Immunocytochemical demonstration of monoamine oxidase B in brain astrocytes and serotonergic neurons.

An antiserum to monoamine oxidase B (MAO-B) was used to define the distribution of this metabolic enzyme in the adult rat brain immunocytochemically. MAO-B is specifically located in two major central nervous system cell classes, astrocytes and serotonin-containing neurons. Double-immunofluorescence experiments using antisera to glial fibrillary acidic protein and MAO-B showed that both protoplasmic and fibrillary astrocytes throughout the brain contain MAO-B, whereas oligodendrocytes do not contain the enzyme. Areas lacking a blood-brain barrier, such as the specialized circumventricular organs, also contain MAO-B-positive cells. A double-immunofluorescence experiment using antisera to serotonin and MAO-B enabled the positive identification of neurons containing both molecules. The catecholamine-containing neurons of the brain did not contain detectable amounts of MAO-B. The specific distribution of MAO-B in the adult central nervous system indicates that the role of MAO-B in monoamine metabolism may be more specifically defined than previously believed.