Electron microscope studies of Schwann cells during the Wallerian degeneration with special reference to the cytoplasmic filaments.

Abstract

The fine structure of Schwann cells of the sciatic nerve of adult rabbits during the several phases of Wallerian degeneration was studied. For electron microscopy buffered osmium tetroxide, Vestopal W and the lead and uranyl staining was used As a result of the axon degeneration, the Schwann cells are activated and the myelin sheaths break down. During the phase of intraplasmatic digestion of the myelin, the ribosomes increase considerably and the ER swells. Afterwards a conspicuous granular thickening of the ground plasm is to be noted (stage of “dark cells”). The granular ground plasm forms into filaments, which stand out clearly before the light background as tender strings about 60–80 A in thickness (stage of “light cells”). During this stage, the ribosomes have disappeared almost completely and the ER has collapsed. The Schwann cell has entered into its stage of rest which is characterized by a high amount of plasmatic filaments. Schwann cell filaments differ from so-called “neurofilaments” in respect of their genesis and their ultrastructure. In conclusion, the differences in genesis and morphology between the two filamentous structures are discussed.