Effects of phencyclidine on aggressive behavior in mice.

The effects of phencyclidine on aggressive behavior in mice and the possible mechanism of action for these effects were examined. PCP at a dose of 10.0 mg/kg significantly decreased the number of attacks by resident mice toward intruders. Significant increases in the number of attacks by non-drugged residents toward the intruders who were given high doses of PCP (6.0 and 10.0 mg/kg) were observed. Only the higher doses of PCP (6.0 and 10.0 mg/kg) significantly increased the duration of locomotion. The increase in locomotion was dependent upon the time after administration of the drug. Hyperactivity was present at 30 minutes for both doses and hypoactivity was present at three hours after administration of 3.0 mg/kg. PCP did not significantly alter the frequency of attacks in an unfamiliar test locale. Pretreatment with haloperidol (1 mg/kg) partially blocked the PCP-induced hyperactivity but pretreatment with methysergide (3 mg/kg) did not. Neither haloperidol nor methysergide blocked the suppressive effects of PCP on aggressive behavior. It is concluded that PCP does not increase aggressive behavior in mice but high doses will decrease aggression. PCP-treated intruder animals provoke more aggression by non-drugged animals. PCP-induced hyperactivity appears to be mediated by dopaminergic systems.