[3H]tryptamine binding sites are not identical to monoamine oxidase in rat brain

• Published in: Journal of neurochemistry Vol. 51; no. 5; p. 1535
• Main Authors: Perry, D C, Grimm, L J, Kettler, K G, Kellar, K J
• Format: Journal Article
• Language: English
• Published: England 01-11-1988
• Subjects: 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine; Animals; Binding, Competitive; Brain - metabolism; Clorgyline - metabolism; Male; Mitochondria - metabolism; Monoamine Oxidase - metabolism; Monoamine Oxidase Inhibitors; Pargyline - metabolism; Pyridines - metabolism; Rats; Rats, Inbred Strains; Selegiline - metabolism; Synaptosomes - metabolism; Tissue Distribution; Tryptamines - metabolism
• ISSN: 0022-3042
• DOI: 10.1111/j.1471-4159.1988.tb01122.x

Competition binding studies, subcellular distribution, and in vitro autoradiography were employed to compare the binding in rat brain of [3H]tryptamine with two radioligands for monoamine oxidase (MAO), [3H]pargyline, and [3H]1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine ([3H]MPTP). The MAO inhibitors pargyline, clorgyline, and deprenyl all yielded biphasic competition curves versus [3H]tryptamine. At low concentrations, these drugs stimulated binding by protecting the radioligand from MAO oxidation; at considerably higher concentrations, they inhibited binding by direct competition at the [3H]tryptamine binding site. In subcellular distribution studies, [3H]tryptamine was localized preferentially to the synaptosomal fraction, whereas [3H]pargyline showed greater binding to the mitochondrial fraction. Equilibrium binding studies revealed that the potencies of a series of seven compounds at inhibiting [3H]tryptamine binding were completely different from their potencies at inhibiting [3H]MPTP binding. Finally, the autoradiographic distribution of [3H]tryptamine binding in rat brain was different from that of [3H]MPTP and [3H]pargyline. We conclude that the [3H]tryptamine binding site in rat brain is not equivalent to MAO.