Rat Brain Cortical Slices Research Articles

D-myo-inositol 1,4,5-trisphosphate 3-kinase A is activated by receptor activation through a calcium:calmodulin-dependent protein kinase II phosphorylation mechanism.

D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] 3-kinase, the enzyme responsible for production of D-myo-inositol 1,3,4,5-tetrakisphosphate, was activated 3- to 5-fold in homogenates of rat brain cortical slices after incubation with carbachol. The effect was reproduced in response to UTP in Chinese hamster ovary (CHO) cells overexpressing Ins(1,4,5)P3 3-kinase A, the major isoform present in rat and human neuronal cells. In ortho-32P-labelled cells, the phosphorylated 53 kDa enzyme could be identified after receptor activation by immunoprecipitation. The time course of phosphorylation was very similar to that observed for carbachol (or UTP)-induced enzyme activation. Enzyme phosphorylation was prevented in the presence of okadaic acid. Calmodulin (CaM) kinase II inhibitors (i.e. KN-93 and KN-62) prevented phosphorylation of Ins(1,4,5)P3 3-kinase. Identification of the phosphorylation site in transfected CHO cells indicated that the phosphorylated residue was Thr311. This residue of the human brain sequence lies in an active site peptide segment corresponding to a CaM kinase II-mediated phosphorylation consensus site, i.e. Arg-Ala-Val-Thr. The same residue in Ins(1,4,5)P3 3-kinase A was also phosphorylated in vitro by CaM kinase II. Phosphorylation resulted in 8- to 10-fold enzyme activation and a 25-fold increase in sensitivity to the Ca2+:CaM complex. In this study, direct evidence is provided for a novel regulation mechanism for Ins(1,4,5)P3 3-kinase (isoform A) in vitro and in intact cells.

Interactive effects of pH and temperature on N-methyl-D-aspartate receptor activity in rat cortical brain slices.

Low extracellular pH decreases the activity of the N-methyl-D-aspartate (NMDA) glutamate receptor, and may thus limit neuronal calcium overload during cerebral ischemia. During induced hypothermia, alkaline pH ("alphastat regulation") is often used to preserve cardiac and enzymatic function. The purpose of this study is to measure the functional activity of cerebral cortex NMDA receptors over the range of temperatures used in profound hypothermic cardiopulmonary bypass (20-37 degrees C). Extracellular pH was varied over a broad range relevant to both alphastat and pH stat acid-base management (7.0-7.8). Change in cytosolic free calcium evoked by 50 microM NMDA in brain slices was used as an index of NMDA receptor activity. Cortical slices (300 microns thick) were loaded with fura-2 Aspartate Methyl for study in a fluorometer. At 37 degrees C, a change in extracellular pH from 7.1 to 7.8 increased the NMDA-evoked change in cytosolic calcium in brain slices by a factor of 4 (p < 0.05). In contrast, at 20 degrees C there was minimal effect of changing extracellular pH from 7.1 to 7.8 (27% increase). We conclude that hypothermia results in decreased pH sensitivity of the NMDA receptor. The results predict that different strategies of pH management during induced hypothermia may have limited impact on NMDA receptor-mediated processes, such as neuronal calcium overload.

Effects of NMDA on carbachol-stimulated phosphatidylinositol resynthesis in rat brain cortical slices.

N-methyl-D-aspartate (NMDA) inhibits carbachol-stimulated phosphoinositide breakdown in rat brain cortical slices but not in isolated membranes (1). To gain insight into the mechanisms, we examined the effects of NMDA on carbachol-stimulated [3H]inositol phosphate and intermediates of phosphatidylinositol cycle accumulation in rat cortical slices. The inhibition is primarily on the synthesis of inositol phospholipids subsequent to activation of muscarinic cholinergic receptors. In the absence of lithium, NMDA inhibited carbachol-stimulated [32P]PtdIns but not [32P]PtdOH synthesis. Carbachol-stimulated CDP-DAG formation required trace amount of Ca2+ and the response was inhibited by NMDA at low but not high extracellular Ca2+ concentrations. The inhibition due to NMDA was only seen at millimolar extracellular Mg2+. The inhibition of carbachol-stimulated CDP-DAG formation was not affected by adding tetrodotoxin or cobalt chloride suggesting the inhibitory effect was not due to releasing of neurotransmitters. The inhibitory effects of NMDA could be abolished by MK-801, the specific NMDA receptor associated channel antagonist. When cortical slices were preincubated with ligands and lithium to allow the build up of CDP-DAG, carbachol stimulated the incorporation of [3H]PtdIns. However, this response was not inhibited by NMDA. These results suggest that CDP-DAG synthesis is the primary site of regulation by NMDA. Because CDP-DAG cytidyltransferase requires Mg2+ as cofactor and is sensitive to Ca2+ it is possible that NMDA inhibits ligand-stimulated PtdIns breakdown by blocking the replenish of agonist-sensitive PtdIns pool through changes of divalent cation homeostasis.

