Fig. 1.
Effects of amphetamine exposure (2 mg/kg/day × 5 days) one month earlier on instrumental responding for food reward. (A) Effects of prior amphetamine exposure on instrumental responding for food under fixed ratio schedules. Bars indicate number of lever presses under each fixed ratio schedule. There were no differences in performance under the FR1, 3, and 10 schedules, but amphetamine exposed rats (filled bars) had significantly more lever presses under the higher ratio schedules (FR20 and FR40) than saline exposed controls (open bars). * p<.05 (B) Effects of prior amphetamine exposure on 4 sessions of testing under a progressive ratio of responding for food reward. Data points indicate the highest response ratio achieved on each day. Amphetamine exposed rats achieved significantly higher response ratios compared to saline controls.