Aberrant frequency tuning and early stereociliary derangement in genetic inner ear disease

Cochlear histopathology of the mutant bustling mouse, BUS/Idr

The inner ear of mutant bustling mice, BUS/Idr, was examined histopathologically. LM examinations revealed an age-dependent degeneration of the auditory organ of Corti in BUS homozygotes, but not heterozygotes. Cochlear base-to-apex gradient in severity of the degeneration was noted. First signs of degeneration were found in the outer hair cells of the cochlear basal turn at about 3 weeks of age, followed by degeneration of the spiral ganglion cells which occurred slowly. As examined by SEM, stereociliary derangements of both the inner and outer hair cells were apparent in homozygotes as early as after 10 days. No normal arrays of stereocilia were found in homozygotes examined at 10 days through 6 months. The results of immunohistochemical examinations suggest that the sensory cells of the Corti's organ of homozygotes are structurally once normally innervated. No significant difference was found in the expression of protooncogene c-mos in the CNS between BUS homozygotes and control mice. We propose that BUS mice be categorized as a member of the so-called "waltzer-shaker" mutants group.

Morphologically specific vestibular hair cell degeneration in the jerker mouse mutant

The vestibular organs in homozygote (je/je) and heterozygote (je/+) 1- to 12-month-old jerker mouse mutants were analyzed morphologically using light microscopy and transmission and scanning electron microscopy. The pathological changes were initially confined to the surface structure of predominantly type I hair cells. The latter cells showed disintegration of the cuticular plate, disarray of stereocilia and finally fusion of sensory hairs. The hair cells were then expelled into the endolymphatic space. A notable finding was that most expelled hair cells still showed a rather normal ultrastructure of their cytoplasm and nuclei. The morphological type of pathology was the same in je/je and je/+ mutants. However, in je/je animals the degeneration occurred within 1-3 months after birth, whereas in je/+ mutants a slowly progressive degeneration lasted for up to 1 year of age or even more. The degeneration was more extensive in the two maculae than in the three cristae ampullares.