Activation of dopamine D1-like receptors in nucleus accumbens is critical for the acquisition, but not the expression, of nutrient-conditioned flavor preferences in rats

The present study investigated the role of dopamine neurotransmission within the nucleus accumbens (NAc) in flavor preference learning induced by the postoral consequences of carbohydrates. In Experiment 1, rats fitted with a gastric catheter were trained with a flavor (CS+) paired with intragastric (IG) infusions of 8% glucose and a different flavor (CS-) paired with IG water infusions. The CS+ preference was then evaluated in two-bottle preference tests following bilateral injection of the dopamine D1-like receptor antagonist SCH23390 into the NAc shell at total doses of 0, 12, 24 and 48 nmol. SCH23390 produced dose-related reductions in CS+ intake but did not block the CS+ preference except at the highest dose, which also greatly suppressed the CS intakes. In Experiment 2, new rats were injected daily in the NAc shell with either saline or SCH23390 (12 nmol), 10 min prior to training sessions with CS+ with IG glucose and CS- with IG water. In the two-bottle preference tests, the drug-treated rats, unlike the control rats, did not significantly prefer the CS+ (61 vs. 83% preference). In Experiment 3, new rats were trained with the same procedures as Experiment 2, except that brain injections were in the NAc core. In contrast to control rats, SCH-treated rats failed to prefer the CS+ to the CS- in two-bottle tests (55% vs. 89% preference). These results demonstrate that D1-like receptors in the NAc shell and core are greatly involved in the acquisition, but less so in the expression, of a flavor preference conditioned by postingestive effects of glucose.