The nucleus accumbens core and shell are critical for the expression, but not the consolidation, of Pavlovian conditioned approach

The nucleus accumbens (NAc) is important for the ability of motivationally significant stimuli to guide behavior. To further delineate its role in appetitive Pavlovian conditioning, we tested the hypothesis that the NAc contributes to memory consolidation and expression for a goal-tracking version of Pavlovian conditioned approach (PCA) in rats. We found that neither post-training reversible inactivation with the GABA receptor agonists muscimol and baclofen nor inhibition of protein synthesis with anisomycin (ANI) in either the core or shell regions of the NAc had an effect on approach to a reward port in response to a reward-predictive cue (conditioned stimulus, CS+). In contrast, pre-test reversible inactivation of both the core and shell decreased conditioned responding during the CS+. Unlike inactivation of the core, however, reversible inactivation of the shell also produced an increase in responding during the CS- and the intertrial interval. This suggests that the NAc is not involved in the consolidation of goal-tracking PCA, but that once the memory is formed, the core is required for expression of the CS- unconditioned stimulus (US) association and the shell is required to inhibit conditioned approach behavior at times when the CS+ is not presented. (C)2008 Elsevier B.V. All rights reserved.