Different effects of reducing agents on omega-conotoxin GVIA inhibition of [3H]-acetylcholine release from rat cortical slices and guinea-pig myenteric plexus.

1. The effect of reducing reagents on omega-conotoxin GVIA (omega-CgTX) inhibition of the release of [3H]-acetylcholine ([3H]-ACh) induced by tityustoxin, K+ 50 mM and electrical stimulation was investigated in rat brain cortical slices. 2. In cortical slices the inhibition of tityustoxin or electrically-stimulated [3H]-ACh release by omega-CgTX was dramatically increased by reducing reagents ascorbate or beta-mercaptoethanol. Dehydroascorbic acid did not substitute for ascorbate. 3. Depolarization induced by K+ 50 mM caused [3H]-ACh release from cortical slices which was not inhibited by omega-CgTX, even in the presence of ascorbate. 4. In the guinea-pig myenteric plexus, omega-CgTX inhibition of the tityustoxin induced release of [3H]-ACh was independent of ascorbate. 5. It is suggested that N-type-like calcium channels in guinea-pigs myenteric plexus may have pharmacological/biochemical diversity from similar channels of rat cerebral cortex.

Acetylcholine release from rat brain cortical slices evoked by the fraction P4 of the venom of the spider Phoneutria nigriventer has Ca 2+ and temperature independent components

Fractionation of the venom of the spider Phoneutria nigriventer revealed that it was a mixture of several neurotoxic peptides. The peptides so far characterized either inhibited or induced neurotransmitter release. These effects were mediated by Ca 2+ channels or increasing Na + permeability through voltage sensitive Na +-channels, respectively. The pooled toxic components (fraction P4) showed stimulatory effects on acetylcholine release from brain cortical slices. In addition, a component of the observed effects resembling that of α-latrotoxin was identified, which was characterized by the ability to provoke release of acetylcholine (ACh) at low temperature and in a manner independent of extracellular Ca 2+ and of voltage sensitive Na +-channels.

Hypothermia and isoflurane similarly inhibit glutamate release evoked by chemical anoxia in rat cortical brain slices.

Accumulation of the excitatory neurotransmitter glutamate in ischemic brain tissue contributes to neuronal cell death. Volatile anesthetics at clinically relevant concentrations are neuroprotective in in vivo models of brain ischemia and reduce glutamate release in vivo and in vitro, but they appear to have weaker neuroprotective effects than hypothermia. The purpose of this study was to determine whether isoflurane reduces glutamate release in hypoxic brain slices, how large this effect is compared to that of hypothermia, and if it is diminished by hyperthermia. Glutamate released from rat cortical brain slices during chemical anoxia (100 microM NaCN) was measured continuously with a fluorescence assay. The release rate was compared at three temperatures (28 degrees C, 37 degrees C, and 39 degrees C) with and without isoflurane at concentrations equipotent to 1 minimum alveolar concentration. At the same three temperatures, glutamate release rates before and after exposure to isoflurane were compared. Isoflurane reduced glutamate release from brain slices during chemical anoxia at 37 degrees C (19.6%, P < 0.01) and at 39 degrees C (25.4%, P < 0.01), but not at 28 degrees C. The reduction in glutamate release with hypothermia was similar to that with isoflurane. Hyperthermia (39 degrees C) caused greater glutamate release under basal and anoxic conditions than normo- and hypothermia. Isoflurane caused a slight increase in basal glutamate release rates, although this effect was smaller than the increase caused by hyperthermia. In a brain slice model of cerebral anoxia, 1 minimum alveolar concentration isoflurane decreases glutamate release to a similar extent that hypothermia (28 degrees C) does. The increased glutamate release with hyperthermia (39 degrees C) is not prevented by isoflurane.

