RATS SELF-ADMINISTER CARBACHOL DIRECTLY INTO THE NUCLEUS-ACCUMBENS

The potential reinforcing effect of the muscarinic cholinergic agonist carbachol within the nucleus accumbens (ACB) was examined in female W istar rats by using the technique of intracranial self-administration. Rats dose dependently self-administered solutions of 0.0-6.6 mM (in a volume of 100 nL per injection) directly into the ACE. Rats self-admi nistered the 3.3 and 6.6 mM doses significantly more than the group gi ven only vehicle. The caudate putamen did not support reliable self-ad ministration of the 6.6-mM dose. Rats exhibited preference for the lev er that produced infusions of 3.3 and 6.6 nM carbachol into the ACB ov er the lever that had no consequence. The self-infusion of the 6.6-mM dose into the ACB was inhibited by the coadministration of the muscari nic antagonist scopolamine (0.25 mM), but not by the nicotinic antagon ist mecamylamine (6.6 mM). The present results suggest that direct act ivation of muscarinic receptors within the ACB supports self-administr ation and could result from reinforcement or from elicitation of a nov el stimulus. (C) 1998 Elsevier Science Inc.