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In this study the functional interaction of the antidepressant drugs amitriptyline, mianserin, maprotiline, imipramine, fluoxetine and the putative antidepressant drug flibanserin has been studied on 5-HT7-mediated responses to 5-carboxamidotryptamine (5-CT) in the guinea-pig ileum. 5-CT induced a concentration-dependent inhibition of the contractile response to substance P (100 nM). Except for fluoxetine and flibanserin, all the antidepressants antagonized by different degrees the 5-CT inhibitory response with the following rank affinity order: mianserin > maprotiline > imipramine > amitriptyline. Mianserin was the only antidepressant to show a profile of competitive antagonism at 5-HT7 receptors in a tenfold range of concentrations (0.1-1 microM), with an affinity (pA2) value of 8.1 +/- 0.6. The antagonism of the other antidepressants was not concentration-dependent (amitriptyline) or was associated with slight or moderate reduction of the maximal 5-CT response (imipramine or maprotiline). The apparent affinity (pKB) values were: amitriptyline, 7.0 +/- 0.2; maprotiline, 7.3 +/- 0.6; imipramine, 7.2 +/- 0.4. Our results show that various antidepressant drugs belonging to different chemical classes behave as antagonists at enteric 5-HT7 receptors through competitive or allosteric mechanisms. This evidence extends our previous findings demonstrating the interaction of antidepressants with other 5-HT receptors, namely 5-HT3 and 5-HT4 receptors.

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Depression is the most prevalent functional psychiatric disorder in late life. The problem of motor disorders associated with antidepressant use is relevant in the elderly. Elderly people are physically more frail and more likely to be suffering from physical illness, and any drug given may exacerbate pre-existing diseases, or interact with other drug treatments being administered for physical conditions. Antidepressants have been reported to induce extrapyramidal symptoms, including parkinsonism. These observations prompted us to review the neurobiological mechanism that may be involved in this complex interplay including neurotransmitters and neuronal circuits involved in movement and emotion control and their changes related to aging and disease. The study of the correlations between motor and mood disorders and their putative biochemical bases, as presented in this review, provide a rationale either to understand or to foresee motor side effects for psychotropic drugs, in particular antidepressants. Molecular Psychiatry (2001) 6, 134-142.

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