[Effects of scopolamine upon delayed radial-arm maze performance in rats]

Behavioral impairment induced by the muscarinic anticholinergic drug, scopolamine (SCP) has been widely used to make preclinical evaluation of nootropic drugs. To further investigate the disruptive effect of SCP on memory-related behavior, male Wistar-Imamichi strain rats were tested in the 8-arm radial maze task with a delay interval between choices 4 and 5. In this task, the animals were first allowed to obtain 4 food rewards out of 8 arms and then removed from the maze. They were replaced on the maze to collect the remaining 4 pellets after a delay interval, during which they were kept in their home cages. In experiment 1, a 1-6 hr delay interval was imposed. SCP (0.5 mg/kg, i.p.) was administered immediately after choice 4. In experiment 2, a delay interval was always 4 hr, but SCP was administered 0-2 hr after choice 4. In both experiments, SCP significantly reduced the number of correct choices in choices 5-8, but did not show any effects depending on delay intervals or drug-administration time. These results suggest that the performance deficits induced by SCP might be due to its effects on the primary stage of information processing rather than those on the consolidation or storage process of memory.