Scopolamine-induced impairment in concurrent fixed-interval responding in a radial maze task

The present study investigated the effects of scopolamine hydrobromide (SCOP: 0.06-1.0 mg/kg IP) and its quartenary analogue, scopolamine methylbromide (SCOPMB), on performance in a radial arm maze foraging task, to dissociate general drug-induced alterations of motor performance from measurement of impairments on more complex behaviors involving timing and memory. In this paradigm. rats are trained to free run a radial maze under an eight-alternative concurrent fixed-interval (FI) schedule of food reinforcement. The eight FIs (55 to 759 s) were assigned randomly to the arms of the maze, with a different pattern for each animal. SCOP produced dose-dependent degradation in response patterning and response rates in the concurrent FI schedules without significantly affecting the rates of arm entries or arm traversal latencies. The peripheral cholinergic antagonist, SCOPMB, generally produced small to moderate depressions in all measures with the exception of patterning of arm entries and pellets earned, but there were no clear dose-response relationships evident in the data. These results are consistent with the notion that central cholinergic mechanisms are involved in the mediation of complex conditioned behaviors.