Gentamicin ototoxicity: histological and ultrastructural alterations after transtympanic administration.

The histological and ultrastructural appearances of the inner ear vestibulum were studied after transtympanic administration of gentamicin in guinea-pigs. The animals were treated with a single transtympanic dose (0.2 cm3) of 4% gentamicin sulphate solution in the right ear; the left one was considered as control. After 7 days they were sacrificed and the vestibula of both inner ears were removed to be examined both by light and electron microscopy. In the treated inner ear damage was not always evident at light microscopical level, even if a case of complete disepithelialization of cristae ampullares was found. The examination by TEM revealed evident damage in the vestibular non-sensorial cells, such as severe cellular vacuolation, whereas sensorial elements presented heterochromatinic thickenings and cytoplasmic wrinkling, as compared to controls. The tunica fibrosa presented an irregular fibrillar plot, as well as that of the myelinic lamellae in the vestibular nerve fibres.