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-METHYLTYROSINE ON OPERANT BEHAVIOR AND BRAIN CATECHOLAMINE LEVELS
1 Departments of Pharmacology and Psychiatry, University of Chicago, Chicago, Illinois
-Methyltyrosine (AMT) was administered to rats trained to press a level for water on either a fixed-ratio (FR) or fixed-interval (FI) schedule of reinforcement in order to examine the role of catecholamines in the maintenance of conditioned behavior. Fixed-ratio performance was most severely decreased by AMT, although no differences could be detected in brain amine levels between FI or FR rats killed immediately after testing and untrained rats. The greater decrease in FR performance after AMT was not accompanied by a greater decrease in brain amines. However, the effect of AMT on performance was greatly attenuated by pretreatment with L-dihydroxyphenylalanine on an FR schedule, and there was a significant correlation between response output on this schedule and brain catecholamine concentration. In addition, it was found that with extended lever-pressing sessions on a variable interval (VI) schedule, brain amines were decreased more than in untrained, nondeprived rats. The effect of AMT on fixed-ratio performance and the interaction between AMT and VI performance suggest that the AMT effect is dependent upon initial performance during the test session, which is a function of the schedule of reinforcement.
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