D₁ but not D₂ dopamine receptor antagonism blocks the acquisition of a flavor preference conditioned by intragastric carbohydrate infusions

The effects of dopamine D₁ (SCH23390) and D₂ (raclopride) receptor antagonists 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 saccharin solution (CS+) with intragastric (ig) infusions of 16% sucrose, and another flavored saccharin solution (CS-) with water infusions. Flavor preferences were then measured in two-bottle tests. In Experiment 1A, rats that received the D₂ antagonist (raclopride, 200 nmol/kg; RAC group) throughout training consumed less CS+ and CS- than did saline-treated Control rats; a saline-treated Yoked group had its intake limited to that of the RAC group. All three groups displayed CS+ preferences during two-bottle tests when treated with saline or raclopride, except at doses that greatly suppressed intake. Experiment 1B obtained similar results with rats treated with 400 nmol/kg raclopride throughout training. In Experiment 2, rats that received the D₁ antagonist (SCH23390, 200 nmol/kg; SCH group) throughout training consumed less CS+ and CS- than did saline-treated Control rats; a saline-treated Yoked group had its intake limited to that of the SCH group. Unlike the Control 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 block CS+ preference in the Control or Yoked groups, except at doses that greatly suppressed intake. We conclude that D₁, but not D₂, 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 expression of this preference.