CLONIDINE ANTAGONIZES THE AVERSIVE EFFECTS OF OPIATE WITHDRAWAL AND THE REWARDING EFFECTS OF MORPHINE ONLY IN OPIATE WITHDRAWN RATS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 ago nist, would block selectively the motivational effects of opiate withd rawal and whether clonidine's effects would respect the boundary betwe en nondeprived and deprived motivational states. In a place conditioni ng paradigm, clonidine (0.05 mg/kg ip) blocked the rewarding effects o f morphine in opiate-withdrawn rats (as well as the aversive propertie s of withdrawal itself), but did not affect morphine place preferences (2 and 20 mg/kg) in drug-naive rats. Furthermore, clonidine blocked t he acquisition of morphine (15 mg/kg), but not LiCl (15 mg/kg), condit ioned taste aversions in water-deprived rats. The results suggest that the motivational system activated in deprived animals includes dopami nergic and noradrenergic components that are in series with each other .