bluuebunny/crossref_metadata_2025 huggingface dataset:
Cerebral Blood Flow Autoregulation during Hypobaric Hypotension Assessed by Laser Doppler Scanning
Authors: Heimann A. , Kroppenstedt S. , Ulrich P. , Kempski O. S.
Published: April 2011

Hypobaric hypotension was used to reduce systemic blood pressure in rats below the lower threshold of CBF autoregulation to evaluate a new laser Doppler (LD) “scanning” technique. Spontaneously breathing male Wistar Kyoto rats (n = 8) were anesthetized with chloral hydrate and the head fixed in a stereotaxic head holder. A cranial window with intact dura mater was introduced to assess local CBF (lCBF) by LD. One stationary probe served to detect rapid flow changes, whereas the second probe was used to sample lCBF recordings from many cortical locations by means of a stepping motor-controlled micromanipulator to obtain lCBF frequency histograms. Advantages are an improved spatial resolution together with the easy detection of low-flow areas and a better comparison of data from individual experiments. Arterial blood pressure was stepwise reduced by exposing the lower body portions to subatmospheric pressures (hypobaric hypotension), thus avoiding the use of drugs or heparinization. The lower threshold of CBF autoregulation was detected by “scanning” at arterial pressures between 50 and 46 mm Hg, with low-flow spots occurring immediately. The data suggest LD scanning as a method suited particularly for studies where lCBF inhomogeneities are expected, e.g., the ischemic penumbra or sinus vein thrombosis.
Modulation of Intracellular Formation of Reactive Oxygen Intermediates in Peritoneal Macrophages and Microglia/Brain Macrophages by Propentofylline
Authors: Banati R. B. , Schubert P. , Rothe G. , Gehrmann J. , Rudolphi K. , Valet G. , Kreutzberg G. W.
Published: April 2011

Ischemia-induced nerve cell death can partly be prevented by propentofylline, a pharmacon structurally related to xanthine derivates that interacts with the neuromodulatory function of endogenous adenosine. To evaluate a possible mechanism of neuroprotection by propentofylline, we studied its effect on the cellular production of reactive oxygen intermediates in microglial cells, which under pathological conditions can differentiate into brain macrophages, in comparison to peritoneal macrophages. Using a flow cytometric assay, we determined the intracellular formation of reactive oxygen intermediates by measuring the oxidation of the membrane-permeable and nonfluorescent dihydrorhodamine 123 to the cationic and intracellularly trapped, green fluorescent rhodamine 123 in single viable cells. Propentofylline at the therapeutic concentration of 50 μ M completely inhibited the Ca2+-dependent Con A-induced increase in the production of reactive oxygen intermediates in peritoneal macrophages. In isolated and cultured microglial cells, which have a high spontaneous respiratory burst activity, the spontaneous production of reactive oxygen intermediates was reduced by ∼30%. A phorbol 12-myristate 13-acetate-induced rise in the respiratory burst activity could not be inhibited by propentofylline in either cell type. An increased generation of reactive oxygen intermediates is thought to contribute to nerve cell death after brain ischemia, edema, and neurodegenerative diseases like Alzheimer's disease. These pathological conditions are all accompanied by an activation of microglial cells. We therefore suggest that the neuroprotective properties of propentofylline might in part be due to a modulation of the microglial production of potentially harmful reactive oxygen intermediates.
Effects of Theophylline and Cyclohexyladenosine on Brain Injury following Normo- and Hyperglycemic Ischemia: A Histopathologic Study in the Rat
Authors: Zhou Jie-Gang , Meno Joseph R. , Hsu Sean S.-F. , Winn H. Richard
Published: April 2011

The present study was designed to determine the effects of theophylline, an adenosine receptor antagonist, and cyclohexyladenosine (CHA), an adenosine receptor agonist, on ischemic brain injury following normo- and hyperglycemic ischemia and reperfusion in fasted male Wistar rats. Moderate hyperglycemia was achieved by administering 17% D-glucose (3 g/kg i.p.), whereas normoglycemic animals received an equal volume of saline. The animals were further divided into two groups: One group was pretreated with either theophylline (0.20 μmol/g i.p.) or an equal volume of saline; the second group received either intraventricular CHA (6.25 nmol) or mock CSF prior to the onset of ischemia. During ischemia, pericranial temperature was maintained at 36°C and EEG was monitored. Cerebral ischemia was induced for 15 min, after which flow was restored and the animals were allowed to recover completely. There were no significant differences in physiologic parameters among the groups studied. Five days following the ischemic episode, the rats were perfused with formalin and the brains sub-serially sectioned (8 μm) in the coronal plane and stained with celestine blue/acid fuchsin. Histopathologic analysis was performed in a blinded fashion to determine percentage of dead neurons. Hyperglycemic animals had significantly greater ischemic injury in CA1, cortex, and caudate than the normoglycemic group (p < 0.01). Moreover, rats pretreated with theophylline had a significantly (p < 0.01) higher percentage of dead neurons in CA1, cortex, and caudate than corresponding controls. On the other hand, rats treated with CHA exhibited significantly (p < 0.01) less cerebral ischemic injury than corresponding controls, in either normo- or hyperglycemic conditions. These data confirm previous studies showing the deleterious effects of hyperglycemia on cerebral ischemia-reperfusion injury. Moreover, our results illustrate a protective effect of adenosine on both normo- and hyperglycemic ischemia-reperfusion injury and thus support the hypothesis that attenuated cerebral ischemic production of adenosine contributes to increased tissue injury observed under hyperglycemic conditions.
Nitric Oxide Synthase Inhibition and Cerebrovascular Regulation
Authors: Iadecola Costantino , Pelligrino Dale A. , Moskowitz Michael A. , Lassen Niels A.
Published: April 2011

