Effects of selection delays on radial maze performance: acquisition and effects of scopolamine

The effects of post-selection confinement (delays) on both the acquisition of performance and the response to the muscarinic blocker, scopolamine, were examined in an automated version of the eight arm radial maze. Long-Evans rats, exposed to post-selection delays of 0.5 sec (n = 4) or 100 sec (n = 4) during daily training trials did not differ in either the number of trials to acquire an accurate baseline of performance or in the amount of time required to obtain all eight food pellets. However, the pattern (delta-arm scores) of within-session arm selections demonstrated by the two groups of rats differed. Rats exposed to the 0.5-sec delay typically selected arms adjacent to arms from which they exited while rats exposed to the 100-sec delay were more likely to enter arms 2-removed from the exit arm. When scopolamine (0.03 to 1.0 mg/kg) was administered prior to testing, rats in the 100-sec delay group showed a greater reduction of accuracy and a larger increase in selection latency than rats in the 0.5-sec delay group. The differential effect of delay value on delta-arm scores was also eliminated in a dosage dependent manner with scopolamine. Scopolamine methylbromide (0.3 mg/kg) was found to have little effect on performance. In summary, the results indicate that the post-selection delay procedure is a sensitive and selective test for chemical-induced dysfunctioning of spatial memory in rats.