NALOXONE ADMINISTRATION FOLLOWING OPERANT TRAINING OF SUCROSE WATER DISCRIMINATION IN THE RAT/

The suppression of food intake observed following naloxone administrat ion has often been ascribed to palatability or taste. Unfortunately, m any confounds become apparent when attempts are made to isolate such f actors in the investigation of ingestive behaviors. In the present stu dy, rats (two groups) were trained to discriminate either a 10% or 5% sucrose solution from water (0.1 ml). These mildly food deprived subje cts (95% of free-feeding weight) were trained to press the appropriate lever in a two-lever operant chamber following sampling of sucrose or water; successful responding was reinforced by delivery of a 45 mg gr ain food pellet. Following random exposure to reduced sucrose concentr ations tested under extinction, a sucrose concentration gradient (1.0, 0.5, 0.1, 0.05, 0.01 and 0.005% sucrose solution) was established for both training groups under IP saline administration. Data collected u nder IP saline were then compared to those collected following random IP naloxone administration (3.0, 1.0, 0.3 and 0.1 mg/kg). No significa nt differences were observed between the sucrose concentration gradien ts obtained under saline and those obtained under naloxone, suggesting that the anorectic effect of naloxone is not primarily determined by discrimination of sweet taste.