Modulation of intracellular calcium changes and glutamate release by neuropeptide Y1 and Y2 receptors in the rat hippocampus: differential effects in CA1, CA3 and dentate gyrus

In the present work, we investigated the role of pre- and post-synaptic neuropeptide Y1 (NPY1) and Y2 receptors on the calcium responses and on glutamate release in the rat hippocampus. In cultured hippocampal neurones, we observed that only NPY1 receptors are involved in the modulation of intracellular free calcium concentration ([Ca(2+)](i)). In 88% of the neurones analysed, the increase in the [Ca(2+)](i), in response to depolarization with 50 mM KCl, was inhibited by 1 microM [Leu31,Pro34]NPY, whereas 300 nM NPY13-36 was without effect. However, studies with hippocampal synaptosomes showed that both NPY1 and Y2 receptors can modulate the [Ca(2+)](i) and glutamate release. The pharmacological characterization of the NPY-induced inhibition of glutamate release indicated that Y2 receptors play a predominant role, both in the modulation of Ca(2+)-dependent and -independent glutamate release. However, we could distinguish between Y1 and Y2 receptors by using [Leu31,Pro34]NPY and NPY13-36. Active pre-synaptic Y1 receptors are present in the dentate gyrus (DG) as well as in the CA3 subregion, but its activity was not revealed by using the endogenous agonist, NPY. Concerning the Y2 receptors, they are present in the three subregions (CA1, CA3 and DG) and were activated by either NPY13-36 or NPY. The present data support a predominant role for NPY2 receptors in mediating NPY-induced inhibition of glutamate release in the hippocampus, but the physiological relevance of the presently described DG and CA3 pre-synaptic NPY1 receptors remains to be clarified.     

Mechanisms of Adenosine Release in the Developing and Adult Mouse Hippocampus

Adenosine is a neuromodulator known to inhibit the synaptic release of neurotransmitters, e.g., glutamate, and to hyperpolarize postsynaptic neurons. The release of adenosine is markedly enhanced under ischemic conditions. It may then act as an endogenous neuroprotectant against cerebral ischemia and excitotoxic neuronal damage. The mechanisms by which adenosine is released from nervous tissue are not fully known, particularly in the immature brain. We now characterized the release of [³H]adenosine from hippocampal slices from developing (7-day-old) and adult (3-month-old) mice using a superfusion system. The properties of the release differed only partially in the immature and mature hippocampus. The K⁺-evoked release was Ca²⁺ and Na⁺ dependent. Anion channels were also involved. Ionotropic glutamate receptor agonists potentiated the release in a receptor-mediated manner. Activation of metabotropic glutamate receptors enhanced the release in developing mice, with group II receptors alone being effective. The evoked adenosine release apparently provides neuroprotective effects against excitotoxicity under cell-damaging conditions. Taurine had no effect on adenosine release in adult mice, but depressed the release concentration dependently in the immature hippocampus.     

Involvement of metabotropic glutamate receptors in taurine release in the adult and developing mouse hippocampus

