INFLUENCE OF PREFEEDING AND SCOPOLAMINE UPON PERFORMANCE IN A DELAYEDMATCHING-TO-POSITION TASK

The present study compared the influence of prefeeding (0, 10, 20 g or an unlimited amount of food pellets for a 90 min period prior to test ing) with the effects of scopolamine (0, 0.03, 0.075 or 0.1 mg/kg s.c. ) and scopolamine methylbromide (0.1 mg/kg s.c.) upon performance in t he food reinforced delayed matching-to-position (DMTP) task. In prelim inary studies using separate groups of rats, both scopolamine (but not scopolamine methylbromide) and prefeeding impaired choice accuracy in a seemingly delay-independent manner. Both treatments also increased omissions. However, while prefeeding increased all task latencies, sco polamine only increased sample latency. In a subsequent experiment, an intermediate dose of scopolamine (0.075 mg/kg s.c.) was directly comp ared with prefeeding in the same animals. Both treatments impaired cho ice accuracy, however, the effects of scopolamine were significantly l arger than prefeeding. Conversely, prefeeding caused significantly gre ater omissions and larger increases in task latencies compared with sc opolamine. These findings demonstrate some dissociation between the ef fects of scopolamine and prefeeding in the DMTP task, suggesting that the actions of scopolamine are not entirely due to reduction in motiva tion. Furthermore, the effects of scopolamine are likely to be central ly mediated.