Clozapine-N-oxide (CNO) is a metabolite of clozapine, which reduces the density of 5-HT2 receptor in rat primary cortical cells.  Clozapine-N-oxide (CNO) also activates an evolved M3-muscarinic receptor and then can be used in chemogenetics. 
Clozapine is a known atypical antipsychotic medication used in the treatment of schizophrenia. The two major metabolites of clozapine are norclozapine and clozapine-N-oxide (CNO) . Clozapine is also formed from its N-oxide metabolite. It means that a reversible metabolic pathway exists for clozapine and clozapine-N-oxide (CNO) . In rat primary cortical cells and SHS5Y5 neuroblastoma cells, a significant decrease was found for 5-HT2 receptor density with 200 ng/ml clozapine-N-oxide (CNO) . About the method of identification, reversed-phase HPLC has been reported to detect clozapine and its two major metabolites in human plasma.
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