Ontogenesis of Multiple Forms of Monoamine Oxidase in Rat Brain Regions and Liver

Abstract

The postnatal development of total, type-A and type-B monoamine oxidase (MAO) in the brain stem, forebrain and cerebellum, determined with preferred substrates or selective inhibitors, were found to follow different patterns. In the brain regions, MAO-A activity reached adult levels in the brain stem first, followed by the forebrain and cerebellum, while MAO-B reached adult levels in these regions at about the same time and later in postnatal life. On the other hand, both MAO-A and B activities were almost fully developed in the newborn liver. Moreover, total and type-A, but not type-B, showed a caudal-to-rostral sequence of biochemical maturation in the brain. The spatiotemporal pattern of differentiation of type-A and type-B activities in the brain tends to support the classification of brain MAO into two distinct isoenzymic forms.