There is increasing evidence that nitric oxide (NO) is an important molecular messenger involved in a wide variety of biological processes. Recent data suggest that NO is also involved in the regulation of the cerebral circulation. Thus, NO participants in the maintenance of resting cerebrovascular tone and may play an important role in selected vasodilator responses of the cerebral circulation. Furthermore, evidence has been presented suggesting that NO participates in the mechanisms of cerebral ischemic damage. Despite the widespread attention that NO has captured in recent years and the large number of studies that have been published on the subject, there is considerable controversy regarding the role of this agent in cerebrovascular regulation and in ischemic damage. In this paper the results of investigations on NO and the cerebral circulation are reviewed and the evidence for and against a role of NO is critically examined.
Local Cerebral Blood Flow during Hibernation, a Model of Natural Tolerance to “Cerebral Ischemia”
Authors: Frerichs Kai U. , Kennedy Charles , Sokoloff Louis , Hallenbeck John M.
Published: April 2011

The breakdown of cellular homeostasis and progressive neuronal destruction in cerebral ischemia appears to be mediated by a complex network of causes that are intricately interrelated. We have investigated a physiological state existing normally in nature in which mammals appear to tolerate the ordinarily detrimental effects of ischemia with reduced oxygen availability and to resist activation of self-destructive processes, i.e., mammalian hibernation. Ground squirrels (Spermophilus tridecemlineatus) were chronically implanted with arterial and venous catheters and telemetry devices for electroencephalography, electrocardiography, and monitoring of body temperature. The animals were placed in an environmental chamber at an ambient temperature of 5°C. Entrance into hibernation was characterized by a drop in heart rate followed by a gradual decline in body temperature and an isoelectric electroencephalogram. Cold-adapted active animals that were not hibernating served as controls. Cerebral blood flow (CBF) was measured in both groups with the autoradiographic [14C]iodoantipyrine method. Mean (±SD) mass-weighted CBF in the brain as a whole was 62 ± 16 ml/100 g/min (n = 4) in the control group but was reduced to ischemic levels, 7 ± 4 ml/100 g/min (n = 4), in the hibernating animals (p < 0.001). No neuropathological changes were found in similarly hibernating animals aroused from hibernation. Hibernation appears to be actively regulated, and hormonal factors may be involved. The identification and characterization of such factors and of the mechanisms used by hibernating species to increase ischemic tolerance and to blunt the destructive effects of ischemia may enable us to prevent or minimize the loss of homeostatic control during and after cerebral ischemia in other species.
Acidosis Induced by Hypercapnia Exaggerates Ischemic Brain Damage
Authors: Katsura Ken-Ichiro , Kristián Tibor , Smith Maj-Lis , Siesjö Bo K.
Published: April 2011

Although preischemic hyperglycemia is known to aggravate damage due to transient ischemia, it is a matter of controversy whether or not this is a result of the exaggerated acidosis. It has recently been reported that although tissue acidosis of a comparable severity could be induced in normoglycemic dogs by an excessive rise in arterial CO2 tension, short-term functional recovery was improved, rather than compromised. In the present experiments we induced excessive hypercapnia (Paco2, ∼300 mm Hg) in normoglycemic rats before inducing forebrain ischemia of 10-min duration. This reduced the brain extracellular pH to values normally encountered in hyperglycemic rats subjected to ischemia. The events induced by hypercapnia clearly enhanced ischemic brain damage, as assessed histologically after 7 days of recovery. We hypothesize that the decisive event was an exaggerated decrease in extra- and intracellular pH and that the results thus demonstrate an adverse effect of acidosis. However, since postischemic seizures did not occur in the hypercapnic ischemic rats, the results also demonstrate that changes in intra-extracellular pH and bicarbonate concentrations modulated ischemic damage in an unexpected way.
Functional Study of the Brain by NMR
Authors: Prichard James W. , Rosen Bruce R.
Published: April 2011

Nuclear magnetic resonance (NMR) methods allow a wide variety of noninvasive measurements to be made on living animals and humans. The most extensively developed application of such methods is magnetic resonance imaging (MRI) of the brain and other organs, which has already come to the attention of most biomedical scholars, many physicians, and even much of the lay public because of its widespread use in neurological research and medical diagnosis.
Neuroprotective Effect of the AMPA Receptor Antagonist LY-293558 in Focal Cerebral Ischemia in the Cat
Authors: Bullock R. , Graham D. I. , Swanson S. , McCulloch J.
Published: April 2011

The effects of the glutamate α-amino-3-hydroxy 5-methyl-4-isoxazole propionate (AMPA) receptor antagonist LY-293558 in reducing ischemic brain damage have been assessed in halothane-anesthetized cats. Focal cerebral ischemia was produced by permanent occlusion of one middle cerebral artery, and the animals were killed 6 h later. The amount of early irreversible ischemic damage was assessed at 16 predetermined stereotactic planes by an observer blinded to treatment paradigm employed. Treatment with LY-293558 (15 mg/kg i.v., plus infusion of 7 mg/kg/h) initiated 30 min prior to middle cerebral artery occlusion reduced significantly (p < 0.02) the volume of ischemic damage (from 3,423 ± 212 mm3 of the cerebral hemisphere in vehicle-treated cats to 2,822 ± 569 mm3 in LY-293558-treated cats). The present data demonstrate that an AMPA receptor antagonist can reduce focal ischemic damage in a gyrencephalic species in which key physiological variables have been controlled and monitored throughout the postischemic period. These data provide additional support for the clinical evaluation of AMPA receptor antagonists in focal cerebral ischemia in humans.
Induction of Ischemic Tolerance following Brief Focal Ischemia in Rat Brain
Authors: Glazier Steven S. , O'Rourke Donald M. , Graham David I. , Welsh Frank A.
Published: April 2011

