Cochlear hair cell stereocilia loss in LP/J mice with bone dysplasia of the middle ear

LP/J inbred mice spontaneously develop bony lesions of the middle ear and otic capsule that are similar to those of human otosclerosis and tympanosclerosis. These mice also have progressive loss of hearing due to cochlear hair cell loss. The purpose of this study was to describe quantitatively the deterioration and loss of cochlear hair cells to serve as a basis for future experiments attempting to alter the course of this disorder. Cochleas from 37 LP/J inbred mice were examined by scanning electron microscopy. The stereocilia loss in the cochlea was evident as early as 15 weeks of age and progressed from the basal turn to the apex. Outer hair cells were affected more than inner hair cells. As outer hair cells deteriorated we observed fusion, bending, and breakage of stereocilia. There were no apparent differences in the mode of deterioration among the three rows of outer hair cells. Stereocilia fusion of inner hair cells occurred at an older age, and giant, elongated stereocilia were found in some of the animals.