Effect of acoustic trauma on cytochrome oxidase activity in stria vascularis

The present study was undertaken to determine the role of metabolic disturbance in noise-induced hearing loss by histochemical studies of cytochrome oxidase activity. Adult normal albino guinea pigs were used. The experimental animals were exposed to broad-band noise at 105 dB SPL for 24 h. The control animals were not exposed to the noise. The thresholds of the auditory brainstem response (ABR) of all guinea pigs were measured 3 times: before noise exposure, 1 day and 1 month later. The difference between the ABR thresholds before and after noise exposure was statistically significant. Vibratome sections of decalcified cochleae of the noise-exposed (n = 8) and control groups (n = 4) were incubated with Spector's medium and embedded with Epon. Thin sections (2 mu m) and ultrathin sections (100 nm) were cut to observe cytochrome oxidase activity in the stria vascularis under light and electron microscopes, respectively. A decreased activity of cytochrome oxidase was consistently shown in the normal-appearing stria vascularis of most noise-exposed ears. Acoustic trauma has an adverse effect on cytochrome oxidase activity in the stria vascularis as well as on hearing. A decrease in the activity of cytochrome oxidase implicates that metabolic damage may play a role in noise-induced hearing loss.