The effects of nucleus accumbens core and shell lesions on intravenous heroin self-administration and the acquisition of drug-seeking behaviour undera second-order schedule of heroin reinforcement

Rationale Evidence has implicated the nucleus accumbens (NAcc) in drug-seek ing and -taking behaviour. However, the importance of the "core" and "shell " subdivisions of the NAcc in heroin-seeking and -taking behaviour remains unclear. Objectives: To investigate the function of the NAce con and shell in heroin self-administration and heroin-seeking behaviour. Methods: Male r ats wen trained to self-administer heroin (0.12 mg/kg per in fusion) under a continuous reinforcement (CRF) schedule. After responding stabilised, rat s were given excitotoxic (or sham) lesions of either the NAce core or shell and after recovery were assessed for their retention of heroin self-admini stration under CRE At this point a second-order schedule of reinforcement w as introduced, commencing at FR10 (FR1:S) and terminating at FR10 (FR10:S), in which ten lever Dresses resulted in presentation of the heroin-associat ed CS+, and completion of ten such units resulted in drug infusion. Results : Within 7 days, all groups re-acquired responding for heroin under CRF at rates similar to their pre-lesion performance. However, rats with lesions o f the NAce core, but not shell, were severely impaired in the acquisition o f heroin-seeking behaviour. Conclusions: These results indicate an importan t role for the core of the NAcc in the acquisition of heroin-seeking behavi our under the control of drug-associated stimuli.