模拟失重条件下飞船内噪声对豚鼠耳蜗形态与功能的影响

目的探讨模拟失重条件下,飞船内稳态噪声对豚鼠耳蜗形态与功能的影响。方法32只豚鼠随机分为单纯失重组16只、失重＋稳态噪声组16只。后肢悬吊法模拟失重,暴露于模拟飞船内在天飞行段的噪声环境,共5天。实验前、实验结束后即刻和实验结束后3天测试脑干诱发电位（ABR）阈值,取耳蜗标本行扫描电镜和透射电镜观察。结果实验组实验结束后即刻ABR阈值较实验前及实验结束后3天均增高（P〈0.01）;实验结束后3天ABR阈值较实验前高（P〈0.05）;实验结束后即刻及实验结束后3天失重＋稳态噪声组ABR阈值均较单纯失重组高（P〈0.01）。扫描电镜观察实验组实验结束后即刻耳蜗内、外毛细胞均受损。实验结束后3天,单纯失重组少数耳蜗各回内、外毛细胞的损伤程度比实验结束即刻加重;失重＋稳态噪声组耳蜗各回内毛细胞损伤较实验结束即刻重,外毛细胞损伤较实验结束即刻轻。实验组各时间段内毛细胞的损伤均重于外毛细胞,自第一回至第四回毛细胞损伤逐渐加重。透射电镜观察实验组耳蜗毛细胞及神经节细胞均可见空泡样改变,线粒体分布减少,细胞核固缩,可见细胞凋亡和细胞坏死两种细胞死亡现象。结论失重及失重＋稳态噪声均可造成豚鼠耳蜗形态和功能损伤,后者造成的损伤更重。失重对耳蜗毛细胞损伤以内毛细胞为重,损伤从底回至顶回逐渐加重。实验结束后3天较实验后即刻的听功能有所恢复但内毛细胞损伤加重。

Changes in cochlear infrastructure and hearing in guinea pigs in response to simulated weightlessness and space craft noise

Objective To investigate the influence of spacecraft noise on auditory function and cochlear ultrastruc-ture in guinea pigs in weightlessness. Methods Thirty-two guinea pigs were randomly divided into weightlessness-only and weightlessness plus noise groups. Weightlessness was simulated by suspending the hind limbs of the guinea pigs. Animals in the weightlessness plus noise group were also exposed to simulated flying spacecraft noise for 5 days. Auditory Brainstem Response (ABR) and Scanning Electron Microscopy (SEM) and Transmission Electron Microscope (TEM) examinations were performed before, immediately following and at 3 days after the experiment. Results In both groups, ABR thresholds were significantly higher immediately following the exposure than before and 3 days after experiment (P < 0.01). ABR thresholds at of the third day after the experiment were also higher than pre-experiment (P < 0.05). Post-exposure ABR thresholds (both immediately and on Day 3) in the weightlessness and noise group were higher than weightlessness-only group (P < 0.01). SEM examination showed damage of both outer hair cells (OHC) and inner hair cells (IHC) in both groups immediately following exposure. On Day 3, in a few cochleae in the weightlessness-only group,hairs cell damage were found more severe compared at the end of exposure, with scattered OHC regeneration, while in the weightlessness and noise group, increased IHC damaged and relatively less severe OHC damage were noticed in all turns on Day 3 compared to at the end of experiment. In both groups and at all post-exposure times, IHC damage was more severe than OHC, and more so in the first turn than the apical turns. TEM examination demonstrated ultrastructural changes in hair cells and in gangliocytes in both groups, including intracellular vacuoles, mitochondria decrease, and karyon pycnosis. Conclusion Cochlea infrastructure and function can be damaged by weightlessness and noise exposure in the guinea pigs. Combined weightlessness and noise cause increased damage. Weightlessness causes damage to hair cells, more so in the IHC, which gradually increases from the basal to apical turns. Auditory function shows partial recovery on Day 3 following exposure, although IHC damage appears to be worsening, compared to immediately after exposure.