Clonidine antagonizes the aversive effects of opiate withdrawal and the rewarding effects of morphine only in opiate withdrawn rats.

The researchers asked whether clonidine, an alpha 2-noradrenergic agonist, would block selectively the motivational effects of opiate withdrawal and whether clonidine's effects would respect the boundary between nondeprived and deprived motivational states. In a place conditioning paradigm, clonidine (0.05 mg/kg ip) blocked the rewarding effects of morphine in opiate-withdrawn rats (as well as the aversive properties of withdrawal itself), but did not affect morphine place preferences (2 and 20 mg/kg) in drug-naive rats. Furthermore, clonidine blocked the acquisition of morphine (15 mg/kg), but not LiCl (15 mg/kg), conditioned taste aversions in water-deprived rats. The results suggest that the motivational system activated in deprived animals includes dopaminergic and noradrenergic components that are in series with each other.