D-AMINO-ACID OXIDASE IS CONFINED TO THE LOWER BRAIN-STEM AND CEREBELLUM IN RAT-BRAIN - REGIONAL DIFFERENTIATION OF ASTROCYTES

Based on enzymatic activity, the localization and the identification o f D-amino-acid oxidase-containing cells in rat whole brain was systema tically studied in serial fixed sections. The oxidase activity was abs ent or scarce in the forebrain, was confined to the brain stem (midbra in, pens and medulla oblongata) and cerebellum, and its localization w as extended to the spinal cord. In the brain stem the oxidase was main ly localized in the tegmentum, particularly in the reticular formation . The intense oxidase reactions were present in the red nucleus, oculo motor nucleus, trochlear nucleus, ventral nucleus of the lateral lemni scus, dorsal and ventral cochlear nuclei, vestibular nuclei, nuclei of posterior funiculus, nucleus of the spinal tract of the trigeminal ne rve, lateral reticular nucleus, inferior olivary nucleus, and hypoglos sal nucleus. In the cerebellum the activity in the cortex was much mor e intense than that in the medulla. In all the fields described above, the oxidase-containing cells were exclusively astrocytes including Be rgmann glial cells, and neither neuronal components, endothelial cells , oligodendrocytes nor ependymal cells showed oxidase activity. These results indicated that the astrocytes regionally differentiated into t wo distinct types, one of which expressed oxidase in the midbrain, rho mbencephalon and spinal card, and the other which did not in the foreb rain. The localization of the oxidase was inversely correlated with th e distribution of free D-serine in mammalian brains (Nagata, Y., Horii ke, K. and Maeda, T., Brain Res., 634 (1994) 291-295). Based on the ch aracteristic localization of the oxidase-containing astrocytes, we dis cussed the physiological role of the oxidase.