SECRETION OF A NEW BASAL LAYER OF TECTORIAL MEMBRANE FOLLOWING GENTAMICIN-INDUCED HAIR CELL LOSS

Scanning electron microscopy (SEM) and video-enhanced DIC light micros copy 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 T Ms were examined in both fixed and unfixed preparations at days 5 and 10 after the initial injection. Although this protocol induced hair ce ll damage extending up to 75% of the length of the basilar papilla, th ere was no apparent damage to the TM itself. However, the ejection of damaged hair cells appeared to sever the filamentous attachments betwe en the TM and the apical surface of the basilar papilla. In SEM prepar ations this detachment caused the TM to shrink back toward the superio r edge. Interestingly, despite the lack of TM damage, gentamicin treat ment 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 basil ar papilla and the overlying original TM, a step thought to be necessa ry for the restoration of auditory function in the regenerating cochle a.