6-Hydroxydopamine lesions of the medial prefrontal cortex fail to influence intravenous self-administration of cocaine

It has been suggested that the initiation and maintenance of cocaine self-administration (SA) is critically dependent on the dopaminergic (DA) projection to the medial prefrontal cortex (mPFC). Evidence for this hypothesis has been obtained from intracranial SA of cocaine, but a role of the mPFC in IV cocaine SA has not been established. The present experiment investigated the effect of destruction of DA-containing terminals in the mPFC on the rate and pattern of IV cocaine SA. Rats were trained to self-administer cocaine during daily 3-h sessions. After stable response patterns were obtained, the rats received either bilateral injections of 6-hydroxydopamine (6-OHDA) into the mPFC, or sham operations. The lesions did not affect either the rate or pattern of IV cocaine SA, despite producing substantial DA depletions in the mPFC. Thus, the mPFC does not appear to be a critical substrate for the maintenance of IV cocaine SA. The 6-OHDA lesions of the mPFC resulted in an apparent increase in DA turnover in both the striatum and the nucleus accumbens, suggesting that DA terminals in the mPFC may have an inhibitory influence on the activity of subcortical DA projections.