A study of degeneration and regeneration in the divided rat sciatic nerve based on electron microscopy. I. The traumatic degeneration of myelin in the proximal stump of the divided nerve.

TLDR: In this paper, the authors examined the processes of traumatic degeneration of myelin in the proximal stump of divided rat sciatic nerves with the electron microscope, revealing a complete and coherent series of Schwann cells which are progressively more advanced in the degradation of the myelin.

Abstract: Examination of the processes of traumatic degeneration of myelin in the proximal stump of divided rat sciatic nerves with the electron microscope reveals a complete and coherent series of Schwann cells which are progressively more advanced in the degradation of the myelin. The earlier stages appear to be a wrinkling and distortion of the myelin lamellae, followed by erosion of the circumferential lamellae with subsequent loss of cohesion and fragmentation of the myelin systems. Retraction of the myelin from the region of the node of Ranvier is observed. Myelin debris in the cytoplasm of Schwann cells occurs as vacuoles containing membranous material and pale staining globular inclusions which may develop from the membrane containing vacuoles. Cells containing similar inclusions are present ‘free’ in the endoneurium. The presence of similar cells associated with axons and only partly covered by basement membrane suggests that the cells ‘free’ in the endoneurium are ‘transformed’ Schwann cells digesting their myelin. These cells are most frequent between 3 and 6 days after nerve section and gradually disappear thereafter. We did not see any indications that cells other than Schwann cells were extensively involved in the traumatic degeneration of myelin.