Effects of different noisy environments on noise-induced hearing loss in guinea pigs

Abstract

Objective To investigate the effects of different noisy environments on hearing loss after severe noise exposure in guinea pigs.Methods Thirty guinea pigs were randomly divided into 5 groups,each consisting of 6 animals.The guinea pigs in group A,B,C and D were subjected to noise at 84 decibels sound pressure level (dB SPL) for 4,8,24 and 0 hours respectively after traumatic noise exposure; the guinea pigs in group E were kept in quiet cages.Auditory brainstem response was determined at 3 time points:Ⅰ day before,1 day after and 7 days after noise exposure.Blood plasma was obtained to determine the active levels of SOD,TNOS and the content of MDA at the end of the experiment.Results The guinea pigs in group D developed noise-induced hearing loss following traumatic noise exposure.At the seventh day after exposure,the thresholds of C-ABR and PTS in group A[(2.51 ± 0.44)μmol/L] and B [(2.57 ± 0.57)μmol/L] decreased,as compared with that of group D[(1.21 ±0.34) μmol/L] (P ＜0.05).At the first day after exposure,TTS for group A,B and C decreased,as compared with that of group D (P ＜ 0.05) at frequencies of 12 kHz and 24 kHz.At the seventh day after exposure,the content of MDA increased (P ＜ 0.05) for group A and B,while the activity of TNOS for group A and C decreased (P ＜ 0.05),as compared with that of group D.Conclusions Moderate level of noise environment seemed to have some effects on the recovery of noise-induced hearing loss at low frequencies one day after noise exposure,while exposure to moderate noisy environment might also have some effects on the recovery of noise-induced hearing loss at high frequencies,7 days after noise exposure. Key words: Noise; Auditory brainstem response; Noise-induced hearing loss ; Free oxygen radical