HAIR CELL RECOVERY IN THE CHINCHILLA CRISTA-AMPULLARIS AFTER GENTAMICIN TREATMENT - A QUANTITATIVE APPROACH

The mechanisms for hair cell recovery were investigated after intraoti c application of 50,mu g gentamicin into the perilymphatic space of th e superior semicircular canal of the chinchilla. Histologic evaluation of one normal group and four posttreatment groups (7, 14, 28, and 56 days) was made with light and transmission electron microscopic techni ques. The numeric changes of hair cells and supporting cells was quant ified with the dissector technique. At 7 and 14 days after treatment, no type I hair cells were present, and 85% and 88% of type II hair cel ls were lost. Supporting cells decreased to 76% at 7 days, but they re covered to 91% at 14 days. Recovery of the epithelia was evident 28 da ys after treatment; 83% were type II hair cells, and 3% were type I ha ir cells. The supporting cell number remained close to normal (86%). B etween 14 and 28 days after treatment, there was an increase of 1758 o f type II hair cells, representing approximately 125 new hair cells pe r day. At the same time interval the number of supporting cells remain ed near normal. These results suggest that new hair cells might be the result of supporting cell mitotic division and differentiation.