  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.
