An Ultrastructural Study on the Reactive Oligodendrocytes, Myeloclasts, and Myelophages in Transected Dog Spinal Cord

As early as 1 to 3 hr after cord transection, proliferation of many reactive oligodendrocytes was observed. Bundles of microfilaments and microtubules were observed in those cells that sent out long, complex pseudopodlike processes near the area of injury. These reactive oligodendrocytes may be comparable to Vaughn's multipotential glia cells. Between 1 day and 1 wk, hypertrophy of the oligodendrocytes was observed. These hypertrophied oligodendrocytes also became hyperactive and infiltrated into the axons within the myelin sheath. These infiltrating hyperactive oligodendrocytes had a scanty fibrillary cytoplasm and are believed to correspond to Jakob's "myeloclasts". The infiltration of macrophages into the nerve fibers and myelin sheaths was also observed. These macrophages were found to be very active in phagocytosis and removal of degenerated debris within the nerve fiber and are believed to represent the "myelophages" described by Jakob in 1913.