CORRESPONDENCE BETWEEN MIDDLE FREQUENCY AUDITORY LOSS IN-VIVO AND OUTER HAIR CELL SHORTENING IN-VITRO

The aromatic hydrocarbon, toluene, has been reported to disrupt audito ry system function both in occupational epidemiological and in laborat ory animal investigations. This agent, along with several other organi c solvents, impairs hearing preferentially at middle frequencies - a f inding that distinguishes these agents from the traditional high frequ ency impairment observed with ototoxic drugs such as aminoglycoside an tibiotics and cisplatin. Prior investigations performed in vivo have i dentified the outer hair cell as a probable target for toluene exposur e. The purpose of this investigation was to determine directly whether outer hair cells isolated from the guinea pig cochlea show morphologi cal alterations consistent with the toxic response seen in physiologic al studies with toluene exposure. The effect of toluene superfusion on outer hair cell shortening was assessed for cells harvested from diff erent locations within the cochlea. Control studies included assessmen t of cell shortening among outer hair cells exposed to trimethyltin an d cells exposed to benzene. Trimethyltin disrupts high frequency heari ng preferentially and benzene does not produce hearing loss in vivo. T oluene at a concentration of 100 mu M produced a marked shortening of outer hair cells although the effect was significantly greater among c ells isolated from the apical half of the cochlea than from the basal half of the cochlea.-By contrast, trimethyltin at the same concentrati on produced a preferential shortening among outer hair cells from the base of the cochlea. Benzene (100 mu M) did not disrupt outer hair cel l length of cells harvested from the apex. The results indicate that i ntrinsic features of outer hair cells contribute significantly to the site of ototoxic impairment observed in vivo for toluene.