Dopamine D1 and D2 antagonists reduce the acquisition and expression of flavor-preferences conditioned by fructose in rats

The effects of dopamine (DA) D-1 and D-2 receptor antagonists on the acquisition and expression of flavor-preferences conditioned by the sweet taste of fructose were examined. Food-restricted rats were trained over eight alternating one-bottle sessions to drink an 8% fructose solution containing one novel flavor (CS+) and a less preferred 0.2% saccharin solution containing a different flavor (CS-). Three groups of rats were treated daily with either vehicle (control group), SCH23390 (200 nmol/kg; D-1 group), or raclopride (200 nmol/kg; D-2 group) during training. Additional groups of vehicle-treated rats had their daily training intakes matched to that of the D-1 and D-2 groups. Preferences were assessed in two-bottle tests with the CS+ and CS - flavors presented in 0.2% saccharin solutions following doses of 0, 50, 200, 400, or 800 nmol/kg of either D-1 or D-2 antagonists. The D-1 and D-2 groups, unlike the control and yoked-control groups, failed to display a significant CS+ preference in the two-bottle tests following vehicle treatment. In addition, treatment with SCH23390 prior to the two-bottle tests blocked the expression of the CS+ preference in the control groups. Pretest raclopride treatment attenuated the CS+ preference at some dose levels. Raclopride also attenuated the preference for fructose in rats given two-bottle training with the CS+/fructose (CS+/F) and CS-/saccharin (CS-/S) solutions. These findings indicate that D-1 and D-2 antagonists block flavor-preference conditioning by sweet taste and that D-1, and to a lesser extent D-2, receptor antagonists attenuate the expression of a previously acquired preference. (C) 2003 Elsevier Science Inc. All rights reserved.