Morphological evidence of vestibular pathology in long-term experimental diabetes mellitus. II. Connective tissue and neuroepithelial pathology.

The influence of long-term experimental diabetes on the saccule and utricle was investigated with light and electron microscopy. Pathological changes involving the connective tissue cells of the subneuroepithelial connective tissue suggest that these cells may play a potentially important role in diabetic pathology of the inner ear. In diabetic animals there was an increased incidence of secondary lysosomes within the connective tissue cells as well as an accumulation of intracellular lipid droplets that increased with the level of hyperglycemia. Five animals with relatively more severe diabetes also had an extensive accumulation of extracellular matrix. Two of these rats with longer diabetes duration had a small number of degenerating type I hair cells scattered through the saccular neuroepithelium, possibly due to chronic stresses from impaired diffusion of oxygen, nutrients and waste material through the dense extracellular matrix. Utricles of these same animals did not have any degenerating hair cells.