PREEXPOSURE 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 am phetamine-induced stereotypy in the d-amphetamine-pretreated group. re lative to the saline-pretreated group. In thr second phase of the stud y, all rats were implanted with chronic jugular catheters and trained to self-administer d-amphetamine (0.2 mg/kg per infusion) under a fixe d-ratio schedule of reinforcement. The progressive ratio paradigm was then imposed for 7 consecutive days, d-amphetamine-pretreated rats att ained significantly higher break points than saline-pretreated animals . These data suggest that pre-exposure to cl-amphetamine may enhance t he motivation to self-administer this drug.