Fig. 1.

The effects of intravenous MPEP on operant responding for nicotine. Rats were trained to lever-press for nicotine on an FR3 schedule of reinforcement with a 20-s timeout. The figure shows mean responding on the active lever (open columns) and the inactive lever (filled columns) for rats pretreated with saline or MPEP (N = 8 for 2.5 mg/kg; N = 4 for 5.0 mg/kg) prior to the session. Data for the day after the MPEP session are also presented. The data are reported as means ± SEM. Significantly different from rats pretreated with saline *P < 0.05; **P < 0.01