(S)-3,5-DHPG

mGluR5 antagonists that block calcium mobilization in vitro also reverse (S)-3,5-DHPG-induced hyperalgesia and morphine antinociceptive tolerance in vivo.[Pubmed:18022146]

Brain Res. 2008 Jan 2;1187:58-66.

The present study comparatively evaluated the potency of a series of new phenylethyl[1,2,4]methyltriazines which are analogues of the classical metabotropic glutamate (mGlu) receptor subtype 5 (mGluR5) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) in blocking hyperalgesia induced by the group I mGlu receptor agonist (S)-3,5-DHPG as well as in reversing morphine antinociceptive tolerance in mice. Hyperalgesia was assessed in mice using the tail immersion test. Intrathecal (i.t.) pre-treatment with the test compounds 5-methyl-3-phenylethynyl-[1,2,4]triazine (RTI-4229-707), 5-methyl-3-(4-phenoxy-phenylethynyl-[1,2,4]triazine (RTI-4229-766), and 3-(3-methylphenylethynyl)-5-methyl-[1,2,4]triazine (RTI-4229-787) resulted in a dose-dependent blockade of (S)-3,5-DHPG-induced hyperalgesia. The inhibitory dose-50 (ID(50)) values were 0.49, 0.72 and 0.44 nmol/mouse, for RTI-4229-707, RTI-4229-766 and RTI-4229-787, respectively, compared to 18.63 nmol/mouse for MPEP. The other two compounds tested 3-(2,5-dimethylphenylethynyl)-5-methyl[1,2,4]triazine (RTI-4229-785) and 3-(2-methylphenylethynyl)-5-methyl[1,2,4]triazine (RTI-4229-828) were totally inactive. Morphine tolerance was induced in mice by implanting a 75 mg morphine pellet and assessing morphine-induced antinociception 72-h later. The morphine-pelleted mice showed a 5.5-fold tolerance to the antinociceptive effect of acute morphine compared to placebo-pelleted mice in the tail immersion test. Intracerebroventricular (i.c.v.) administration of the three active mGluR5 antagonists dose-dependently reversed morphine antinociceptive tolerance. The ID(50) values were 57.7, 25.8 and 64.3 nmol/mouse, for RTI-4229-707, RTI-4229-766 and RTI-4229-787, respectively, compared to 1050 nmol/mouse for MPEP. Similar to the hyperalgesia study, test compounds RTI-4229-785 and RTI-4229-828 were totally inactive in reversing morphine tolerance. These results are in agreement with our previous study in which we demonstrated that the same active mGluR5 antagonists blocked glutamate-mediated mobilization of internal calcium in a selective mGluR5 in vitro efficacy assay.

Behavioral and convulsant effects of the (S) enantiomer of the group I metabotropic glutamate receptor agonist 3,5-DHPG in mice.[Pubmed:15829250]

Neuropharmacology. 2005 May;48(6):779-87.

The purpose of the present studies was to investigate the behavioral and convulsant effects produced by the group I metabotropic glutamate receptor agonist (S)-3,5-dihydroxyphenylglycine (DHPG). Administered i.c.v. to mice, (S)-3,5-DHPG produced a behavioral syndrome consisting of scratching and/or facial grooming, tremors, slow forelimb clonus, rearing, and falling that increased over the dose range of 10-400 nmol. The full syndrome, produced by 400 nmol of (S)-3,5-DHPG, was antagonized by the selective mGlu1 receptor antagonist LY456236 but not by the mGlu5 receptor antagonist MPEP or the mGlu2/3 receptor antagonist LY341495. The behaviors induced by the 400 nmol dose were not blocked by the NMDA receptor antagonist MK-801, but were attenuated by the non-NMDA receptor antagonists GYKI 52466 and NBQX, and the Ca2+ mobilization inhibitor dantrolene, but at motor-impairing doses. The scratching behaviors produced by 30 nmol of (S)-3,5-DHPG were antagonized by LY456236 but not by MPEP, LY341495 or MK-801. GYKI 52466 and dantrolene, but not NBQX, inhibited scratching at motor-impairing doses. Both 400 and 30 nmol of (S)-3,5-DHPG produced a generalized seizure as recorded by surface EEG electrodes. LY456236 blocked the seizures produced by 30 nmol but not by 400 nmol; dantrolene was ineffective in blocking seizures produced by either dose. The present findings suggest that (S)-3,5-DHPG produces an increase in excitation that is mediated by mGlu1 and non-NMDA receptors.

