THE EFFECT OF EXPLANTATION AND NEOMYCIN ON HAIR-CELLS AND SUPPORTING CELLS IN ORGANOTYPIC CULTURES OF THE ADULT GUINEA-PIG UTRICLE

Recent reports suggest that immature hair bundles are observed followi ng aminoglycoside-induced hair-cell loss in the mammalian utricle in v itro as well as in vivo. It is therefore important to document the ini tial morphological changes associated with both culturing and aminogly coside application so that degeneration can be clearly distinguished f rom regeneration. In this study, utricles from adult guinea pigs were maintained in culture for either 3 or 8 days, half being exposed to ne omycin for days 2 and 3. They were then processed for microscopical ex amination and compared with control utricles from animals of the same age. The numbers of hair-cell and supporting-cell nuclei were counted and hair-cell morphology assessed. Bundles were classified as having e ither stepped (SHB) or unstepped (UHB) stereocilia, and their density determined. The numbers of hair-cell, but not supporting-cell, nuclei declined significantly compared with controls in both untreated and tr eated explants, the greatest reduction occurring 5 days after neomycin administration. The density of SHBs also declined but there was no si gnificant change in UHB density resulting in a residual population of hair bundles of more immature appearance in both untreated and treated utricles in vitro than In vivo. Although degenerative events such as hair-cell ejection from, or retraction into, the sensory epithelium we re observed, no evidence of regeneration was found. (C) 1998 Elsevier Science B.V.