FEEDING INDUCED BY OPIOID STIMULATION OF THE VENTRAL STRIATUM - ROLE OF OPIATE RECEPTOR SUBTYPES

Previous work has shown that morphine infusion into the ventral striat um results in marked hyperphagia in satiated rats. The present investi gation was undertaken to determine the relative involvement of opiate receptor subtypes in this phenomenon. Equimolar doses of the synthetic ligands [D-Ala2, NMe-Phe4, Gly-ol5]-enkephalin (DAMGO; 0, 0.025, 0.25 and 2.5 mug/0.5 mul), [D-Pen2,5]-enkephalin (DPEN; 0, 0.031, 0.31, 3. 1 and 6.2 mug/0.5 mul) and U50,488H (0, 0.01 86, 0.186,1.86 and 3.72 m ug/0.5 mul), which are selective for mu, delta and kappa receptors, re spectively, were microinfused into three striatal sites: the nucleus a ccumbens. ventromedial striatum and ventrolateral striatum. Food intak e (grams), feeding, drinking, locomotion, rearing and grooming were me asured. After injection into all three sites, DAMGO induced a robust, dose-dependent increase in food intake that was blocked by coadministr ation of naltrexone (5 mg/kg i.p.). DAMGO-induced feeding was delayed in onset and was long lasting. Injections of DPEN were 2 to 3 times le ss effective in eliciting feeding. DPEN-induced feeding occurred immed iately and was short lasting. U50,488H had no effect on food intake. N o changes in drinking were noted for any agonist. Spontaneous motor be haviors were also increased by DAMGO and DPEN. These findings demonstr ate that mu opiate receptors within the ventral striatum mediate the o piate-induced feeding response.