N-desmethylclozapine, an allosteric agonist at muscarinic 1 receptor, potentiates N-methyl-D-aspartate receptor activity.
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| Abstract |
The molecular and neuronal substrates conferring on clozapine its unique and superior efficacy in the treatment of schizophrenia remain elusive. The interaction of clozapine with many G protein-coupled receptors is well documented but less is known about its biologically active metabolite, N-desmethylclozapine. Recent clinical and preclinical evidences of the antipsychotic activity of the muscarinic agonist xanomeline prompted us to investigate the effects of N-desmethylclozapine on cloned human M1-M5 muscarinic receptors. N-desmethylclozapine preferentially bound to M1 muscarinic receptors with an IC50 of 55 nM and was a more potent partial agonist (EC50, 115 nM and 50% of acetylcholine response) at this receptor than clozapine. Furthermore, pharmacological and site-directed mutagenesis studies suggested that N-desmethylclozapine preferentially activated M1 receptors by interacting with a site that does not fully overlap with the acetylcholine orthosteric site. As hypofunction of N-methyl-d-aspartate (NMDA) receptor-driven neuronal ensembles has been implicated in psychotic disorders, the neuronal activity of N-desmethylclozapine was electrophysiologically investigated in hippocampal rat brain slices. N-desmethylclozapine was shown to dose-dependently potentiate NMDA receptor currents in CA1 pyramidal cells by 53% at 100 nM, an effect largely mediated by activation of muscarinic receptors. Altogether, our observations provide direct evidence that the brain penetrant metabolite N-desmethylclozapine is a potent, allosteric agonist at human M1 receptors and is able to potentiate hippocampal NMDA receptor currents through M1 receptor activation. These observations raise the possibility that N-desmethylclozapine contributes to clozapine's clinical activity in schizophrenics through modulation of both muscarinic and glutamatergic neurotransmission.
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| Authors | Cyrille Sur, Pierre J Mallorga, Marion Wittmann, Marlene A Jacobson, Danette Pascarella, Jacinta B Williams, Philip E Brandish, Douglas J Pettibone, Edward M Scolnick, P Jeffrey Conn |
| Journal | Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 100 Issue 23 Pg. 13674-9 (Nov 11 2003) ISSN: 0027-8424 [Print] United States |
| PMID | 14595031 (Publication Type: Journal Article) |
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