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

Rationale Evidence has implicated the nucleus accumbens (NAcc) in drug-seeking 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 rats wen trained to self-administer heroin (0.12 mg/kg per in fusion) under a continuous reinforcement (CRF) schedule. After responding stabilised, rats were given excitotoxic (or sham) lesions of either the NAce core or shell and after recovery were assessed for their retention of heroin self-administration under CRE At this point a second-order schedule of reinforcement was introduced, commencing at FR10 (FR1:S) and terminating at FR10 (FR10:S), in which ten lever Dresses resulted in presentation of the heroin-associated 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 of the NAce core, but not shell, were severely impaired in the acquisition of heroin-seeking behaviour. Conclusions: These results indicate an important role for the core of the NAcc in the acquisition of heroin-seeking behaviour under the control of drug-associated stimuli.