THE DEVELOPMENT OF D‐AMINO ACID OXIDASE IN RAT CEREBELLUM

Abstract

Abstract—D‐Amino acid oxidase (D‐amino acid: O2 oxidoreductase (deaminating), EC 1.4.3.3; D‐AAO) activity is biochemically undetected in rat brain stem, cerebellum and forebrain until 14 days after birth. Adult levels are attained by day 30 in the brain stem, and by day 36 in the cerebellum. At adulthood, forebrain D‐AAO activity per g wet weight of tissue is less than 2% that of the cerebellum. In contrast to the pattern in the CNS, substantial D‐AAO activity is present in both liver and kidney 2 days before birth and adult levels are approached within 2 weeks of birth. Nonetheless, D‐AAO activities in rat liver, kidney, brain stem and cerebellum are likely to be due to a single enzyme which has properties very similar to the purified hog D‐AAO. The late ontogenesis of D‐AAO activity in cerebellum and brain stem relative to that in liver and kidney parallels reported phylogenetic data.Histochemical staining for D‐AAO in rat cerebellar cortex is absent until 15 days after birth when activity is first observed in some cells of the external germinal zone and adjacent molecular layer. These cells appear to migrate to a final destination around the Purkinje cell soma and leave processes at the pial surface. By 21 days of age an adult pattern of staining is manifest throughout the cerebellum but it is of weak intensity. The adult pattern includes some staining in the granular layer which seems to be associated with mossy fibers and certain cerebellar glomeruli, and strong staining at the pial surface, in the molecular layer, and in cells surrounding, but not within, the Purkinje cell soma. The data suggest that the biochemical appearance of D‐AAO in developing cerebellum derives from two sources: one associated with differentiation of one of the last cell types to form from the external germinal zone, and the other with maturation of mossy fibers and their synapses (cerebellar glomeruli).