The objective of this study was to determine whether brief focal ischemia induces ischemic tolerance in rat brain. Focal ischemia was produced in Wistar rats by occluding the middle cerebral artery (MCA) for 20 min at a distal site. Following recovery for 24 h, the animals were subjected to a 10-min episode of forebrain ischemia using a combination of bilateral carotid artery occlusion and systemic hypotension. Histologic injury, assessed after a survival period of 3–4 days, consisted of selective neuronal necrosis bilaterally in cerebral cortex, striatum, hippocampus, and thalamus superimposed upon a small cortical infarct adjacent to the site of MCA occlusion. However, the intensity of neuronal necrosis in the MCA territory of the neocortex ipsilateral to MCA occlusion was markedly less than that in the contralateral MCA cortex. In contrast, the extent of neuronal necrosis in subcortical structures was similar in both hemispheres Unexpectedly, animals in which the MCA was manipulated, but not occluded, also exhibited a marked reduction of neuronal necrosis in the ipsilateral MCA neocortex following forebrain ischemia. However, in animals with craniotomy alone, forebrain ischemia caused a similar extent of neuronal necrosis in the MCA neocortex of both hemispheres. Transient occlusion of the MCA induced the focal expression of the 72-kDa heat-shock protein (hsp72) in the MCA territory of the neocortex. Limited expression of hsp72 was also detected following sham occlusion, but not after craniotomy alone. These results demonstrate focal induction of ischemic tolerance in rat neocortex that may be related to expression of heat-shock proteins.
Importance of Nitric Oxide Synthase Inhibition to the Attenuated Vascular Responses Induced by Topical L-Nitroarginine during Vibrissal Stimulation
Authors: Irikura Katsumi , Maynard Kenneth I. , Moskowitz Michael A.
Published: April 2011

We assessed the regional cerebral blood flow (rCBF) response to vibrissal stimulation before and after nitric oxide synthase (NOS) inhibitors were topically applied through a closed cranial window placed over the cortical barrel fields in anesthetized Sprague–Dawley rats. In the presence of L-nitroarginine (1 m M), both the maximum and total responses became reduced, but only in those animals demonstrating >50% inhibition of NOS activity as determined by the conversion of [3H]arginine to [3H]citrulline within homogenates taken from cortical gray matter under the cranial window. The degree of enzyme inhibition depended in part, upon duration after topical application of NOS inhibitor. When >50%, enzyme inhibition correlated with the decrease in maximum and total rCBF response (p < 0.01). These findings emphasize the merits of assessing enzyme activity after administering NOS inhibitors, and suggest that NO generated from parenchymal NOS activity plays an important role in the cerebrovascular response to physiologic somatosensory stimulation under the stated conditions.
Transient Spinal Ischemia in Rat: Characterization of Spinal Cord Blood Flow, Extracellular Amino Acid Release, and Concurrent Histopathological Damage
Authors: Marsala Martin , Sorkin Linda S. , Yaksh Tony L.
Published: April 2011

Extracellular concentrations of amino acids in halothane-anesthetized rats were measured using a microdialysis fiber inserted transversely through the dorsal spinal cord at the level of the lumbar enlargement in conjunction with HPLC and ultraviolet detection. After a 2-h washout and a 1-h control period, 20 min of reversible spinal cord ischemia was achieved by the inflation of a Fogarty F2 catheter passed through the femoral artery to the descending thoracic aorta. After 2 h of postischemic reperfusion, animals were transcardially perfused with saline followed by 10% formalin or 4% paraformaldehyde. The glutamate concentration in the dialysate was significantly elevated after 10 min of occlusion and returned to near-baseline during the first 30 min of reperfusion. Taurine was elevated significantly 0.5 h postocclusion and continued to increase throughout the 2 h of reperfusion. Glycine concentrations showed a tendency to be slightly above baseline during the reperfusion period. Glutamine concentrations modestly increased following 2 h of reperfusion. No significant changes in aspartate, asparagine, and serine were detected. In control animals no significant changes in any amino acids were detected. To assess the role of complete spinal ischemia on spinal glutamate release, studies were carried out using cardiac arrest. Twenty minutes after induction of cardiac arrest, the glutamate concentration was increased about 350–400%. In a separate group of animals, spinal cord blood flow (SCBF) and its response to decreased CO2 were measured using a laser probe implanted into the epidural space at the level of the L2 vertebral segment. SCBF decreased to 5–6% of the control during aortic occlusion. After reversible ischemia, marked hyperemia was seen for the first 15 min, followed by hypoperfusion at 60 min. Under control–preischemic conditions a decrease in arterial CO2 content caused a decrease in SCBF of about 25%. This autoregulatory response was almost completely absent when assessed 60 min after a 20-min interval of aortic occlusion. Histopathological analysis of spinal cord tissue from these animals demonstrated heavy neuronal argyrophilia affecting small and medium-sized neurons located predominantly in laminae III–V. These changes corresponded to signs of irreversible damage at the ultrastructural level. Occasionally, small areas of focal necrosis, located in the dorsolateral part of the dorsal horn and anterolateral part of the ventral horn, were found. The results are consistent with a role for glutamate in ischemically induced spinal cord damage and suggest that taurine elevation detected during the early reperfusion period may serve as an important indicator of irreversible spinal cord neuronal damage.
Mild Intraischemic Hypothermia Reduces Postischemic Hyperperfusion, Delayed Postischemic Hypoperfusion, Blood-Brain Barrier Disruption, Brain Edema, and Neuronal Damage Volume after Temporary Focal Cerebral Ischemia in Rats
Authors: Karibe Hiroshi , Zarow Gregory J. , Graham Steven H. , Weinstein Philip R.
Published: April 2011

