Role of D-1 and D-2 dopamine receptors in the acquisition and expression of flavor-preference conditioning in sham-feeding rats

The present study examined the effects of D-1 and D-2 antagonists on flavor -preference conditioning by the sweet taste of sucrose. All sessions were c onducted under sham-feeding conditions to minimize post-ingestive influence s. The rats were trained in alternating, one-bottle sessions to sham-feed a 16% sucrose solution containing one novel flavor (CS+) and a less-preferre d 0.2% saccharin solution containing a different flavor (CS -). Three group s of food-restricted rats were treated with either vehicle (control group), the D-1 antagonist, SCH23390 (200 nmol/kg), or the D-2 antagonist, raclopr ide (200 nmol/kg) during one-bottle training. A fourth group (yoked group) was vehicle-treated and its training intakes were matched to that of the D- 1 and D-2 drug groups. Preferences were assessed in two-bottle tests with t he CS+ and CS - flavors presented in mixed 8% sucrose + 0.10% saccharin sol utions following systemic doses of 0, 200, or 800 nmol/kg of either the D-1 or D-2 antagonists. All groups significantly preferred the CS+ flavor in v ehicle tests, although the preferences were weaker in the D-1, D-2, and yok ed groups compared to the control group. All groups selectively reduced the ir CS+ intakes when treated with either D-1 or D-2 antagonists during two-b ottle testing, and the CS+ preference was blocked at the higher doses. Thes e data show that D-1 and D-2 receptor antagonists block the expression of a sucrose-conditioned preference, but produces substantially lesser effects upon the acquisition of this form of flavor conditioning. (C) 2000 Elsevier Science Inc. All rights reserved.