Secretion of a new basal layer of tectorial membrane following gentamicin-induced hair cell loss

Scanning electron microscopy (SEM) and video-enhanced DIC light microscopy were used to assess morphological changes in the chick tectorial membrane (TM) following gentamicin-induced hair cell loss. Gentamicin was administered (100 mg/kg/day for 3 days) and isolated and in-situ TMs were examined in both fixed and unfixed preparations at days 5 and 10 after the initial injection. Although this protocol induced hair cell damage extending up to 75% of the length of the basilar papilla, there was no apparent damage to the TM itself. However, the ejection of damaged hair cells appeared to sever the filamentous attachments between the TM and the apical surface of the basilar papilla. In SEM preparations this detachment caused the TM to shrink back toward the superior edge. Interestingly, despite the lack of TM damage, gentamicin treatment did reveal the secretion of a new basal layer of TM. Secretion of this new basal layer had begun by day 5 and it was well organized by day 10. This new layer formed attachments to both the recovering basilar papilla and the overlying original TM, a step thought to be necessary for the restoration of auditory function in the regenerating cochlea.