[Effects of scopolamine and diazepam on delayed discrimination behavior in rats]

The effects of subcutaneously administered scopolamine and diazepam on simultaneous as well as delayed light-dark discrimination behavior were studied in a Y-maze situation using rats. In simultaneous discrimination behavior, running responses to the lighted side of either the right or left arm of the Y-maze were regarded as correct choices. In delayed discrimination behavior, running responses to the lighted side at several delay times (0. 2, 4, and 8 sec) after extinguishment of the light were regarded as correct choices. In the saline test, the percentage of correct choices decreased as the delay time was extended. Scopolamine at 0.03 mg/kg decreased the percentage of correct choices as the delay time was extended within the range of 0 sec through 4 sec. Diazepam both at 1 mg/kg and at 2 mg/kg decreased the percentage at the delay times of 0, 2, and 4 sec but this decreasing effect was not dependent on the delay time. The same doses of these drugs had no effect on simultaneous discrimination behavior. These results suggest that scopolamine at 0.03 mg/kg and diazepam both at 1 mg/kg and at 2 mg/kg disrupt delayed discrimination behavior in different ways.