EARLY RECRUITMENT OF OLIGODENDROCYTE PRECURSORS IN CNS DEMYELINATION

The source of the new population of oligodendrocytes which successfull y remyelinates experimentally induced demyelination of the cat optic n erve was studied with a combination of techniques. These included corr elative light microscopy, immunocytochemistry, electron microscopy and autoradiography in transverse and longitudinal sections. Extending th e analysis from the newly generated oligodendrocyte back to the very e arly demyalinative phase of the lesion enabled the identification of a glial precursor cell (GPC) outside the lesion which appeared to be re adily recruitable and motile. This cell is likely to be the product of the division of a putative resting progenitor cell residing in a cent ral fascicular location of the normal optic nerve surrounding the lesi on. On arriving at the fringe of the lesion, GPCs are transformed into vimentin-positive small glial cells (SGCs) possibly by signals fr om demyelinated axons to which the SGCs become closely apposed. Small gli al cells, which together with GPCs share several features in common wi th 0-2A perinatal progenitors of the rodent optic nerve, then differen tiate into oligodendrocytes. Together these findings suggest that the events leading to remyelination of adult mammalian optic nerve commenc e soon after the demyelinating injury and might recapitulate the princ ipal events of developmental myelinogenesis.