, 2003). Studies employing neurotoxic lesion support these correlational findings; post-training core but not shell lesions impair performance FK506 nmr on simple Pavlovian conditioning (Parkinson et al., 1999; Cardinal et al., 2002b), whereas lesions
of the NAc centered on the core during a cued go/no-go task resulted in behavioral deficits suggestive that rats were insensitive to cued outcome value (Schoenbaum & Setlow, 2003). Further, reversible inactivation of the NAc core but not shell has been shown to selectively disrupt cue-induced reinstatement of cocaine self-administration (Fuchs et al., 2004). These data argue for a specific role for the NAc core for acquiring critical cue-related information for guiding behavior. Interestingly, although much cue encoding was dependent on the core, only shell neurons in naive animals showed cue-modulated operant encoding that was correlated with the behavioral performance of PIT. Several studies have now suggested that the shell is critical for the transfer effect. For example, Corbit et al. (2001) showed that lesions of the NAc shell made prior to conditioning failed to impair either Pavlovian or instrumental conditioning, but selectively abolished cue-potentiated transfer,
whereas NAc core lesions had no effect on transfer. Similarly, intrashell Selleckchem GW-572016 infusions of amphetamine (Wyvell & Berridge, 2000) or corticotropin-releasing factor (Pecina et al., 2006) results in potentiating the transfer effect, whereas lesions of the shell but not the core block this amphetamine potentiating effect (Parkinson et al., 1999). These findings are somewhat at odds with other work that has shown specificity for the NAc core in PIT (Hall et al., 2001; de Borchgrave et al., 2002). In those studies, normal Pavlovian and instrumental conditioning were largely unaffected, but transfer was impaired. Importantly, in those studies, lesions
of the core were made prior to any conditioning, whereas the above work by Parkinson et al. (1999) showing the importance of the shell was performed in experiments where the lesion was administered after first-order conditioning but prior these to transfer (Parkinson et al., 1999). This suggests an important distinction between the acquisition of Pavlovian information vs. the potentiation of instrumental responding in the presence of learned cues. In line with this finding, the enhancement of PIT following a period of prolonged drug-taking was accompanied by a concurrent increase in shell-specific neural encoding. These results mirror the findings from Parkinson et al. (1999) in which post-training shell lesions abolished the ability for amphetamine to potentiate already-learned responses.