The cochlea of the two species of hereditary and spontaneously diabetic mice were examined. One species was the non-obese diabetic (NOD) mouse, which becomes diabetic due to severe insulitis as seen in the juvenile onset or Type I diabetes in the human, and the other species was the Kondo-Kasugabe (KK) mouse with characteristics resembling the adult onset or Type II diabetes in the human. The animals were examined morphologically by electron microscopy and functionally by auditory brainstem response hearing test. The lesion in the cochlea of NOD and KK mice were found mainly in the vascular stria, with the pathological changes occurring mainly in the marginal cells and intermediate cells. Protrusions of the surface of the marginal cells into the endolymphatic space, swelling and the vacuolization of the intermediate cell were observed. No changes, however, were noted in the capillary of the stria vascularis.
Severe degenarative changes occurred in the organ of Corti of NOD mice, with some animals exhibiting a total loss of outer hair cell and denuclearization of Deiters' cell on the basal turn. These findings were not observed in KK mice. No degenerative changes were found in the spiral ganglion of either species. A loss of Preyer's reflex of NOD mice and an elevated threshold of auditory brainstem response were observed in KK mice at 5 months of age.