Persistent effects of chronic clozapine on the cellular and behavioral responses to LSD in mice.

In schizophrenia patients, optimal treatment with antipsychotics requires weeks to months of sustained drug therapy. However, single administration of antipsychotic drugs can reverse schizophrenia-like behavioral alterations in rodent models of psychosis. This raises questions about the physiological relevance of such antipsychotic-like activity. This study evaluates the effects of chronic treatment with clozapine on the cellular and behavioral responses induced by the hallucinogenic serotonin 5-HT(2A) receptor agonist lysergic acid diethylamide (LSD) as a mouse model of psychosis. Mice were treated chronically (21 days) with 25 mg/kg/day clozapine. Experiments were conducted 1, 7, 14, and 21 days after the last clozapine administration. [(3)H]Ketanserin binding and 5-HT ( 2A ) mRNA expression were determined in mouse somatosensory cortex. Head-twitch behavior, expression of c-fos, which is induced by all 5-HT(2A) agonists, and expression of egr-1 and egr-2, which are LSD-like specific, were assayed. Head-twitch response was decreased and [(3)H]ketanserin binding was downregulated in 1, 7, and 14 days after chronic clozapine. 5-HT ( 2A ) mRNA was reduced 1 day after chronic clozapine. Induction of c-fos, but not egr-1 and egr-2, was rescued 7 days after chronic clozapine. These effects were not observed after short treatment (2 days) with clozapine or chronic haloperidol (1 mg/kg/day). Our findings provide a murine model of chronic atypical antipsychotic drug action and suggest downregulation of the 5-HT(2A) receptor as a potential mechanism involved in these persistent therapeutic-like effects.