DYSGENESIS OF MELANOCYTES AND COCHLEAR DYSFUNCTION IN MUTANT MICROPHTHALMIA (MI) MICE

In order to evaluate the cytological homology of intermediate cells an d melanocytes, and to investigate the function of melanocytes in the i nner ear, hearing acuity and cochlear pathology were studied in three strains of mice, namely, wild type mice (+/+), albino mice without mel anin (c(2J)/c(2J)) and microphthalmia mice with no melanocytes (mi(bw) /mi(bw)). Our histochemical data indicated that intermediate cells sho wed cytological characteristics almost identical to those of melanocyt es and that disorders of melanin and/or melanocytes were reflected in the stria vascularis of each mouse. While c(2J)/c(2J) presented the sa me normal hearing acuity and normal structure of the stria vascularis as +/+, the hearing acuity of mi(bw)/mi(bw) mutants was severely impai red. Their stria vascularis was abnormally thin, lacking intermediate cells. According to these results, lack of melanin has little influenc e on hearing acuity; however, the absence of intermediate cells or mel anocytes causes severe hearing loss, presumably due to a strial dysfun ction.