INTRACELLULAR-DISTRIBUTION OF MONOAMINE OXIDASE-A IN SELECTED REGIONSOF RAT AND MONKEY BRAIN AND SPINAL-CORD

Monoamine oxidase A and B (MAO A and B; EC 1.4.3.4) are integral prote ins of the outer mitochondrial membrane that degrade monoamines includ ing the neurotransmitters norepinephrine, dopamine, and serotonin. In this study, monoclonal antibodies that recognize rat or monkey MAO A w ere used in immunocytochemical studies to visualize the subcellular lo calization of this enzyme within neurons in the central nervous system of these species. The regions examined included the locus coeruleus, substantia nigra, spinal cord, and pallidostriatum, which are known to contain MAO A-positive structures. Ultrastructural studies revealed t hat most MAO A staining was associated with the outer membrane of mito chondria, within the cell bodies, dendrites, axons and terminals. Howe ver, some immunoreactive staining for MAO A was also observed in the r ough endoplasmic reticulum in the cell bodies. Staining for mitochondr ial MAO A in dendrites was observed in terminal fields of the monoamin e system, including the spinal cord and the pallidostriatum. The inten sity of staining also increased in the subsynaptic density. MAO A was also found associated with mitochondria in ependymal cells lining the fourth ventricle adjacent to the locus coeruleus and in the endothelia l cells lining the blood vessels. Localization of MAO A in noradrenerg ic neurons, ependymal cells, and subsynaptic regions of dendrites in m onoamine terminal fields supports the concept that this neurotransmitt er-degrading enzyme may play a protective role in the central nervous system.