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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Exposure of cultured cerebellar granule cells to glutamate results in a concentration-dependent (EC50 = 22.7 +/- 0.4 microM) and delayed (24-72 hr) neurotoxicity, which is blocked by the specific N-methyl-D-aspartate (NMDA) receptor antagonists 2-amino-5-phosphovalerate and MK-801 but is unaffected by the non-NMDA receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione and 6,7-dinitroquinoxaline-2,3-dione. Although glutamate toxicity in these cells is mediated by the NMDA subtype of glutamate receptor, pretreatment of cerebellar granule cells with subtoxic concentrations of NMDA markedly antagonizes the neurotoxic actions of glutamate, with an IC50 of 55 +/- 4 microM. The neuroprotective effect of NMDA requires a preincubation time of approximately 120 min to be fully manifested and does not require the presence of NMDA during glutamate exposure. These data demonstrate that NMDA receptors mediate both neurotoxicity and neuroprotection in cerebellar granule cells. Among four glutamate receptor agonists tested (NMDA, quisqualate, ibotenate, and kainate), only NMDA was able to provide a robust neuroprotection against glutamate toxicity. Quisqualate was neither neurotoxic nor neuroprotective, whereas ibotenate, which was nontoxic by itself, induced a small degree of neuroprotection. In contrast, kainate, which was neurotoxic to cerebellar granule cells, also provided considerable neuroprotection against glutamate toxicity. Because preincubation of cerebellar granule cells with NMDA fails to alter NMDA receptor-mediated phosphoinositide hydrolysis or the specific binding of [3H]MK-801 to NMDA receptors, it appears that the neuroprotective effects of NMDA are not due to NMDA receptor desensitization.
Mol Pharmacol 1992 Aug
PMID:N-methyl-D-aspartate exposure blocks glutamate toxicity in cultured cerebellar granule cells. 135 59

Poly(A)+ Messenger ribonucleic acid (mRNA) was extracted from leg muscles of the locust Schistocerca gregaria and injected into oocytes of Xenopus laevis. After 5-10 days incubation, receptors for L-glutamate, L-quisqualate, DL-ibotenate and gamma-aminobutyric acid (GABA) were expressed. Agonist-induced currents were dose-dependent, and, in the concentration range 1 microM to 1 mM, generally had peak values of 50 nA. The responses to all agonists, apart from GABA, exhibited desensitization which could not be reversed even by prolonged washing with Ringer. Application of 100 microM GABA to oocytes voltage clamped at -60 mV produced a smooth inward current with a reversal potential of -22 +/- 1 mV, which is consistent with the involvement of chloride ions. At 100 microM, picrotoxin reversibly abolished this current, while 100 microM bicuculline had no effect. L-Glutamate elicited a smooth current with a reversal potential of -52 +/- 3 mV. L-Quisqualate elicited an inward current at -60 mV with a reversal potential of -9 +/- 2 mV; this current occasionally had an oscillatory component. The response to ibotenate comprised a smooth inward current with a reversal potential of -21 +/- 3 mV which was probably mediated by chloride ions.
Brain Res Mol Brain Res 1990 Oct
PMID:Amino acid receptors from insect muscle: electrophysiological characterization in Xenopus oocytes following expression by injection of mRNA. 217 11

Intracellular recordings were obtained from guinea pig hippocampal neurons maintained in vitro. Current- and voltage-clamp techniques were used to study the effect of microiontophoresis of excitatory amino acid agonists. Modification of agonist responses by bath application of known concentrations of antagonist agents was also examined. All agonists used, glutamate, aspartate, N-methyl-D-aspartic acid (NMDA), and quisqualate, depolarized hippocampal neurons and caused repetitive firing. NMDA was also noted to induce burst-firing in some neurons. Quisqualate and NMDA were more potent than glutamate or aspartate. In slices perfused with a nominally calcium-free saline containing tetrodotoxin and manganese, quisqualate application produced a depolarization associated with a conductance increase. Under those conditions, NMDA-induced depolarizations caused apparent decreases as well as increases in conductance. The apparent decreases in conductance were observed in the voltage range of -40 to -70 mV, whereas increases in conductance were observed at membrane potentials more positive than -35 mV. Under voltage-clamp conditions, quisqualate produced an inward current whose amplitude increased with hyperpolarization and decreased upon depolarization, reversing near 0 mV. The conductance change induced by quisqualate was independent of voltage. NMDA application resulted in an inward current that was maximal around the resting potential and decreased with both hyperpolarization and depolarization. Response reversal was not observed with hyperpolarization to -100 mV but was apparent with depolarization beyond 0 mV. Conductance changes induced by NMDA were voltage dependent, and the application of this agent was associated with the appearance of a region of negative slope conductance in the current-voltage relationship. Apparent decreases in conductance in response to NMDA were reduced when the extracellular magnesium concentration was lowered. Response amplitudes were not affected. The NMDA receptor antagonist DL-2-amino-5-phosphonovalerate (DL-APV) was a potent and selective blocker of NMDA responses, whereas the antagonist DL-2-amino-4-phosphonobutyric acid (DL-APB) was less potent and did not select between NMDA and quisqualate responses. Analysis of iontophoretic dose-response curves indicated that DL-APV was a competitive antagonist. The results of these experiments indicate that hippocampal CA1 pyramidal neurons possess separate receptors for quisqualate and NMDA, with different pharmacological and electrophysiological profiles.
Cell Mol Neurobiol 1985 Dec
PMID:Action of excitatory amino acids and their antagonists on hippocampal neurons. 286 26

