Do Central Antiadrenergic Actions Contribute to the Atypical Properties of Clozapine?

Abstract

Full neuropharmacological understanding of the atypical antipsychotic agent clozapine remains elusive. Antidopaminergic actions of most neuroleptics probably contribute to their antipsychotic benefits, but also to neurological side-effects. Clinical evidence of abnormalities of dopamine (DA) and serotonin (5-HT) in psychotic disorders is inconsistent, but there is substantial metabolic and post-mortem evidence for hyperactivity of noradrenalin (NA). Clozapine is only weakly antidopaminergic but is a potent antagonist at brain α1-adrenergic, 5-HT2-serotonergic, and muscarinic receptors. Its apparent limbic-over-extrapyramidal neuro-physiological selectivity can be mimicked by combining a typical neuroleptic with a central α1 antagonist. Clozapine strongly upregulates α1, but not DA, receptor abundance, and may supersensitise α1 but not DA receptors in rat brain. Clozapine also selectively increases activity of NA neurons and metabolic turnover in NA more than DA areas of rat brain, and also increases NA, but not DA or 5-HT, metabolites in human CSF. Potential psychotropic effects of selective central antiadrenergic agents may deserve reconsideration.