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The possible pathways of inhibitory influences mediated by two kinds of metabotropic receptors, group III metabotropic glutamate receptors (mGluRs III) and GABAB receptors (GABABRs) to the miniature glycinergic events were investigated in the isolated spinal cord of the frog Rana ridibunda. The glycinergic events prevailed within the miniature inhibitory activity of motoneurons [3]. Selective agonists of GABABRs (baclofen) and group III mGluR (LAP4) reduce the frequency of miniature events to 48.0 ± 5.56% (n = 8) and 48.5 ± 8.6% (n = 5) respectively. The mean amplitude of miniature potentials was not modified significantly which indicates the presynaptic mode of their action on the synaptic transmission. To reveal the stages of metabotropic receptors regulatory effects on the glycine exocitosis the application of their selective agonists was performed after selective blockade of putative links of glycinergic transmission modulation. It was shown that the mGluRsIII influences are due to the negative feedback with adenylyl cyclase (AC) whereas the following step is formed by protein kinase A (PKA), because their selective blockade eliminate the effect of group III mGluRs activation. The AC is not involved in transdusing the GABABRs signal to the glycine miniature activity because SQ22536, an AC-inhibitor does not eliminate the inhibitory action of baclofen. The action of GABABRs depends on the activity of the phospholipase C (PLC) because its inhibition with U73122 prevents the effect of baclofen. The next possible link of this pathway could be the protein kinase C (PKC); but it is not involved in the realization of GABABRs influences because the PKC blocker (GF 109302X) does not modify the baclofen effect. The common link of group III mGluRs and GABABRs influences on the glycinergic miniature activity realization can be the inositol trisphosphate receptors (IP3Rs) that regulate the Ca2+ outflow from the nerve terminal depots and are connected (according to the literature data) with PKA, cAMP and PLC. In our experiments 2-APB, an IP3Rs antagonist, reduced to 26 ± 8% (n = 7) the frequency of glycinergic miniature activity and prevented the inhibitory effects of group III mGluRs and GABABRs. Our data suggest that collision and cross-talk of these Glu- and GABA-metabotropic pathways which was described earlier [2] may take place at this level.

The data on the structure, location and functions of the metabotropic glutamate receptor is shown. The family consists of 8 mGluRs subtypes and is divided into three groups: I group--mGluRs1/mGluRs5, II group--mGluRs2/mGluRs3, III group--mGluRs4/mGluRs6/mGluRs7/mGluRs8. They are associated with G-protein; signaling in the cells is carried out by IP3 or adenylate cyclase signaling pathways, in the result of which, mGluRs modify glial and neuronal excitability. Receptors are localized in the CNS and periphery in non-neuronal tissues: bone, heart, kidney, pancreas pod and platelets, the gastrointestinal tract, immune system. Their participation in the mechanisms of neurodegenerative diseases, mental and cognitive disorders, autoimmune processes, etc. is displayed. Agonists, antagonists, allosteric modulators of mGluRs are considered as potential medicines for treatment of mental diseases, including depression, fragile X syndrome, anxiety, obsessive-compulsive disorders, Parkinson's disease, etc.

Stroke is the second leading cause of death in the world. Unfortunately, only a few drugs have been proved in clinical trials. Drug development of the last decade has been focused substantially on a promising and heterogeneous group of neuroprotective drugs. Hundreds of compounds were suggested as new putative neuroprotectors, which effectiveness was confirmed in preclinical trials only. At the present time discrepancy between results of preclinical studies and clinical trials requires careful analysis. One of the least evaluated and probably the most noticeable reasons is general anesthesia--an obligatory component of an overwhelming majority of existing animal stroke models. The aim of the review is to describe known mechanisms of common general anesthetics influence on ionotropic and metabotropic plasma membrane receptors, and key signal pathways involved in neuronal hypoxic-ischemic injury and survival.