Mild to moderate hypothermia (30–33°C) reduces brain injury after brief (<2-h) periods of focal ischemia, but its effectiveness in prolonged temporary ischemia is not fully understood. Thirty-two Sprague–Dawley rats anesthetized with 1.5% isoflurane underwent 3 h of middle cerebral artery occlusion under hypothermic (33°C) or normothermic (37°C) conditions followed by 3 or 21 h of reperfusion under normothermic conditions ( n = 8/group). Laser–Doppler estimates of cortical blood flow showed that intraischemic hypothermia reduced both postischemic hyperperfusion ( p ≤ 0.01) and postischemic delayed hypoperfusion ( p ≤ 0.01). Hypothermia reduced the extent of blood-brain barrier (BBB) disruption as estimated from the extravasation of Evans blue dye at 6 h after the onset of ischemia ( p ≤ 0.01). Hypothermia also reduced the volume of both brain edema ( p ≤ 0.01) and neuronal damage ( p ≤ 0.01) as estimated from Nissl-stained slides at both 6 and 24 h after the onset of ischemia. These results demonstrate that mild intraischemic hypothermia reduces tissue injury after prolonged temporary ischemia, possibly by attenuating postischemic blood flow disturbances and by reducing vasogenic edema resulting from BBB disruption.
Augmentation of Blood Flow through Cerebral Collaterals by Inhibition of Nitric Oxide Synthase
Authors: Muhonen Michael G. , Heistad Donald D. , Faraci Frank M. , Loftus Christopher M.
Published: April 2011

We examined the influence of nitric oxide (NO) on normal and collateral cerebral blood flow after occlusion of the middle cerebral artery (MCA). Effects of NG-nitro-l-arginine (nitroarginine), an inhibitor of NO synthase, were examined during normotension and hypotension (arterial pressure, 50 mm Hg) in 49 anesthetized dogs. Following a craniotomy, a branch of the MCA was cannulated, and collateral-dependent tissue was identified using the shadow-flow technique. Regional cerebral blood flow was measured with microspheres, and pial artery pressure was measured with a micropipette. Intravenous nitroarginine reduced blood flow to normal cerebrum by approximately 40% (p < 0.05) during normotension and hypotension, with aortic pressure maintained constant after nitroarginine administration. Injection of nitroarginine during hypotension, without control of pressor effects, increased aortic and pial artery pressure approximately twofold. Concurrently, blood flow to normal cerebrum decreased (p < 0.05), while flow to collateral-dependent cerebrum increased (p < 0.05). Phenylephrine was infused during hypotension to increase arterial pressure to values similar to those achieved following nitroarginine. Blood flow to collateral-dependent cerebrum increased (p < 0.05), but flow to normal cerebrum was not altered during infusion of phenylephrine. Thus, inhibition of NO synthase during hypotension increases arterial pressure, decreases blood flow to normal cerebrum, and increases blood flow to collateral-dependent cerebrum. Phenylephrine also increases perfusion pressure and blood flow to collateral-dependent cerebrum, but in contrast to nitroarginine, it does not redistribute blood flow from normal cerebrum.
Electron Paramagnetic Resonance (EPR) Detection of Nitric Oxide Produced during Forebrain Ischemia of the Rat
Authors: Tominaga Teiji , Sato Shinya , Ohnishi Tomoko , Ohnishi S. Tsuyoshi
Published: April 2011

To detect if nitric oxide (NO) is produced in rat forebrain ischemia, we applied an electron paramagnetic resonance (EPR) NO-trapping technique. We also performed a detailed characterization of the technique. Diethyldithiocarbamate (DETC) and Fe-citrate were used as NO-trapping reagents. Under controlled ventilation, forebrain ischemia was produced by occlusion of both carotid arteries combined with hemorrhagic hypotension at 50 mm Hg for 15 min. DETC and Fe were administered 30 min prior to the onset of ischemia. During ischemia, the cerebral cortex was removed, and EPR samples were prepared. At liquid nitrogen temperatures, the NO-Fe-DETC signal (a triplet signal centered at g = 2.039 with the hyperfine coupling constant aN of 13 G) was detected overlapping Cu-DETC signals. By perfusing various concentrations of an NO-generating agent, 1,1-diethyl-2-hydroxy-2-nitrosohydrazine, into the rat brains, the amount of the “trapped NO” was calibrated. The size of the NO-Fe-DETC signal was well correlated with the NO concentrations in the perfusate (correlation coefficient r = 0.998, p < 0.01). Based on this calibration curve, it was found that the amount of trapped NO during forebrain ischemia increased to seven times that of the control (control n = 5, forebrain ischemia n = 4, p < 0.005).
The Effect of Acetazolamide on Regional Cerebral Blood Oxygenation at Rest and under Stimulation as Assessed by MRI
Authors: Bruhn Harald , Kleinschmidt Andreas , Boecker Henning , Merboldt Klaus-Dietmar , Hänicke Wolfgang , Frahm Jens
Published: April 2011

