Cocaine is self-administered into the shell but not the core of the nucleus accumbens of Wistar rats.

The rewarding properties of cocaine have been postulated to be regulated, in part, by the mesolimbic dopamine system. However, the possibility that the rewarding properties of cocaine are mediated by direct activation of this system has yielded contradictory findings. The intracranial self-administration technique is used to identify specific brain regions involved in the initiation of response-contingent behaviors for the delivery of a reinforcer. The present study assessed whether adult Wistar rats would self-administer cocaine directly into the nucleus accumbens shell (AcbSh) and core (AcbC). For each subregion, subjects were placed in standard two-lever operant chambers and randomly assigned to one of five groups for each site that were given either artificial cerebrospinal fluid (aCSF), or 400, 800, 1200, or 1600 pmol of cocaine/100 nl to self-administer. The data indicate that rats with placements within the AcbSh readily self-administered 800 to 1600 pmol of cocaine/100 nl and responded significantly more on the active than inactive lever. These subjects also decreased responding on the active lever when aCSF was substituted for cocaine and reinstated responding on the active lever when cocaine was reintroduced. Coinfusion of the D2-like receptor antagonist sulpiride inhibited cocaine self-infusion in the AcbSh. In contrast to the AcbSh data, rats failed to self-administer any tested dose of cocaine into the AcbC or areas ventral to the AcbSh. These findings suggest that the AcbSh is a neuroanatomical substrate for the reinforcing effects of cocaine and that activation of D2-like receptors is involved.