Continuous hair cell turnover in the inner ear vestibular organs of a mammal, the Daubenton's bat (Myotis daubentonii)

In both humans and mice the number of hair cells in the inner ear sensory e pithelia declines with age, indicating cell death (Park et al. 1987; Rosenh all 1973). However, recent reports demonstrate the ability of the vestibula r sensory epithelia to regenerate after injury (Forge et al. 1993, 1998; Ku ntz and Oesterle 1998; Li and Forge 1997; Rubel et al. 1995; Tanyeri et al. 1995). Still, a continuous hair cell turnover in the vestibular epithelia has not previously been demonstrated in mature mammals. Bats are the only f lying mammals, and they are known to live to a higher age than animals of e qual size. The maximum age of many species is 20 years, with average lifesp ans of 4-6 years (Schober and Grimmberger 1989). Further, the young are ful ly developed and able to fly at the age of 2 months, and thus the vestibula r organs are thought to be differentiated at that age. Consequently, long-l ived mammals such as bats might compensate for the loss of hair cells by pr oducing new hair cells in their postembryonic life. Here we show chat the u tricular macula of adult Daubenton's bats (more than 6 months old) contains innervated immature hair cells as well as apoptotic hair cells, which stro ngly indicates a continuous turnover of hair cells, as previously demonstra ted in birds.