Inhibition by NMDA of carbachol-stimulated inositol tetrakisphosphate accumulation in rat brain cortical slices

The present studies examined the effect of NMDA on carbachol-stimulated accumulation of inositol polyphosphates, with emphasis on the accumulation of inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5-P 4), at short time periods in rat brain cortical slices. There was a stimulatory effect of NMDA on accumulation of labeled inositol mono-, bis- and trisphosphates but not on labeled inositol tetrakisphosphates. In the presence of carbachol Ins 1,3,4,5-P 4 accumulation was preferentially inhibited by NMDA at early time periods (within 30 seconds after NMDA addition). Subsequently, total phosphoinositide breakdown was inhibited by NMDA. NMDA did not stimulate accumulation of total Ins 1,3,4,5-P 4 but immediately inhibited carbachol stimulated accumulation of Ins 1,3,4,5-P 4. The inhibitory effect of NMDA (1 mM) was not mimicked by increasing K + in the medium from 10 to 30 mM. However 30 mM K + reversed the inhibitory effect of 1 mM NMDA on carbachol-stimulated Ins 1,3,4,5-P 4. Parallel experiments with veratridine (a sodium channel activator) suggest that the early inhibitory effects of NMDA on Ins 1,3,4,5-P 4 accumulation are not due to decreases in ATP availability or elevations in intracellular Na +. These data indicate that NMDA increases inositol mono-, bis- and trisphosphate accumulation while blocking muscarinic cholinergic stimulated accumulation of Ins 1,3,4,5-P 4.

226 Physiological differences between two types of presynaptic terminals respectively generating large and small excitatory junctional potentials

In this paper, the effect of calcium channel blockers on acetylcholine release induced by tityustoxin and ouabain in rat brain cortical slices is described. Cadmium, a non-specific blocker of calcium channels, inhibited the release of ACh induced by tityustoxin. L-type calcium channel blockers (verapamil, nifedipine and diltiazen) had no effect on the release of ACh induced by tityustoxin. The release of ACh was also unaffected by nickel, a T-type calcium channel blocker, and the conotoxins GVIA and MVIIC, blockers of N and Q-type calcium channels. Agatoxin IVA, a specific blocker of the P-type calcium channel, inhibited the release of ACh induced by tityustoxin by 50%. The spontaneous release of ACh as well as ouabain-induced release of ACh was unaffected by any of the calcium channel blockers studied. It is concluded that ACh release induced by tityustoxin is mediated by Ca2+ influx via P-type calcium channels.

β-Amyloid 1–40 inhibits electrically stimulated release of [ 3H]norepinephrine and enhances the internal calcium response to low potassium in rat cortex: Prevention with a free radical scavenger

We examined the effects of β-amyloid 1–40 (A β 1–40) on the electrically stimulated release of [ 3H]norepinephrine (NE) and the potassium chloride (KCl)-evoked increases in intrasynaptosomal calcium ([Ca 2+] i) from rat brain cortical slices and synaptosomes, respectively. The results show that 3nM A β 1–40 decreased electrically stimulated [ 3H]NE release approximately 50%, and the same concentration of A β 1–40 increased [Ca 2] i by 78% above control during low level (10 mM) KCl depolarization. Complete prevention of both effects was observed when the free radical scavenger 1mM N-tert-butyl-α-phenylnitrone (PBN) was present. Also, when PBN was exposed to the slice first and then followed by A β 1–40, the inhibition of [ 3H]NE was blocked. Alone, PBN had no effect in either paradigm. Our experiments show that 3 nM A β 1–40 allows a PBN-sensitive free radical to deleteriously effect both evoked [ 3H]NE release and [Ca 2+] i regulation in rat cotical slices and synaptosomes.

Inhibition of potassium-stimulated acetylcholine release from rat brain cortical slices by two high-affinity analogs of vesamicol

In this work, we investigated the effects of two structural analogs of the drug vesamicol, which inhibits the vesicular acetylcholine (ACh) transport, on the potassium-stimulated release of ACh from rat brain cortical slices. These vesamicol analogs, 4-aminobenzove-samicol (ABV) and ( trans)-cyclohexovesamicol (transDec), were almost as potent as vesamicol in inhibiting the evoked release of ACh from cortex slices. Similar to vesamicol, the presence of these analogues inhibited the ability of ACh newly-synthesized from [ 3H]choline to become releasable. However, vesamicol's action was reversible, while ABV and transDec caused a persistent block of this [ 3H]ACh release. In addition, vesamicol did not affect the release of pre-stored [ 3H]ACh, but ABV and transDec partially inhibited the release of [ 3H]ACh, in this condition, suggesting that the two latter drugs may alter some of the steps posterior to the entry of [ 3H]ACh, into synaptic vesicles. The rank order of potency for these drugs to reduce ACh release (vesamicol = transDec > ABV) is close to the rank order for inhibition of ACh vesicular transport (transDec > vesamicol > ABV), but is completely different from the order of affinities of these drugs for the vesamicol receptor (ABV > transDec > > vesamicol). These results suggest that although these two vesamicol analogs are able to block ACh release due to their effects on the vesicular transport system, they may have other unexpected actions not shared by vesamicol.

