The amnesic action of phencyclidine (PCP) was investigated in mice using a passive avoidance- and escape-learning method. PCP (10-30 mg/kg) administered immediately after the training test dose-dependently shortened and prolonged the step-down latency and escape latency, respectively in the retention test. There was a significant inverse relationship between the step-down and escape latencies, indicating that PCP had induced amnesia. The amnesic actions of PCP were retrograde, being observed when mice were given PCP within 10 min but not more than 30 min after the training test. The amnesic effects of PCP on both variables were antagonized significantly by physostigmine and naloxone, whereas cyproheptadine and haloperidol had no effect. None of these drugs by themselves affected passive avoidance- or escape-learning performance. These results suggest that the retrograde amnesic actions of PCP were produced via either the cholinergic or the opioidergic systems or both, but not through the serotonergic and the dopaminergic systems.
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