Serotonin-2 and dopamine-1 binding components of clozapine in frontal cortex and striatum in the human brain visualized by positron emission tomography

Abstract

The specific binding of N-methyl- 11C-clozapine in the human brain was studied in five healthy volunteers with positron emission tomography (PET). Four of the volunteers were reaxamined after treatment with the dopamine D 1 and D 2 receptor antagonist flupenthixol, and all five volunteers were reexamined after pretreatment with the serotonin 2 receptor antagonist ritanserin. The examinations after flupenthixol and ritanserin treatment were performed on different occassions. In the flupenthixol part of the study, two of the subjects were given an oral dose of 1 mg flupenthixol 2–3 h before the posttreatment study with PET. The other two subjects received 0.5 mg orally three times during the 24 h preceding the posttreatment PET study, with the last dose being administered ≤4 h before the scan. All five ritanserin-treated subjects followed the same dosing regimen. During the 5 days preceding the posttreatment PET study, they were given a 10-mg tablet of ritanserin in the evening. The last dose was administered 2- 1 2 hours before the study. Both flupenthixol and ritanserin pretreatment were associated with decreased binding of N-methyl- 11C-clozapine in dorsolateral and medial frontal cortical regions. These results support previous findings that clozapine has affinity for both dopamine D 1 and serotonin 5-HT 2 receptors in the human frontal cortex. No consistent change of binding was observed in striatal regions following flupenthixol or ritanserin pretreatment. The clinical aspects of this feature are discussed, both with respect to efficacy and side effects.