| Abstract #505, Date 2/16/99, Session R1, Poster (J5) |
| Hair cell loss and supporting cell rearrangement in the chick cochlea after gentamicin treatment |
| *S. Goklani (WT Clarke High School, Westbury, LI, NY); E.P. Messana (Children's Hospital); D.A. Cotanche (Children's Hospital and Harvard Medical School) |
Many studies have used aminoglycoside treatment to induce hair cell regeneration in the avian cochlea. While details of these studies have differed, the basic result has generally been the same, i.e. loss of both tall and short hair cells from the proximal (high frequency) end of the cochlea and a gradual replacement of these missing cells by regeneration. SEM and LM studies of damaged cochleae have led to the hypothesis that the dying hair cells were ejected up into the scala media and overlying tectorial membrane. Thus, the surviving cells in the damaged region were thought to be almost exclusively supporting cells. However, it has recently been proposed that the hair cells eject only their sensory bundles in response to aminoglycosides and that the remaining portion of the hair cell rebuilds a new bundle in order to regain its functional capacity. We have set out to test this idea in the two-week-old chick cochlea damaged by a single injection of gentamicin at 300 mg/kg. Whole-mount preparations of the cochlea were made at 3, 4, and 5 days after the gentamicin injection and were labeled with phalloidin to detect the actin cytoskeleton, pan-cadherin antibodies to outline the cells’ apical junctional complexes, and myosin VIIa antibodies (kindly provided by Dr. Tama Hasson, Yale University) to specifically identify hair cells. On day 3 all of the hair cells were ejected from the proximal 20% of the cochlea, based on phalloidin and myosin VIIa labeling. However, the lost hair cells still labeled with the myosin VIIa antibody and were found to be trapped in the overlying tectorial membrane. Pan-cadherin labeling of the damaged region showed that the supporting cells had reorganized their surfaces to accommodate the large number of lost hair cells. On day 4 a few small cells that labeled for myosin VIIa were seen in the basal portions of the damaged epithelium. By day 5 there were a large number of flask-shaped cells in the damaged region that stained with myosin VIIa. These results support our original hypothesis that most, if not all, of the damaged hair cells are extruded from the damaged region in response to gentamicin treatment. |