Thermal sensitivity of hypoxic responses in neocortical brain slices

The Integrative Function of Silent Synapses on Subplate Neurons in Cortical Development and Dysfunction

The thalamocortical circuit is of central importance in relaying information to the cortex. In development, subplate neurons (SPNs) form an integral part of the thalamocortical pathway. These early born cortical neurons are the first neurons to receive thalamic inputs and excite neurons in the cortical plate. This feed-forward circuit topology of SPNs supports the role of SPNs in shaping the formation and plasticity of thalamocortical connections. Recently it has been shown that SPNs also receive inputs from the developing cortical plate and project to the thalamus. The cortical inputs to SPNs in early ages are mediated by N-methyl-D-aspartate (NMDA)-receptor only containing synapses while at later ages α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-receptors are present. Thus, SPNs perform a changing integrative function over development. NMDA-receptor only synapses are crucially influenced by the resting potential and thus insults to the developing brain that causes depolarizations, e.g., hypoxia, can influence the integrative function of SPNs. Since such insults in humans cause symptoms of neurodevelopmental disorders, NMDA-receptor only synapses on SPNs might provide a crucial link between early injuries and later circuit dysfunction. We thus here review subplate associated circuits, their changing functions, and discuss possible roles in development and disease.

Review : Neuroprotection in Brain Ischemia: An Update (Part II

Ischemic brain injury produced by stroke or cardiac arrest is a major cause of human neurological disability. Steady advances in the neurosciences have elucidated the pathophysiological mechanisms of brain ischemia and have suggested many therapeutic approaches to achieve neuroprotection of the acutely ischemic brain that are directed at specific injury mechanisms. In the second portion of this two-part review, the following potential therapeutic approaches to acute ischemic injury are considered: 1) modulation of nonglutamatergic neurotransmission, including monoaminergic systems (dopamine, norepinephrine, serotonin), γ-aminobutyric acid, and adenosine; 2) mild-to-moderate therapeutic hypothermia; 3) calcium channel antagonism; 4) an tagonism of oxygen free radicals; 5) modulation of the nitric oxide system; 6) antagonism of cytoskeletal proteolysis; 7) growth factor administration; 8) therapy directed at cellular mediators of injury; and 9) the rationale for combination pharmacotherapy. The Neuroscientist 1:164-175, 1995

Perinatal asphyxia, hyperthermia and hyperferremia as factors inducing behavioural disturbances in adulthood: A rat model

Alertness was studied in adult male Wistar rats after neonatal critical anoxia applied under three different thermal conditions: (i) at physiological neonatal body temperature of 33 degrees C, (ii) at body temperature elevated to 37 degrees C, and (iii) at body temperature elevated to 39 degrees C (both during anoxia and for 2 h postanoxia). To elucidate the effect of iron-dependent postanoxic oxidative damage to the brain, half of the group (iii) was injected with deferoxamine, a chelator of iron. Postanoxic behavioural disturbances were recorded in open-field, elevated plus-maze, and sudden silence tests when the rats reached the age of 4 month. Moreover, spontaneous motor activity of the rats was recorded radiotelemetrically in their home-cages. Both open-field stress-induced and spontaneous motor activity were reduced in rats subjected to neonatal anoxia under hyperthermic conditions. In contrast, these rats were hyperactive in the plus-maze test. Both the plus-maze and sudden silence tests revealed that these rats show reduced alertness to external stimuli signalling potential dangers. The behavioural disturbances were prevented by the body temperature of 33 degrees C and by postanoxic administration of deferoxamine. These data support the conclusion that permanent postanoxic behavioural disturbances are due to iron-dependent oxidative damage to the brain, which can be prevented by the reduced neonatal body temperature.

