An evaluation of the mechanism of scopolamine-induced impairment in two passive avoidance protocols.

The effects of several doses of the centrally-acting muscarinic antagonist, scopolamine, on subsequent learning and memory were examined using two versions of a standard light versus dark passive avoidance paradigm. The first protocol was employed primarily to examine the effects of scopolamine on the acquisition component of learning and memory as subject performance was measured during five successive (repeated) training trials. The second protocol employed a one-trial twenty-four hour retention task in which subjects were given one training trial followed by one testing trial twenty-four hours later. This latter test encompasses acquisition, retention, and recall components of learning and memory. Dose response studies indicated an effective dose range of 0.4-1.2 mg/kg with 0.8 mg/kg producing maximal performance decrement. Differential scopolamine treatment demonstrated that the drug's primary effect was on the acquisition component only under the present experimental protocols. Furthermore, scopolamine was not found to produce state-dependent learning. Animals administered scopolamine before training and testing failed to perform better than animals receiving pre-training administration only.