Interleukin 8 can affect inner ear function.

Abstract

The chemokine interleukin 8 (IL-8) was instilled into the round window niche of rats through a small perforation in the tympanic membrane in order to study its effect on inner ear function by electrophysiological and morphological techniques. The frequency-specific auditory brainstem response (ABR) was recorded at the frequencies 4, 8, 10, 12, 16 and 20 kHz just before and 1, 2, 5 and 14 days after instilling IL-8 to ascertain the hearing level during each interval. Morphological examination by light microscopy was performed during the same interval following the instillation of IL-8. On day 1, the rise in ABR threshold was within 5 dB SPL (non-significant elevation). However, a significant threshold elevation (above 5 dB SPL) occurred in high-frequency areas (16 and 20 kHz) on day 2, and in middle frequency areas (10 and 12 kHz) on day 5 with sensorineural hearing loss type intensity-latency curves. By day 14, the elevated thresholds had returned to pre-instillation levels. In the lowest areas (4 and 8 kHz), no significant threshold elevation was detected at any time during the observation period. By light microscopy, on day 1, clusters of inflammatory cells (predominantly neutrophils) were observed just outside the round window membrane (RWM), while only a few neutrophils were detected in the cochlea. These cells were still present outside the RWM on day 2. The neutrophils had disappeared by day 5 and only macrophages were present on the middle ear side of the RWM. However, throughout the observation period, the organ of Corti and stria vascularis appeared to be intact. These results suggest that IL-8 in the middle ear cavity is able to influence inner ear function.