LEARNED PREFERENCES FOR REAL-FED AND SHAM-FED POLYCOSE IN RATS - INTERACTION OF TASTE, POSTINGESTIVE REINFORCEMENT, AND SATIETY

Nutrient-conditioned flavor preferences have been obtained with a vari ety of procedures, but one study indicates that rats do not readily le arn to prefer the flavor of real-fed food to the flavor of sham-fed fo od. This issue was reexamined in food-deprived rats trained to real fe ed (gastric fistula closed) and sham feed (gastric fistula open) diffe rent flavored Polycose solutions (cherry or grape). Sham-feeding intak es in the one-bottle training sessions (30 min) were limited to the am ount consumed in real-feeding sessions; intakes were not limited durin g two-bottle preference tests (10 min). In Experiment 1, when tested w ith 32% Polycose solutions, the animals tended to prefer the sham-fed Polycose to the real-fed Polycose. When subsequently trained and teste d with 8% Polycose solutions, the same animals displayed a strong pref erence (approximate to 90%) for the real-fed Polycose. These findings were confirmed in Experiment 2 using separate groups. Rats trained wit h 8% Polycose readily learned to prefer the real-fed solution, and rat s trained with 32% Polycose initially preferred the sham-fed Polycose solution. With additional training the 32% Polycose group developed a preference for the real-fed solution. In Experiment 3, rats trained to real feed flavored 8% and 32% Polycose solutions developed strong pre ferences for the 32% solution. This finding suggests that the tendency to prefer sham-fed to real-fed 32% Polycose is not due to aversive po stingestive effects of the real-fed solution. Taken together, the resu lts indicate that Polycose has a postingestive positive reinforcing ef fect that can be revealed using the sham-feeding preparation. The lack of an immediate preference for real-fed over sham-fed 32% Polycose ma y occur because 1) postingestive reinforcement only slightly improves the already highly preferred taste of the real-fed solution and 2) pos tingestive satiety reduces the attractiveness of the real-fed solution .