Monoclonal antibodies specific for monoamine oxidase (MAO) A and MAO B, respectively, were used to localize these enzymes in primate brain. The reagents recognized different populations of neurons: those that recognized MAO A were located in cell groups containing catecholamines, including the substantia nigra, nucleus locus coeruleus, nucleus subcoeruleus, and the periventricular region of the hypothalamus, whereas those that recognized MAO B were observed in serotonin regions, including the nucleus raphe dorsalis and nucleus centralis superior. These data illustrate the physiological independence of MAO A and B and show that neurons may be specialized for their degradative as well as their synthetic functions.

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