HETEROGENEOUS PATTERNS OF OLIGODENDROGLIAL DIFFERENTIATION IN THE FOREBRAIN OF THE OPOSSUM DIDELPHIS-MARSUPIALIS

The differentiation of oligodendrocytes in the forebrain of the opossu m (Didelphis marsupialis) has been studied by the immunohistochemical identification of 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPas e) and by the autoradiographic detection of the uptake of H-3-thymidin e. CNPase is expressed early in oligodendroglia somata and fibre sheat hs (myelin) in the forebrain and its persistence in the cell bodies is regionally heterogeneous, being ephemeral in cells within the optic p athway, supraoptic decussation, and posterior commissure, of intermedi ate duration in the mamillo-thalamic fascicle, and stria medullaris, a nd long-lasting in other diencephalic and in telencephalic tracts. In the cerebral cortex, most CNPase + cells have small somata and multipl e processes (types I and II). CNPase-expressing oligodendrocytes are a lso regionally heterogeneous in terms of proliferative capability, whi ch could not be detected in forebrain tracts or diencephalon, but has appeared in a small proportion of cells in the neocortical white matte r and in the fimbria. Our findings provide additional evidence in favo ur of the heterogeneity of oligodendrocytes.