(RS)-MCPG

(RS)-MCPG is a non-selective group I/group II metabotropic glutamate receptor antagonist.

References:
[1]. Yang B et al. Regulation of GABA Equilibrium Potential by mGluRs in Rat Hippocampal CA1 Neurons. PLoS One, 2015 Sep 21, 10(9):e0138215. [2]. Eaton SA et al. Competitive antagonism at metabotropic glutamate receptors by (S)-4-carboxyphenylglycine and (RS)-alpha-methyl-4-carboxyphenylglycine. Eur J Pharmacol. 1993 Jan 15;244(2):195-7. [3]. Watkins J et al. Phenylglycine derivatives as antagonists of metabotropic glutamate receptors. Trends Pharmacol Sci. 1994 Sep;15(9):333-42.

Agonist action of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) in the amygdala.[Pubmed:7632895]

Neuroreport. 1995 May 9;6(7):1058-62.

Glutamatergic excitatory postsynaptic potentials (EPSPs) in the basolateral amygdala (BLA) are reduced in amplitude following agonist activation of presynaptic metabotropic glutamate receptors (mGluR). In this study, the effect of a presumed mGluR antagonist, (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG), was investigated on the EPSP recorded intracellularly in BLA neurons. Superfusion of MCPG (500 microM) significantly reduced the amplitude of evoked EPSPs. In the presence of MCPG, postsynaptic responses to alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA, 1 microM) were unaltered while responses to N-methyl-D-aspartate (NMDA, 3-5 microM) were potentiated. These data suggest that the MCPG-induced reduction of EPSP amplitude is due to a mGluR agonist action at a presynaptic mGluR 'autoreceptor'.

The metabotropic glutamate receptor antagonist (RS)-MCPG produces hyperlocomotion in amphetamine pre-exposed rats.[Pubmed:9680243]

Neuropharmacology. 1998;37(2):189-97.

It is known that, over a wide range of doses, the selective metabotropic glutamate receptor (mGluR) agonist, 1-aminocyclopentane-trans-1,3-dicarboxylic acid [(1S,3R)-ACPD], increases locomotion whereas the selective mGluR antagonist, (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) [(RS)-MCPG], is without effect when microinjected into the nucleus accumbens (NAcc) of drug-naive rats. The present experiments determined whether these responses are altered by pre-exposing rats to a regimen of systemic amphetamine (AMPH) injections known to produce locomotor sensitization. Rats in different groups were administered four injections of saline or AMPH (1.0 mg/kg, i.p.), one injection every third day. Two weeks after the last injection, rats were challenged with microinjections of either saline, (RS)-MCPG (2.5 nmole/side) or (1S,3R)-ACPD (0.5 nmole/side) into the NAcc. While (1S,3R)-ACPD increased locomotor activity when injected into the NAcc, no significant difference between saline and AMPH pre-exposed rats was observed. However, and interestingly, (RS)-MCPG which had no effect on locomotor activity when given to saline pre-exposed rats induced significantly higher locomotor activity in AMPH compared to saline pre-exposed rats. These results indicate that glutamatergic neurotransmission mediated by mGluRs in the NAcc is altered by repeated systemic injections of AMPH. Such changes may ultimately position the mGluR to contribute to the expression of sensitization by AMPH as well as other psychomotor stimulant drugs.

(RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) does not block theta burst-induced long-term potentiation in area CA1 of rat hippocampal slices.[Pubmed:8041499]

Neurosci Lett. 1994 Mar 28;170(1):17-21.

We have used the selective metabotropic glutamate receptor antagonist (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) to investigate in the CA1 hippocampal subregion in vitro whether coactivation of N-methyl-D-aspartate (NMDA) and metabotropic glutamate receptors is necessary for the induction of long-term potentiation (LTP) when LTP is induced by theta burst stimulation (TBS). When MCPG (500 microM) was bath applied 14-30 min prior to a triple high-frequency tetanization (100 Hz, 1 s) and washed out immediately afterwards the potentiation of the extracellularly recorded field potentials decayed gradually to baseline (P < 0.05) over 2-3 h. However, when MCPG was applied in the same manner before a triple TBS (10 bursts at 5 Hz, 100 Hz within the bursts) the resulting potentiation remained stable for at least 4 h. MCPG had no effect on baseline synaptic transmission or post-tetanic potentiation. These results demonstrate a clear difference in the mechanisms underlying these two different forms of LTP.