The influence of NMDA and metabotropic neostriatal glutamate receptors blockade to avoidance conditioning (in shuttle box) and free locomotor behavior (in open field) in chronic experiments in rats were investigated. The glutamate receptor antagonists were injected bilateral into striatum separately and with the GABA-A receptor antagonist picrotoxin (2 microg), that produced in rats the impairment of avoidance conditioning and choreo-myoklonic hyperkinesis. The most effective in preventing of negative picrotoxin influence on behavior was 5-type metabotropic glutamate receptors antagonist MTEP (3 microg). Separately injected MTEP did not influence on avoidance conditioning and free locomotor behavior. Unlike that, 1-type metabotropic glutamate receptors antagonist EMQMCM (3 microg) impaired normal locomotor behavior and did not prevent the picrotoxin effects. The NMDA glutamate receptors MK 801 (disocilpin--1 and 5 microg) impaired the picrotoxin-induced hyperkinesis, but did not to prevent the negative effects on avoidance conditioning; separately injected MK 801 reduced free locomotor activity. Based on location of investigated receptor types in neostriatal neurons membranes, we proposed that the most effective influence on 5-type metabotropic glutamate receptors is associated with their involvement in "indirect" efferent pathway, suffered in hyperkinetic extrapyramidal motor dysfunction--Huntington's chorea in human.

The metabotropic glutamate receptor 5 (mGluR5) is one of the important excitatory neurotransmitter receptors in the central nervous system, and its desensitization by G protein-coupled receptor kinases (GRKs) plays an important role in neuron protection against receptor overstimulation. It is reported that GRK2 could down-regulate the mGluR5 signaling in both HEK 293 cells and neurons. However, whether GRK2-mediated mGluR5 desensitization is phosphorylation dependent remains controversial. Here, we demonstrated that the signal intensity and kinetics of mGluRS desensitization was inhibited or changed by GRK2 in HEK 293 cells. By using the catalytically inactive GRK2 mutant K220R, and the receptor mutants that lack potential phosphorylation sites in the C-terminal tail, we demonstrated that the GRK2-mediated mGluR5 desensitization was phosphorylation-independent. Furthermore, overexpression of an N-terminal regulator of G protein signaling (RGS) homology (RH) domain of GRK2 was sufficient to attenuate the mGluR5 signaling, whereas the expression of GRK2 D110A mutant devoid in Galphaq binding was unable to inhibit mGluRS signaling. In summary, this study provides evidence that GRK2 mediates phosphorylation-independent mGluR5 desensitization via the interaction between the RGS domain and Galphaq in HEK 293 cells.

Group I of metabotropic glutamate receptors (ImGluRs) are a family of G-protein-coupled receptors which activate a multitude of signaling pathways important for modulating neuronal excitability and synaptic plasticity as well as anti- and prosurvival pathways initiated by hypoxia. However these functions are still not complete and sometimes controversial. The present work is a review of data concerning involvement of ImGluRs in mechanisms of cell response to hypoxia. We also present original data demonstrating their participation in forming pathogenic and adaptogenic intracellular events, appearing in rat neocortex during a day after severe or moderate hypobaric hypoxia, respectively. Ca2+ responses to ImGluRs stimulation in survival cortical slices and expression of ImGluRs, IP3Rs and PLCbeta1 in immunolabelled cortical preparations were estimated for these two different hypoxic models.

Ca(2+)-mediated signal transduction of group I metabotropic glutamate receptors (ImGluR) was studied in the brain of young (15 days) and old rats (90 days) exposed to severe hypobaric hypoxia on gestation days 14-16. Changes in the concentration of bound intracellular Ca(2+) (Ca(2+) response) were evaluated after repeated application of a selective ImGluR agonist 3,5-dihydroxyphenylglycine (DHPG) to cultured brain slices. Primary application of DHPG for 2 min induced a negative Ca(2+) response in slices from 15-day-old intact animals, while repeated application caused a positive response. In slices from 90-day-old control animals, both responses were negative. In slices from rats of both age groups subjected to severe prenatal hypobaric hypoxia, both responses were mainly positive, but short-term negative components were present in adult animals. Our results suggest that severe hypobaric hypoxia changes the balance between the two constitutive signal pathways triggered by ImGluR (inosine triphosphate and diacylglycerol pathways). This procedure is followed by the increased influx of extracellular Ca(2+) (as compared to Ca(2+) release from the intracellular stores). This imbalance is particularly pronounced at the early stage of ontogeny.