Glutamate is able to stimulate inositol phosphate (IP) formation in striatal neurons in primary culture, mainly via an excitatory amino acid receptor of the quisqualate subtype. In the present study we show that carbachol (Carb)-(a cholinergic agonist), but not neurotensin or norepinephrine-induced IP production could be reduced by 40% when measured in the presence of Glu. The inhibition of the Carb response by Glu was dose dependent and reproduced by N-methyl-D-aspartate (NMDA). Quisqualate elicited an additive response with Carb. 2-Amino-5-phosphonovalerate (APV) completely reversed the NMDA-induced inhibition. APV had no significant effect on Glu- or kainate-induced inhibition. Therefore, striatal neurons contain at least three different excitatory amino acid receptors: a quisqualate receptor triggering the stimulation of IP metabolism, and an NMDA and a kainate receptor, both able to decrease the Carb-induced IP formation.
Mol Pharmacol 1987 Sep
PMID:Dual action of excitatory amino acids on the metabolism of inositol phosphates in striatal neurons. 289 92

The properties of excitatory amino acid (EAA) receptors transplanted into Xenopus oocytes were investigated by voltage clamp 48 hr to 5 days after oocytes had been injected with mRNA isolated from rat brain. The application of EAA agonists to mRNA-injected cells, but not to uninjected or water-injected cells, produced several different inward currents, two of which are characteristic of neuronal EAA receptors. Currents with properties expected from activation of N-methyl-D-aspartate (NMDA) receptors were evoked by L-glutamate (EC50 = 2.3 microM), D-aspartate (10 microM), L-aspartate (13 microM), NMDA (31 microM), and ibotenate (35 microM). Inward currents activated by these agonists were blocked by Mg2+ in a voltage-dependent manner and antagonized by 10-50 microM D-2-amino-5-phosphonovaleric acid (D-APV). The D-APV block was not voltage dependent. A second type of inward current was produced by kainate, domoate, (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and L-glutamate. This smooth inward current was insensitive to Mg2+ and D-APV. L-Glutamate and domoate were equipotent for activating this current (EC50 = 14 microM) whereas kainate was less potent (98 microM). The kainate potency was somewhat voltage dependent, inasmuch as the EC50 was 33% lower when measured at +38 mV than when measured at -60 mV in the same cells. Quisqualate (50 microM) and AMPA (50 microM) drastically reduced the kainate current, suggesting these agonists also interact with this receptor. Some mRNA preparations encoded only receptors for the kainate response, which argues for distinct NMDA and non-NMDA receptors. A third type of inward current was produced by quisqualate. This current, consisting of oscillating and smooth components, was carried by chloride and not evoked by AMPA, suggesting it is not likely caused by activation of the conventional neuronal quisqualate receptor. The utility of the oocyte preparation for quantitative pharmacological studies of EAA receptors is discussed.
Mol Pharmacol 1988 Sep
PMID:Excitatory amino acid receptors expressed in Xenopus oocytes: agonist pharmacology. 290 62

