REPLACEMENT OF HAIR-CELLS AFTER LASER MICROBEAM IRRADIATION IN CULTURED ORGANS OF CORTI FROM EMBRYONIC AND NEONATAL MICE

This study examined the potential for hair cell regeneration in embryo nic and neonatal mouse organs of Corti maintained in vitro, Small numb ers of hair cells were killed by laser microbeam irradiation and the s ubsequent recovery processes were monitored by differential interferen ce contrast (DIG) microscopy combined with continuous time-lapse video recordings, Replacement hair cells were observed to develop in lesion sites in embryonic cochleae and on rare occasions in neonatal cochlea e, In embryonic cochleae, replacement hair cells did not arise through renewed proliferation, but instead developed from preexisting cells t hat changed from their normal developmental fates in response to the l oss of adjacent hair cells, In cochleae established from neonates, los t hair cells usually were not replaced, but 11 apparently regenerated hair cells and a single hair cell labeled by H-3-thymidine were observ ed as rare responses to the creation of hair cell lesions in these org ans. The results indicate that the organ of Corti can replace lost hai r cells during embryonic and on rare occasions during early neonatal d evelopment, The ability of preexisting cells to change their developme ntal fates in response to hair cell death is consistent with the hypot hesis that during embryonic development hair cells may inhibit neighbo ring cells from specializing as hair cells, In neonatal cultures, the rare occurrence of apparently regenerated hair cells indicates that so me cells in the postembryonic organ of Corti retain response mechanism s that can lead to self-repair.