REGENERATIVE PROLIFERATION IN ORGAN-CULTURES OF THE AVIAN COCHLEA - IDENTIFICATION OF THE INITIAL PROGENITORS AND DETERMINATION OF THE LATENCY OF THE PROLIFERATIVE RESPONSE

Sensory hair cells in the cochleae of birds are regenerated after the death of preexisting hair cells caused by acoustic over-stimulation or administration of ototoxic drugs. Regeneration involves renewed proli feration of cells in an epithelium that is otherwise mitotically quies cent, To determine the identity of the first cells that proliferate in response to the death of hair cells and to measure the latency of thi s proliferative response, we have studied hair-cell regeneration in or gan culture. Cochleae from hatchling chicks were placed in culture, an d hair cells were killed individually by a laser microbeam. The cultur e medium was then replaced with a medium that contained a labeled DNA precursor. The treated cochleae were incubated in the labeling media f or different time periods before being fixed and processed for the vis ualization of proliferating cells. The first cells to initiate DNA rep lication in response to the death of hair cells were supporting cells within the cochlear sensory epithelium, All of the labeled supporting cells were located within 200 mu m of the hair-cell lesions. These cel ls first entered S-phase similar to 16 hr after the death of hair cell s. The results indicate that supporting cells are the precursors of re generated hair cells and suggest that regenerative proliferation of su pporting cells is triggered by signals that act locally within the dam aged epithelium.