Pentobarbital differentially inhibits N-methyl- d-aspartate and kainate-stimulated [ 3H]noradrenaline overflow in rat cortical slices

1. 1. This study examined the ability of pentobarbital to inhibit NMDA and kainate-stimulated [ 3H]noradrenaline ([ 3H]NA) overflow in rat brain cortical slices. 2. 2. Pentobarbital inhibited NMDA-evoked [ 3H]NA overflow at 100 μM and greater and inhibited kainate-evoked [ 3H]NA overflow at 10 μM and greater. 3. 3. The ability of pentobarbital to inhibit concentration-response curves for NMDA and kainate-evoked overflow of [ 3H]NA were also examined. Pentobarbital (300 μM) caused a 20% reduction in NMDA and a 50% reduction in kainate-induced maximal responses.

Inhibition by veratridine of carbachol-stimulated inositol tetrakisphosphate accumulation in rat brain cortical slices

The present studies examined the inhibitory effect of veratridine (a Na+ channel activator) on carbachol (a cholinergic agonist) stimulated inositol 1,3,4,5-tetrakisphosphate accumulation in rat brain cortical slices. Veratridine inhibited carbachol stimulation of inositol 1,3,4,5-tetrakisphosphate formation (after a delay of about 30 seconds) at 60 or 120 seconds when there was little inhibition of inositol 1,4,5 trisphosphate accumulation. The inhibitory effect of veratridine on carbachol stimulated inositol 1,3,4,5-tetrakisphosphate accumulation was abolished in the presence of ouabain or tetrodotoxin but was unaffected in low calcium conditions. Veratridine reduced the total ATP content and this effect was abolished by tetrodotoxin. The inhibitory effect of 10 but not 30 microM veratridine on inositol 1,3,4,5-tetrakisphosphate accumulation in the presence of carbachol was reversed by the presence of exogenous 8-bromo cyclic AMP or forskolin which activates adenylyl cyclase. However, the decrease in brain slice ATP seen in the presence of veratridine was unaffected by forskolin. Our results are compatible with the hypothesis that veratridine inhibition of carbachol-stimulated inositol 1,3,4,5-tetrakisphosphate formation is due to depletion of ATP at the site of Ins 1,3,4,5-P4 formation from Ins 1,4,5-P3.

Histamine H1 and endothelin ETB receptors mediate phospholipase D stimulation in rat brain hippocampal slices.

Different neurotransmitter receptor agonists [carbachol, serotonin, noradrenaline, histamine, endothelin-1, and trans-(1S,3R)-aminocyclopentyl-1,3-dicarboxylic acid (trans-ACPD)], known as stimuli of phospholipase C in brain tissue, were tested for phospholipase D stimulation in [32P]Pi-prelabeled rat brain cortical and hippocampal slices. The accumulation of [32P]phosphatidylethanol was measured as an index of phospholipase D-catalyzed transphosphatidylation in the presence of ethanol. Among the six neurotransmitter receptor agonists tested, only noradrenaline, histamine, endothelin-1, and trans-ACPD stimulated phospholipase D in hippocampus and cortex, an effect that was strictly dependent of the presence of millimolar extracellular calcium concentrations. The effect of histamine (EC50 18 microM) was inhibited by the H1 receptor antagonist mepyramine with a Ki constant of 0.7 nM and was resistant to H2 and H3 receptor antagonists (ranitidine and tioperamide, respectively). Endothelin-1-stimulated phospholipase D (EC50 44 nM) was not blocked by BQ-123, a specific antagonist of the ETA receptor. Endothelin-3 and the specific ETB receptor agonist safarotoxin 6c were also able to stimulate phospholipase D with efficacies similar to that of endothelin-1, and EC50 values of 16 and 3 nM, respectively. These results show that histamine and endothelin-1 stimulate phospholipase D in rat brain through H1 and ETB receptors, respectively.

Glial fibrillary acidic protein mRNA isotypes: expression in vitro and in vivo.

