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.