MPEP hydrochloride is a highly selective and potent non-competitive antagonist at the mGlu5 (metabotropic glutamate receptor subtype 5) receptor subtype (IC50 = 36 nM). It is a positive allosteric modulator at mGlu4. MPEP hydrochloride reduces DHPG (S-3, 5-dihydroxyphenylglycine)-induced excitations but not the excitations induced by AMPA (-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid). In vivo studies show it reverses mechanical hyperalgesia in the inflamed rat hind paw. MW: 229.71. Purity ≥98% by HPLC