SEROTONERGIC LESIONS DECREASE MU-OPIATE AND DELTA-OPIATE RECEPTOR-BINDING IN DISCRETE AREAS OF THE HYPOTHALAMUS AND IN THE MIDBRAIN CENTRALGRAY

Serotonergic nerve terminals in the brain were lesioned by intraventri cular infusion of the selective neurotoxin 5,7-dihydroxytryptamine (5, 7-DHT) and levels of mu- and delta-opiate binding were measured in bra in areas implicated in reproductive behavior and gonadotropin secretio n. The lesion decreased mu-receptor binding in the preoptic area (mPOA ) and the midbrain central gray, while delta-receptor binding was decr eased in the mPOA and the dorsomedial nucleus of the hypothalamus. Hyp othalamic serotonergic lesions also attenuated morphine inhibition of female sexual behavior. These results indicate the existence of seroto nergic-opiate interactions in select regions of the brain and suggest that these interactions may be important in the regulation of lordosis behavior.