We examined the origin of regenerated hair cell, triggers for regeneration and cell death in the avian basilar papilla and the possibility of hair cell regeneration in the mammalian vestibular sensory epithelia.
1) To determine the origin of regenerated hair cells, we did an immune-TEM study using bromodeoxyuridine (BrdU) in damaged basilar papilla after noise exposure. Label-ing in the basilar papilla was initially detected in the supporting cells, which suggested that supporting cells were the original cells of regenerated hair cells.
We examined two candidates of triggers for regeneration in damaged basilar papilla using an organ culture technique. One of the candidates was epidermal growth factor (EGF) and another was the extrusion of hair cells. Regarding the extrusion of hair cells, we compared those after collagenase treatment with those after noise exposure. Consequently, EGF had a potency to stimulate cell proliferation. Cell proliferation was recognized after noise exposure but not recognized after collagenase treatment. These results suggested that EGF might be one of triggers but extrusion itself could not be a trigger.
2) We examined whether apoptosis occurred during the process of hair cell regeneration after noise exposure using the TUNEL method. Consequently, apoptosis was recognized in hair cells just after noise exposure and at 2 days after noise exposure, which suggested that hair cell damage induced by noise exposure was due to apoptosis and apoptosis took part in the process of hair cell regeneration.
3) We did an in vivo immunohistochemical study using BrdU in the ampullar cristae after damage by gentamicin in the guinea pig. Labeled cells were recognized in the luminal portion of the sensory epithelia 60 days after gentamicin treatment, which indicated a possibility of hair cell regeneration in the vestibular epithelia.
