THE COMPOSITION OF THE MAINTENANCE DIET ALTERS FLAVOR-PREFERENCE CONDITIONING BY INTRAGASTRIC FAT INFUSIONS IN RATS

Prior studies indicate that intragastric (IG) fat infusions condition only weak flavor preferences in chow-fed rats using brief daily traini ng sessions. The present study attempted to facilitate fat conditionin g by feeding rats a high-fat maintenance diet or by adding an oily fla vor to the conditioning stimuli. In Experiment 1, rats were fed restri cted rations of either a chow-corn oil mixture (48% energy as fat, HF group) or regular chow (12% fat, LF group). During 1-bottle training s essions, drinking a flavored (CS+, e.g., cherry) saccharin solution wa s paired with IG far (7.1% corn oil emulsion). On other days, an alter nate flavor (CS-, e.g., grape) was paired with IG water. In subsequent 2-bottle tests between the CS+ and CS- flavors, the HF rats displayed a stronger CS+ preference than the LF rats (90% vs. 62%). Experiment 2 tested the effect of a semisynthetic HF maintenance diet (48% fat en ergy), using a conditioning procedure similar to that of Experiment 1. The rats displayed only a moderate (72%) CS+ preference. When switche d to the chow-oil maintenance diet and retrained with new CS flavors, they developed a 90% CS+ preference. In Experiment 3, chow-fed rats we re trained and tested with oily CSs (i.e., 2% corn oil was added to fl avored saccharin solutions). They failed to show a preference for the CS+ paired with IG oil. Thus, increasing the level of fat in the maint enance diet can greatly enhance preference conditioning with IG fat, b ut the amplitude of the effect is influenced by the composition of the high-fat food. In contrast, adding a fatty flavor to the conditioning stimuli did not improve fat conditioning.