Activation of mGluR7s inhibits cocaine-induced reinstatement of drug-seeking behavior by a nucleus accumbens glutamate-mGluR2/3 mechanism in rats.

The metabotropic glutamate receptor 7 (mGluR7) has been reported to be involved in cocaine and alcohol self-administration. However, the role of mGluR7 in relapse to drug seeking is unknown. Using a rat relapse model, we found that systemic administration of AMN082, a selective mGluR7 allosteric agonist, dose-dependently inhibits cocaine-induced reinstatement of drug-seeking behavior. Intracranial microinjections of AMN082 into the nucleus accumbens (NAc) or ventral pallidum, but not the dorsal striatum, also inhibited cocaine-primed reinstatement, an effect that was blocked by local co-administration of MMPIP, a selective mGluR7 antagonist. In vivo microdialysis demonstrated that cocaine priming significantly increased extracellular dopamine in the NAc, ventral pallidum and dorsal striatum, while increasing extracellular glutamate in the NAc only. AMN082 alone failed to alter extracellular dopamine, but produced a slow-onset long-lasting increase in extracellular glutamate in the NAc only. Pre-treatment with AMN082 dose-dependently blocked both cocaine-enhanced NAc glutamate and cocaine-induced reinstatement, an effect that was blocked by MMPIP or LY341497 (a selective mGluR2/3 antagonist). These data suggest that mGluR7 activation inhibits cocaine-induced reinstatement of drug-seeking behavior by a glutamate-mGluR2/3 mechanism in the NAc. The present findings support the potential use of mGluR7 agonists for the treatment of cocaine addiction.