ELECTRON MICROSCOPE OBSERVATIONS ON DEMYELINATION AND REMYELINATION IN EXPERIMENTAL ALLERGIC NEURITIS .1. DEMYELINATION

Electron microscope observations have been made on experimental allergic neuritis in guinea-pigs, produced by the intradermal inoculation of an emulsion of rabbit sciatic nerve combined with Freund's adjuvants. The leucocyte infiltration of the endoneurium consisted predominantly of lymphocytes and monocytes with a smaller proportion of polymorphonuclear leucocytes. The early changes seen at the nodes of Ranvier were separation of the terminal myelin loops from the axon, the myelin lamellae then undergoing vesicular disintegration. The Schwann cell nodal processes were lost and at times the Schwann cell cytoplasm extended into the region formerly occupied by the nodal processes. On more severely-affected fibres disruption of the internodal myelin occurred, the myelin breaking down into small ovoids with multi-lamellar walls or into single-walled vesicles. The myelin was then removed by macrophages, the origin of which was uncertain. Leucocytes were not identified within the Schwann tubes at the time myelin breakdown commenced, but were noted within the tubes in which the demyelination was further advanced. Occasional complete degeneration of axons was observed, but changes in demyelinated axons were not conspicuous. © 1969.