Stress-induced behaviour in juvenile rats: effects of neonatal asphyxia, body temperature and chelation of iron

Newborn mammals, showing reduced normal body temperature, might be protected against iron-mediated, delayed neurotoxicity of perinatal asphyxia. Therefore, we investigated the effects of (1) neonatal body temperature and neonatal critical anoxia as well as (2) postanoxic chelation of iron with deferoxamine, on open-field stress-induced behaviour in juvenile rats. The third aim of this study was to compare (after the above-mentioned treatments) circadian changes in spontaneous motor activity and body temperature in juvenile rats permanently protected from any stress. Neonatal anoxia at body temperature adjusted (both during anoxia and 2 h reoxygenation) to a level typical of healthy (37 degrees C) or febrile (39 degrees C) adults led to the stress-induced hyperactivity in juvenile (5-45 days old) rats. Both normal neonatal body temperature of 33 degrees C and chelation of iron prevented the hyperactivity in rats. Neither neonatal body temperature nor neonatal anoxia affected spontaneous motor activity or body temperature of juvenile rats, recorded in their home-cages with implantable transmitters. Circadian rhythmicity was also undisturbed. Presented data support the hypothesis that physiologically reduced neonatal body temperature can provide a protection against iron-mediated postanoxic disturbances of behavioural stress responses in juvenile rats.

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

Twenty-four hours of mild hypothermia in unsedated newborn pigs starting after a severe global hypoxic-ischemic insult is not neuroprotective

Three to 12 h of mild hypothermia (HT) starting after hypoxia-ischemia is neuroprotective in piglets that are anesthetized during HT. Newborn infants suffering from neonatal encephalopathy often ventilate spontaneously and are not necessarily sedated. We aimed to test whether mild posthypoxic HT lasting 24 h was neuroprotective if the animals were not sedated. Thirty-nine piglets (median weight 1.6 kg, range 0.8-2.2 kg; median age 24 h, range 7-48 h) were anesthetized and ventilated and subjected to a 45-min hypoxic (FiO(2) approximately 6%) global insult (n = 36) or sham hypoxia (n = 3). On reoxygenation, 18 were maintained normothermic (NT, 39.0 degrees C) for 72 h, and 21 were cooled from 39 (NT) to 35 degrees C (HT) for the first 24 h before NT was resumed (18 experimental, three sham hypoxia). Cardiovascular parameters and intermittent EEG were documented throughout. The brain was perfusion fixed for neuropathology and five main areas examined using light microscopy. The insult severity (duration in minutes of EEG amplitude < 7 microV) was similar in the NT and HT groups, mean +/- SD (28 +/- 7.2 versus 27 +/- 8.6 min), as was the mean FiO(2) (5.9 +/- 0.7 versus 5.8 +/- 0.8%) during the insult. Six NT and seven HT piglets developed posthypoxic seizures that lasted 29 and 30% of the time, respectively. The distribution and degree of injury (0.0-4.0, normal-maximal damage) within the brain (hippocampus, cortex/white matter, cerebellum, basal ganglia, thalamus) were similar in the NT and HT groups (overall score, mean +/- SD, 2.3 +/- 1.5 versus 2.4 +/- 1.3) as was the EEG background amplitude at 3 h (13 +/- 3.5 versus 10 +/- 3.3 microV). The HT animals shivered and were more active. The sham control group (n = 3) shivered but had normal physiology and neuropathology. Plasma cortisol was significantly higher in the HT group during the HT period, 766 +/- 277 versus 244 +/- 144 microM at 24 h. Mild postinsult HT for 24 h was not neuroprotective in unsedated piglets and did not reduce the number of animals that developed posthypoxic seizures. Cortisol reached 3 times the NT value at the end of HT. We speculate that the stress of shivering and feeling cold interfered with the previously shown neuroprotective effect of HT. Research on the appropriateness of sedation during clinical HT is urgent.

Mechanisms of spreading depression and hypoxic spreading depression-like depolarization

Spreading depression (SD) and the related hypoxic SD-like depolarization (HSD) are characterized by rapid and nearly complete depolarization of a sizable population of brain cells with massive redistribution of ions between intracellular and extracellular compartments, that evolves as a regenerative, "all-or-none" type process, and propagates slowly as a wave in brain tissue. This article reviews the characteristics of SD and HSD and the main hypotheses that have been proposed to explain them. Both SD and HSD are composites of concurrent processes. Antagonists of N-methyl-D-aspartate (NMDA) channels or voltage-gated Na(+) or certain types of Ca(2+) channels can postpone or mitigate SD or HSD, but it takes a combination of drugs blocking all known major inward currents to effectively prevent HSD. Recent computer simulation confirmed that SD can be produced by positive feedback achieved by increase of extracellular K(+) concentration that activates persistent inward currents which then activate K(+) channels and release more K(+). Any slowly inactivating voltage and/or K(+)-dependent inward current could generate SD-like depolarization, but ordinarily, it is brought about by the cooperative action of the persistent Na(+) current I(Na,P) plus NMDA receptor-controlled current. SD is ignited when the sum of persistent inward currents exceeds persistent outward currents so that total membrane current turns inward. The degree of depolarization is not determined by the number of channels available, but by the feedback that governs the SD process. Short bouts of SD and HSD are well tolerated, but prolonged depolarization results in lasting loss of neuron function. Irreversible damage can, however, be avoided if Ca(2+) influx into neurons is prevented.

