MORPHINE-INDUCED AND COCAINE-INDUCED CONDITIONED PLACE PREFERENCE - EFFECTS OF QUINPIROLE AND PRECLAMOL

The role of dopamine in opioid reward is unresolved. Furthermore, the issue is somewhat unclear regarding cocaine and the place preference p aradigm. In the present study we investigated whether the drugs activa ting dopamine autoreceptors affect cocaine- and morphine-induced place preference in rats. Neither the dopamine D-2/D-3 receptor agonist, qu inpirole (0.05 mg/kg, SC), nor the partial dopamine autoreceptor agoni st, preclamol (2 or 8 mg/kg, SC), induced place conditioning by itself . Quinpirole had no significant influence on the place preference indu ced either by morphine (3 mg/kg, SC) or cocaine (5 mg/kg, IF). Preclam ol, when given at the dose of 8 mg/kg SC, significantly attenuated the effect of cocaine but failed to modify the effect of morphine. Our re sults suggest that the rewarding properties of morphine involve DA-ind ependent mechanisms whereas in the cocaine-induced reward the role of brain DA is critical. Furthermore, as regards place conditioning, we p ropose that the activation of DA autoreceptors is not sufficient to re liably modify the rewarding effect of cocaine.