BEHAVIORAL-EFFECTS OF NALOXONE ON NEUROPEPTIDE Y-INDUCED FEEDING

We evaluated the effect of naloxone on neuropeptide Y (NPY)-induced fe eding behavior using two methods; operant chambers and observational a nalysis. In the first study rats were trained on a FR 80 (first pellet ) FR 3 (subsequent pellets) reinforcement schedule. Following training , rats were injected with NPY (intraventricular, 5 mu g) and various d oses of naloxone (subcutaneous, 0, 0.1, 0.3, 1, 3, and 10 mg/kg). NPY significantly increased the number of pellets consumed during the one hour session and naloxone (1, 3, and 10 mg/kg) blocked this effect. NP Y failed to alter the time to the first response, but did decrease the time needed to complete the first ratio (FR 80). Naloxone (3 and 10 m g/kg) increased the latency to the first response and blocked NPY's ef fect on completion of the first ratio. In the second study, we observe d rats continually following injection of saline, NPY (5 mu g ICV) and /or naloxone (1 mg/kg SC). NPY increased food intake during the 1-h se ssion and naloxone blocked this effect. NPY decreased the latency to e at, but naloxone failed to significantly antagonize this effect. The a mount of time spent eating was greater in the NPY group compared to th e saline group and naloxone antagonized this effect. Lag sequential an alysis indicated that NPY induced a move-eat-move behavioral sequence that disappeared following naloxone administration. These data lend su pport to the notion that opioids are involved in maintenance of NPY-in duced feeding but affect meal initiation in a minor way. Only relative ly high doses of naloxone (3 and 10 mg/kg) altered NPY-induced changes in meal initiation.