Effect of temperature on postanoxic, potentially neurotoxic changes of plasma pH and free iron level in newborn rats

In asphyxiated newborns, iron, released from heme and ferritin and deposited in the brain, contributes to neurodegeneration. Because hypothermia provides neuroprotection, newborn mammals, showing reduced body temperature, might avoid iron-mediated neurotoxicity. However, hypothermia leads to acidosis, which induces hyperferremia. Therefore, we decided to study the effects of body temperature on plasma pH and iron levels in newborn rats exposed to a critical anoxia. Rectal temperature was kept at 33 degrees C (typical of neonates), reduced by 2 degrees C, or elevated to a level typical of healthy (37 degrees C) or febrile (39 degrees C) adults. Arterial blood samples were collected at 0, 10, 20, 30, and 120 min postanoxia. Control samples were obtained from normoxic, temperature-matched neonates. Anoxia tolerance time decreased progressively at rectal temperatures exceeding 33 degrees C. Neither pH nor plasma iron were significantly affected by anoxia at 33 degrees C. Although hypothermia (31 degrees C) resulted in acidosis in normoxic rats, both pH and iron levels were hardly influenced by anoxia. However, acidosis and hyperferremia, proportional to body temperature, developed at 37 and 39 degrees C. In conclusion, reduced body temperature is likely to protect asphyxiated newborns against iron-mediated brain injury.

Chemical preconditioning with 3-nitropropionic acid in gerbil hippocampal slices: therapeutic window and the participation of adenosine receptor

Ischemic tolerance induced by a subtoxic dose of neurotoxin, 3-nitropropionic acid (3-NPA), was recently reported as "chemical preconditioning." We electrophysiologically investigated the therapeutic window and the effect via action at the adenosine receptor using a gerbil hippocampal slice model of the tolerance phenomenon. 3-NPA at the dose of 4 mg/kg was administered intraperitoneally at 3, 24, and 72 h prior to slice preparation. Prolonged delay to hypoxic depolarization (HD) and improvement of the field excitatory postsynaptic potential recovery following a fixed period of hypoxia (8 min) were observed in the groups pretreated at 3 and 24 h compared with the control (P < 0.05). Correlation between the delay to HD and the recovery was highly significant (r = 0.37, P < 0.001). These effects were completely reversed by administration of theophylline (20 mg/kg), an adenosine receptor blocker. These findings indicate that chemical preconditioning with 3-NPA induces early onset (3 h) and long-lasting (24 h) tolerance of hypoxic damage to excitatory synaptic mechanisms in the hippocampus by delayed calcium entry, and the activation of adenosine receptor contributes to this neuroprotective effect.

Effects of acidosis on the post-hypoxic recovery of synaptic transmission in gerbil hippocampal slices

We investigated the effects of acidosis on the hypoxic neuronal damage using gerbil hippocampal slices. Acidosis has delayed the onset of harmful hypoxic depolarization, resulting in a decrease in the total hypoxic period and the hypoxic depolarization. This effect has been considered to be protective. However, the synaptic recovery after reoxygenation was attenuated when acidosis (pH: 6.2-6.9) was sustained. Conversely, the synaptic recovery was potentiated when the acidosis was restored to the physiological milieu during the reoxygenation period. These results suggest that acidosis plays a protective effect against the hypoxic neuronal damage only when rapid appreciable pH recovery is achieved during reoxygenation.

