A Role for Dopamine D1 Receptors of the Nucleus Accumbens Shell in Conditioned Taste Aversion Learning

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Abstract
The involvement of dopamine (DA) in conditioned taste aversion (CTA) learning was studied with saccharin or sucrose as the conditioned stimulus (CS) and intraperitoneal lithium as the unconditioned stimulus (US). The dopamine D1 antagonistR(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390) (12.5–50 μg/kg, s.c.), given 5 min after the CS, impaired the acquisition of CTA in a paradigm consisting of three or a single CS–lithium association. SCH 23390 failed to impair CTA acquisition given 45 min after, 30 min before, or right before the CS. (−)-trans-6,7,7a,8,9,13b-hexahydro-3-chloro-2-hydroxy-N-methyl-5a-benzo-(d)-naphtho-(2,1b) azepine (SCH 39166) (12.5–50.0 μg/kg, s.c), a SCH 23390 analog that does not bind to 5HT2 receptors, also impaired CTA. No significant impairment of CTA was obtained after administration of the specific D2/D3 antagonist raclopride (100 and 300 μg/kg, s.c.). The ability of SCH 23390 to impair CTA learning was confirmed by its ability to reduce the conditional aversive reactions to a gustatory CS (sweet chocolate) as estimated in a taste reactivity paradigm. SCH 39166 impaired CTA also when infused in the nucleus accumbens (NAc) shell 5 min after the CS. No impairment was obtained from the NAc core or from the bed nucleus stria terminalis. The results indicate that D1 receptor blockade impairs CTA learning by disrupting the formation of a short-term memory trace of the gustatory CS and that endogenous dopamine acting on D1 receptors in the NAc shell plays a role in short-term memory processes related to associative gustatory learning.