IC50: 36 nM

MPEP is a potent, selective and systemically active mGlu5 receptor antagonist.

Metabotropic glutamate (mGlu) receptors are a of G-protein-coupled receptor family linked to multiple second messengers and modulation of ion channel functions in the nervous system. Group I receptors (mGlu1 and -5) couple to phospholipase C and up or down regulate neuronal excitability (Gereau and Conn, 1995) whereas group II (mGlu2 and -3) and group III (mGlu4, -6, -7, and -8) receptors inhibit adenylyl cyclase and reduce synaptic transmission.

In vitro: In recombinant expressed cells human mGlu5a receptor, MPEP inhibited quisqualate-stimulated phosphoinositide hydrolysis completely with an IC50 value of 36 nM whereas with no agonist or antagonist activities at cells expressing the human mGlu1b receptor. MPEP did not show agonist or antagonist activity on human mGlu2, -3, -4a, -7b, and -8a receptors [1].

In vivo: In rat neonatal brain slices, MPEP inhibited DHPG-stimulated phosphoinositide hydrolysis with a potency and selectivity similar to that observed on human mGlu receptors. Moreover, in extracellular recordings in the hippocampus CA1 area of anesthetized rats, the microiontophoretic application of DHPG induced neuronal firing that was blocked when MPEP was administered [1].

Clinical trial: N/A

Reference:
[1] Gasparini F,Lingenhhl K,Stoehr N,Flor PJ,Heinrich M,Vranesic I,Biollaz M,Allgeier H,Heckendorn R,Urwyler S,Varney MA,Johnson EC,Hess SD,Rao SP,Sacaan AI,Santori EM,Velielebi G,Kuhn R.  2-Methyl-6-(phenylethynyl)-pyridine (MPEP), a potent, selective and systemically active mGlu5 receptor antagonist. Neuropharmacology.1999 Oct;38(10):1493-503.