Face-washing behavior induced by the group I metabotropic glutamate receptor agonist (S)-3,5-DHPG in mice is mediated by mGlu1 receptor.[Pubmed:18378225]

Eur J Pharmacol. 2008 May 31;586(1-3):212-6.

It is known for the non-selective group I metabotropic glutamate (mGlu) receptors agonist (S)-3,5-dihydroxyphenylglycine (S-3,5-DHPG) to cause convulsions, which are mediated by mGlu1 receptor. However, the behavioral changes other than convulsions caused by (S)-3,5-DHPG have not been well studied. The purpose of the present study was to explore the behavioral changes elicited by activation of group I mGlu receptors with (S)-3,5-DHPG and to clarify which, mGlu1 receptor or mGlu5 receptor, is responsible for such behavior. (S)-3,5-DHPG at doses of 3-30 nmol caused characteristic face-washing behavior. This behavioral change was inhibited by both the competitive mGlu1 receptor antagonists (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) and (S)-4-carboxyphenylglycine (S-4CPG) and the non-competitive mGlu1 receptor antagonist, 4-[1-(2-fluoropyridin-3-yl)-5-methyl-1H-1,2,3-triazol-4-yl]-N-isopropyl-N-methyl- 3,6-dihydropyridine-1(2H)-carboxamide (FTIDC), but not by the mGlu5 receptor antagonist 2-Methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP), the mGlu2/3 receptor agonist (-)-2-oxa-4-aminobicyclo[3.1.0]hexane-4,6-dicarboxylate (LY379268), the mGlu2/3 receptor antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (LY341495), the N-methyl-d-asparate (NMDA) receptor antagonist 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801), or the competitive non-NMDA receptor antagonist 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX). These findings indicate that face-washing behavior is due to selective activation of mGlu1 receptor by (S)-3,5-DHPG, and that the face-washing behavior induced by (S)-3,5-DHPG in mice can be used for in vivo testing of the antagonistic potency of both competitive and non-competitive mGlu1 receptor antagonists.

Effect of (S)-3,5-DHPG on microRNA expression in mouse brain.[Pubmed:22309833]

Exp Neurol. 2012 Jun;235(2):497-507.

MicroRNAs are small non-coding RNAs that regulate post-transcriptional gene expression. In the short time since the discovery of microRNAs, the literature has burgeoned with studies focused on the biosynthesis of microRNAs, target prediction and binding, and mechanisms of translational repression by microRNAs. Given the prominent role of microRNAs in all areas of cell biology, it is not surprising that microRNAs are also linked to human diseases, including those of the nervous system. One of the least-studied areas of microRNA research is how their expression is regulated outside of development and cancer. Thus, we examined a role for regulation of microRNAs by neurotransmitter receptor activation in mouse brain. We focused on the group I metabotropic glutamate receptors by using intracerebroventricular injection of the selective agonist, (S)-3,5-dihydroxyphenylglycine (DHPG) in mouse brain. We then examined the expression of microRNAs in the cerebral cortex by Ambion and Invitrogen microarrays, and the expression of mature microRNA sequences by SABiosciences qPCR arrays, at 4, 8 and 24 h after DHPG injection. These studies revealed that the largest number of significantly regulated microRNAs was detected 8h after DHPG injection in the microarrays and qPCR arrays. We then used RNA blots to quantify microRNA expression, and in situ hybridization to examine cellular distribution of the microRNAs regulated by DHPG. Bioinformatic analysis of the microRNAs regulated 8 h after DHPG in all three arrays revealed KEGG pathways that are known to correlate with group I mGluR effects, as well as recently described and novel pathways. These studies are the first to show that DHGP regulates the expression of microRNAs in mouse cerebral cortex, and support the hypothesis that group I mGluRs may regulate microRNA expression in mouse brain.

(S)-3,5-DHPG: a review.[Pubmed:12070529]

CNS Drug Rev. 2002 Spring;8(1):101-16.

