ABSTRACT
A number of monoamine oxidase (MAO) inhibitors have been shown to have true antidepressant activity and some have found their way into clinical use. The existence of multiple forms of MAO, described early in the 1960s, was reinforced by the discovery of clorgyline, an irreversible inhibitor of the enzyme. Ex vivo experiments in which animals are pretreated with the selective MAO-A (clorgyline) or MAO-B (L-deprenyl) inhibitors and the tissue is subsequently removed, homogenized, and assayed for MAO activity with various monoamine substrates substantiate the presences of two enzyme forms8 as outlined by Johnston. In the human brain the situation is rather similar but the proportion of MAO-A to MAO-B is significantly different. Early uncontrolled studies with the MAO-B inhibitor, deprenyl, reported beneficial effects in anergic, negativistic patients, several of whom had not responded to imipramine, electroconvulsive therapy, and other treatments. Deprenyl dosages in these early studies were in the range now known to be non-MAO-B selective.
