Pre-exposure of rats to amphetamine sensitizes self-administration of this drug under a progressive ratio schedule

Two groups of male rats were tested to determine whether pre-exposure to ci-amphetamine would enhance the motivation to self-administer the drug under a progressive ratio schedule of reinforcement. In the first phase of the experiment, one group of rats received d-amphetamine (2 mg/kg IF), while a second group received saline on alternate days for a total of ten injections, Following a 21-day drug withdrawal period, behavioral sensitization was confirmed by a significant increase in amphetamine-induced stereotypy in the d-amphetamine-pretreated group. relative to the saline-pretreated group. In thr second phase of the study, all rats were implanted with chronic jugular catheters and trained to self-administer d-amphetamine (0.2 mg/kg per infusion) under a fixed-ratio schedule of reinforcement. The progressive ratio paradigm was then imposed for 7 consecutive days, d-amphetamine-pretreated rats attained significantly higher break points than saline-pretreated animals. These data suggest that pre-exposure to cl-amphetamine may enhance the motivation to self-administer this drug.