The sensitivity of gradient echo magnetic resonance imaging (MRI) to changes in cerebral blood oxygenation (CBO) has been introduced for mapping functional brain activation. Here, we report that this approach allows monitoring autoregulation in the human brain under vasodilatory stress. Following the administration of acetazolamide, signal intensities of deoxyhemoglobin-sensitive images increased in cortical and subcortical gray matter and to a lesser extent in white matter. This result reflects a venous hyperoxygenation stemming from an increase in cerebral perfusion with oxygen consumption remaining constant. In addition, pharmacologic induction of vasodilation attenuated activity-related MRI signal changes in the visual cortex under photic stimulation. Although intersubject variability was high, this finding indicates individually persisting autoregulatory responsiveness to functional challenge despite an “exhausted” reserve capacity. It is suggested that recording CBO by MRI will foster our understanding of modulation of vasomotor tone and cerebral perfusion. Furthermore, this technique may prove valuable for assessing the cerebrovascular reserve capacity in patients with carotid artery occlusive disease.
The Regional Rate of Serotonin Synthesis Estimated by the α-Methyl-Tryptophan Method in Rat Brain from a Single Time Point
Authors: Diksic M. , Nagahiro S. , Grdiša M.
Published: April 2011

A simplified approach to the measurement of the rate of serotonin (5-HT) synthesis in laboratory animals is presented using autoradiography and labeled α-methyl-l-tryptophan. The method is based on the assumption that the volume of distribution of an apparent precursor pool is the same in all brain structures. The apparent distribution volume ( Vapp) of the tracer was estimated from our previous data and found to be 0.45 ± 0.1 ml g−1 (n = 147) as an average in all brain structures. When this value of Vapp was used, the rates of 5-HT synthesis in the rat brain structures, calculated from the single time point method, were not significantly different from those calculated by the dual time point method, where both Vapp and K* were estimated. The rates from the two approaches did not differ when compared by analysis of variance (p > 0.8), Mann–Whitney rank sum test (p > 0.11), Bonferroni-corrected two-tailed t test, or when the ratio between two groups was tested against the hypothesis of being 1. The agreement between rates of 5-HT synthesis estimated by the two methods was very good, suggesting that the simplified method proposed here is appropriate for these kind of measurements.
Blood—Brain Barrier Taurine Transport during Osmotic Stress and in Focal Cerebral Ischemia
Authors: Stummer Walter , Betz A. Lorris , Shakui Parvin , Keep Richard F.
Published: April 2011

Little is known about blood to brain taurine transport despite substantial evidence suggesting a role of taurine in brain volume regulation during osmotic stress or conditions inducing cell swelling, such as ischemia. We have made measurements of the taurine influx rate constant ( K1) with [3H]taurine in three conditions: raised plasma taurine concentrations induced by infusion with 50 m M taurine (10 μl/100 g/min); osmotic stress induced by i.p. injections of 1.5 M NaCl (2 ml/100 g) or distilled water (10 ml/100 g); and 4 h of middle cerebral artery occlusion (MCAo). In rats with MCAo, additional determinations were made of tissue water and taurine contents, and blood-brain barrier passive permeability with [3H]α-aminoisobutyric acid. Taurine infusion increased plasma taurine from 110 ± 63 μ M (SD) to 407 ± 63 (p < 0.001) and decreased taurine K1 at the blood–brain barrier by 70% (p < 0.001), signifying saturable uptake that maintained unidirectional influx constant. Similarly, although hypo- and hyperosmolality increased and decreased plasma taurine concentration, respectively, a reciprocal relationship between K1 and plasma taurine in these experiments ensured that unidirectional fluxes of taurine into' brain were unchanged by osmotic stress. During MCAo, the taurine K1 was reduced 80% in the ipsilateral ischemic tissue compared with the contralateral nonischemic tissue (p < 0.001). This decline may be due to a release of taurine into the brain circulation, because there was a concomitant loss of tissue taurine of 7.4 ± 2.4 mmol/g dry weight (p < 0.05). Alternately, if taurine uptake is sodium dependent, the decline might reflect a disruption of the endothelial sodium gradient.
Correlation of CGS 19755 Neuroprotection against in vitro Excitotoxicity and Focal Cerebral Ischemia
Authors: Pérez-Pinzón Miguel A. , Maier Carolina M. , Yoon Edward J. , Sun Guo-Hua , Giffard Rona G. , Steinberg Gary K.
Published: April 2011

The in vivo neuroprotective effect and brain levels of cis-4-phosphonomethyl-2-piperidine carboxylic acid (CGS 19755), a competitive N-methyl-D-aspartate (NMDA) antagonist, were compared with its in vitro neuroprotective effects. The dose-response for in vitro neuroprotection against both NMDA toxicity and combined oxygen-glucose deprivation (OGD) was determined in murine neocortical cultures. Primary cultures of neocortical cells from fetal mice were injured by exposure to 500 μM NMDA for 10 min or to OGD for 45 min. The effect of CGS 19755 in both injury paradigms was assessed morphologically and quantitated by determination of lactate dehydrogenase release. Near complete neuroprotection was found at high doses of CGS 19755. The ED50 for protection against NMDA toxicity was 25.4 μmM, and against OGD the ED50 was 15.2 μM. For the in vivo paradigm rabbits underwent 2 h of left internal carotid, anterior cerebral, and middle cerebral artery occlusion followed by 4 h reperfusion; ischemic injury was assessed by magnetic resonance imaging and histopathology. The rabbits were treated with 40 mg/kg i.v. CGS 19755 or saline 10 min after arterial occlusion. CSF and brain levels of CGS 19755 were 12 μM and 5 μM, respectively, at 1 h, 6 μM and 5 μM at 2 h, and 13 μM and 7 μM at 4 h. These levels were neuroprotective in this model, reducing cortical ischemic edema by 48% and ischemic neuronal damage by 76%. These results suggest that a single i.v. dose penetrates the blood-brain barrier, attaining sustained neuroprotective levels that are in the range for in vitro neuroprotection.
Alterations in Cyclic AMP Generation and G Protein Subunits following Transient Ischemia in Gerbil Hippocampus
Authors: Suyama Kazuhiko , Saito Kuniaki , Chen Guang , Pan Bai-Shen , Manji Husseini K. , Potter William Z.
Published: April 2011