The influence of glutamate and its analogues on the expression of BDNF mRNA was studied in cultured cerebellar granule cells. Four-hour exposure of the neurons to the glutamate receptor agonists, quisqualate, kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA), increased levels of BDNF mRNA. Glutamate in combination with antagonists of the ionotropic glutamate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), D-2-amino-5-phosphonovalerate (AP-5) and/or (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine hydrogen maleate (MK-801), also increased levels of BDNF mRNA. However, the addition of glutamate itself to the cultures produced severe neuronal death and failed to increase the mRNA level. The onset of the increase in BDNF mRNA by kainate and NMDA lagged behind that by quisqualate. These results indicate that the non-ionotropic glutamate receptor might be involved in the induction of BDNF mRNA. Quisqualate is known to be a potent agonist of both the AMPA/kainate receptor and the metabotropic glutamate receptor. The specific antagonists of the AMPA/kainate receptor, CNQX and 6,7-dinitroquinoxaline-2,3-dione (DNQX) failed to block the increase of BDNF mRNA by quisqualate. Moreover, the desensitization of the metabotropic glutamate receptor by phorbol ester abolished the increase of BDNF mRNA by quisqualate. These results suggest that stimulation of the metabotropic glutamate receptor may be the most predominant component to increase BDNF mRNA in cerebellar granule cell culture.
Brain Res Mol Brain Res 1993 May
PMID:Glutamate receptor agonists enhance the expression of BDNF mRNA in cultured cerebellar granule cells. 768 81

Metabotropic glutamate receptors (mGluRs) are G protein-linked receptors that operate through the formation of different second messengers. Utilizing quantitative autoradiographic techniques, we have characterized [3H]glutamate binding to mGluRs in discrete regions of adult rat brain. [3H]Glutamate binding, in the presence of high concentrations of alpha-amino-3-hydroxymethyl-4-isoxazolepropionic acid (10 microM), N-methyl-D-aspartate (100 microM), and 2.5 mM calcium chloride (CaCl2), was saturable. Scatchard plots were linear in all regions examined and revealed similar affinity constants of about 500 nM. The largest number of sites was found in the outer cerebral cortical layers (10 pmol/mg of protein). [3H]Glutamate binding was displaced by quisqualate, trans-1-amino-1,3-cyclopentane dicarboxylic acid (t-ACPD) (racemic mixture), and (1S,3R)-ACPD but not by (1R,3S)-ACPD. The guanine nucleotide analogue guanosine-5'-O-(3-thio) triphosphate (100 microM) reduced the binding by affecting the affinity but not the total number of sites, as predicted for G protein-coupled receptor sites. Quisqualate displacement curves were always biphasic and resolved two binding sites, with Ki values in the low nanomolar (15 nM) and micromolar (63 microM) ranges. (1S,3R)-ACPD displaced [3H]glutamate binding both in the absence and in the presence of 2.5 microM quisqualate, suggesting that both high and low affinity quisqualate sites are linked to mGluRs. (1S,3R)-ACPD competition curves were broad (Hill coefficient = 0.73) but monophasic under both conditions, with Ki values in the micromolar range (14-116 microM), suggesting that (1S,3R)-ACPD acts on the two quisqualate sites with similar apparent affinities. The regional distributions of the two sites were different. The highest levels of the high affinity quisqualate binding site were found in the cerebellar molecular layer. The highest levels of the low affinity quisqualate binding sites were found in the outer cerebral cortex. The pharmacological profile and regional distribution suggest that the high and low affinity quisqualate-sensitive components of [3H]glutamate binding sites might correspond to the mGluR1/mGluR5 and mGluR2/mGluR3 subgroups of cloned mGluRs, respectively.
Mol Pharmacol 1994 Apr
PMID:Metabotropic glutamate receptor heterogeneity in rat brain. 818 41

Oligonucleotides of consensus sequences from rat metabotropic glutamate receptor (mGluR) genes were synthesized and used to amplify human DNA by the polymerase chain reaction (PCR). Five unique human sequences homologous to these rat receptor genes were isolated including mGluR4. A human cerebellum cDNA library was screened using this amplified mGluR4 sequence as a probe and yielded clones which between them contained the complete coding sequence for human mGluR4. The coding sequence is very similar to the equivalent rat gene (90% DNA sequence identity and 97% predicted protein sequence identity). The mGluR4 cDNA was transfected in Chinese hamster ovary (CHO) cells and stable clonal cell lines were isolated. Stimulation of the expressed receptor by L-2-amino-4-phosphonobutyrate (L-AP4), L-glutamate or (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD) resulted in a reduction of forskolin-stimulated cyclic AMP (cAMP) with EC50 values of 0.2, 13 and 90 microM respectively. Quisqualate had little effect at concentrations up to 1 mM. In Northern blots mGluR4 mRNA appears to be brain-specific, and shows a distinct distribution (excluding the cerebellum), being expressed in the thalamus, hypothalamus and caudate nucleus. In situ hybridization studies on human brain sections confirmed this general pattern of distribution. The strongest mGluR4 mRNA signal was found in the cerebellar granule cells consistent with the reported distribution of mGluR4 in the rat brain. The major difference from the rat brain is the presence in the human brain of mGluR4 mRNA in the caudate nucleus and putamen.
Brain Res Mol Brain Res 1996 Apr
PMID:Molecular characterization and localization of human metabotropic glutamate receptor type 4. 873 57

