MPEP

MPEP is a selective and systemically active antagonist of metabotropic glutamate receptor subtype 5 (mGlu5 receptor) with IC50 value of 36nM [1].

MPEP is an antagonist of mGlu5 receptor. It is used as a valuable pharmacological tool to explore the function of its target receptor due to its high selectivity. In L (tk-) cells expressing human mGlu1b receptors, MPEP completely inhibits quisqualate-induced PI hydrolysis with IC50 value of 36nM. MPEP shows no effect in CHO-K1 cells expressing mGlu1b receptor or in L (tk-) mGlu5a cell line. In addition, 100μM MPEP also has no effect on group II and III mGlu receptor subtypes. Moreover, MPEP inhibits the DHPG induced PI hydrolysis in hippocampal, striatal and cortical slices with IC50 values of 8nM, 20.5nM and 17.9nM, respectively. Furthermore, microiontophoretical delivery of MPEP reduces DHPG-induced excitations in vivo. MPEP also shows anxiolytic-or antidepressant-like effects in the Vogel test in rats and in the tail suspension test in mice [1, 2].

References:
[1] Gasparini F, Lingenhöhl K, Stoehr N, et al. 2-Methyl-6-(phenylethynyl)-pyridine (MPEP), a potent, selective and systemically active mGlu5 receptor antagonist. Neuropharmacology, 1999, 38(10): 1493-1503.
[2] Tatarczyńska E, Kłodzińska A, Chojnacka-Wójcik E, et al. Potential anxiolytic-and antidepressant-like effects of MPEP, a potent, selective and systemically active mGlu5 receptor antagonist. British journal of pharmacology, 2001, 132(7): 1423-1430.

Chronic oral administration of MPEP, an antagonist of mGlu5 receptor, during gestation and lactation alters mGlu5 and A2A receptors in maternal and neonatal brain.[Pubmed:28012867]

Neuroscience. 2017 Mar 6;344:187-203.

Antidepressant and anxiolytic drugs are widely consumed even by pregnant and lactating women. The metabotropic glutamate receptor 5 (mGlu5) antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) exerts antidepressant- and anxiolytic-like actions. Given that treatment for anxiety and depression use to be prolonged in time, it is conceivable a possible modulation of metabotropic glutamate receptors (mGlu receptors) after prolonged MPEP exposure, which could also modify adenosine A2A receptors (A2AR) since functional cross-talk between them has been reported. Here we report that MPEP crosses placental barrier and reaches neonatal brain through maternal milk using LC-MS/MS methods. Therefore, we analyzed mGlu receptors, mainly mGlu5, and A2AR in both maternal and fetal brain after chronic maternal consumption of MPEP during gestation and/or lactation using radioligand binding, Western-blotting, real-time PCR and phospholipase C (PLC) activity assays. In maternal brain, chronic MPEP consumption caused a significant loss of mGlu, including mGlu5, and A2AR receptors level in plasma membrane. PLC activity assays showed that mGlu5 signaling pathway was desensitized. No variations on mRNA level coding A2AR, A1R and mGlu5 were found after MPEP treatments. In female neonatal brain, maternal consumption of MPEP caused a significant increase in mGlu, including mGlu5, and A2AR receptors level. Neither mGlu receptors nor A2AR were modified in male neonatal brain after maternal MPEP intake. Finally, neither molecular nor behavioral changes (anxiety- and depression-like behavior) were observed in 3-month-old female offspring. In summary, mGlu5 and A2AR are altered in both maternal and female neonatal brain after chronic maternal consumption of MPEP during gestation and/or lactation.

The mGluR5 antagonist MPEP suppresses the expression and reinstatement, but not the acquisition, of the ethanol-conditioned place preference in mice.[Pubmed:26521964]

Pharmacol Biochem Behav. 2016 Jan;140:33-8.

