Long-term treatment with haloperidol or clozapine does not affect dopamine D4 receptors in rat frontal cortex

We examined the effects of long-term treatment with haloperidol and clozapine on dopamine D4 receptors in rat frontal cortex. Dopamine D4 receptor binding sites were indirectly determined from the displacement experiments of [3H]clozapine binding using nemonapride. Three-weeks administration of haloperidol (0.5mg/kg) or clozapine (10mg/kg) did not significantly affect the D4 receptors in the frontal cortex. The density of D2 receptors, determined by [3H]spiperone binding to striatum, was increased by long-term treatment with haloperidol, but it was not significantly changed by that with clozapine.