MK801-INDUCED HYPERACTIVITY - DURATION OF EFFECTS IN RATS

MK801, a noncompetitive NMDA antagonist, induces hyperactivity, the du ration of which is unknown. Thus, the hyperactivity induced by three d ifferent doses of MK801 was measured for 4 h using an automated open-f ield system. Adult male rats were habituated to the monitors for 1 h i mmediately prior to data collection. Rats were then administered one o f three doses (0.05 mg/kg, n = 15; 0.1 mg/kg, n = 14; 0.5 mg/kg, n = 1 1) of MK801 or equivalent volumes of saline (n = 14). Upon injection, individual monitors were activated, and 48 consecutive 5-min samples w ere collected. Results indicated that MK801 induced hyperactivity in a dose-dependent fashion, with the two lower doses being significantly different from saline controls, but not from each other. The 0.5 mg/kg dose indicated that the peak behavioral activation occurred approxima tely 30 min after administration. This was followed by either a slow d ecline or a plateau phase, dependent upon the measure examined. By app roximately 3 h after administration all measures had returned to the l evel of saline controls.