Time dependent changes in anterograde scopolamine-induced amnesia in rats

These experiments studied the effect of scopolamine on memory formation and subsequent memory recall. Different groups of rats were trained on a Y-maze brightness discrimination task 20 min after IP injection of 2 mg/kg scopolamine HBr, an anticholinergic. Retention tests were then conducted 1 day or 2, 4, or 6 weeks after training. Deficits in retention performance were observed at 1 day and 2 weeks after training but not at the longer intervals. In addition, other rats were trained in the same manner and after the same dose of scopolamine but were then retention tested 20 min after 0.5 mg/kg physostigmine salicylate, a cholinesterase inhibitor. These subjects also showed deficits at 1 day and 2 weeks but were not different from controls at the longer intervals. Amnesia was not, however, produced after treatment with scopolamine methyl nitrate or by injections of scopolamine HBr administered immediately after training. These results suggest that scopolamine, present in the central nervous system during training or within the first few moments thereafter, modifies the formation of the memory trace in such a way that memory is not available for recall for a period of weeks.