Antidepressant-like effects of nicotinic acetylcholine receptor antagonists, but not agonists, in the mouse forced swim and mouse tail suspension tests.

Current literature suggests involvement of nicotinic acetylcholine receptors (nAChRs) in major depression. However, it is controversial whether the antidepressant-like effect of nAChR modulation is induced by activation, desensitization or inhibition of central nAChRs. In addition, the specific nAChR subtype/s involved remains unknown. In this study, we systematically compared the effects of non-selective and selective nicotinic agonists and antagonists in two different tests for antidepressant effects in mice: the tail suspension test and the forced swim test. Compounds: nicotine, RJR-2403 (alpha4beta2-selective agonist), PNU-282987 (alpha7-selective agonist), mecamylamine (non-selective antagonist), dihydro-beta-erythroidine (DHbetaE; alpha4beta2-selective antagonist), methyllycaconitine (MLA; alpha7-selective antagonist) and hexamethonium (non-brain-penetrant non-selective antagonist). All compounds were tested in a locomotor activity paradigm to rule out non-specific stimulant effects. The data show that blockade of nAChRs with mecamylamine, or selective antagonism of alpha4beta2 or alpha7 nAChRs with DHbetaE or MLA, respectively, has antidepressant-like effects. These effects were not confounded by motor stimulation. Hexamethonium did not show antidepressant-like activity, supporting the involvement of central nAChRs. At the dose levels tested, none of the nAChR agonists displayed antidepressant-like profiles. In conclusion, antagonism of central alpha4beta2 and/or alpha7 nAChRs induced antidepressant-like effects in mice. A strategy involving antagonism of central nAChRs could potentially lead to the development of novel antidepressant therapeutics.