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Abstract

Two groups of male Long-Evans rats were compared to determine whether preexposure to amphetamine would enhance the motivation to self-administer the drug under a progressive ratio schedule of reinforcement. In the first phase of the experiment each animal received a single injection of either amphetamine or saline on alternate days for a total of ten injections. Following a 21 day withdrawal period, behavioral sensitization was confirmed by a significant increase in amphetamine-induced stereotypy in the amphetamine-pretreated group, relative to the saline-pretreated group. In the second phase of the study all rats were implanted with chronic jugular catheters and trained to'self-administer amphetamine under a fixed-ratio schedule of reinforcement. The progressive ratio paradigm was then imposed for seven days; amphetamine-pretreated rats attained significantly higher breaking points than saline-pretreated animals. These data indicate that preexposure to psychoactive agents may enhance the motivation of drug self-administration, suggesting augmentation in drug addiction liability.