Effect of scopolamine on the hippocampal theta rhythm during an eight-arm radial maze task in rats.

The changes in the hippocampal theta rhythm during an impairment of reference and working memory of radial maze task induced by scopolamine administration were studied. Intraperitoneal injection of scopolamine at doses of 0.5 and 1.0 mg/kg caused a significant increase in the number of total, reference memory and working memory errors. On the other hand, scopolamine significantly increased the hippocampal theta power (5-12 Hz) at doses (0.5 and 1.0 mg/kg) that caused an impairment of reference and working memory. A significant increase in the peak frequency of the hippocampal theta rhythm was also observed with scopolamine, even at a dose of 0.2 mg/kg. At doses of 0.2, 0.5 and 1.0 mg/kg, scopolamine caused a decrease in the locomotor activity during the radial maze task. From these results, it may be concluded that an increase in amplitude of the hippocampal theta rhythm induced by scopolamine is closely associated with memory/learning function of the eight-arm radial maze.