Dopamine D1-like receptor antagonism in amygdala impairs the acquisition of glucose-conditioned flavor preference in rats

This study examined the role of dopamine within the amygdala (AMY) in flavor preference learning induced by post-oral glucose. In Experiment 1, rats were trained with a flavor [conditioned stimulus (CS+)] paired with intragastric (IG) infusions of 8% glucose and a different flavor (CS-) paired with IG water infusions. The CS+ preference was evaluated in two-bottle tests following bilateral injection of the dopamine D1-like receptor antagonist, SCH23390 (SCH), into the AMY at total doses of 0, 12, 24 and 48 nmol. SCH produced dose-dependent reductions in CS+ intake but did not block the CS+ preference except at the two highest doses, which also greatly suppressed the CS intakes. In Experiment 2, new rats were injected daily in the AMY with either saline or SCH (12 nmol), prior to training sessions with CS+/IG glucose and CS-/IG water. In the two-bottle tests, SCH rats, unlike the control rats, failed to prefer the CS+ (55 vs. 81%). In Experiments 3 and 4, new rats were trained as in Experiment 2, except that brain injections were in the basolateral and central nuclei of the AMY, respectively. SCH rats learned to prefer the CS+ to the CS-, although their preference was weaker than that displayed by the control rats (Experiment 3: 59 vs. 80%; Experiment 4: 73 vs. 88%). These results show an essential role for D1-like receptor activation in the AMY in the acquisition of flavor preference learning induced by the post-oral reinforcing properties of glucose. A distributed network mediating flavor-nutrient incentive learning is discussed.