Summary The inhibitory amino acid taurine has been held to function as an osmoregulator and modulator of neural activity, being particularly important in the immature brain. lonotropic glutamate receptor agonists are known markedly to potentiate taurine release. The effects of different metabotropic glutamate receptor (mGluR) agonists and antagonists on the basal and K⁺-stimulated release of [³H]taurine from hippocampal slices from 3-month-old (adult) and 7-day-old mice were now investigated using a superfusion system. Of group I metabotropic glutamate receptor agonists, quisqualate potentiated basal taurine release in both age groups, more markedly in the immature hippocampus. This action was not antagonized by the specific antagonists of group I but by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX), which would suggest an involvement of ionotropic glutamate receptors. (S)-3,5-dihydroxyphenylglycine (DHPG) potentiated the basal release by a receptor-mediated mechanism in the immature hippocampus. The group II agonist (2S, 2R, 3R)-2-(2,3-dicarboxycyclopropyl)glycine (DCG IV) markedly potentiated basal taurine release at both ages. These effects were antagonized by dizocilpine, indicating again the participation of ionotropic receptors. Group III agonists slightly potentiated basal taurine release, as did several antagonists of the three metabotropic receptor groups. Potassium-stimulated (50 mM K⁺) taurine release was generally significantly reduced by mGluR agents, mainly by group I and II compounds. This may be harmful to neurons in hyperexcitatory states. On the other hand, the potentiation by mGluRs of basal taurine release, particularly in the immature hippocampus, together with the earlier demonstrated pronounced enhancement by activation of ionotropic glutamate receptors, may protect neurons against excitotoxicity.Abbreviations ACPD (1±)-1-aminocyclopentane-trans-1,3-dicarboxylate - AIDA (RS)-1-aminoindan-1,5-dicarboxylate - AMPA 2-amino-3-hydroxy05-methyl-4-isoxazolepropionate - CNQX 6-cyano-7-nitroquinoxaline-2,3-dione - CPPG (RS)-2-cyclopropyl-4-phosphonophenylglycine - DCG IV (2S,2R,3R)-2-(2,3-dicarboxycyclopropyl)glycine - DHPG (S)-3,5-dihydroxyphenylglycine - EGLU (2S)-2-ethylglutamate - L-AP3 L(+)-2-amino-3-phosphonopropionate - L-AP4 L(+)-2-amino-4-phosphonobutyrate - L-AP6 L(+)-2-amino-6-phosphonohexanoate - L-SOP O-phospho-L-serine - MPPG (RS)-2-methyl-4-phosphonophenylglycine - MSOP (RS)-2-methylserine-O-phosphate - MSOPPE (RS)-2-methylserine-O-phosphate monophenyl ester - MTPG (RS)-2-methyl-4-tetrazolylphenylglycine - NBQX 6-nitro-7-sulphamoyl[f]quinoxaline-2,3-dione - NMDA N-methyl-D-aspartate - QA quisqualate - S-3C4H-PG (S)-3-carboxy-4-hydroxyphenylglycine - S-4C-PG (S)-4-carboxyphenylglycine; - S-MCGP (S)-2-methyl-4-carboxyphenylglycine     

Glutamate receptor changes in brain synaptic membranes from human alcoholics

Brains from human alcoholics and non-alcoholics were obtained shortly after death. The hippocampus was dissected, homogenized, and processed for the isolation of a synaptic membraneenriched fraction and the study ofl-[³H]glutamic acid and 3-((±)-2-carboxypiperazin-4-yl)-[1,2³H]propyl-l-phosphonic acid ([³H]CPP) binding sites. The pharmacological characteristics ofl-[³H]glutamic acid binding to synaptic membranes isolated from hippocampus corresponded to the labeling of a mixture of N-methyl-d-aspartate (NMDA), kainate and quisqualic acid receptor sites. Synaptic membranes prepared from the hippocampus of individuals classified as alcoholics had significantly higher density of glutamate binding sites than identically prepared membranes from non-alcoholic individuals. In addition, there was a clear definition of a population ofl-glutamate binding sites (approx. 10% of total) in the membranes from alcoholics that had a higher affinity for the ligand than the major set of sites labeled in membranes from both alcoholics and non-alcoholics. Neither the age of the individuals at the time of death nor the time that elapsed between death and processing of brain tissue were significant factors in determining either recovery of purified synaptic membranes from brain homogenates orl-[³H]glutamate binding to synaptic membranes. In order to determine whether some of the changes inl-[³H]glutamic acid binding were due to alterations in binding at the NMDA receptor subtype, we also measured binding of [³H]CPP to extensively washed crude synaptosomal membranes. Membranes from brains of alcoholics had higher affinity (3-fold) for [³H]CPP but lower binding capacity (3-fold) when compared with those of non-alcoholics. These observations suggest selective changes among different glutamate receptor subtypes in human brain under conditions of chronic alcohol intake.     

