THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS Copyright © 1993 by The American Society for Pharmacology and Experimental Therapeutics Electrophysiological Effects of Cocaine in the Rat Nucleus

The nucleus accumbens (NAc) is intricately involved in maintain-ing cocaine self-administration. Cocaine inhibits the firing of most NAc cells due to its ability to prevent the reuptake of dopamine (DA) and 5-hydroxytryptamine (5-HT), both of which predomi-nantly inhibit NAc cell discharge in vivo. The present studies investigated the roles of DA and 5-HT in the effects of iontopho-retically applied cocaine. Most NAc cells exhibited negative/ positive waveforms (Type I cells). These cells were significantly more sensitive to cocaine than Type II cells (positive/negative waveforms), apparently due to differences in the actions of 5-HT. Whereas DA was equipotent at inhibiting Type I and Type II cells, 5-HT inhibited Type I cells but, primarily excited Type II cells. Thus the ability of cocaine to potentiate the effects of both DA and 5-HT resulted in a pronounced inhibition of Type I cells, whereas the 5-HT-mediated excitation of Type II cells appeare