Myelin-sheath abnormalities in the vestibular nerves of chronically diabetic rats.

Electron microscopic examination of the saccular and utricular nerves of rats with streptozocin-induced diabetes mellitus revealed differences from age-matched control animals, mainly related to myelin sheaths. Nerves from diabetic rats had a high incidence of a variety of osmiophilic inclusion bodies, often associated with disrupted myelin-sheath lamellae, lysosomal bodies, and periaxonal expansions of Schwann cell cytoplasm. The occurrence of osmiophilic inclusion bodies within nerve profiles was correlated with the severity of diabetes as measured by blood glucose levels (p < 0.001, linear-regression ANOVA). Duration of diabetes was not related to incidence of inclusion bodies. No evidence of demyelination/remyelination or neuronal degeneration was observed. An unusual Schwann cell reaction was noted, involving lysosomal digestion of large, pinched-off portions of myelinated nerve fibers of some diabetic rats. Both this Schwann cell reaction and the high incidence of inclusion bodies may be due to increased nonenzymatic glycosylation of myelin proteins in the diabetic animals.