Pharmacological stimulation of group ii metabotropic glutamate receptors reduces cocaine self-administration and cocaine-induced reinstatement of drug seeking in squirrel monkeys

Abstract

Group II metabotropic glutamate receptors (mGluRs) have been implicated in regulating the psychopharmacologic effects of cocaine and other drugs of abuse. The present study investigated the interactions between the group II mGluR agonist LY379268 [(-)-2-oxa-4-aminobicyclo [3.1.0] hexane-4,6-dicarboxylate] and cocaine in squirrel monkeys whose operant behavior was maintained under a second order schedule of i.v. cocaine self-administration with or without presentations of a cocaine-paired visual stimulus, extinguished and subsequently reinstated by priming injections of cocaine with or without presentations of a cocaine-paired stimulus, and controlled by cocaine trained as a discriminative stimulus. Antagonism studies with the group II mGluR antagonist LY341495 [2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl) propanoic acid] investigated the extent to which the cocaine-modulating effects of LY379268 could be reversed by blocking group II mGluRs. Quantitative observational studies investigated the effects of LY379268 and LY341495 on species-typical behaviors, balance, and muscle resistance. Pretreatment with LY379268 reduced cocaine self-administration and cocaine-induced reinstatement of drug seeking in a dose-dependent, LY341495-reversible manner. Significant effects of LY379268 were observed both in the presence and absence of the cocaine-paired stimulus. LY379268 did not alter the discriminative stimulus effects of cocaine, nor did it markedly affect observed behavior, with the exception of an increase in visual scanning. Emesis frequently was observed after the highest dose of LY379268 (1.0 mg/kg). The results suggest that LY379268, by stimulating group II mGluRs, can attenuate the reinforcing and priming effects of cocaine at doses that do not alter its perceptibility or markedly suppress other behaviors.