Styrene-induced hearing loss: a membrane insult

Styrene is an aromatic solvent widely used as a precursor for polystyrene p lastics in many factories which produce glass-reinforced plastic. This solv ent has been shown to disrupt the auditory system in both humans and animal s. In order to study the sequence of events which could explain the cochlea r impairments. a time course experiment was carried out with 6-month-old ra ts. Male LongEvans rats were exposed to 1000 ppm styrene for 6 h/day, 5 day s/week, for either 1, 2, 3, or 4 consecutive weeks. Auditory function was t ested by recording the near field evoked potentials from the inferior colli culus, and histological analyses of the cochleae were performed with light and transmission electron microscopy. The electrophysiological results supp ort a toxic mid-frequency process which keeps worsening even after the end of the exposure. The histological findings demonstrate that supporting cell s are the first targets of the solvent. Then. the outer hair cells of the t hird row (OHC3) are disrupted, followed successively by OHC2 and OHC1 from the basal (20 kHz) to the upper turn (4 kHz) of the cochlea. Basically, the disorganization of the membranous structures could be the starting point f or the cochlear injury induced by styrene. This paper presents a hypothesis that the accumulation of K+ in the spaces of Nuel underlies the toxic effe cts of styrene. (C) 2001 published by Elsevier Science B.V.