Injections (i.p.) of either saline (1 ml/kg/day) or cocaine (10 mg/kg/day) were administered to rats chronically instrumented with microelectrode/microcannulae assemblies in NAc in the activity apparatus on the days indicated. Behavioral and electrochemical responses were obtained in the freely moving rats on days 0, 1, 3, 5, and 7. Additionally, responses were recorded on day 15, following a 7-day withdrawal in the experimental group only. In the control group, the same rats were used in the two sequentially conducted control experiments.