Effect of physostigmine and atropine on the single-trial passive avoidance response in rats. 
Rats received a single training trial on an inhibitory avoidance (passive avoidance) task and retention trials 24 hr (R-I) and 48 hr (R-II) later, in a special two-chambered apparatus, and the mean step-through latency was determined.  The animals were given the drug, either pre-trial, pre-trial plus pre-retention, pre-retention or post-trial.  Physostigmine (0.1 mg/kg, ip) and atropine (6.0 mg/kg, ip) had no effect on learning, but they adversely affected retention, particularly at 24 hr.  The effect seems to involve central cholinergic mechanisms of retention.