A SUCROSE-BASED MAINTENANCE DIET INCREASES SENSITIVITY TO APPETITE-SUPPRESSANT EFFECTS OF NALOXONE

Rats maintained under restricted access to food (but at 100% free-feed ing weights) received one of two diets in their home cages: a palatabl e sucrose-based diet, or regular chow (grain based diet), and could re spond for either sucrose-or grain-based reinforcers under an FR 40 rei nforcement schedule (crossover design). Naloxone (0, 0.1,0.3, 1.0, and 3.0 mg/kg) was more potent in reducing operant-chamber responding in rats maintained on a sucrose-based diet in their home cages than those fed a grain-based diet, regardless of the type of pellets available i n the operant chambers. Whereas naloxone decreased response rate over the session, it had no effect on initiation of responding. Results sup port the hypothesis that opioids are involved in the maintenance, but not the initiation of consummatory behavior. Furthermore, increased po tency of naloxone following chronic ingestion of palatable food is sim ilar to that observed following chronic opiate administration, suggest ing a relationship between palatability and opioids. (C) 1997 Elsevier Science Inc.