LOW-DOSE APOMORPHINE ATTENUATES MORPHINE-INDUCED ENHANCEMENT OF BRAIN-STIMULATION REWARD

Thresholds for brain stimulation reward (BSR) delivered to the medial forebrain bundle-lateral hypothalamus were determined by means of a ra te free psychophysical method. Lower doses of apomorphine (0.5 to 0.2 mg/kg) produced modest elevations in BSR thresholds. A 0.4 mg/kg dose of apomorphine resulted in emergence of stereotypic behaviors and the loss of stimulus control. Morphine's BSR threshold lowering effects we re significantly blocked by the concurrent administration of a 0.1 mg/ kg dose of apomorphine. These results support the hypothesis that pres ynaptic dopamine neurons are involved in the mediation of morphine's r einforcing effects and that dopamine autoreceptor agonists may be of s ome use in the pharmacotherapy of opiate abuse.