Inhibitory glutamate receptors (IGluRs) are a family of ion channel proteins closely related to ionotropic glycine and gamma-aminobutyric acid (GABA) receptors; They are gated directly by glutamate; the open channel is permeable to chloride and sometimes potassium. Physiologically and pharmacologically, IGluRs most closely resemble GABA receptors; they are picrotoxin-sensitive and sometimes crossdesensitized by GABA. However, the amino acid sequences of cloned IGluRs are most similar to those of glycine receptors. Ibotenic acid, a conformationally restricted glutamate analog closely related to muscimol, activates all IGluRs. Quisqualate is not an IGluR agonist except among pulmonate molluscs and for a unique multiagonist receptor in the crayfish Austropotamobius torrentium. Other excitatory amino acid agonists are generally ineffective. Avermectins have several effects on IGluRs, depending on concentration: potentiation, direct gating, and blockade, both reversible and irreversible. Since IGluRs have only been clearly described in protostomes and pseudocoelomates, these effects may mediate the powerful antihelminthic and insecticidal action of avermectins, while explaining their low toxicity to mammals. IGluRs mediate synaptic inhibition in neurons and are expressed extrajunctionally in striated muscles. The presence of IGluRs in a neuron or muscle is independent of the presence or absence of excitatory glutamate receptors or GABA receptors in the cell. Generally, extrajunctional IGluRs in muscle have a higher sensitivity to glutamate than do neuronal synaptic receptors. Some extrajunctional receptors are sensitive in the range of circulating plasma glutamate levels, suggesting a role for IGluRs in regulating muscle excitability The divergence of the IGlu/GABA/Gly/ACh receptor superfamily in protostomes could become a powerful model system for adaptive molecular evolution. Physiologically and pharmacologically, protostome receptors are considerably more diverse than their vertebrate counterparts. Antagonist profiles are only loosely correlated with agonist profiles (e.g., curare-sensitive GABA receptors, bicuculline-sensitive AChRs), and pharmacologically identical receptors may be either excitatory or inhibitory, and permeable to different ions. The assumption that agonist sensitivity reliably connotes discrete, homologous receptor families is contraindicated. Protostome ionotropic receptors are highly diverse and straightforward to assay; they provide an excellent system in which to study and integrate fundamental questions in molecular evolution and adaptation.
Mol Neurobiol 1996 Oct
PMID:Inhibitory glutamate receptor channels. 893 47

The G-protein coupled metabotropic glutamate receptor mGlu5 plays a pivotal role as a modulator of synaptic plasticity, ion channel activity and excitotoxicity. Two splice variants, hmGlu5a and -5b have been reported previously. During screening of a human brain cDNA library for hmGlu5a, we identified a novel variant (hmGlu5d) generated by alternative splicing at the C-terminal domain. The predicted hmGlu5d protein has a C-terminal 267 amino acid shorter than that of hmGlu5a. The pattern of mRNA expression of mGluR5 variants in human brain were analyzed by RT-PCR and in situ hybridization histochemistry. RT-PCR analysis demonstrated the presence of the hmGlu5d transcript, although at low level, in human whole brain, cerebellum, cerebral cortex and hippocampus. [3H]Quisqualate displayed similar affinity at the hmGlu5 splice variants (K(D) values of 80+/-8 and 54+/-17 nM for hmGlu5a and -5d receptors, respectively). For the five mGlu agonists studied, a similar rank order of potency was observed on both hmGlu5a and -5d receptors: quisqualate>glutamate>DHPG>L-CCGI approximately ACPD. MPEP inhibited the glutamate (2 microM)-induced [Ca(2+)](i) response in hmGlu5a and -5d-HEK293 cells also with similar potency (IC(50) values 25+/-1.5 and 20+/-1.4 nM, respectively). Therefore, the large truncation of the C-terminal tail of mGlu5 does not have any apparent major effect on the potency and efficacy of agonists as measured by the [Ca(2+)](i) responses or by activation of recombinant G-protein coupled inwardly rectifying K(+) (GIRK) channel currents. The only major functional difference is the increased sensitivity of hmGlu5d to protein kinase C (PKC)-mediated desensitization, relative to hmGlu5a.
Brain Res Mol Brain Res 2002 Dec 30
PMID:Identification and characterization of a novel splice variant of the metabotropic glutamate receptor 5 gene in human hippocampus and cerebellum. 1253 26


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