Effect of violation of the labyrinth on the sensory epithelium in the chick cochlea.

Models in which a single large systemic dose of gentamicin is used to cause near-synchronous hair cell (HC) loss in the basal end of the chick cochlea have proven increasingly useful in the study of HC regeneration. We quantified the amount of HC death, as a percentage of the length of the basilar papilla, following single doses of 200 mg/kg and 300 mg/kg of gentamicin in 23-day-old chicks. Following 200 mg/kg of gentamicin, there was total HC loss in the basal 18.0% of the sensory epithelium and partial HC loss in the basal 26.3%. Following 300 mg/kg of gentamicin, there was total HC loss in the basal 30.5% of the epithelium and partial HC loss in the basal 40.9%. The second goal of this study was to determine whether cannula implantation in the inner ear, and infusion of bromodeoxyuridine causes HC damage. We found that creation of a fistula in the labyrinth is not associated with HC damage, but that cannula implantation can cause HC death, and can also cause potentiation of gentamicin-induced HC death. Revision of the cannula and surgical technique to ensure minimal penetration into the labyrinth almost entirely eliminated these effects. We conclude that surgical technique is critical in experimental models in which the labyrinth is violated.