hippocampal Organ Culture Parallels that Seen in Vivo
Authors: Kunkler Phillip E. , Kraig Richard P.
Published: November 2003

Reactive astrocytes influence not only the severity of brain injury, but also the capacity of brain to reshape itself with learning. Mechanisms responsible for astrogliosis remain unknown but might be best studied in vitro, where improved access and visualization permit application of modern molecular and cellular techniques. We have begun to explore whether gliosis might be studied in hippocampal organotypic cultures (HOTCs), where potential cell-to-cell interactions are preserved and the advantages of an in vitro preparation are still realized. Following HOTC exposure to N-methyl-D-aspartate (NMDA), dose-dependent changes occurred in the optical density (OD) values for the astrocytic immunohistochemical [immunostaining (IS)] markers glial fibrillary acidic protein (GFAP) and vimentin. Exposure of HOTCs to NMDA (10 μ M) caused selective death in the CA1 hippocampal region and the dentate gyrus. It also significantly increased GFAP IS and vimentin IS OD values in these regions. Increased GFAP IS and vimentin IS OD values were also seen in CA3, a hippocampal region that displayed no cell death. Light microscopic examination revealed hypertrophied GFAP and vimentin IS cells, characteristic of reactive astrocytes. Cellular proliferation, as assessed by proliferating cell nuclear antigen IS, was also significantly increased in all three of these hippocampal regions. In contrast, exposure of HOTCs to a noninjurious level of NMDA (1 μ M) caused only minor changes in GFAP IS and vimentin IS OD values but a significantly reduced cellular proliferation in all HOTC regions. These results show that reactive astrocytosis from excitotoxic injury of HOTC parallels changes seen in vivo after global ischemia. Furthermore, since resting astroglia within HOTCs are also similar to their counterparts in vivo, HOTCs may be used to examine mechanisms by which these cells are transformed into reactive species within tissue that resembles intact brain.
Blood Glucose Concentration Does Not Affect Outcome in Brain Trauma: A 31P MRS Study
Authors: Vink Robert , Golding Elke M. , Williams John P. , McIntosh Tracy K.
Published: November 2003

Effects of blood glucose concentration on biochemical and neurologic outcome following lateral fluid percussion-induced traumatic injury of moderate severity (2.8 atm) in rats were studied using radioactive phosphorus (31P) magnetic resonance spectroscopy (MRS) and a battery of tests designed to evaluate posttraumatic neurologic motor function. Prior to injury, male Sprague-Dawley rats (n = 18) were randomly assigned to receive either dextrose, 2 ml 50% (wt/vol), zinc insulin (10 IU/kg) or no treatment, thus dividing the animals into hyperglycemic, hypoglycemic, and normoglycemic groups, respectively. Animals were then injured, monitored for 4 h by 31P MRS before being allowed to recover, and assessed for posttraumatic motor function. Following brain injury, there was no difference in brain intracellular pH between groups over the 4-h posttraumatic MRS monitoring period. Similarly, intracellular free magnesium, cytosolic phosphorylation potential, and neurologic outcome posttrauma were not significantly different between groups. We conclude that, unlike models of ischemia, blood glucose concentration may not be a significant factor affecting outcome in traumatic brain injury.
Cerebral [15O] Water Clearance in Humans Determined by Positron Emission Tomography: II. Vascular Responses to Vibrotactile Stimulation
Authors: Fujita Hitoshi , Meyer Ernst , Reutens David C. , Kuwabara Hiroto , Evans Alan C. , Gjedde Albert
Published: November 2003

When used to measure blood flow, water leaves a residue in the vascular bed, which may contribute to the calculation of increased blood flow during functional activation of brain tissue. To assess the magnitude of this contribution with the two-compartment positron emission tomography (PET) method, we mapped the water clearance ( K1) of the brain as an index of cerebral blood flow (CBF) and the apparent vascular distribution of nonextracted H215O ( Vo). The latter map represented mainly the cerebral arterial and arteriolar volume. We also prepared subtraction maps (Δ K1, Δ Vo) of the response to vibrotactile stimulation of the fingertips of the right hand of six normal volunteers. Using magnetic resonance (MR) images of all subjects, the data were rendered into Talairach's stereotaxic coordinates and the averaged subtraction images (activation minus baseline) merged with the corresponding averaged MRI image. The Δ K1 map revealed the expected response in the primary sensory hand area; the Δ Vo response was located about 13 mm more anteriorly, close to the central fissure, most likely reflecting changes of the arteries feeding the primary sensory hand area. We conclude that cerebral perfusion and cerebrovascular responses to vibrotactile stimulation may occur in disparate locations that can be identified separately by using the two-compartment method.