Ethanol-conditioned flavor preferences compared with sugar- and fat-conditioned preferences in rats

Rats can learn to prefer flavors paired with ethanol and various nutrients. The present study examined the relative strengths of flavor preferences conditioned by 5% ethanol and isocaloric solutions of 7.18% sucrose, 7.18% fructose, or 3.26% corn oil. In three experiments, nondeprived rats were trained with different flavored solutions (conditioned stimuli, CS) paired with intragastric (IG) infusions: a CS+E flavor paired with ethanol infusion, a second CS+ paired with a nutrient infusion, and a CS- paired with water infusion. In two-bottle tests, rats strongly preferred a sucrose-paired CS+S over the CS- and over the CS+E. The preference for the CS+E over CS- was weaker. These effects occurred when the rats drank substantially more CS+S than CS+E in training and when training intakes were matched. Similar results were obtained when the nutrient infusion was fructose or corn oil, except that preferences for the CS+F or CS+O over the CS+E were less pronounced than with CS+S. Consistent with the IG results, rats trained to drink flavored sucrose and ethanol solutions preferred the CS+S to CS+E in a flavored water test. These results confirm prior reports of ethanol-conditioned preferences but show that ethanol is less effective than other nutrients at isocaloric concentrations. The marked individual differences in ethanol-conditioned preferences may be related to the impact of the sugar or fat infusions on the reward evaluation of the ethanol-paired flavor. (C) 2004 Elsevier Inc. All rights reserved.