Ongoing production of sensory cells in the vestibular epithelium of the chick.

Recent studies have shown that the vestibular and auditory systems of some species of birds have the capacity to generate sensory hair cells postnatally. We used a traditional technique, 3H-thymidine autoradiography, and a newer method, bromodeoxyuridine immunocytochemistry, to determine whether ongoing proliferation of hair cells occurs in the intact chick vestibular epithelium. A ten-day course of 3H-thymidine, bromodeoxyuridine, or both was administered to twelve-day-old chicks. Both autoradiographic and immunocytochemical labeling demonstrated ongoing production of supporting cells and Type II hair cells in all chick vestibular organs. No evidence for production of Type I hair cells was seen in this investigation. New sensory cells were distributed throughout the epithelium; there was no peripheral growth zone analogous to that found in other vertebrates. Labeled Type II hair cells were frequently seen immediately above labeled supporting cells. This observation suggests that supporting cells are precursors for new hair cells. The ongoing, postnatal regeneration of vestibular epithelial cells also suggests that this epithelium may retain the potential for repair after trauma or ototoxic damage.