The effects of excitotoxic lesions of the nucleus accumbens core or shell regions on intravenous heroin self-administration in rats.

RATIONALE: It has been suggested that the nucleus accumbens (NAcc) may be involved in heroin reward, and the core and shell regions respond differently following administration of a number of drugs of abuse. OBJECTIVE: The possible role of the NAcc core and shell subregions in the acquisition of heroin self-administration behaviour was investigated. METHODS: Rats were given selective excitotoxic lesions of either the nucleus accumbens core or shell before the acquisition of responding for i.v. heroin (0.04 mg/infusion) under a continuous reinforcement schedule in daily 3 h sessions. After sham-lesioned rats reached a stable baseline, a between-sessions heroin dose-response function was established. RESULTS: Rats with lesions of the NAcc shell did not differ significantly from sham controls in either the acquisition of heroin self-administration or in their heroin dose-response function. The NAcc core lesion group showed reduced levels of responding during the acquisition of heroin self-administration and a reduction in responding during the heroin dose-response function, although this behaviour was sensitive to changes in the dose of heroin. CONCLUSIONS: The NAcc shell does not appear to be critical for heroin self-administration, whereas the NAcc core, although apparently not essential in mediating the rewarding effect of i.v. heroin, may mediate processes that are of special importance during the acquisition of instrumental behaviour.