Lack of dopamine supersensitivity in rats after chronic administration of blonanserin: Comparison with haloperidol.

Long-term treatment with antipsychotic drugs in patients with schizophrenia can lead to dopamine supersensitivity psychosis. It is reported that repeated administration of haloperidol caused dopamine supersensitivity in rats. Blonanserin is an atypical antipsychotic drug with high affinity for dopamine D2, D3 and serotonin2A receptors. In this study, we investigated whether chronic administration of blonanserin leads to dopamine supersensitivity. Following oral treatment with blonanserin (0.78 mg/kg) or haloperidol (1.1 mg/kg) twice daily for 28 days, the dopamine D2 agonist quinpirole-induced hyperlocomotion test and a dopamine D2 receptor binding assay were conducted. We found that haloperidol significantly enhanced both quinpirole-induced hyperlocomotion and striatal dopamine D2 receptor density in rats. On the other hand, repeated administration of blonanserin had no effect on either locomotor activity or striatal dopamine D2 receptor density. Further, our results show that mRNA levels of dopamine D2 and D3 receptors in several brain regions were unaffected by repeated administration of both agents. In addition, we examined the effect of the dopamine D3 receptor antagonist PG-01037 on development of dopamine supersensitivity induced by chronic haloperidol treatment and showed that PG-01037 prevents the development of supersensitivity to quinpirole in chronic haloperidol-treated rats. Given the higher affinity of blonanserin at dopamine D3 receptors than haloperidol, antagonism of blonanserin at dopamine D3 receptors may play a role in lack of dopamine supersensitivity after chronic administration. The present findings suggest long-term treatment with antipsychotic dose of blonanserin may be unlikely to lead to dopamine supersensitivity.