Glial fibrillary acidic protein (GFAP) and its mRNA, primarily expressed in astrocytes, are also expressed in peripheral nervous system Schwann cells as well as in certain non-neural tissues. Schwann cells express a GFAP mRNA (GFAP-beta) which differs from the CNS-type mRNA (GFAP-alpha) by the presence of an extended 5' untranslated region. We have developed a polymerase chain reaction assay which allows distinction of these two GFAP mRNAs, as well as quantitative analysis of their levels. In the cultured rat Schwannoma cell line RT4-D6, GFAP-beta was the major GFAP mRNA species, accounting for at least 75% of total GFAP (alpha + beta) mRNA. GFAP-beta was also detected in primary rat astrocyte cultures, where it constituted approximately 5% of the total GFAP mRNA, as well as in RNA samples prepared from normal rat cerebral cortex, and from hamster and human brain. In rat cortex, the temporal expression of GFAP-beta mRNA paralleled that of total GFAP mRNA, with plateau levels reached between postnatal days 15 and 20. In astrocyte cultures, the relative levels of GFAP-alpha and -beta mRNAs were differentially regulated by exposure to interferon-gamma (10 to 25 units/ml), which caused an increase in GFAP-beta levels while at the same time no change or a small decrease in total GFAP levels. In rat brain cortical slices, 4 hr exposure to 25 units/ml interferon-gamma decreased total GFAP mRNA levels over tenfold, while GFAP-beta levels were unaffected. These data indicate that a second form of the GFAP mRNA is expressed in astrocytes both in vivo and in vitro and provide evidence for independent regulation of these two GFAP mRNA species.

Differential effects of calcium channel antagonists on tityustoxin and ouabain-induced release of [ 3H]acetylcholine from brain cortical slices

In this paper, the effect of calcium channel blockers on acetylcholine release induced by tityustoxin and ouabain in rat brain cortical slices is described. Cadmium, a non-specific blocker of calcium channels, inhibited the release of ACh induced by tityustoxin. L-type calcium channel blockers (verapamil, nifedipine and diltiazen) had no effect on the release of ACh induced by tityustoxin. The release of ACh was also unaffected by nickel, a T-type calcium channel blocker, and the conotoxins GVIA and MVIIC, blockers of N and Q-type calcium channels. Agatoxin IVA, a specific blocker of the P-type calcium channel, inhibited the release of ACh induced by tityustoxin by 50%. The spontaneous release of ACh as well as ouabain-induced release of ACh was unaffected by any of the calcium channel blockers studied. It is concluded that ACh release induced by tityustoxin is mediated by Ca 2+ influx via P-type calcium channels.

Effects of Tityustoxin on Central Nervous System

Tityustoxin mimics many effects of electrical stimulation causing cell depolarization that increases the uptake of Na+ and Ca2+ ions and the release of acetylcholine in rat brain cortical slices and synaptosomes. Tityustoxin caused mobilization of acetylcholine from the cytoplasmic and crude vesicular fractions. The release of acetylcholine by tityustoxin is Na+ and Ca2 + dependent and is inhibited by tetrodotoxin. Tityustoxin-stimulated release of acetylcholine is blocked by ω-Agatoxin an antagonist of P-type calcium channel. The toxin activates the voltage dependent sodium channel stimulating the turnover of inositol phosphates. Chemical groups in the cell membrane, particularly SH groups, are essential for the tityustoxin-induced release of acetylcholine. Tityustoxin increased the incorporation of 32P into synapsin I and the effect is blocked by calmodulin inhibitors. Tityustoxin increased the release of norepinephrine, glutamate, γ-aminobutyric and excitatory aminoacids. It is concluded that tityustoxin is an important tool in studies of neurotransmitter release and signal transduction.

The role of histamine receptors in the regulation of the oxygen uptake of rat brain cortical and hypothalamic slices

Chemically oversulfated galactosaminoglycans with potential as therapeutic agents (inhibitors of human leukocyte elastase) were tested as chiral selectors in capillary electrophoresis of basic racemates. The high anionic character of these compounds provides them with anodic mobility in acidic buffer; using uncoated capillaries, the enantioresolution of racemic basic drugs was obtained at pH 2.5. Dimethindene, chloroquine and chlorpheniramine were enantioresolved applying negative voltage (−15 kV) while the other analytes (propranolol, pindolol, tetrahydrozoline and cloperastine) exhibited catodic migration. The addition of organic solvents to the running buffer was evaluated in order to increase the resolution; methanol provides the best results and in general, baseline separation of the analytes was reached. The studied oversulfated mucopolysaccharide, shows the same ionic character of heparin but presents different stereochemistry and sites of sulfation. A comparison with heparin, used in the same acidic conditions, may underline the role of ionic, spatial and steric features of glycosaminoglycans in the enantiorecognition.