The influence of nootropic drugs of different groups (piracetam, phenotropil, nooglutil, noopept, semax, meclofenoxate, pantocalcine, and dimebon) on the binding of the corresponding ligands to AMPA, NMDA, and mGlu receptors of rat brain has been studied by the method of radio-ligand binding in vitro. It is established that nooglutil exhibits pharmacologically significant competition with a selective agonist of AMPA receptors ([G-3H]Ro 48-8587) for the receptor binding sites (with IC50 = 6.4 +/- 0.2 microM), while the competition of noopept for these receptor binding sites was lower by an order of magnitude (IC50 = 80 +/- 5.6 microM). The heptapeptide drug semax was moderately competitive with [G-3H]LY 354740 for mGlu receptor sites (IC50 = 33 +/- 2.4 microM). Dimebon moderately influenced the specific binding of the ligand of NMDA receptor channel ([G-3H]MK-801) at IC50 = 59 +/- 3.6 microM. Nootropic drugs of the pyrrolidone group (piracetam, phenotropil) as well as meclofenoxate, pantocalcine (pantogam) in a broad rage of concentrations (10(-4)-10(-10) M) did not affect the binding of the corresponding ligands to glutamate receptors (IC50 100 pM). Thus, the direct neurochemical investigation was used for the first time to qualitatively characterize the specific binding sites for nooglutil and (to a lower extent) noopept on AMPA receptors, for semax on metabotropic glutamate receptors, and for dimebon on the channel region of NMDA receptors. The results are indicative of a selective action of some nootropes on the glutamate family.

The review is devoted to experimental investigations of metabotropic glutamate receptors and the properties of drugs (ligands) belonging to agonists, antagonists, and modulators of the activity of these receptors. Possibilities of the treatment of neurodegenerative disorders, cognitive disturbances in schizophrenia patients, and narcotic dependency by using drugs of this class are considered.

Localization of metabotropic glutamate receptors (MGR) in head ganglion of honeybee Apis mellifera, and mechanisms of participation of activated MGR in CNS plasticity are investigated by means of complex approach using immunochemical, electrophysiological and behavioral methods. Influense of MGR activation on GABAergic system and ionotropic glutamate receptors (IGR) of AMPA- and NMDA-subtypes in studied. MGRa are revealed in lateral and medial calices of mushroom bodies. The inhibiting influence of MGR on AMPA- and NMDA receptors is shown using method of conditioned reflex. Previous activation of MGR neutralizes the inhibiting effect of GABA. Modulating role of heterogeneous MGR population in mechanisms of CNS plasticity on the level of glutamate-ergic synapse, and at interaction with GABAergic system is discussed.

Glutamate, major excitatory neurotransmitter in mammalian CNS, acts via ionotropic and metabotropic receptors. In agreement with the results of in vitro studies that pointed at close interactions between ionotropic NMDA and metabotropic glutamate mGlu5 receptors, blockade ofmGlu5 receptors was reported to enhance behavioral effects of NMDA receptor channel blockers. The present study aimed to study the effects of a highly selective mGluR5 antagonist MTEP, alone and in combination with NMDA receptor channel blocker MK-801, in rats trained to perform a delay-non-match-to-position task (working memory test). Acute administration of MK-801 (0.1 mg/kg) produced specific working memory impairment expressed as proactive interference (poor performance in the current trial due to the interfering influence of the experience in past trials). However, administration of MTEP (5.0 mg/kg), either alone or in combination with MK-801, had no appreciable effects. While these data clearly indicate little or no involvement of mGlu5 receptors in the mechanisms of working memory, present results demonstrate a robust experimental approach to study cognitive deficits associated with psychotomimetic drug treatment.

Homocysteine and homocysteic acid increased the stationary level of reactive oxygen species in rat lymphocytes, homocysteic acid being more potent in this respect. The effect of this compound was realized via ionotropic NMDA receptors and group III metabotropic glutamate receptors. Incubation of lymphocytes with homocysteic acid increased intracellular Ca(2+)concentration, activated of protein kinase C, and induced accumulation of reactive oxygen species, which reflected the involvement of homocysteic acid into cell signaling mechanisms.

Specificity of glutamate receptors in the P2 synaptosomal fraction from the cerebral cortex of newborn rats was studied by measuring (45)Ca(2+) uptake by synaptosomes in the presence of agonists of ionotropic and metabotropic glutamate receptors. It was shown that P2 synaptosomal fraction from rat cortex contains NMDA receptors, kainate receptors, and group 1 metabotropic receptors.