The effect of nifedipine, Ca(2+) antagonist, on activity of MAO inhibitors, N-acetylserotonin and melatonin in the mouse tail suspension test.

An antidepressive effect is associated with the A type monoamine oxidase (MAO) inhibitors which selectively stimulate serotonin conversion into N-acetylserotonin and melatonin. The current study compared the effect of these compounds with the non-selective MAO inhibitors and selective MAO-B inhibitors on the duration of immobility in the mouse tail suspension test, a variant of the 'behavioural despair' test. Since the Ca(2+) antagonist, nifedipine, potentiated the effect of tricyclic and atypical antidepressants in the tail suspension test, the additional aim of the current study was to evaluate the effect of nifedipine in combination with ineffective doses of MAO inhibitors. Befloxatone, a selective reversible MAO-A inhibitor, N-acetylserotonin and melatonin decreased the duration of immobility. Non-selective MAO inhibitors (phenelzine and niamid), selective MAO-B inhibitors (deprenyl and Ro 196327) and selective MAO-A inhibitors (brofaromine, moclobemide and clorgyline) did not affect the duration of immobility. Nifedipine decreased the duration of immobility in combination with ineffective doses of all tested drugs, except the selective MAO-B inhibitor, Ro 196327. The results of our study suggest the antidepressant-like activity of N-acetylserotonin and melatonin and the possibility of the potentiation of the effect of practically all known classes of antidepressants by Ca(2+) antagonist, nifedipine.