D-1 but not D-2 dopamine receptor antagonism blocks the acquisition of a flavor preference conditioned by intragastric carbohydrate infusions

The effects of dopamine D-1 (SCH23390) and D-2 (raclopride) receptor antago nists on the acquisition and expressions of flavor preferences conditioned by the postingestive actions of sucrose were investigated. Food-restricted rats were trained in one-bottle sessions to associate one flavored sacchari n solution (CS+) with intragastric (ig) infusions of 16% sucrose, and anoth er flavored saccharin solution (CS-) with water infusions. Flavor preferenc es were then measured in two-bottle tests. In Experiment 1A, rats that rece ived the D-2 antagonist (raclopride, 200 nmol/kg; RAC group) throughout tra ining consumed less CS+ and CS- than did saline-treated Control rats; a sal ine-treated Yoked group had its intake limited to that of the RAC group. Al l three groups displayed CS+ preferences during two-bottle tests when treat ed with saline or raclopride, except at doses that greatly suppressed intak e. Experiment 1B obtained similar results with rats treated with 400 nmol/k g raclopride throughout training. In Experiment 2, rats that received the D I antagonist (SCH23390, 200 nmol/kg; SCH group) throughout training consume d less CS+ and CS- than did saline-treated Control rats; a saline-treated Y oked group had its intake limited to that of the SCH group. Unlike the Cont rol and Yoked groups, the SCH group failed to prefer the CS+ to the CS- in two bottle tests. SCH23390 treatment during two-bottle testing did not bloc k CS+ preference in the Control or Yoked groups, except at doses that great ly suppressed intake. We conclude that D-1, but not D-2, dopamine receptors are critically involved in the acquisition of a sucrose-conditioned flavor preference, and both receptor subtypes have a more limited role in the exp ression of this preference. (C) 2001 Elsevier Science Inc. All rights reser ved.