A new perspective on myelinated nerve fibre pathology in experimental diabetes

Quantitative electron-microscopical techniques were used to investigate the effects of experimental streptozotocin-diabetes on the longitudinal morphology of myelinated fibres in rat sural nerve. The morphology of myelinated fibres was symmetrical at proximal and distal levels in the nerves of control animals aged three months. Further development of myelinated fibres in control animals between three and seven months of age involved proximal and distal fibre growth with the simultaneous formation of a proximo-distal taper. The same pattern of fibre growth was not observed in animals with experimental diabetes. Although both fibre and axon size increased with age in both proximal and distal regions of sural nerve in the diabetic animals, a taper was not established. This impairment of fibre maturation by experimental diabetes was manifest more strongly in the proximal part of the nerve. There was no evidence favouring selective involvement of the axon or Schwann cell in the fibre pathology found in the diabetic animals. The results of this study do not support previous suggestions that experimental diabetic neuropathy is mainly a dying-back axonopathy. This report reaffirms that normal maturation of myelinated fibres is prevented by experimental diabetes mellitus.