Effects of simulated weightlessness and continuous noise in a spaceship on auditory function of rats
- LI Yuanchao, WU Wei, WANG Gang, QU Changbei, WANG Lei, LU Wenjun, LI Dan, HAN Haolun, LIU Gang
Journal of Otolaryngology and Ophthalmology of Shandong University. 2021, 35(5):
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Objective To explore the time-effect relationship of simulated weightlessness and moderate-intensity continuous noise in a spaceship on the auditory function of rats. Methods Ninety-six male Sprague-Dawley(SD)rats were randomly divided into the weightlessness group, noise group, weightlessness + noise group, and a control group(n=24 per group). On this basis, the rats in each group were divided into 1-week and 4-week groups according to exposure time(n=12 per subgroup). Half of the rats were killed immediately after exposure(P0)as the immediate after exposure group, and the other half were killed 7 days after exposure(P7)as the recovery group(n=6). The tail suspension method(Morey Holton method)was used to simulate weightlessness, and the white noise signal generation system was used to simulate moderate continuous noise:(72±2)dB sound pressure level(SPL)continuous noise for 8 h /d and(50±2)dB SPL continuous noise for 16 h /d in the spaceship. Auditory brainstem response(ABR)thresholds and distortion product otoacoustic emission(DPOAE)were measured at B0, P0, and P7. Results ABR thresholds were(10.83±5.25),(8.13±4.62),(13.54±8.53),(7.08±2.52)dB SPL in the weightlessness group, noise group, weightlessness + noise group, and control group at 1 week P0;(6.67±2.46),(5.83±1.95),(8.75±4.33),(7.92±3.34)dB SPL at 1 week P7;(18.13±7.19),(16.04±5.71),(19.58±8.33),(6.04±2.54)dB SPL at 4 weeks P0; and(7.92±3.96),(7.92±3.34),(14.17±7.93), and(6.25±2.26)dB SPL at 4 weeks P7. The ABR threshold of rats in the weightlessness and weightlessness + noise groups after exposure for 1 week were higher than before exposure and became further aggravated as time progressed. However, there was no significant difference in ABR threshold of noise group between after 1 week exposure and before exposure, although there was significant difference 4 weeks after exposure. There was no significant difference in ABR threshold in the weightlessness + noise group between P7 and P0; thus, the ABR threshold showed no recovery. The ABR threshold of the other exposure groups recovered completely at P7. There was no significant difference in the DPOAE extraction rate between the experimental groups before and after exposure. Conclusion Weightlessness and continuous noise have a significant cumulative and synergistic effect on hearing impairment, with weightlessness being dominant. The ABR threshold shift induced by 4-week simulated weightlessness or moderate continuous noise exposure alone is reversible, but the combined exposure for 4 weeks may have caused irreversible hearing damage, with damage mainly linked to the function of inner hair cells.