The negative allosteric modulator of mGluR5, MPEP, potentiates the rewarding properties of cocaine in priming-induced reinstatement of CPP.

Cocaine addiction is a chronic disorder with high relapse rates; therefore, understanding the neuronal mechanisms underlying drug-seeking during relapse is a priority to develop targeted pharmacotherapy. The metabotropic glutamate receptor 5 (mGluR5) seems to be involved in the reinstatement induced by cocaine-associated cues. The main objective of the study was to evaluate the efficacy of MPEP, a negative allosteric modulator of mGluR5, in attenuating or potentiating the reinstatement induced by priming doses of cocaine in the CPP paradigm, ultimately to further knowledge regarding the role of the mGluR5 in relapse into cocaine abuse. OF1 mice (48 female and 48 male) were conditioned in the CPP paradigm with cocaine (20 mg/kg) and were exposed to an extinction program. We evaluated the efficacy of MPEP (30 mg/kg) in blocking the successive cocaine-priming reinstatements in the CPP when extinction of the conditioning preference was confirmed. MPEP did not block the reinstatement of priming cocaine-induced CPP, but increased the potential of cocaine for reinstating conditioning preference. The contingent administration of MPEP with cocaine increased the drug-seeking behaviour and the number of reinstatements with priming doses of cocaine. Moreover, MPEP produced cross reinstatement of cocaine-induced CPP. Rather than preventing the reinstatements of conditioned preference induced by priming doses of cocaine, MPEP increased them. These findings may help to understand the role of mGluR5 in the relapse into cocaine abuse.