Pharmacology of flavor preference conditioning in sham-feeding rats: Effects of dopamine receptor antagonists

Opioid and dopamine systems are both implicated in the response to sweet so lutions. Our laboratory previously reported that the opioid antagonist, nal trexone, reduced the intake of sweet solutions, yet had little or no effect on sucrose-conditioned flavor preferences in sham-feeding rats. The presen t study examined the role of dopamine D-1 and D-2 receptors in the expressi on of flavor preferences conditioned by the sweet taste of sucrose. All ses sions were conducted under sham-feeding conditions to minimize postingestiv e influences. Training was accomplished by adding a novel flavor (CS+) to a 16% sucrose solution, a different flavor (CS-) to a less-preferred 0.2% sa ccharin solution in alternating, one-bottle sessions. Preferences were asse ssed in two-bottle tests with the CS+ and CS- flavors presented in mixed su crose (8%)-saccharin (0.1%) solutions following systemic doses of 0, 50, 20 0, 400, or 800 nmol/kg of the D-2 antagonist, raclopride (Experiment 1) or the D-1 antagonist, SCH23390 (Experiment 2) under either food-restricted or unrestricted conditions. Rats significantly preferred the CS+ solutions in vehicle tests, and displayed equipotent and dose-dependent reductions in t otal intake and CS+ preference following either D-1 or D-2 receptor antagon ism. Similar results were obtained with SCH23390 and raclopride in Experime nt 3 conducted with water restricted rats. These data indicate that dopamin ergic D-1 and D-2 receptors play pivotal and functionally equivalent roles in the expression of flavor preferences conditioned by the sweet taste of s ucrose. (C) 2000 Elsevier Science Inc.