Spontaneous reversibility of damage to outer hair cells after sodium salicylate induced ototoxicity.

BACKGROUND: High sodium salicylate doses can cause reversible hearing loss and tinnitus, possibly due to reduced outer hair cell electromotility. Sodium salicylate is known to alter outer hair cell structure and function. This study determined the reversibility and cochlear recovery time after administration of an ototoxic sodium salicylate dose to guinea pigs with normal cochlear function. STUDY DESIGN: Prospective experimental investigation. METHODS: All animals received a single 500 mg sodium salicylate dose, but with different durations of action. Function was evaluated before drug administration and immediately before sacrifice. Cochleae were processed and viewed using scanning electron microscopy. RESULTS: Changes in outer hair cell function were observed to be present 2 hours after drug administration, with recovery of normal anatomy beginning after 24 hours. Subsequently, derangement and distortion of cilia reduced, with effects predominantly in row three. At 168 hours, cilia were near-normal but with mild distortions which interfered with normal cochlear physiology. CONCLUSIONS: Ciliary changes persisted for up to 168 hours after ototoxic sodium salicylate administration.

Histological effects of intratympanic gentamicin on the vestibular organ of guinea pigs.

BACKGROUND: Transtympanic administration of gentamicin may be suitable to achieve unilateral vestibular ablation, in order to control unilateral Ménière's disease. In low doses, gentamicin appears to affect selectively the vestibular system, with relative sparing of the cochlea. An experimental study on guinea pigs was conducted to determine what single dose of gentamicin would produce a unilateral vestibular organ lesion when applied to the middle ear. STUDY DESIGN: Experimental and prospective. METHODS: Four groups of guinea pigs received different gentamicin doses (1, 5, 10 and 25 mg) administered to the middle ear. The animals' vestibular organs were then assessed by scanning electron microscopy, in order to quantify the level of vestibular damage. RESULTS: Study of the utricular macula and the ampullar crista of the lateral semicircular canal revealed vestibular neuroepithelial lesions in all infused ears. CONCLUSIONS: The severity of the vestibular neuroepithelial lesions was dose-dependent. Lower gentamicin doses were observed to damage vestibular structures more than cochlear structures.