Rapid brain cooling in diving ducks

Hypothermia may limit asphyxic damages to the brain, and many small homeotherms have been shown to use anapyrexic strategies when exposed to asphyxic conditions. Larger homeotherms do not seem to use the same strategy, but could save oxygen and prevent hypoxic brain damage by employing selective brain cooling (SBC) in connection with asphyxia. To test the hypothesis that selective brain cooling may take place in connection with asphyxia, we have recorded brain [hypothalamic (THyp)] and body [colonic (TC)] temperatures and heart rates in four Pekin ducks during 5-min simulated (head submersion) diving in cold water (10 degrees C). Diving resulted in a drop in THyp (3.1 +/- 1.4 degrees C) that continued into the recovery period (P < 0.001). Restricting heat loss from the buccal cavity and eyes during diving compromised brain cooling in an additive manner. TC was not influenced by diving. Control cooling of the head with crushed ice during a 5-min period of undisturbed breathing had no effect on THyp. Warm water (35 degrees C) markedly reduced brain cooling, and dive capacity was reduced by approximately 14% (P < 0.05) compared with diving in water at 10 degrees C. The data suggest that SBC is used in ducks during diving, and we propose that this mechanism may enable the bird to save oxygen for prolonged aerobic submergence and to protect the brain from asphyxic damages.

Effect of preceding in vivo sublethal ischemia on the evoked potentials during secondary in vitro hypoxia evaluated with gerbil hippocampal slices

We investigated the mechanism of 'ischemic tolerance phenomenon' by characterizing the physiological events, modified by preceding sublethal ischemia, during secondary hypoxia. Slices from brains after pretreatment of sublethal forebrain ischemia were subjected to a 70% reduction of PO2 (threshold hypoxia). Although evoked potentials disappeared completely in five of eight slices from sham-operated brain, they were sustained in 28/32 slices from pretreated brains. This study indicates that the maintenance of membrane function might be the mechanism of ischemic tolerance.

NMDA receptor-mediated differential laminar susceptibility to the intracellular Ca2+ accumulation induced by oxygen-glucose deprivation in rat neocortical slices

Slices of somatosensory cortex taken from immature rats on postnatal day (P)7-14 were labeled with fura-2. Intracellular Ca2+ concentration ([Ca2+]i) was monitored in identified pyramidal cells as the ratio of fluorescence intensities (RF340/F380) during oxygen-glucose deprivation. The RF340/F380 ([Ca2+]i) of individual pyramidal cells was monitored in each of the cortical layers II-VI simultaneously. Neurons in all neocortical layers exhibited significant increases in [Ca2+]i that varied with the duration of oxygen-glucose deprivation. Individual neurons responded to oxygen-glucose deprivation with abrupt increases in [Ca2+]i after various latencies. The ceiling level of the [Ca2+]i increase differed from cell to cell. Neurons in layer II/III showed significantly greater increases in [Ca2+]i than those in layers IV, V, or VI. Kynurenic acid, a nonselective glutamate receptor antagonist, and bicuculline, a selective gamma-aminobutyric acid (GABA)A receptor antagonist, suppressed the intracellular Ca2+ accumulation induced by oxygen-glucose deprivation in all neocortical layers examined. After kynurenic acid, but not after bicuculline, there was no longer a differential [Ca2+]i increases in layer II/III. Both 2-amino-5-phosphonopentanoic acid (AP5), a selective N-methyl-D-aspartate (NMDA) receptor antagonist, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, strongly suppressed the intracellular Ca2+ accumulation induced by oxygen-glucose deprivation in all layers. The laminar difference in terms of the [Ca2+]i increases was abolished by AP5, but not by CNQX. These results indicate that layer II/III cells are the most prone to oxygen-glucose deprivation-induced intracellular Ca2+ accumulation, and that this is primarily mediated by NMDA receptors. Thus, layer II/III neurons would be more likely to suffer cellular Ca2+ overload and excitotoxicity during ischemia than layer IV-VI cells. Such a differential laminar vulnerability might play an important role in determining the pathological characteristics of the immature cortex and its sequelae later in life.

Limited but significant protective effect of hypothermia on ultra-early-type ischemic neuronal injury in the thalamus

We investigated the protective effect of hypothermia on ultra-early-type ischemic injury in the thalamic reticular nucleus of the rat. Cerebral ischemia was produced by 5 min of cardiac arrest followed by resuscitation. Rectal and cranial temperature during and after cardiac arrest was maintained at 37-38 degrees C in the normothermic group and at 32-33 degrees C in the hypothermic group. In the postischemic hypothermic group, temperature was maintained at 32-33 degrees C starting 15 min after normothermic ischemia. Histological damage was evaluated quantitatively. While after 5 min of recirculation there was no difference in morphological changes in terms of neuronal halo formation, intraischemic hypothermia reduced the severity of the degenerative changes represented by vacuolated or dark neurons by 15 min. Postischemic hypothermia failed to show any evidence of protection by 30 min. The protective effect of intraischemic hypothermia remained significant when evaluated at 14 days after ischemia by volumetry of the lesion and neuronal density analysis, whereas postischemic hypothermia had no clear protective effect. These results suggest that the protective effect of intraischemic hypothermia applies to neurons susceptible to ultra-early-type injury, but the effect of postischemic hypothermia is limited because normothermic ischemia results in extensive degeneration in these neurons by 15 min.