不同刺激形式在成年大鼠海马CAl区诱导长时程压抑的谷氨酸受体机制

前期研究显示低频率多串刺激能够在成年大鼠海马CAl区诱发稳定的长时程压抑(long-term depression,LTD),而这种LTD的受体机制目前还不清楚.本研究采用成年大鼠海马脑片标本,电刺激Schaffer侧枝传入纤维,在CAl区锥体细胞层记录群体锋电位(population spikes,PS),并分别应用N-甲基-D-天冬氨酸(N-methyl-D-aspartate,NMDA)受体和代谢型谷氨酸(metabotropic glutamate,mGlu)受体的拮抗剂AP5和MCPG,观察两组低频率(2-Hz和5-Hz)多串刺激能否诱导LTD,以揭示不同刺激形式诱导成年大鼠LTD的可能受体机制.结果显示,AP5和MCPG都能抑制由2-Hz多串刺激诱导的LTD:强直刺激后20 min时PS幅度分别为基础值的(96.0±3.5)%(n=10)和(95.7±4.1)%(n=8).MCPG能够抑制5-Hz多串刺激诱导的LTD的产生,而AP5不能:分别应用AP5和MCPG后,强直刺激后35 min时PS的幅度分别为基础值的(73.6±4.4)%(n=10)和(98.2±8.9)%(n=8).以上结果提示,2-Hz多串刺激诱导的LTD可能依赖于NMDA受体与mGlu受体的共同活化,而5-Hz多串刺激诱导的LTD只与mGlu受体有关.因此,不同频率的多串刺激诱导的LTD涉及不同的谷氮酸受体机制.     

Changes in the Glutamate Release and Uptake of Cerebellar Cells in Perinatally Nicotine-Exposed Rat Pups

Cerebellar granule and glial cells were cultured from 7 day-old rat pups after pre- and post-natal nicotine treatment. Ten days later, the basal release of glutamate in the granule cells prepared from the pre- and post-natally nicotine-exposed pups was higher and lower than the controls, respectively. The N-methyl-D-aspartate-induced release of glutamate was higher in the granule cells of post-natal nicotine exposed rats. However, the nicotine-induced glutamate release was either unchanged or was lower in the granule cells of all nicotine-treated pups. The basal glutamate uptake was higher in the glial cells from those exposed pre-natally and lower in the continuously nicotine-exposed pups. The sensitivities of L-trans-pyrrolidine-2,4-dicarboxylic acid on glutamate uptake were higher in all nicotine treated groups. There was a higher number of specific [³H]dizocilpine binding sites in the pre- or continuously nicotine-exposed group. These results suggest that the cerebellar cell properties are altered after perinatal nicotine exposure and that the development of an excitatory amino acid system might be affected differently depending on the nicotine exposure time.     

Arginine vasopressin increases glutamate release and intracellular Ca2+ concentration in hippocampal and cortical astrocytes through two distinct receptors

Arginine vasopressin (AVP), released from the CNS, plays an important role in regulating several aspects of CNS functions including aggression, anxiety, and cognition. In this study, we report a novel finding that AVP induces glutamate release from astrocytes isolated from the cerebral cortex and hippocampus. We also investigated the types of AVP receptors involved in the AVP-induced increase in glutamate release from astrocytes isolated from the hippocampus and cortex of neonatal rats. We showed that the AVP (0.1-1000 nmol/L) induced increase in glutamate release and [Ca(2+)](i) is brought about by two distinct subtypes of V(1) receptors (V(1a) and V(1b)). Our results suggested that V(1b) receptors are predominantly expressed in astrocytes isolated from the hippocampus and V(1a) receptors are solely expressed in astrocytes isolated from the cerebral cortex of neonatal rats. The results of the western blot analyses confirmed these pharmacological data. In addition, the AVP-induced increase in glutamate did not contribute to an increase in [Ca(2+)](i), as blockade of metabotropic glutamate receptors did not alter the AVP-induced increase in [Ca(2+)](i). In addition, the administration of a phospholipase A(2) inhibitor failed to alter AVP-induced [Ca(2+)](i) increase suggesting the lack of involvement of this enzyme.     

In vivo modulation of extracellular hippocampal glutamate and GABA levels and limbic seizures by group I and II metabotropic glutamate receptor ligands

The effects of several metabotropic receptor (mGluR) ligands on baseline hippocampal glutamate and GABA overflow in conscious rats and the modulation of limbic seizure activity by these ligands were investigated. Intrahippocampal mGluR group I agonist perfusion via a microdialysis probe [1 mm (R,S)-3,5-dihydroxyphenylglycine] induced seizures and concomitant augmentations in amino acid dialysate levels. The mGlu1a receptor antagonist LY367385 (1 mm) decreased baseline glutamate but not GABA concentrations, suggesting that mGlu1a receptors, which regulate hippocampal glutamate levels, are tonically activated by endogenous glutamate. This decrease in glutamate may contribute to the reported LY367385-mediated anticonvulsant effect. The mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)-pyridine (50 mg/kg) also clearly abolished pilocarpine-induced seizures. Agonist-mediated actions at mGlu2/3 receptors by LY379268 (100 microm, 10 mg/kg intraperitoneally) decreased basal hippocampal GABA but not glutamate levels. This may partly explain the increased excitation following systemic LY379268 administration and the lack of complete anticonvulsant protection within our epilepsy model with the mGlu2/3 receptor agonist. Group II selective mGluR receptor blockade with LY341495 (1-10 microm) did not alter the rats' behaviour or hippocampal amino acid levels. These data provide a neurochemical basis for the full anticonvulsant effects of mGlu1a and mGlu5 antagonists and the partial effects observed with mGlu2/3 agonists in vivo.     

