Baclofen inhibits opiate-induced conditioned place preference and associated induction of Fos in cortical and limbic regions.

In C57BL/6 mice, pretreatment with GABA(B) receptor agonist baclofen blocked the rewarding effects of morphine as measured by acquisition of conditioned place preference. Fos immunoreactivity, a neuronal activity marker, was induced in opiate conditioned mice in several forebrain regions including the nucleus accumbens core and shell, anterior cingulate cortex, and prelimbic cortex. Baclofen pretreatment blocked the induction of Fos in opiate conditioned subjects. These result suggest that GABA(B) receptor transmission has a role in reversing morphine-induced activation of motivational circuitry and conditioned reward.