A study of degeneration and regeneration in the divided rat sciatic nerve based on electron microscopy

Summary

Changes in the proximal stump of axons of divided rat sciatic nerves in the first 6 weeks after nerve section were studied, particularly in terms of alterations in the organelle content, axoplasmic ultrastructure and the diameter of the axons. A variety of organelle types were observed; quasi-membranous structures, multivesicular bodies, dense bodies, vesicles and tubules, dense cored vesicles and alveolate vesicles: their identification and the functional implications of their presence are discussed. Alterations in the ultrastructure of the “stained” elements of the axoplasm are described. Axons containing excess organelles were divided into classes, comprising myelinated axons; and “supergiant”, “giant” and “conventional” non-myelinated axons. Temporal changes in these axons are described. The characteristics of the various classes of apparently non-myelinated axon are considered in terms of their identification as regenerating terminal sprouts of myelinated axons, segmentally demyelinated axons, sections through abnormal nodes of Ranvier or merely non-myelinated axons. The structure of axons in “regenerating units” is described. Changes in the neurofilament microtubule ratio of small axons without excess organelles are demonstrated, and “spiralling” of neurofilaments in some myelinated and non-myelinated axons with normal axoplasmic ultrastructure is illustrated and discussed.