EFFECTS OF IMIPRAMINE AND MIRTAZAPINE ON OPERANT PERFORMANCE IN RATS

The effects of the tricyclic antidepressant imipramine and the atypical antidepressant mirtazapine were compared on the performance of rats in three operant procedures: a differential reinforcement of low rates schedule (DRL), a delayed matching to position (DMTP), and simultaneous visual discrimination tasks. Both compounds improved performance in the DRL task in a similar dose-related manner. Imipramine, but not mirtazapine, disrupted performance in the visual discrimination task. Imipramine reduced accuracy and increased response latencies and missed trials. Neither compound effected accuracy in the DMTP; both compounds caused some slowness of responding and imipramine caused several animals to fail to respond in a manner similar to that observed in the visual discrimination task. These data suggest that although imipramine and mirtazapine are similarly effective in putative tests of antidepressant activity, imipramine has a greater tendency to disrupt other aspects of cognitive performance, as well as exert generally depressive effects on operant responding. (C) 1994 Wiley-Liss, Inc.