DEGENERATIVE HAIRLETS ON THE VESTIBULAR SENSORY CELLS IN MUTANT BUSTLING (BUS IDR) MICE/

The bustling mouse (BUS/Idr: bus) is a mutant mouse strain which exhib its deafness, bustling/hyperkinetic behaviour and functional disorders seemingly related to the vestibular system. This phenotype develops i n homozygous (bus/bus) mice and has been shown from cross experiments to be genetically induced by a single autosomal recessive gene. We pre viously detected, with light and electron microscopy, post-natal degen eration of the inner ear sensory cells in homozygotes. In the present study, we examined, by electron microscopy, the development of patholo gical changes in the sensory epithelia of the macula acustica and cris ta ampullar's of homozygous mice of various ages, paying special atten tion to the detailed morphology of the sensory hairlets. The homozygou s mice exhibited specific pathological changes: a decrease in the numb er of hairs; disarrangement of the kinocilium-stereocilia pattern; and , fused and/or very large stereocilia. Homozygotes also frequently exh ibited apical cytoplasmic herniation, or bleb of hair cells, as well a s a degenerated kinocilium in the sensory epithelium. Heterozygotes sh owed similar changes, but to a lesser degree and frequency. As for the vestibular organs, similar pathological changes had developed at day 17 of gestation. These pathological findings and onset suggest that th e BUS mouse may be a mutant mouse strain distinct from other reported strains which display similar behaviour, and may be a useful animal mo del for the study of human degenerative vestibular disorders.