Performance influence on the development of tolerance to amphetamine

Abstract

This experiment was performed to determine whether performance of a behavior in the drug state was necessary for behavioral tolerance to the effects of that drug to occur. Eight rats trained on a DRL 17.5-sec schedule received daily injections of 1.5 mg/kg d-amphetamine sulfate; four received amphetamine 30 min presession, and four received amphetamine 30 min postsession. Amphetamine given presession initially resulted in a disruption of timing behavior, an increase in response rate, an increase in short IRTs and a decrease in the number of reinforcements received. With continued administration of presession amphetamine the rats developed a partial tolerance to these disruptive effects. Postsession amphetamine had no effect on performance. When tolerance developed in rats receiving presession amphetamine, they were switched to postsession amphetamine; rats receiving postsession amphetamine were switched to presession amphetamine. Amphetamine produced the same disruption of performance in the rats switched to presession amphetamine as was observed in the initial pressession amphetamine group, indicating that tolerance did not develop to amphetamine given postsession. In addition changes in the pattern of responding were observed when amphetamine was initially administered presession.