Effects of High Level Low Frequency Noise on Hearing and Expression of Caspase-3 in Rats

YIN Zhili; WU Wei; WANG Gang; WANG Hongnan; HAN Haolun; LI Baowei; ZHOU Libin; YU Meng; QU Changbei; ZHANG Jianzhong; WU Jihua; ZENG Xinwu; GONG Changchao; TIAN Zhangfu; LIU Long

doi:10.3969/j.issn.1672-2922.2014.03.038

Abstract：Objective To study the effect of high intensity low frequency noise on hearing and apoptosis of inner ear cells. Methods Rats (n=52 ) were randomly divided into a control group (Pr) (n=13), and three noise exposure groups (n=39) that were examined immediately (E0 group, n=13), three days (E3 group, n=13) or 7 days (E7 group, n=13) following exposure to a 150 dB SPL steady noise centered around 500 Hz for 10 minutes, respectively, The auditory brainstem response was record-ed, followed by cochlear morphology examination after the animals were sacrificed and cochlear paraffin sections were prepared and stained using immunohistochemical techniques. Results Immediately after exposure to the 150 dB SPL noise, ABR thresholds were significantly elevated. Moderate recovery was seen at 3 days after exposure, with little further improvement at 7 days after exposure. ABR thresholds at all time points following exposure were higher than before exposure (P<0.01) ABR thresholds showed significant differences between the E0 group and E3 and E7 groups (P<0.05), but not between the E3 and E7 groups (P>0.05). Immunohistochemistry results showed various levels of caspase-3 expression in the Organ of Corti, spiral gan-glion cells, stria vascularis and spiral ligaments in the low-frequency sound exposure groups but not in the control group. The average optical density was different between the control and exposure groups, among the E0, E3 and E7 groups (P<0.01) and between the E3 and E7 groups (P<0.01). There was no significant caspase-3 expression in the control group. Conclusion High-intensity low-frequency noise can cause significant hearing damage, which can later partially recover. Caspase-3-medi-ated inner ear apoptosis may play an important role in the pathogenesis of noise-induced hearing loss.