Presynaptic Modulation Controlling Neuronal Excitability and Epileptogenesis: Role of Kainate, Adenosine and Neuropeptide Y Receptors

Based on the idea that seizures may arise from an overshoot of excitation over inhibition, all substances that may decrease glutamatergic function while having no effect or even increasing GABAergic neurotransmission are likely to be effective anticonvulsants. We now review the possible role of three such neuromodulators, kainate, adenosine, and neuropeptide Y receptors in controlling hyperexcitability and epileptogenesis. Particular emphasis is given on the robust neuromodulatory role of these three groups of receptors on the release of glutamate in the hippocampus, a main focus of epilepsy. Moreover, we also give special attention to the mechanisms of receptor activation and coupled signaling events that can be explored as attractive targets for the treatment of epilepsy and excitotoxicity. The present paper is a tribute to Arsélio Pato de Carvalho who has been the main driving force for the development of Neuroscience in Portugal, notably with a particular emphasis on the presynaptic mechanisms of modulation of neurotransmitter release.     

Repeated Restraint Stress Alters Hippocampal Glutamate Uptake and Release in the Rat

Glutamatergic mechanisms are thought to be involved in stress-induced changes of brain function, especially in the hippocampus. We hypothesized that alterations caused by the hormonal changes associated with chronic and acute stress may affect glutamate uptake and release from hippocampal synaptosomes in Wistar rats. It was found that [3H]glutamate uptake and release by hippocampal nerve endings, when measured 24 h after 1 h of acute restraint, presented no significant difference. The exposure to repeated restraint stress for 40 days increased neuronal presynaptic [3H]glutamate uptake as well as basal and K+-stimulated glutamate release when measured 24 h after the last stress session. Chronic treatment also caused a significant decrease in [3H]glutamate binding to hippocampal membranes. We suggest that changes in the glutamatergic system are likely to take part in the mechanisms involved in nervous system plasticity following repeated stress exposure.     

Adenosine A2A receptors and metabotropic glutamate 5 receptors are co-localized and functionally interact in the hippocampus: a possible key mechanism in the modulation of N-methyl-D-aspartate effects

Hippocampal metabotropic glutamate 5 receptors (mGlu5Rs) regulate both physiological and pathological responses to glutamate. Because mGlu5R activation enhances NMDA-mediated effects, and given the role played by NMDA receptors in synaptic plasticity and excitotoxicity, modulating mGlu5R may influence both the physiological and the pathological effects elicited by NMDA receptor stimulation. We evaluated whether adenosine A2A receptors (A(2A)Rs) modulated mGlu5R-dependent effects in the hippocampus, as they do in the striatum. Co-application of the A(2A)R agonist CGS 21680 with the mGlu5R agonist (RS)-2-chloro-s-hydroxyphenylglycine(CHPG) synergistically reduced field excitatory postsynaptic potentials in the CA1 area of rat hippocampal slices. Endogenous tone at A(2A)Rs seemed to be required to enable mGlu5R-mediated effects, as the ability of CHPG to potentiate NMDA effects was antagonized by the selective A(2A)R antagonist ZM 241385 in rat hippocampal slices and cultured hippocampal neurons, and abolished in the hippocampus of A(2A)R knockout mice. Evidence for the interaction between A(2A)Rs and mGlu5Rs was further strengthened by demonstrating their co-localization in hippocampal synapses. This is the first evidence showing that hippocampal A(2A)Rs and mGlu5Rs are co-located and act synergistically, and that A(2A)Rs play a permissive role in mGlu5R receptor-mediated potentiation of NMDA effects in the hippocampus.     