We examined alterations in the cyclic AMP generating system and G protein subunits in gerbil hippocampus following 10 min of transient ischemia. In hippocampal slices, basal and isoproterenol- and forskolin-stimulated cyclic AMP accumulations were markedly increased at 6 and 24 h after ischemia. Interestingly, both the inhibition of forskolin-stimulated cyclic AMP and the potentiation of β-adrenoceptor-stimulated cyclic AMP by a γ-aminobutyric acidB receptor agonist were attenuated at these time points. Ischemia did not affect the immuno-labeling of any of the G protein α subunits; only that of β subunits was significantly decreased, by 28.2%, 4 days after ischemia. In contrast, pertussis toxin-catalyzed [32P]ADP ribosylation declined progressively during the late recirculation period, reaching a significant reduction (25.4%) at 6 h after ischemia. These results suggest that ischemia affects the heterotrimeric conformation (αβγ) of Gi/Go during the recirculation period, thereby leading to increased cyclic AMP production. Because cyclic AMP-dependent protein kinase A modulates the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-kainate receptor channels, postischemic sensitization of the cyclic AMP generating system may contribute to neuronal degeneration in the hippocampus.
Resistance to Cerebral Ischemia in Developing Gerbils
Authors: Kusumoto Masayuki , Arai Hajime , Mori Kentaro , Sato Kiyoshi
Published: April 2011

Two-, three-, four-, five-, and twelve-week-old gerbils were subjected to various periods of bilateral carotid occlusion (BCO). Rectal and cranial temperatures were maintained at 37°C during BCO, and only rectal temperature was monitored for 30 min of reperfusion. Seven days after ischemia, animals were perfusion-fixed and the neuronal densities in the hippocampal CA1 sub-fields were counted. The extent of cerebral ischemia during BCO was evaluated with [14C]iodoantipyrine autoradiography. The rectal temperature spontaneously fell to 33–34°C during reperfusion in 2-week-old gerbils, although animals over 3 weeks old presented postischemic hyperthermia. Two-week-old animals therefore were divided into three experimental groups: In one group (2-week-old group I) rectal temperature was not regulated during 30 min of reperfusion, while in the other two groups (2-week-old groups II and III) rectal temperature was regulated at 37 and 38°C, respectively, during reperfusion. Five-minute BCO produced almost complete destruction of the CA1 neurons in 12-week-old animals. In contrast, most CA1 neurons survived 30 min of BCO in 2-week-old group I and 15 min of BCO in 2-week-old groups II and III. [14C]Iodoantipyrine autoradiography revealed that BCO produced severe forebrain ischemia in 2-week-old gerbils as well as in 12-week-old gerbils. These findings indicate that developing gerbils have a greater tolerance to cerebral ischemia and that such ischemic tolerance is not due to a collateral network between the vertebrobasilar and the carotid circulations previously reported to develop more abundantly in developing gerbils.
Efficient Calculation of the Principal Components of Imaging Data
Authors: Weaver John B.
Published: April 2011

Principal components analysis (PCA) of images is important in many applications such as positron emission tomography and functional magnetic resonance imaging. PCA is difficult for image data because the correlation matrix is very large. We present a direct method of calculating the PCA of the voxels from the small matrix expressing the correlations between images, instead of the larger matrix representing the correlations between voxels. The method is fast and accurate. It is faster and requires less memory than a singular value decomposition, although it is less accurate. It is much faster and more accurate than iterative and other approximate methods developed for this problem.
Effect of Delayed MK-801 (Dizocilpine) Treatment with or without Immediate Postischemic Hypothermia on Chronic Neuronal Survival after Global Forebrain Ischemia in Rats
Authors: Dietrich W. Dalton , Lin Baowan , Globus Mordecai Y.-T. , Green Edward J. , Ginsberg Myron D. , Busto Raul
Published: April 2011

In contrast to intraischemic hypothermia, immediate postischemic hypothermia (30°C) has been shown to delay but not chronically protect the CA1 hippocampus from transient global forebrain ischemia. The inability of a relatively short postischemic hypothermic period to protect chronically might involve a delayed or secondary injury mechanism. We determined whether delayed treatment with the noncompetitive N-methyl-d-aspartate receptor antagonist MK-801 (dizocilpine), alone or in combination with immediate postischemic hypothermia, would chronically protect histopathologically. Wistar rats underwent 10 min of normothermic forebrain ischemia induced by bilateral common carotid artery occlusion plus hypotension (50 mg Hg). Four ischemia groups were studied after normothermic (37°C) ischemia: no treatment; 3 h of immediate postischemic hypothermia (30°C); delayed MK-801 treatment (4 mg/kg) on postischemic days 3, 5, and 7; and postischemic hypothermia combined with multiple MK-801 treatments. Two months after the ischemic insult, rats were perfusion-fixed for quantitative histopathological assessment. Postischemic hypothermia alone or MK-801 treatment alone failed to protect the CA, hippocampus chronically. However, immediate postischemic hypothermia combined with delayed MK-801 treatment led to significant increases in normal CA1 neuron counts per microscopic field compared with normothermic ischemia. For example, neuronal counts within the hippocampal CA1 areas were 58 ± 39 (mean ± SD) in normothermic ischemic rats compared with 395 ± 198 in rats treated with postischemic hypothermia and MK-801. Chronic survival also led to pronounced striatal damage. Within the dorsolateral striatum, significant protection was documented with either postischemic hypothermia alone or delayed MK-801 treatment alone. In the striatum, neuronal counts were 8 ± 5, 47 ± 29, and 63 ± 30 in normothermic, MK-801-treated, and postischemic hypothermic rats, respectively. Significant protection within the somatosensory cortex was not observed with any of the treatment protocols. These findings indicate that the postischemic hippocampus and striatum undergo a delayed excitotoxic insult as late as postischemic day 3. Based on chronic histopathological assessment, the therapeutic window for striatal neuroprotection after a brief global ischemic insult appears to be longer than previously appreciated.
Rat Brain Glucose and Energy Metabolites: Effect of + Gz (Head-to-Foot Inertial Load) Exposure in a Small Animal Centrifuge
Authors: Shahed A. R. , Barber J. A. , Galindo S. , Werchan P. M.
Published: April 2011