Causes of calcium accumulation in rat cortical brain slices during hypoxia and ischemia: role of ion channels and membrane damage

To better understand why neurons accumulate calcium during cerebral ischemia, the influence of specific ion channel inhibitors on the rise in cytosolic free calcium ([Ca 2+] c) during hypoxia or ischemia was evaluated in rat cerebrocortical brain slices. [Ca 2+] c was measured fluorometrically with the dye fura-2 during hypoxia (95% N 2/5% CO 2 or 100 μM NaCN), simulated ischemia (100 μM NaCN plus 3.5 mM iodoacetate), or 0.5–1.0 mM glutamate. Hypoxia or ischemia increased [Ca +2] c from 100–250 mM to 1,000–2,500 nM within 3–5 min. Greater than 85% of the calcium accumulation was influx from the extracellular medium. The non-competitive N-methyl- d-aspartate (NMDA) inhibitor MK-801 reduced [Ca 2+] c accumulation during hypoxia, but antagonism of α-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptors or voltage-gated sodium or calcium channels or Na +/Ca 2+ exchangers had no effect. During ischemia, combined antagonism of NMDA, AMPA and voltage-gated sodium channels slowed the rate of calcium accumulation, but not concentration at 5 min. Membrane damage, as indicated by leakage of lactate dehydrogenase into superfusate, occurred coincidentally with calcium influx and ATP loss during both hypoxia and ischemia. We conclude that cytosolic calcium changes during hypoxia or ischemia in cortical brain slices are due to multiple mechanisms, are incompletely inhibited by combined ion channel blockade, and are associated with disruption of cell membrane integrity.

Effects of isoflurane and hypothermia on glutamate receptor-mediated calcium influx in brain slices.

To understand how volatile anesthetics protect neurons during cerebral ischemia, we studied the effects of isoflurane on cerebral glutamate receptor-mediated calcium influx. Calcium influx via these key excitatory receptors may mediate pain transmission, memory, and the pathophysiologic sequelae of cerebral anoxia or ischemia. Because cerebral protection by hypothermia may involve a decrease in glutamate receptor activity, we also examined the interaction of temperature and isoflurane on glutamate receptor inhibition. We measured glutamate receptor-mediated changes in cytosolic calcium in 300-microns-thick rat cortical brain slices. Temperature was varied to 28, 34, 37, or 39 degrees C and isoflurane partial pressure to 0.016-0.019 atm (equivalent to 1.16 minimum alveolar concentration [MAC], adjusted for temperature and age). Brain slices were loaded with fura-2 to permit measurement of cytosolic free calcium. Calcium changes due to the glutamate receptor agonist N-methyl-D-aspartate (NMDA) (50 microM), to ischemia levels of L-glutamate (1.0 mM) or to simulated ischemia (1.0 mM glutamate, 100 microM NaCN, and 3.5 mM iodoacetate) was then measured. Slice lactate dehydrogenase leakage and adenosine triphosphate were measured as indices of cellular integrity. Isoflurane reduced both L-glutamate and NMDA-mediated calcium fluxes by approximately 60%. Neither the activity of the NMDA receptor nor its inhibition by isoflurane was altered by temperature. The rate of calcium influx during ischemia was significantly reduced both by temperature and by isoflurane (P < 0.05). Adenosine triphosphate loss and lactate dehydrogenase leakage were reduced by isoflurane during simulated ischemia by 37% and 73% (P < 0.05), respectively. (1) At 1.16 MAC, isoflurane potently inhibits glutamate receptors and delays cellular injury induced by simulated ischemia, and (2) hypothermia does not reduce the intrinsic activity of cortical glutamate receptors but delays calcium accumulation during simulated ischemia. Isoflurane reduces the severity of key pathophysiologic events in an in vitro model of simulated cerebral ischemia.

Comparison of TBARS production and iron release in lactic acid- and hydrochloric acid-induced upld peroxidation in rat cortical brain slices

Comparison of TBARS production and iron release in lactic acid- and hydrochloric acid-induced upld peroxidation in rat cortical brain slices