CELL-DEATH, CELL-PROLIFERATION, AND ESTIMATES OF HAIR CELL LIFE SPANSIN THE VESTIBULAR ORGANS OF CHICKS

We have examined the level of on-going cell death in the chick vestibu lar epithelia using the TUNEL method and compared this to the rate of on-going cell proliferation. Utricles contained 22.6+/-6.8 TUNEL-label ed cells (mean+/-s.e.m.) while saccules contained 15.1+/-4.0, with app roximately 90% being labeled hair cells. In separate experiments, chic ks were given a single injection of BrdU and killed 2 h later. Utricle s contained 116.9+/-6.5 BrdU-labeled cells (mean+/-s.e.m.) and saccule s contained 41.0+/-2.2. After 24 h in culture, utricles treated with 1 mM neomycin contained 115.5+/-38.9 TUNEL-labeled cells, an increase o f 270% over controls. After 48 h, neomycin-treated saccules contained 40.9+/-7.8, an increase of 152% over controls. The majority of labeled cells were in the hair cell layer. Thus, neomycin exposure results in an apoptotic death of hair cells. The in vivo data measured here were used to estimate that the average life span of utricular hair cells i n young chickens is approximately 20 days, in sharp contrast to the li fe spans assumed for hair cells in humans. (C) 1997 Elsevier Science B .V.