Presynaptic kainate receptor-mediated facilitation of glutamate release involves Ca(2+) -calmodulin at mossy fiber-CA3 synapses

J. Neurochem. (2012) 122, 891-899. ABSTRACT: Presynaptic kainate receptors (KARs) modulate the release of glutamate at synapses established between mossy fibers (MF) and CA3 pyramidal cells in the hippocampus. The activation of KAR by low, nanomolar, kainate concentrations facilitates glutamate release. KAR-mediated facilitation of glutamate release involves the activation of an adenylate cyclase/cyclic adenosine monophosphate/protein kinase A cascade at MF-CA3 synapses. Here, we studied the mechanisms by which KAR activation produces this facilitation of glutamate release in slices and synaptosomes. We find that the facilitation of glutamate release mediated by KAR activation requires an increase in Ca(2+) levels in the cytosol and the formation of a Ca(2+) -calmodulin complex to activate adenylate cyclase. The increase in cytosolic Ca(2+) underpinning this modulation is achieved, both, by Ca(2+) entering via Ca(2+) -permeable KARs and, by the mobilization of intraterminal Ca(2+) stores. Finally, we find that, congruent with the Ca(2+) -calmodulin support of KAR-mediated facilitation of glutamate release, induction of long-term potentiation at MF-CA3 synapses has an obligate requirement for Ca(2+) -calmodulin activity.     

Displacement of endogenous glutamate withd-aspartate: an effective strategy for reducing the calcium-independent component of glutamate release from synaptosomes

d-aspartate was used in the present study to partially deplete the cytosolic pool of glutamate, which is released independent of extracellular Ca²⁺, prior to measuring the K⁺-evoked release of this endogenous acidic amino acid from rat hippocampal mossy fiber synaptosomes. This pretreatment is known to be an effective method for substantially reducing the Ca²⁺-independent component of glutamate release. The rate of glutamate efflux is dependent on the concentration of sodium ions in the external medium and can be stimulated by exposure of hippocampal mossy fiber synaptosomes to externald-aspartate (50 M). Following the partial displacement of this cytosolic pool of glutamate withd-aspartate, the K⁺-evoked release of the residual, presumably vesicular, pool of endogenous glutamate has a strict requirement for external calcium and is highly dependent on the extent to which depolarization elevates the level of free cytosolic calcium. It is concluded that the protocol described in this study for the displacement of cytosolic glutamate withd-aspartate provides a useful alternative method of controlling for the Ca²⁺-independent component of glutamate release in synaptosomal preparations.Abbreviations used Ca calcium - Ca²⁺ free calcium - EGTA (ethylene-dioxy)diethylenedinitrilotetraacetic acid - KBM Krebs-bicarbonate medium The animals involved in this study were procured, maintained and used in accordance with the Animal Welfare Act and the Guide for the Care and Use of Laboratory Animals prepared by the Institute of Laboratory Animal Resources, National Research Council.     

Carbachol-Induced Hydrolysis of Phospholipids in Hippocampal Slices May Be Mediated in Part By Subsequent Activation of Metabotropic Glutamate Receptors

We observed that AP-3, an antagonist of metabotropic glutamate receptors, reduced carbachol-induced hydrolysis of phospholipids in hippocampal slices. This inhibition could be explained in different ways, e.g.: 1) AP-3 acts also as antagonist of muscarinic receptors mediating the hydrolysis of phospholipids induced by carbachol, 2) Carbachol induces the release of glutamate which, by activating metabotropic glutamate receptors, leads to additional hydrolysis of phospholipids. The aim of this work was to test these possibilities. It is shown that AP-3 reduces carbachol-induced hydrolysis of phospholipids in hippocampal slices but not in cerebellar neurons at 10–14 days of culture, when these cells are not able to induce hydrolysis of phospholipids following activation of metabotropic glutamate receptors. It is also shown that carbachol induces a release of [³H]aspartate in hippocampal slices. The results reported suggest that the hydrolysis of phospholipids induced by carbachol in hippocampal slices would have two components. One part would be due to direct activation by carbachol of muscarinic receptors associated to activation of phospholipase C. This part would not be inhibited by AP-3. The second part would be due to subsequent release of glutamate and activation of metabotropic glutamate receptors. This part would be inhibited by AP-3.     