A unique small animal centrifuge with on-line physiological monitoring and brain tissue collection (in < 1 s) capability was used to investigate the effect of increasing + Gz levels, exposure duration, number of exposures, and time course of metabolic changes in the rat brain. To determine the + Gz tolerance, rats were exposed to +7.5 to 25 Gz (30 s each) and EEG was monitored. G-induced loss of consciousness ( G-LOC) defined as isoelectric EEG (I-EEG) occurred only at +22.5 and 25 Gz within 14.5 ± 3 s. To study the effect of increasing + Gz levels on metabolism, rats were exposed to either 0.5 (control) or +7.5 to 25 Gz (30 s each), and brains were collected 1 min postcentrifugation by freeze fixation. A significant increase in lactate (≥ + 7.5 Gz) and a decrease in glucose, creatine phosphate (Cr-P), and ATP levels were observed at + 15 Gz and higher. The effect of exposure duration was investigated by exposing the rats to + 22.5 Gz for 15–60 s. Brain lactate levels increased sixfold while glucose decreased (75%) following the 60-s exposure. The level of Cr-P and ATP decreased significantly after the 15- and 30-s exposures with no further changes at longer + Gz exposures. For time course studies, brains were collected both during (5–35 s) and after (1–15 min) a +25 Gz exposure. A significant decrease in Cr-P occurred within 5 s, but changes in glucose, ATP, and lactate required 15 s. All metabolites returned to control levels within 3 min, except lactate and adenosine, which required 15 min. Exposure of rats to either one, three, or five runs at +22.5 Gz (30 s each) resulted in an increase in lactate (ninefold) and a decrease in glucose (87%). Both Cr-P and ATP decreased after one exposure with no further change after three and five exposures. These results show that + Gz exposures of short duration cause significant transient metabolic alterations consistent with global cerebral ischemia. We propose that G-LOC (I-EEG) may be an acute response of the CNS to high + Gz-imposed ischemic stress. G-LOC would reduce the overall brain energy demand and thus reduce anaerobic glycolysis and lactate production.
Effects of Intracellular Mg2+ on the Properties of Large-Conductance, Ca2+-Dependent K+ Channels in Rat Cerebrovascular Smooth Muscle Cells
Authors: Zhang Xian , Puil Ernest , Mathers David A.
Published: April 2011

The effects of intracellular magnesium ions, Mg2+i on large-conductance, Ca2+-dependent K+ channels (BK channels) of adult rat cerebrovascular smooth muscle cells (CVSMCs) were studied using patch clamp techniques and cells enzymatically dispersed from basilar, middle, and posterior cerebral arteries. Recordings used inside-out membrane patches and took place at 20–24°C. One millimeter [Mg2+]i produced a fast block of BK channel currents, as well described by the Woodhull model of channel occlusion by a charged species. However, the affinity and voltage-sensitivity of Mg2+i block were dependent on the concentration of free intracellular calcium ions, [Ca2+]i. Calcium ions may stabilize a channel conformation in which Mg2+i binding sites are relocated closer to the inner membrane surface. In the presence of 1 μ M [Ca2+]i, 0.5 m M [Mg2+]i shifted the Boltzmann curve relating BK channel open probability, Po, to membrane voltage leftward on the voltage axis, without any change in its slope. The enhancing effect of Mg2+i on Po was, therefore, insensitive to membrane potential. Quantitative considerations suggest that physiological levels of Mg2+i tonically facilitate BK channel activation. Alterations of [Mg2+]i during hyper- or hypomagnesemia may contribute to the dilation or contraction of cerebral vessels seen under these two conditions.
Effects of Adenosine and 2-Chloroadenosine on Cerebral Collateral Vessels
Authors: Muhonen Michael G. , Loftus Christopher M. , Heistad Donald D.
Published: April 2011