Molecular, functional, and pharmacological characterization of the metabotropic glutamate receptor type 5 splice variants: comparison with mGluR1.[Pubmed:7751958]

J Neurosci. 1995 May;15(5 Pt 2):3970-81.

The main excitatory neurotransmitter in the brain, glutamate (Glu), activates not only receptor-channels, but also receptors coupled to G-protein called metabotropic Glu receptors (mGluRs). Eight genes coding for mGluRs have been characterized to date giving rise to even more proteins due to alternative splicing phenomena. Here we characterized a splice variant of mGluR5, called mGluR5b which contains a 32 amino acid fragment inserted in the cytoplasmic tail, 50 residues after the 7th transmembrane domain. mGluR5b mRNAs are present in different regions of the adult rat brain and are expressed at a higher level than mGluR5a mRNA. Functional analysis of mGluR5a and mGluR5b revealed that they share all the properties of mGluR1a, but not those of mGluR1b or 1c. Like mGluR1a, both mGluR5a and mGluR5b activate a rapid and transient current in Xenopus oocytes. When expressed in LLC-PK1 cells, they show the same subcellular distribution as mGluR1a, and stimulate both inositol phosphate (IP) and cAMP production. Moreover, cells expressing mGluR5a or mGluR5b, like those expressing mGluR1a have a higher basal PLC activity that is not inhibited by glutamate-pyruvate transaminase (GPT), suggesting that these receptors have an intrinsic activity. Interestingly, the pharmacological profiles of mGluR5a and b are identical, but different from that of mGluR1a. Most agonists, except glutamate, are more potent on mGluR5a/b than on mGluR1a. Interestingly, the mGluR1a antagonists MCPG and 4CPG have no effect on mGluR5a/b; 4C3HPG which is a full antagonist at mGluR1a is a partial agonist at mGluR5a/b. These results indicate that the long C-terminal intracellular domain present only in mGluR1a and mGluR5a/b, although not well conserved, is likely to be involved in the specific functional properties of these receptors. Although the ligand recognition sites of mGluR5a/b and mGluR1a are highly conserved, these receptors have different pharmacology.

Phenylglycine derivatives as antagonists of metabotropic glutamate receptors.[Pubmed:7992387]

Trends Pharmacol Sci. 1994 Sep;15(9):333-42.

Metabotropic glutamate receptors represent a family of G protein-coupled receptors that can be activated by L-glutamate, the principal excitatory neurotransmitter in the brain. Until recently, progress in identifying the physiological and pathological roles of metabotropic glutamate receptors has been hampered by the lack of selective antagonists. In this article, Jeff Watkins and Graham Collingridge describe the pharmacology of, and initial physiological studies using, certain phenylglycine derivatives and related substances--the first definitive antagonists of metabotropic glutamate receptors.

Competitive antagonism at metabotropic glutamate receptors by (S)-4-carboxyphenylglycine and (RS)-alpha-methyl-4-carboxyphenylglycine.[Pubmed:8381746]

Eur J Pharmacol. 1993 Jan 15;244(2):195-7.

Two phenylglycine derivates, (S)-4-carboxyphenylglycine and (RS)-alpha-methyl-4-carboxyphenylglycine, competitively antagonised (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate (ACPD)-stimulated phosphoinositide hydrolysis in rat cerebral cortical slices. The same phenylglycine derivatives selectively antagonized ACPD-induced depolarization in neonatal rat spinal motoneurones and rate thalamic neurones relative to depolarization or excitation induced by N-methyl-D-aspartate (NMDA) or alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Both phenylglycine derivatives also selectively depressed synaptic excitation in thalamic neurones evoked by noxious thermal stimuli, without affecting the synaptic stimulation of the same cells by non-noxious stimuli.

(RS)-MCPG (alpha-MCPG) is a competitive and selective group I/group II metabotropic glutamate receptor (mGluR) antagonist. (RS)-MCPG blocks theta-burst stimulation (TBS)-induced shifts in both juvenile and neonatal rat hippocampal neurons.

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