3,5-dihydroxyphenylglycine (3,5-DHPG) was the first agonist shown to be group I metabotropic glutamate receptor selective with its agonist effects residing exclusively in the S-isomer. Some results suggest that (S)-3,5-DHPG may be a partial agonist of mGluR1a and mGluR5a in neurons and astrocytes. It has been reported that (S)-3,5-DHPG can, under certain conditions, interact with NMDA receptors. (S)-3,5-DHPG exerts different effects on second messengers in adult and neonatal tissues. It stimulates phosphoinositide hydrolysis in a dose-dependent manner in both the adult and neonate hippocampus, inhibits stimulated cAMP levels in the adult and enhances the cAMP in the neonate. It is an effective antagonist of mGluRs linked to phospholipase D (PLD) in the adult and an agonist in the neonate brain or astrocyte cultures. (S)-3,5-DHPG induces elevation of [Ca2+]i and regulates multiple subtypes of Ca2+ channels. This agonist of group I mGluRs may modulate neurotransmitters release, reflecting the diversity of mechanisms involved. Depending on the dose, (S)-3,5-DHPG enhances or decreases excitatory postsynaptic potentials (EPSPs) and under appropriate conditions it can induce long-term depression (LTD) and long-term potentiation (LTP). Some studies suggested a therapeutic role for (S)-3,5-DHPG in neuronal injury, regulation of intestinal motility and secretion, learning and memory processes and in cardiovascular system. (S)-3,5-DHPG may be useful as a cognitive enhancing agent in memory impairment associated with ischemia or hypoxia. Recent investigations suggested possible beneficial effects of (S)-3,5-DHPG in Alzheimer's disease.

Structure-activity relationships of new agonists and antagonists of different metabotropic glutamate receptor subtypes.[Pubmed:8730745]

Br J Pharmacol. 1996 Apr;117(7):1493-503.

1. We investigated the agonist and antagonist activities of 22 new phenylglycine and phenylalanine derivatives for metabotropic glutamate receptors (mGluRs) by examining their effects on the signal transduction of mGluR1, mGluR2 and mGluR6 subtypes expressed in Chinese hamster ovary cells. This analysis revealed several structural characteristics that govern receptor subtype specificity of the agonist and antagonist activities of phenylglycine derivatives. 2. Hydroxyphenylglycine derivatives possessed either an agonist activity on mGluR1/mGluR6 or an antagonist activity on mGluR1. 3. Carboxyphenylglycine derivatives showed an agonist activity on mGluR2 but an antagonist activity on mGluR1. 4. alpha-Methylation or alpha-ethylation of the carboxyphenylglycine derivatives converts the agonist property for mGluR2 to an antagonist property, thus producing antagonists at both mGluR1 and mGluR2. 5. Structurally-corresponding phenylalanine derivatives showed little or no agonist or antagonist activity on any subtypes of the receptors. 6. This investigation demonstrates that the nature and positions of side chains and ring substituents incorporated into the phenylglycine structure are critical in determining the agonist and antagonist activities of members of this group of compounds on different subtypes of the mGluR family. 7. We also tested two alpha-methyl derivatives of mGluR agonists. (2S, 1'S, 2'S)-2-(2-Carboxycyclopropyl)glycine (L-CCG-I) is a potent agonist for mGluR2 but alpha-methylation of this compound changes its activity to that of an mGluR2-selective antagonist. In contrast, alpha-methylation of L-2-amino-4-phosphonobutyrate (L-AP4) results in retention of an agonist activity on mGluR6. Thus, alpha-methylation produces different effects, depending on the chemical structures of lead compounds and/or on the subtype of mGluR tested.

3,5-dihydroxyphenylglycine is a highly selective agonist for phosphoinositide-linked metabotropic glutamate receptors in the rat hippocampus.[Pubmed:8035201]

J Neurochem. 1994 Aug;63(2):769-72.

Metabotropic glutamate receptors (mGluRs) are a heterogeneous family of G protein-coupled glutamate receptors that are linked to multiple second messenger systems in the CNS. In this study the selectivity of mGluR agonists for different mGluR second messenger effects was characterized in slices of the rat hippocampus. The mGluR agonists (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid and (2S,3S,4S)alpha-(carboxycyclopropyl)glycine produced multiple effects on second messengers that included enhanced phosphoinositide hydrolysis in both adult and neonatal rat hippocampus, inhibition of forskolin-stimulated cyclic AMP (cAMP) formation in adult tissue, and increases in basal cAMP formation in the neonatal hippocampus. In contrast, 3,5-dihydroxyphenylglycine was potent and effective in increasing phosphoinositide hydrolysis in both adult and neonatal hippocampus but unlike the other mGluR agonists did not inhibit forskolin-stimulated cAMP formation (in the adult) or substantially enhance basal cAMP formation (in the neonate). Thus, in the rat hippocampus mGluR agonist-mediated increases or decreases in cAMP formation are not secondary to mGluR-mediated changes in phosphoinositide hydrolysis. Furthermore, 3,5-dihydroxyphenylglycine can be used to activate subpopulations of mGluRs coupled to phosphoinositide hydrolysis with minimal effects on cAMP-mGluR second messenger systems.