Adenosine is a potent cerebral vasodilator. We tested the hypothesis that dilatation of collateral vessels in cerebrum, in response to topical adenosine and 2-chloroadenosine (2-CAD), would increase blood flow to collateral-dependent cerebrum. In dogs anesthetized with halothane, a branch of the middle cerebral artery (MCA) was occluded proximally and cannulated distally. The collateral-dependent area at risk for infarction was perfused from a reservoir with microsphere-free blood, and blood flow to normal cerebrum and to cerebrum dependent on collateral flow was measured with radioactive microspheres injected into the left ventricle through a femoral artery catheter. Perfusion through the cannulated MCA branch was stopped, and flow to normal and collateral-dependent cerebrum was measured after adenosine (10−2 M) or 2-CAD (10−4 M) was added to the superfusate over the cerebrum. In normal cerebrum, topical application of adenosine increased flow to outer but not inner layers. Topical application of adenosine had little effect on flow to collateral-dependent tissue. In normal cerebrum, 2-CAD increased flow to outer layers, whereas flow to inner layers tended to increase. During 2-CAD, flow to outer cortical layers of collateral-dependent cerebrum increased from 140 ± 20 ml/100 g/min (mean ± SD) to 231 ± 68, whereas flow to the inner collateral-dependent tissue did not change. The findings indicate that, after occlusion of a cerebral artery, topical 2-CAD increases blood flow to outer layers of collateral-dependent and normal cerebrum. The findings suggest also that, after arterial occlusion, collateral circulation to cerebrum has dilator reserve, and flow to tissues that are dependent on collaterals may be augmented.
In vivo Models of Cerebral Ischemia: Effects of Parenterally Administered NMDA Receptor Glycine Site Antagonists
Authors: Warner David S. , Martin Huijie , Ludwig Paula , McAllister Alice , Keana John F. W. , Weber Eckard
Published: April 2011

Both in vitro and in vivo experiments have implicated extracellular glycine in the pathogenesis of ischemic brain damage. Recently, halogenated derivatives of quinoxaline-2,3-dione have been synthesized that possess bioavailability when parenterally administered and minimal psychotomimetic properties. Such compounds have allowed investigation into the efficacy of glycine receptor antagonism as a strategy for protection against cerebral ischemic insults. Rats underwent either 90 min of middle cerebral artery filament occlusion or 10 min of forebrain ischemia with recovery while receiving intraperitoneal injections of either a glycine receptor antagonist (ACEA-1021, ACEA-1031, or ACEA-1011) or vehicle (dimethyl sulfoxide). Both ACEA-1021 and ACEA-1031 reduced cerebral infarct volumes and were associated with a reduced incidence of hemiparesis resulting from MCA occlusion. ACEA-1011, administered in a smaller dose had no effect. In the forebrain ischemia model, glycine receptor antagonism had no effect on delayed neuronal necrosis in the hippocampal CA1 sector, neocortex, or caudoputamen. We conclude that pharmacologic antagonism of glycine at the strychnine-insensitive glycine receptor presents a neuroprotective profile similar to that previously observed for antagonists of glutamate at the N-methyl-d-aspartate complex with a potential for fewer side effects.
Development of Susceptibility to Audiogenic Seizures following Cardiac Arrest Cerebral Ischemia in Rats
Authors: Kawai Kensuke , Penix LaRoy P. , Kawahara Nobutaka , Ruetzler Christl A. , Klatzo Igor
Published: April 2011

Susceptibility to audiogenic seizures (AGS) was investigated in Sprague–Dawley rats subjected to cardiac arrest cerebral ischemia (CACI), produced by compression of the major cardiac vessels. The onset of AGS was regularly observed 1 day after CACI of >5 min duration. The duration of postischemic susceptibility to AGS was directly related to the density of cerebral ischemia, with 50% of more severely ischemic animals still showing AGS susceptibility 8 weeks after CACI. Lesioning of the inferior colliculi (IC) abolished the onset of AGS; no such effect was observed after lesioning the medial geniculate (MG). Glutamic acid decarboxylase (GAD) immunochemistry revealed ∼50% loss of GAD-positive neurons in the IC, which was similar in animals with various durations of AGS susceptibility. Otherwise, there was a conspicuous sprouting of γ-aminobutyric acid (GABA)-ergic terminals in the ventral thalamic nuclei, which peaked ∼1 month after the CACI. Evaluation of GABA-A inhibitory function in the hippocampus by the paired pulse stimulation revealed changes indicating loss of GABA-A inhibition coinciding with the onset of AGS, and its return in animals tested 2 months after CACI. Our observations suggest a potential role of GABA-ergic dysfunction in the postischemic development of AGS.
Effects of Pentylenetetrazol-Induced Status Epilepticus on Local Cerebral Blood Flow in the Developing Rat
Authors: de Vasconcelos Anne Pereira , Boyet Sylvette , Koziel Violette , Nehlig Astrid
Published: April 2011

The quantitative autoradiographic [14C]-iodoantipyrine technique was applied to measure the effects of a 30-min period of pentylenetetrazol (PTZ)-induced status epilepticus (SE) on local cerebral blood flow (LCBF) in rats 10 (P10), 14 (P14), 17 (P17), and 21 (P21) days after birth. The animals received repetitive, timed injections of subconvulsive doses of PTZ until SE was reached. At P10, SE induced a 32 to 184% increase in the rates of LCBF affecting all structures studied. In P14- and P17 PTZ-treated rats, LCBF values significantly increased in two-thirds of the structures belonging to all systems studied and were not changed by SE in the parietal cortex, dorsal hippocampus, and dentate gyrus. At P21, rates of LCBF were still increased in 48 of the 73 structures studied; however, LCBF values were decreased by SE in most cortical areas, the hippocampus, and the dentate gyrus. CBF and cerebral metabolic rate for glucose (CMRglc) remained coupled in both controls and PTZ-exposed rats. Our results show that changes in LCBF with seizures are age dependent. At the most immature ages, P10 and P14, both LCBF and local CMRglc (LCMRglc) values are largely increased by long-lasting seizures. At P17 and P21, the blood flow response to SE becomes more heterogeneous, with specific decreases in the hippocampus and cortex at P21. The absence of mismatch between LCBF and LCMRglc in PTZ-exposed rats at all ages may explain at least partly why the immature brain is more resistant to seizure-induced brain damage than the adult brain.