Cochlear findings in the white spotting (Ws) rat

White spotting (Ws) rats possess a c-kit gene mutation at the W locus, resulting in a variety of characteristics including a lack of intermediate cells of the stria vascularis. The present study employs a light microscope (LM), scanning (SEM) and transmission electron microscopes (TEM), diaminobenzidine (DAB) staining techniques and auditory brainstem response (ABR) to investigate the structure and function of the cochlea in 26 homozygous Ws/Ws rats aged 1-6 months. A slight thinning of the stria vascularis and moderate elevation of ABR threshold were about the only defects noted in 1 month animals, while older animals displayed various defects that tended to worsen with age. At 3 months LM revealed pigment granules in the basal turn of most animals, with a loss of pigmentation in the upper turns. The stria vascularis and organ of Corti tended to be well preserved in the lower, pigmented portion, while the upper, unpigmented portion showed severe strial degeneration and some outer hair cell loss. DAB staining revealed a well developed strial capillary net throughout the pigmented portion of the cochlea, with severe degradation in the unpigmented apical portion. ABR thresholds were slightly elevated over 1 month values. At 6 months great differences in degeneration were noted between right and left ears of the same animal.