SENSITIZATION AND CONDITIONING OF FEEDING FOLLOWING MULTIPLE MORPHINEMICROINJECTIONS INTO THE NUCLEUS-ACCUMBENS

The effects of repeated morphine infusions (10 mu g/0.5 mu l) into the nucleus accumbens on feeding were studied in sated rats. As shown pre viously, intra-accumbens morphine infusions induced a large increase i n food intake. After undergoing repeated morphine treatment, animals c onsumed significant quantities of food in response to a saline or sham injection, compared to their pre-morphine baseline. This conditioned feeding was present up to 18 days after the final drug infusion. Addit ionally, repeated morphine administration caused a progressive sensiti zation of feeding; the final morphine infusion elicited nearly double the amount of food intake as the first. Multiple saline infusions had no behavioral effects. Repeated stimulation of opiate receptors may en hance associative mechanisms such that previously neutral environmenta l stimuli acquire the ability to elicit feeding. Abnormal activation o f this system may be a possible neural substrate for compulsive feedin g and bulimia.