Evoked-potential thresholds and cubic distortion product otoacoustic emissions in the chinchilla following carboplatin treatment and noise exposure

Twenty-two chinchillas were given either a single intraperitoneal (ip.) or intravenous (i.v.) injection (50 or 75 mg/kg) of Paraplatin(TM), an asymptotic threshold shift-producing noise or a combination of the drug acid noise in series. Auditory evoked potential (pure-tone) audiograms and cubic distortion product otoacoustic emissions were obtained on each animal before and after treatment, and the sensory epithelium of the cochlea was evaluated using the surface preparation method. Anatomical analysis indicated that the carboplatin alone caused relatively severe but scattered losses of inner hair cells throughout most of the cochlea which were dependent on dose and administration route. The outer sensory cell population remained essentially intact. In animals that had up to 40% scattered losses of only inner hair cells, evoked potential thresholds were near normal and the emission functions either were normal or showed an enhanced output. The severe losses of inner hair cells produced by the drug had no effect on the threshold shift dynamics produced by a five-day uninterrupted noise exposure. In general, there was not a consistent relation between the emission data and both the permanent threshold shift and outer hair cell losses.