The glutamatergic system may play a vital role in regulating neurobehavioral effects of various drugs of abuse. In the present study, we evaluated the effects of 2-methyl-6-(phenylethynyl)-pyridine (MPEP), a selective antagonist of the type 5 metabotropic glutamate receptor (mGluR5) on the acquisition, expression and reinstatement of ethanol conditioned place preference (CPP). In the ethanol acquisition study, mice were conditioned with saline or ethanol (20% v/v, 2g/kg) on alternating days for 8 consecutive days and were given MPEP 10 min before ethanol conditioning. In another experiment, animals were conditioned with 2g/kg ethanol and MPEP was administered 10 min prior to the post-conditioning test. In a reinstatement study, following the extinction phase, animals were pretreated with MPEP 10 min prior to a priming injection of 1.0 g/kg ethanol. The mGluR5 antagonist MPEP significantly reduced the expression and the reinstatement in dose-dependent manner, but not acquisition of ethanol-induced CPP. These results indicate that mGluR5 may be involved in the expression and reinstatement of conditioned rewarding effects of ethanol, but not the acquisition of ethanol, which provide an evidence that mGluR5 blockade might make dissociable contributions during the training (acquisition phase), the performance of behavior (expression phase) and reinstatement.

Conserved Hypothalamic c-Fos Activation Pattern Induced by the mGlu5 Receptor Antagonist MPEP during Peri-pubertal Development in Mice.[Pubmed:27101232]

Pharmacopsychiatry. 2016 Jul;49(4):142-5.

INTRODUCTION: 2-Methyl-6-(phenylethynyl)pyridine (MPEP) is a selective mGlu5 receptor (mGluR5) antagonist intensively studied as potential novel anxiolytic drug. In the adult, MPEP activates stress-related areas, including the paraventricular nucleus of the hypothalamus (PVNh). However, it is unknown if MPEP targets similar structures in the juvenile brain as well. METHODS: Here we examined by immunohistochemical methods the induction pattern of the neuronal activity marker c-Fos by MPEP at peri-pubertal stages (postnatal day P16, P24, P32 and P40) in C57BL6/N mice. RESULTS: Despite the previously reported sharply diminished hypothalamic mGluR5 expression during postnatal development, we found a highly conserved PVNh activation by MPEP together with c-Fos expression in the extended amygdala. Interestingly, MPEP also robustly activated the paraventricular nucleus of the thalamus (PVT) and suprachiasmatic nucleus (SCN), regions associated with the modulation of circadian rhythms. DISCUSSION: These results indicate a conserved activation pattern induced by MPEP in the young vs. adult brain especially in brain areas regulating stress and circadian rhythms and may be of importance regarding the effect of mGluR5 antagonists in the treatment of mood disorders during juvenile development.

Influence of MPEP (a selective mGluR5 antagonist) on the anticonvulsant action of novel antiepileptic drugs against maximal electroshock-induced seizures in mice.[Pubmed:26478256]

Prog Neuropsychopharmacol Biol Psychiatry. 2016 Feb 4;65:172-8.

The aim of this study was to determine the effects of 2-methyl-6-(phenylethynyl)pyridine (MPEP - a selective antagonist for the glutamate metabotropic receptor subtype mGluR5) on the protective action of some novel antiepileptic drugs (lamotrigine, oxcarbazepine, pregabalin and topiramate) against maximal electroshock-induced seizures in mice. Brain concentrations of antiepileptic drugs were measured to determine whether MPEP altered pharmacokinetics of antiepileptic drugs. Intraperitoneal injection of 1.5 and 2mg/kg of MPEP significantly elevated the threshold for electroconvulsions in mice, whereas MPEP at a dose of 1mg/kg considerably enhanced the anticonvulsant activity of pregabalin and topiramate, but not that of lamotrigine or oxcarbazepine in the maximal electroshock-induced seizures in mice. Pharmacokinetic results revealed that MPEP (1mg/kg) did not alter total brain concentrations of pregabalin and topiramate, and the observed effect in the mouse maximal electroshock seizure model was pharmacodynamic in nature. Collectively, our preclinical data suggest that MPEP may be a safe and beneficial adjunct to the therapeutic effects of antiepileptic drugs in human patients.

MPEP is a potent and highly selective non-competitive antagonist at the mGlu5 receptor subtype (IC50 = 36 nM) and a positive allosteric modulator at mGlu4 receptors.

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