Diminished Responsivity on a Passive Avoidance Task to Second Administration of Scopolamine

Rats were given two training sessions, separated by intervals of 1, 3, or 6 days, on a passive avoidance task. For each training interval, control groups receiving saline and experimental groups receiving scopolamine prior to both sessions were run. Although scopolamine impaired acquisition of the task, the drugged groups displayed a marked improvement in performance on the second day of training. The data suggest, however, that the degree of behavioral improvement for the scopolamine groups diminished with intervals of increased duration interposed between the 2 training days. Two alternative explanations are entertained to account for the excellent Day-2 performance of the scopolamine groups: the development of a partial physiological tolerance to the effects of scopolamine or the development of a behavioral tolerance, unrelated to any known physiological tolerance.