Role of dopamine D1 and D2 receptors in the nucleus accumbens shell on the acquisition and expression of fructose-conditioned flavor-flavor preferences in rats.

Systemic administration of dopamine D1 (SCH23390) and less so D2 (raclopride) receptor antagonists significantly reduce acquisition and expression of fructose-conditioned flavor preferences (CFP). Because dopamine in the nucleus accumbens shell (NAcS) is implicated in food reward, the present study examined whether NAcS D1 or D2 antagonists altered acquisition and/or expression of fructose-CFP. In Experiment 1, food-restricted rats with bilateral NAcS cannulae were trained to drink a fructose (8%)+saccharin (0.2%) solution mixed with one flavor (CS+/Fs) and a less-preferred 0.2% saccharin solution with mixed another flavor (CS-/s). Unlimited two-bottle tests with the two flavors in saccharin (0.2%: CS+/s, CS-/s) occurred 10 min following total bilateral NAcS doses of 0, 12, 24 or 48 nmol of SCH23390 or raclopride. Preference for CS+/s over CS-/s following vehicle treatment (76%) was significantly reduced by SCH23390 (48 nmol, 62%) and raclopride (24 nmol, 63%). In Experiment 2, rats received bilateral NAcS injections (12 nmol) of SCH23390 or raclopride on one-bottle training (16 ml) days. Yoked control rats received vehicle and were limited to the CS intakes of the D1 and D2 groups, whereas untreated controls without injections received their CS ration during training. Subsequent unlimited two-bottle tests revealed initial preferences of CS+/s over CS-/s in all groups that remained stable in untreated and yoked controls, but were lost over the six tests sessions in D1 and D2 groups. These data indicate that NAcS D1 and D2 antagonists significantly attenuated the expression of the fructose-CFP and did not block acquisition, but hastened extinction of fructose-CFP.