Influence of prefeeding and scopolamine upon performance in a delayed matching-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 testing) 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 the food reinforced delayed matching-to-position (DMTP) task. In preliminary 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, scopolamine only increased sample latency. In a subsequent experiment, an intermediate dose of scopolamine (0.075 mg/kg s.c.) was directly compared with prefeeding in the same animals. Both treatments impaired choice accuracy, however, the effects of scopolamine were significantly larger than prefeeding. Conversely, prefeeding caused significantly greater omissions and larger increases in task latencies compared with scopolamine. These findings demonstrate some dissociation between the effects of scopolamine and prefeeding in the DMTP task, suggesting that the actions of scopolamine are not entirely due to reduction in motivation. Furthermore, the effects of scopolamine are likely to be centrally mediated.