FURTHER EVIDENCE FOR SUPPORTING CELL CONVERSION IN THE DAMAGED AVIAN BASILAR PAPILLA

Two lines of evidence suggested that a process other than supporting c ell divisions may give rise to new hair cells in the bird inner ear in jured by either noise or ototoxic drugs. This process, supporting cell conversion, occurs when non-dividing supporting cells transdifferenti ate into hair cells. First, noise-exposed chicks received zero, one or two daily i.p. injections of cytosine arabinoside (a DNA synthesis bl ocker), as well as two daily intraperitoneal injections of bromodeoxyu ridine, for four days. Following sacrifice, the papillae were processe d for bromodeoxyuridine immunocytochemistry. All the ears demonstrated dividing cells, but increasing the number of cytosine arabinoside inj ections decreased the number of labeled cells. Indeed, two cytosine ar abinoside injections per day nearly completely blocked supporting cell divisions in the short hair cell region within the sound-induced lesi on. This suggested that unpaired, immature cells observed in a similar region with scanning electron microscopy, despite the presence of cyt osine arabinoside, may have been products of supporting cell conversio n. In the second experiment, birds were treated with gentamicin for th ree days. Upon sacrifice at 6 days post-treatment, papillae were proce ssed for light and transmission electron microscopy. Several unusual c ells were observed with phenotypic features of both hair cells and sup porting cells. The peculiar cells may be in a transition from the supp orting cell phenotype to that of a hair cell. (C) 1997 ISDN.