Electron microscopic studies of wallerian degeneration in rat optic nerves. I. The multipotential glia

Abstract

The development of phagocytes has been studied with the electron and light microscopes in rat optic nerves undergoing Wallerian degeneration. The postoperative survival times ranged from five hours to 250 days. This paper focuses on cells that have been designated either as multipotential glia or as a third neuroglial cell type. Such cells increase markedly in number during the first several weeks of nerve fiber degeneration while the populations of astrocytes and oligodendrocytes remain relatively stable. During this early stage of degeneration, multipotential glial cells develop very irregular shapes and have many processes and complex folds that intermingle with the degenerating nerve fibers. These cells engulf myelin fragments and nerve fibers which become enclosed within vacuoles that show acid phosphatase reaction product in specimens prepared for cytochemistry. The debris containing vacuoles can therefore be considered as phagolysosomes. In addition, the multipotential glial cells show an increase in the number of lipid inclusions over that of cells in normal material. Eventually some multipotential glial cells accumulate large quantities of lipid inclusion and come to resemble the “Gitter” cells described in classical neuropathological studies.The numerical and cytological changes occurring within the multipotential glial population indicate that these cells are an important source of phagocytes in the type of lesion which we have studied. The breakdown of degenerating myelin by multipotential glial cells, the origin of these cells and their relationship to the microglial cells stained in light microscopic preparations are discussed in detail.