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 training sessions. The present study attempted to facilitate fat conditioning by feeding rats a high-fat maintenance diet or by adding an oily flavor to the conditioning stimuli. In Experiment 1, rats were fed restricted 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 sessions, drinking a flavored (CS+, e.g., cherry) saccharin solution was paired with IG far (7.1% corn oil emulsion). On other days, an alternate 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 energy), using a conditioning procedure similar to that of Experiment 1. The rats displayed only a moderate (72%) CS+ preference. When switched to the chow-oil maintenance diet and retrained with new CS flavors, they developed a 90% CS+ preference. In Experiment 3, chow-fed rats were trained and tested with oily CSs (i.e., 2% corn oil was added to flavored saccharin solutions). They failed to show a preference for the CS+ paired with IG oil. Thus, increasing the level of fat in the maintenance diet can greatly enhance preference conditioning with IG fat, but 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.