Fig. 2.

Experiment 1. (a) Acquisition of cocaine self-administration in rats assigned to receive one of four daily treatments during the first 7 days of subsequent extinction training. Rats were trained on an fixed ratio-1 schedule of reinforcement in daily 3-h sessions. Delivery of cocaine (0.50 mg/kg) was accompanied by a tone + flashing cue light conditioned stimulus (CS) presented for 5 s, which was followed by a 20-s time-out period signaled by illumination of the house light. Day 1 represents responding on the first day that acquisition criterion was met. (b) Active lever responses across 13 days of extinction. Responses had no programmed consequences (i.e., no CS or cocaine). Rats received one of four treatments [saline + unstressed, SCH-23390 (10.0 μg/kg) + unstressed, saline + stressed, or SCH-23390 + stressed] once each day (~ 2 hr after extinction session) for the first 7 days of extinction training (n = 7–11/treatment condition). (c) Weight change in chronically stressed and unstressed rats receiving vehicle or SCH-23390 injection. Injections were given immediately prior to placement in restrainers (3 h/day) or transport back to home cages. All data in figure are represented as mean ± SEM.