模拟载人飞船内微重力和噪声环境下大鼠耳蜗毛细胞的形态学变化

Morphological changes on cochlear hair cells of rats in simulated weightlessness and inboard noise

目的:观察模拟载人飞船中微重力和噪声环境下大鼠耳蜗毛细胞的形态学特点,探讨耳蜗三回(底回、中回和顶回)毛细胞的不同变化。方法:选取32只雄性健康SD大鼠,随机分为空白组、失重组、噪声组和失重+噪声组4组,每组8只。失重组以持续尾吊法模拟微重力,噪声组以持续2周的(72±2)d B SPL的稳态噪声及之后的3次高达160 d B SPL的脉冲噪声模拟飞船内复合噪声环境,失重+噪声组同时给予模拟微重力和噪声环境,空白组不做任何处理,常规饲养2周。暴露后检测听性脑干反应(auditory brainstem response,ABR)阈值,处死大鼠即刻取耳蜗基底膜行免疫荧光及扫描电子显微镜(scanning electron microscope,SEM)观察。结果:给予模拟环境暴露后,各组大鼠ABR阈值升高,各实验组大鼠暴露前后ABR阈值差异均有统计学意义(P<0.05)。免疫荧光结果显示:失重组底回以内毛细胞缺失为主,中回可见毛细胞肿胀,顶回毛细胞杂乱不清。噪声组底回以外毛细胞缺失为主,多见于最外层毛细胞,中回毛细胞肿胀,顶回杂乱并有毛细胞的缺失。失重+噪声组底回核缺失较明显,主要存在最外层毛细胞,内毛细胞也存在较多缺失。中回和顶回缺失发生在最内层外毛细胞。电子显微镜观察发现失重组底回纤毛大片倒伏,偶有缺失,顶回和中回毛细胞纤毛无明显异常。噪声组底回纤毛大片倒伏伴缺失,顶回和中回均有缺失,其中顶回最为严重。失重+噪声组底回纤毛大片融合伴缺失,中回纤毛融合、倒伏并缺失,顶回内外毛细胞纤毛大量缺失。4组的损伤程度:失重+噪声组>噪声组>失重组>空白组;三回毛细胞损伤程度:底回>中回>顶回。结论:模拟载人飞船内微重力和噪声环境中暴露2周可致大鼠耳蜗形态学结构发生显著变化,尤以失重+噪声组变化最明显,三回毛细胞中以底回最重,顶回最轻。

Objective: To observe the morphological changes on cochlear hair cells of rats in simulated weightlessness and inboard noise and to investigate the different changes in three turns of hair cells.Methods: Thirty-two healthy SD rats,all males,were randomly divided into four groups: control group,weightlessness group,noise group and weightlessness + noise groups( n = 8). Then rats were exposed to-30° head down tilt as simulated weightlessness and inboard noise including steady-state noise which was( 72 ± 2) d B SPL and impulse noise up to 160 d B SPL in spaceship environment. The control group was kept in normal condition for 8 weeks. Bilateral auditory brainstem response( ABR) thresholds were tested before and after exposure respectively,and immunofluorescence staining and scanning electron microscopy( SEMs) of basilar membrane were applied after exposure. Results: ABR threshold shifts of each group were higher after exposure. There was difference between ABRs of the experiment groups before and after exposure( P < 0. 05). IF showed that the inner hair cells( IHCs) missing was the main damage in the basal turn of weightlessness group,the hair cells in the middle turn were swell and in the top turn,the hair cells were not clear. In noise group,the main loss happened in the outer hair cells( OHCs) of the outermost layer. In weightlessness + noise group,the nuclear missing in the basal turn was apparent,and mainly happened at the outermost layer. Meanwhile,the missing of hair cells in the middle turn and top turn was seen at the innermost layer. SEM showed that the cilia in the basal turn of weightlessness group were serious lodging,and occasional absence. Furthermore,the basal cilia in noise group became lodged and absent,and the other two turns were seriously missing. And in weightlessness +noise group,the cilia missing in the basal turn was apparently seen. The damage degree of the four groups: weightlessness + noise group > noise group > weightlessness group > control group and the damage degree of the four turns of hair cells: basal turn > mid turn > top turn. Conclusion: The rats exposed to the above environment for 2 weeks displayed obvious changes in cochlea morphology,and the weightlessness + noise group had the most obvious damage.