PROLIFERATION OF DIFFERENTIATED GLIAL-CELLS IN THE BRAIN-STEM

Classical studies of macroglial proliferation in muride rodents have p rovided conflicting evidence concerning the proliferating capabilities of oligodendrocytes and microglia. Furthermore, little information ha s been obtained in other mammalian orders and very little is known abo ut glial cell proliferation and differentiation in the subclass Metath eria although valuable knowledge may be obtained from the protracted p eriod of central nervous system maturation in these forms. Thus, we ha ve studied the proliferative capacity of phenotypically identified bra in stem oligodendrocytes by tritiated thymidine radioautography and ha ve compared it with known features of oligodendroglial differentiation as well as with proliferation of microglia in the opossum Didelphis m arsupialis. We have detected a previously undescribed ephemeral, regio nally heterogeneous proliferation of oligodendrocytes expressing the a ctin-binding, ensheathment-related protein 2'3'-cyclic nucleotide 3'-p hosphodiesterase (CNPase), that is not necessarily related to the know n regional and temporal heterogeneity of expression of CNPase in cell bodies. On the other hand, proliferation of microglia tagged by the bi nding of Griffonia simplicifolia B4 isolectin, which recognizes an alp ha-D-galactosyl-bearing glycoprotein of the plasma membrane of macroph ages/microglia, is known to be long lasting, showing no regional heter ogeneity and being found amongst both ameboid and differentiated ramif ied cells, although at different rates. The functional significance of the proliferative behavior of these differentiated cells is unknown b ut may provide a low-grade cell renewal in the normal brain and may be augmented under pathological conditions.