Stereocilium injury mediates hair bundle stiffness loss and recovery following intense water-jet stimulation

Inner ear hair cells exhibit many pathologies following exposure to intense sound, and the hair bundle is a major sits of damage. This paper measures in vitro hair bundle motion on chick cochlear hair cells after intense in v itro and in vivo stimulation to explore the nature of hair bundle injury. H air bundle stiffness, as well as relative and asymmetric motion of individu al stereocilia, is controlled largely by the extracellular tip links, and a change in hail. bundle motion was used to assess tip-link destruction foll owing overstimulation. Intense in vitro stimulation caused a loss in stiffn ess that fully recovered within 10 min post-exposure. Relative and asymmetr ic stereocilia motion, however, were unchanged following the exposure, impl ying that tip links remained intact while the core or rootlet of the stereo cilia were damaged and subsequently repaired. Intense and prolonged in vivo sound exposures produced stereocilia movements, measured in vitro, that we re indicative of damage to stereocilia and tip links. Finally, the relative susceptibility of hair bundles to overstimulation was addressed by compari ng stiffness loss with morphological features in the hair bundles. The loss of stiffness significantly increased as the amount of curvature in the hai r bundle contour increased.