Mild hypothermia reduces penumbral glutamate levels in the rat permanent focal cerebral ischemia model

Although the cerebroprotective effects of hypothermia in focal models of ischemia are undisputed, the underlying mechanisms of this protection are still subject to much controversy. To analyze whether mild hypothermia attenuates glutamate levels in the penumbra surrounding permanent focal infarcts, extracellular glutamate concentration was analyzed bilaterally by microdialysis 20 minutes before to 120 minutes after a middle cerebral artery occlusion (MCAO) in rats. Normothermic animals (n = 11) had a baseline glutamate concentration of 1.14 +/- 0.40 mumol/ml (standard error of the mean) before the MCAO. Extracellular glutamate levels increased gradually after vessel occlusion to peak at 10.1 +/- 1.45 mumol/ml 80 minutes after the MCAO. This level gradually decreased to 5.72 +/- 1.67 mumol/ml by 120 minutes. Hypothermic animals (n = 11) had a baseline glutamate concentration of 1.73 +/- 0.83 mumol/ml before the MCAO. Extracellular glutamate levels increased after vessel occlusion but stabilized at 3.47 +/- 1.37 mumol/ml 30 minutes after the MCAO and remained stable until completion of the experiment. There were no significant differences in cortical blood flow between the normothermic and hypothermic groups at any time during the experiment. Infarct volumes, expressed as a percentage of the volume of the right (ipsilateral) hemisphere, were 19.8 +/- 2.16% in the normothermic group and 13.0 +/- 1.42% in the hypothermic group (P < 0.02). Although the normothermic penumbral glutamate levels began to increase immediately after the MCAO, they did not peak until 80 minutes after occlusion. In contrast, the normothermic core glutamate levels peaked within 30 minutes after the MCAO. Glutamate diffusion from the core region to the penumbra might account for this delay. Hypothermic cerebroprotection might involve a reduction in the pool of potentially diffusable glutamate in the core region but have little direct effect on glutamate release in the penumbra.

Hypoxic neuronal damage in the absence of hypoxic depolarization in rat hippocampal slices: the role of glutamate receptors

The propensity of neurons to undergo profound and precipitous depolarization is believed to contribute to their characteristic vulnerability to hypoxic injury. The length of time a neuron spends in a depolarized state following hypoxic depolarization (HD) is a critical determinant of the extent of irreversible cell damage. It is less clear, however, what the effects of moderate hypoxia are when HD does not occur. The present study examined the effects of prolonged, moderate hypoxia which does not elicit HD in rat hippocampal slices. Extracellularly-recorded population excitatory postsynaptic potentials (pEPSPs) in stratum radiatum of CA1 were eliminated 10-15 min after initiating hypoxia. Physiological damage was related to the hypoxic duration: full, intermediate, or poor recovery of pEPSP slope was observed after 30, 60, or 120 min of hypoxia, respectively. The glutamate receptor antagonists, D,L-2-amino-5-phosphonovaleric acid (APV) or 6,7-dinitroquinoxaline-2,3-dione (DNQX), enhanced the post-hypoxic recovery of synaptic responses. These findings demonstrate that profound HD is not necessary to elicit physiological damage during moderate hypoxia; moreover, the neuroprotective actions of excitatory transmitter antagonists are not limited to their capacity to delay HD. The precise characterization of cellular responses under these conditions will be of particular importance for understanding the pathophysiology of an ischemic penumbra.

