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

Abstract

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

Dopamine receptor signaling in the medial orbital frontal cortex and the acquisition and expression of fructose-conditioned flavor preferences in rats

“…Analysis of central sites of action revealed that the acquisition of fructose-CFP was blocked by DA D1 or D2 antagonists in the mPFC and by DA D2 antagonists in the AMY. In contrast, expression of fructose-CFP was reduced by DA D1 or D2 antagonists in the NAcS or AMY, but not the mPFC (Bernal et al, 2008, 2009; Malkusz et al, 2012), and by DA D1 antagonism in the lateral hypothalamus (Amador et al, 2014). Thus, mPFC DA D1 and D2 receptor signaling in a frontal cortical projection zone of the VTA meso-cortical DA system was intimately involved in the acquisition or learning, but not the expression or maintenance of fructose-CFP.…”

Flavor preferences conditioned by nutritive and non-nutritive sweeteners in mice

“…The dopamine reward system is also implicated in fructose-conditioned flavor preferences [2,5] and the differential sipper tube conditioning response to sucrose and non-nutritive sweeteners (sucralose, saccharin) [3,10]. Conceivably, fructose may activate the dopamine reward system more than does the highly preferred SS or equally preferred saccharin solutions used in the present study.…”

NMDA receptor antagonism differentially reduces acquisition and expression of sucrose- and fructose-conditioned flavor preferences in BALB/c and SWR mice

“…of action revealed that acquisition, but not expression of IG glucose-CFP was blocked by a DA D1 antagonist administered into the nucleus accumbens, amygdala, medial prefrontal cortex and lateral hypothalamus (Touzani et al, , 2009a(Touzani et al, , 2009b(Touzani et al, , 2010, whereas a DA D1 antagonist administered into these same sites differentially reduced acquisition and expression of fructose-CFP (Amador et al, 2014;Bernal et al, 2008Bernal et al, , 2009Malkusz et al, 2012). In contrast, opioid receptor antagonism with naltrexone failed to affect the acquisition or expression of CFPs in rats produced by IG sucrose or orally-consumed fructose (Azzara et al, 2000;Baker et al, 2004).…”