Clozapine (HF 1854) is an antipsychotic used to treat schizophrenia. Clozapine is a potent antagonist of dopamine and a number of other receptors, with a Ki of 9.5 nM for M1 receptor[1][2][3]. Clozapine is also a potent and selective agonist at the muscarinic M4 receptor (EC50=11 nM)[4].
Clozapine shows the unique property of having antipsychotic action but no Parkinson-like motor side effects. The chemical structure of clozapine facilitates a relatively rapid dissociation from D2 receptors. After short-term occupation of D2 receptors, peak neural activity raises synaptic dopamine, which then displaces clozapine. While clozapine also occupies other types of receptors, they may not have a significant role in preventing parkinsonism. Clozapine is very potent at D2 receptor with a Ki of 75 nM. Clozapine is also potent at the α2-adrenoceptor with a Ki value of 51 nM[1]. Clozapine causes paradoxical downregulation of 5-HT2A receptors. Clozapine also binds to 5-HT6 and 5-HT7 receptors with high affnity[2].
Head-twitch response is decreased and [3H]ketanserin binding is downregulated in 1, 7, and 14 days after chronic clozapine. 5-HT2A mRNA is reduced 1 day after chronic clozapine. Induction of c-fos, but not egr-1 and egr-2, is rescued 7 days after chronicclozapine[3].
References:
[1]. Seeman P, et al. Clozapine, a fast-off-D2 antipsychotic. ACS Chem Neurosci. 2014 Jan 15;5(1):24-9.
[2]. Zhukovskaya NL, et al. Clozapine downregulates 5-hydroxytryptamine6 (5-HT6) and upregulates 5-HT7 receptors in HeLa cells. Neurosci Lett. 2000 Jul 21;288(3):236-40.
[3]. Moreno JL, et al. Persistent effects of chronic clozapine on the cellular and behavioral responses to LSD in mice. Psychopharmacology (Berl). 2013 Jan;225(1):217-26.
[4]. Zorn SH, et al. Clozapine is a potent and selective muscarinic M4 receptor agonist. Eur J Pharmacol. 1994 Nov 15;269(3):R1-2.