Functional brain block preparation of the rat auditory cortex

To maintain neural functions in brain block preparations of the rat auditory cortex in vitro, a pressurized oxygenated medium was injected into the blocks. Distribution of indigo carmine contained in the injection medium indicated that a columnar region of 1-2 mm in diameter was homogeneously perfused from the white matter to the pial surface. Stimulation of cortical layers just above the white matter produced supragranular field potentials of two negative peaks. They represented antidromic and postsynaptic activities, of which only the latter was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM). The depth profile and temperature-dependency of field potentials in the blocks were very similar to those recorded in usual slice preparations. The responses in blocks were recorded stably for several hours. The functional brain block preparation may be a useful tool for analyses of neocortical neural networks in vitro.

Hippocampal slices: glutamate overflow and cellular damage from ischemia are reduced by sodium-channel blockade

We evaluated concentrations of excitatory amino acids released from slices into the superfusing solution and also evaluated extracellular field potential recordings and histological appearance of slice tissues to evaluate several sodium-channel modulating drugs as potential treatments for ischemia. The selective sodium-channel blocker tetrodotoxin (TTX, 1 microM) reduced glutamate release from deprivation of oxygen and D-glucose, while calcium-channel blockade was ineffective. Thus, during ischemia, we propose that glutamate may be released from the free cytosolic pool ('metabolic' glutamate) rather than by exocytosis. TTX (100-500 nM) and voltage-dependent sodium-channel blockers (phenytoin, 20-100 microM; lidocaine, 2-200 microM) each prevented damage to slices without blocking action potentials. The reduction of cellular depolarization and sodium loading during ischemia may explain the neuroprotective action of several sodium-channel modulating drugs in our in vitro studies and also in animal models.

Intraischemic hypothermia decreases the release of glutamate in the cores of permanent focal cerebral infarcts

The cerebroprotective effects of hypothermia in focal models of ischemia are well established, but little is known about the underlying mechanisms of this form of brain protection. Cortical cooling in global transient ischemic models suggests that hypothermia limits glutamate excitotoxicity by decreasing the release of glutamate during ischemia. Few studies have examined glutamate release in the more physiological model of permanent focal ischemia. In this study, we used a rat model of middle cerebral artery occlusion (MCAO) of permanent focal ischemia. Extracellular glutamate concentration was analyzed bilaterally by microdialysis for 30 minutes before MCAO to 120 minutes after MCAO. Normothermic animals (n = 13) had a baseline glutamate concentration of 9.23 +/- 2.5 mumol/ml (mean +/- standard error of the mean) before MCAO. Extracellular glutamate rose quickly after vessel occlusion and peaked at 33.95 +/- 6.3 mumol/ml 30 minutes after MCAO. By 60 minutes after MCAO, this level had decreased to 25.14 +/- 6.3 mumol/ml; glutamate levels decreased slightly to 21.35 +/- 6.8 mumol/ml by 120 minutes. Hypothermic animals (n = 11) had an initial extracellular glutamate concentration of 5.22 +/- 1.3 mumol/ml before MCAO. This value rose gradually to a maximum of 10.69 +/- 3.3 microns/ml at 50 minutes after MCAO and then returned to a baseline value of 2.58 +/- 1.2 mumol/ml by 120 minutes. Contralateral control glutamate dialysates in the normothermic and hypothermic groups remained near baseline throughout the experimental period. The mean percentages of right hemispheric volumes occupied by infarcts were 11.96 +/- 1.68% in the hypothermic group and 19.77 +/- 2.03% in the normothermic animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Damage from oxygen and glucose deprivation in hippocampal slices is prevented by tetrodotoxin, lidocaine and phenytoin without blockade of action potentials

In vitro ischemia (IVI) was simulated with rat hippocampal slices in medium lacking D-glucose, equilibrated with 95% nitrogen, 5% carbon dioxide. Within 5-8 min, synaptic potentials disappeared and a DC negative shift (5-15 mV) occurred. Prolonged application of 95% oxygen and D-glucose 12 min later did not allow synaptic potentials to recover. Slices pretreated with sodium channel blocking drugs allowed synaptic potentials to recover after IVI. Tetrodotoxin (TTX, 100-600 nM), the anticonvulsant phenytoin (5.0 to 100 microM) and the local anesthetic lidocaine (2.0 to 200 microM) each delayed or prevented negative DC shifts from IVI. Histological examination showed that drug treatments also prevented CA1 pyramidal cell damage from IVI. Neuroprotection occurred without blocking synaptic potentials or presynaptic fiber volleys, suggesting relevance for treatment of brain ischemia.