General procedure and apparatus described previously (26). Rats were trained under a discrete-trial schedule of food-pellet delivery (FR10, 45-s timeout) to respond on one lever after a subcutaneous (s.c.) injection of a training dose of 0.4 mg/kg nicotine (10 min before the session) and on the other lever after an injection of saline. Sessions lasted for 20 reinforcements or 30 min. WY14643 (40 mg/kg) was substituted for the training dose of nicotine and was also administered together with various doses of nicotine (0.01-0.4 mg/kg) to assess possible alterations of the nicotine dose-response curve.