Glutamate agonists and [3H]GABA release from rat hippocampal slices: Involvement of metabotropic glutamate receptors in the quisqualate-evoked release

The effects of glutamate agonists and their selective antagonists on the Ca²⁺-dependent and independent releases of [³H]GABA from rat coronal hippocampal slices were studied in a superfusion system. The Ca²⁺-dependent release evoked by glutamate, kainate and N-methyl-D-aspartate (NMDA) gradually declined with time despite the continuous presence of the agonists. Quisqualate (QA) caused a sustained release which exhibited no tendency to decline within the 20-min period of stimulation. This release was enhanced in Ca²⁺-free medium. The release evoked by QA in Ca²⁺-containing medium was significantly inhibited by (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohept-5,10-imine hydrogen maleate (MK-801) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), showing that QA activates NMDA receptors directly or indirectly through (RS)--amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors. The inhibition of MK-801 was slightly diminished and that of CNQX totally abolished in Ca²⁺-free medium. Verapamil inhibited the QA-activated release in both Ca²⁺-containing and Ca²⁺-free media. The effect of QA but not that of AMPA was blocked in Ca²⁺-free medium by L(+)-2-amino-3-phosphonopropionate (L-AP3), a selective antagonist of the metabotropic glutamate receptor. It is suggested that the sustained release of GABA is also mediated partly by activation of metabotropic receptors and mobilization of Ca²⁺ from intracellular stores.     

Ischemia-Induced Taurine Release Is Modified by Nitric Oxide-Generating Compounds in Slices from the Developing and Adult Mouse Hippocampus

The novel neurotransmitter/neuromodulator nitric oxide (NO), which is linked to the activation of the N-methyl-D-aspartate class of glutamate receptors, has been shown to modify transmitter release in brain tissue. Release of the inhibitory amino acid taurine is also markedly enhanced by N-methyl-D-aspartate and NO-producing agents under normal conditions in the mouse hippocampus. The release of preloaded [³H]taurine from hippocampal slices from adult (3-month-old) and developing (7-day-old) mice was characterized under ischemic conditions in the presence of different NO-generating compounds, hydroxylamine, sodium nitroprusside, and S-nitroso-N-acetylpenicillamine (SNAP), using a superfusion system. The ischemia-induced taurine release at both ages was markedly enhanced by 1.0 mM nitroprusside and 1.0 mM SNAP, whereas 5.0 mM hydroxylamine was effective only in adults. The nitroprusside- and SNAP-induced releases were reduced by the inhibitors of NO synthase (nitroarginine and 7-nitroindazole) and NO-sensitive soluble guanylyl cyclase [1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one], suggesting involvement of the NO/cGMP pathway. The release in ischemia in the absence of Na⁺ was modified by NO compounds only in adults; the 0.1 mM N-methyl-D-aspartate stimulated taurine release at both ages. The enhanced release of taurine associated with NO production could be beneficial to brain tissue under cell-damaging conditions and corroborates the neuroprotective role of this amino acid, particularly in the immature brain.     

NMDA receptor signaling: death or survival?

Glutamate-induced neuronal damage is mainly caused by overactivation of N-methyl-D-aspartate (NMDA) receptors.Conversely,normal physiological brain function and neuronal survival require adequate activ...     

Effects of Long-Term Hypoxia/Hypoglycemia on Synaptic Transmission between the CA3 and CA1 Zones in Rat Hippocampal Slices

On rat hippocampal slices using a standard patch-clamp technique in the whole-cell configuration, we studied the effects of long-term (40 to 60 min) hypoxia/hypoglycemia (HH) on excitatory postsynaptic currents (EPSC) evoked by stimulation of Schaffer collaterals in the cells of the CA1 zone. In addition to the earlier described effect of an immediate drop in the EPSC amplitude, a significant transient increase in its amplitude 30-50 min after the beginning of HH was observed. A pharmacologically isolated NMDA component of excitatory synaptic events underwent similar changes: 30-50 min after the blockade of NMDA receptor-mediated current, a fast recovery of its amplitude to the control (or even higher) values occurred. A blocker of NMDA/glutamate (Glu) receptors, D-aminophosphonovaleric acid (D-APV), and a competitive nonspecific antagonist of metabotropic Glu receptors, (RS)--methyl-4-carboxyphenylglycine – (RS)-MCPG – did not influence the HH-induced initial suppression of synaptic transmission but completely eliminated its delayed recovery. Our findings allow us to suppose that NMDA receptors, as well as metabotropic Glu receptors, play important roles in the cascade of biochemical reactions resulting in death of hippocampal pyramidal cells in the course of and after long-term ischemia in vivo.