Systemic administration of dopamine D1 (SCH23390) and less so D2 (raclopride) receptor antagonists significantly reduce acquisition and expression of fructoseconditioned 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 6 tests sessions in D1 and D2 groups. These data indicate that NAcS D1 and D2 antagonists

Systemic administration of dopamine D1-like (SCH23390) and, to a lesser degree D2-like (raclopride), receptor antagonists significantly reduce the acquisition and expression of fructoseconditioned flavor preferences (CFP) in rats. Given the role of dopamine in the amygdala (AMY) in the processing and learning of food reward, the present study examined whether dopamine D1-like or D2-like antagonists in this site altered acquisition and/or expression of a fructose-CFP. In Experiment 1, food-restricted rats with bilateral AMY cannulae were trained to drink a fructose (8%) + saccharin (0.2%) solution mixed with one flavor (e.g., grape, CS+/Fs) and a less-preferred 0.2% saccharin solution mixed with another flavor (e.g., cherry, CS-/s) during one-bottle (16 ml) sessions. Two-bottle tests with the two flavors mixed in saccharin solutions (CS+/s, CS-/s) occurred 10 min following total bilateral AMY doses of 0, 12, 24 and 48 nmol of SCH23390 or raclopride. Preference for CS+/s over CS-/s was significantly reduced relative to vehicle baseline by the 48 nmol doses of SCH23390 and raclopride (from 77% to 66% and 68%), but not lower doses. In Experiment 2, rats Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript received bilateral AMY injections (12 nmol) of SCH23390 (D1 group) or raclopride (D2 group) 10 min prior to one-bottle training sessions with CS+/Fs and CS-/s. Yoked control rats received vehicle and were limited to the CS intakes of the D1 and D2 groups; untreated controls were not injected or limited to drug group intakes during training. Subsequent 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 6 tests sessions in the D1 group, but not in the D2 group. These data indicate that dopamine D1-like and D2-like antagonists significantly attenuated the expression of the previously-acquired fructose-CFP, and did not block acquisition of the fructose-CFP. D1-like antagonism during training hastened extinction of the fructose-CFP. The results are similar to those produced by dopamine D1-like and D2-like antagonist injections into the nucleus accumbens shell which suggests that flavor conditioning involves a regionally-distributed brain network.

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