mGluR5 Knockout mice exhibit normal conditioned place-preference to cocaine

TL;DR

This study shows that mGluR5 knockout mice display normal conditioned place preference to cocaine, challenging previous findings that suggested mGluR5 is essential for cocaine reward.

Contribution

The paper demonstrates that mGluR5 is not necessary for cocaine conditioned place preference, providing new insights into its modulatory role rather than an essential one.

Findings

mGluR5 -/- mice show normal cocaine place preference

Locomotor response to cocaine is not abolished in mGluR5 -/- mice

mGluR5 receptors have a modulatory, not essential, role in cocaine effects

Abstract

Metabotropic glutamate receptor 5 (mGluR5) null mutant (-/-) mice have been reported to totally lack the rein- forcing or locomotor stimulating effects of cocaine. We tested mGluR5 -/- and +/+ mice for their locomotor and conditioned place- preference response to cocaine. Unlike the previous finding, here we show that compared to mGluR5 +/+ mice, -/- mice exhibit no difference in the locomotor response to low to moderate doses of cocaine (10 or 20 mg/kg). A high dose of cocaine (40 mg/kg) resulted in a blunted rather than absent locomo- tor response. We tested mGluR5 -/- and +/+ mice for conditioned place-preference to cocaine and found no group differences at a conditioning dose of 10 mg/kg, suggesting normal conditioned rewarding properties of cocaine. These results differ substantially from Chiamulera et al. (2001) and replicates Olsen et al., (2010), who found normal cocaine place-preference in mGluR5 -/- mice at 5 mg/kg. Our results indicate mGluR5 receptors exert a modulatory rather than necessary role in cocaine-induced locomotor stimulation and exert no effect on the conditioned rewarding effects of cocaine.