Metabotropic glutamate receptors in GtoPdb v.2021.3

Metabotropic glutamate (mGlu) receptors (nomenclature as agreed by the NC-IUPHAR Subcommittee on Metabotropic Glutamate Receptors [347]) are a family of G protein-coupled receptors activated by the neurotransmitter glutamate [138]. The mGlu family is composed of eight members (named mGlu1 to mGlu8) which are divided in three groups based on similarities of agonist pharmacology, primary sequence and G protein coupling to effector: Group-I (mGlu1 and mGlu5), Group-II (mGlu2 and mGlu3) and Group-III (mGlu4, mGlu6, mGlu7 and mGlu8) (see Further reading).Structurally, mGlu are composed of three juxtaposed domains: a core G protein-activating seven-transmembrane domain (TM), common to all GPCRs, is linked via a rigid cysteine-rich domain (CRD) to the Venus Flytrap domain (VFTD), a large bi-lobed extracellular domain where glutamate binds. mGlu form constitutive dimers, cross-linked by a disulfide bridge. The structures of the VFTD of mGlu1, mGlu2, mGlu3, mGlu5 and mGlu7 have been solved [198, 271, 264, 399]. The structure of the 7 transmembrane (TM) domains of both mGlu1 and mGlu5 have been solved, and confirm a general helical organization similar to that of other GPCRs, although the helices appear more compacted [87, 429, 61]. Recent advances in cryo-electron microscopy have provided structures of full-length mGlu receptor dimers [189]. Studies have revealed the possible formation of heterodimers between either group-I receptors, or within and between group-II and -III receptors [88]. First well characterized in transfected cells, co-localization and specific pharmacological properties also suggest the existence of such heterodimers in the brain [266].[436, 143, 279]. Beyond heteromerization with other mGlu receptor subtypes, increasing evidence suggests mGlu receptors form heteromers and larger order complexes with class A GPCRs (reviewed in [138]). The endogenous ligands of mGlu are L-glutamic acid, L-serine-O-phosphate, N-acetylaspartylglutamate (NAAG) and L-cysteine sulphinic acid. Group-I mGlu receptors may be activated by 3,5-DHPG and (S)-3HPG [30] and antagonized by (S)-hexylhomoibotenic acid [232]. Group-II mGlu receptors may be activated by LY389795 [265], LY379268 [265], eglumegad [350, 430], DCG-IV and (2R,3R)-APDC [351], and antagonised by eGlu [168] and LY307452 [421, 103]. Group-III mGlu receptors may be activated by L-AP4 and (R,S)-4-PPG [128]. An example of an antagonist selective for mGlu receptors is LY341495, which blocks mGlu2 and mGlu3 at low nanomolar concentrations, mGlu8 at high nanomolar concentrations, and mGlu4, mGlu5, and mGlu7 in the micromolar range [183]. In addition to orthosteric ligands that directly interact with the glutamate recognition site, allosteric modulators that bind within the TM domain have been described. Negative allosteric modulators are listed separately. The positive allosteric modulators most often act as ‘potentiators’ of an orthosteric agonist response, without significantly activating the receptor in the absence of agonist.

Effects of metabotropic glutamate receptor antagonists on a rat model of maximum electroshock

AIM: This study aimed to investigate the effect of metabotropic glutamate (mGlu) receptor antagonists on the development of seizure caused by maximum electric shock (MES) and the content of lipid peroxidation (LPO) products in the brain of rats. MATERIALS AND METHODS: Experiments were carried out on male Wistar rats (n = 87) with a mass of 180210 g. In this work, MES was administered. Selective antagonists of I and V subtype mGlu receptors were administered 1 h before MES was administered. Control rats were injected an equivalent amount of saline. The intensity of LPO processes was assessed in terms of the level of secondary products reacting with thiobarbituric acid via a spectrophotometric method. RESULTS: MES led to the development of pronounced clonictonic seizures and increased the level of LPO products in the cerebral cortex of rats by more than threefold. A selective antagonist of subtype V mGlu receptors almost completely stopped the tonic phase of rat seizures and largely prevented the intensification of LPO processes caused by MES. Tonic convulsions were observed in 44% of the experimental animals after the administration of a selective subtype I mGlu receptor antagonist. This antagonist also partially reduced the content of LPO products caused by the effect of MES. CONCLUSION: Thus, mGlu receptors are involved in the development of MES-induced seizures in rats. The most pronounced weakening of convulsive manifestations and the prevention of an increase in the level of LPO products caused by MES were observed in the block of subtype V mGlu receptors. The obtained data confirmed the possibility of using subtype V metabotropic receptor antagonists as anticonvulsants for the treatment of epilepsy with generalized convulsive seizures.