模拟失重及飞船内稳态噪声对大鼠听功能的影响

Effects of simulated weightlessness and continuous noise in a spaceship on auditory function of rats

目的探讨模拟失重及飞船舱内中等强度稳态噪声对大鼠听功能影响的时效关系。方法96只雄性SD大鼠随机分为失重组、噪声组、失重+噪声组和对照组,各24只鼠,每组大鼠再按暴露时间随机分为1周、4周组,各12只鼠,最后在暴露结束后即刻(P0)测听并处死一半大鼠作为暴露即刻组,另一半脱离暴露环境7 d后(P7)测听并处死作为恢复组,各6只鼠。失重模拟采用尾部悬吊即Morey Holton法模拟失重,噪声模拟采用白噪声信号发生系统模拟飞船舱内中等强度稳态噪声[8 h/d的(72±2)dB SPL稳态噪声+16 h/d的(50±2)dB SPL稳态噪声]。分别在暴露前(B0)、P0、P7检测ABR阈值和畸变产物耳声发射(DPOAE)。结果失重组、噪声组、失重+噪声组和对照组的ABR阈值在暴露1周P0时分别为(10.83±5.25)、(8.13±4.62)、(13.54±8.53)、(7.08±2.52)dB SPL;在暴露1周P7时分别为(6.67±2.46)、(5.83±1.95)、(8.75±4.33)、(7.92±3.34)dB SPL;在暴露4周P0时分别为(18.13±7.19)、(16.04±5.71)、(19.58±8.33)、(6.04±2.54)dB SPL;在暴露4周P7时分别为(7.92±3.96)、(7.92±3.34)、(14.17±7.93)、(6.25±2.26)dB SPL。失重组和失重+噪声组大鼠暴露1周后ABR阈值较暴露前升高,且随时间延长进一步加重,噪声组ABR阈值在暴露1周时与暴露前差异无统计学意义(P=0.054),在暴露4周时升高;失重+噪声暴露4周组ABR阈值在P7时与P0时差异无统计学意义,未见恢复,其余暴露组在P7时ABR阈值完全恢复。暴露前后各实验组DPOAE引出率无统计学差异。结论失重及稳态噪声对听功能的损伤有明显的时间累积效应,二者具有协同作用且失重占据主导。4周模拟失重或飞船舱内中等强度稳态噪声单独暴露导致的大鼠ABR阈移是可逆的,但4周的复合暴露可能已造成不可逆性听损伤,且主要损伤内毛细胞的功能。

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.