GLUCOSE-CONDITIONED AND FRUCTOSE-CONDITIONED FLAVOR PREFERENCES IN RATS - TASTE VERSUS POSTINGESTIVE CONDITIONING

Flavor preferences conditioned by glucose and fructose were compared u sing two training methods. With the simultaneous method preferences ca n be reinforced by the flavor and/or the postingestive consequences of nutrients, whereas with the delayed method preferences are reinforced only by postingestive nutritive effects. In Experiment 1, food-depriv ed rats displayed similar preferences for flavors (CS+) added to an 8% glucose or 8% fructose solution over flavors (CS-) added to a noncalo ric saccharin solution (simultaneous conditioning). Other rats learned to prefer a CS+ flavor paired with the delayed (10 min) presentation of 8% glucose over a CS- flavor paired with delayed saccharin. Fructos e failed to condition a flavor preference with the delayed paradigm. T aken together, these data suggest that the preference for a flavor mix ed in a fructose solution is reinforced by the sweet taste, not the po stingestive effects of the sugar. Experiment 2 tested this idea by dev aluing the taste of the sugar solutions by quinine adulteration. Rats initially avoided both glucose-quinine and fructose-quinine solutions in favor of a saccharin solution. Following one-bottle training, they came to prefer the glucose-quinine but not the fructose-quinine soluti on over the saccharin solution. The glucose-trained rats also showed s tronger preferences for sucrose-quinine solutions than did the fructos e-trained rats. These findings, along with other recent data, indicate that fructose-conditioned preferences are based primarily on the suga r's palatable taste. Glucose, in contrast, can condition strong prefer ences based on its taste as well as its postingestive actions.