Effects of diazepam, citalopram, methadone and naloxone on PCP-induced stereotyped behaviour and social isolation in the rat social interaction test.

Phencyclidine (PCP) can induce a model psychosis in humans that mimics the positive and negative symptoms of schizophrenia. In the social interaction test PCP induces stereotyped behaviour and social isolation in rats, and these behaviours can be inhibited by antipsychotic drugs. In order to further evaluate the predictive validity of this model of schizophrenia the anxiolytic diazepam (0.02-17.5 micromol/kg; 0.005-5.0 mg/kg), the antidepressant citalopram (0.62-19.8 micromol/kg; 0.3-4.0 mg/kg), the opioid agonist methadone (0.36-5.8 micromol/kg; 0.13-2.0 mg/kg) and the opioid antagonist naloxone (0.34-22.0 micromol/kg; 0.13-8.0 mg/kg) were tested as examples of drugs without antipsychotic activity. The experiments demonstrated that these compounds did not specifically inhibit the behavioural effects of PCP. So far only antipsychotic drugs have been able to specifically inhibit the PCP-induced behaviours.