目的探讨噪声暴露前后凋亡诱导因子（AIF）在大鼠不同回基底膜外毛细胞的表达差异以及与噪声性聋高频听力易损性的关系。方法40只SD大鼠随机分为正常对照组和噪声暴露组：噪声暴露组给予声强为115dB SPL白噪声暴露，每天2小时，连续3天，对照组不予噪声暴露。分别于噪声暴露前1日、暴露后1、3、7、14日对两组大鼠行ABR检测，最后一次ABR检测后对两组大鼠耳蜗基底膜行鬼笔环肽—异硫氰酸荧光素(Phalloidin-FITC)染色。West-ern blot和免疫荧光染色法观察两组大鼠耳蜗不同回基底膜处AIF的表达。结果大鼠噪声暴露后与暴露前相比，ABR各频反应阈值于暴露后1天最高，随时间逐渐恢复，14天时趋于稳定，听力低频阈移约10dB，高频阈移有30dB (P<0.05)；基底膜铺片FITC染色示噪声暴露组底回基底膜毛细胞较顶回缺失严重，且有纤毛排列紊乱并出现融合，而对照组毛细胞排列整齐，纤毛呈V或W型，两组间外毛细胞计数比较差异有统计学意义(P<0.05)；Western blot结果示，在正常情况下,顶回基底膜的AIF表达高于底回，噪声暴露后，AIF顶、底回基底膜表达均较对照组相应部位增高，且顶回较底回更为显著(P<0.05)。结论噪声暴露过程中，AIF在促凋亡的同时更发挥出了氧化还原酶的作用，因而AIF在耳蜗基底膜顶、底回的表达差异，可能是噪声性聋高频听力易损性的分子机制之一。%Objective To Investigate differences in expression of apoptosis-inducing factor (AIF) in outer hair cells along the basilar membrane before and after noise exposure, and its potential relationship with vulnerability of high-frequen-cy hearing in noise-induced hearing loss. Methods Forty adult Sprague-Dawley (SD) rats were randomly divided into a con-trol and a noise-exposure group:animals in the noise-exposure group were exposed to white noise at 115 dB SPL, 2 hours a day, for 3 consecutive days, while animals in the control group were not exposed. Auditory thresholds were assessed by audito-ry brainstem response (ABR), prior to and 1, 3, 7 and 14 days after noise exposure. Upon completing ABR testing, animals were randomly selected to be sacrificed for cochlear sensory epithelia surface preparation which were stained by FITC-phal-loidin and examined under a microscope. Western blot and immunofluorescence methods were used to detect changes of AIF expression on the basilar membrane at different cochlear turns. Results Compared with the control group, the ABR thresholds for all frequencies increased most significantly on Day 1 after noise exposure in the exposure group. ABR thresholds recov-ered gradually and stabilized on Day14 post-exposure with a permanent threshold shift of about 10 dB at low-frequencies and about 30 dB at high-frequencies (P<0.05). Basilar membrane staining showed obvious hair cell loss in the basal turn in the noise-exposure group, with cilia disarrangement and fusion, in contrast to the well-arranged V or W shaped cilias in the same areas in animals from the control group.The difference of outer hair count between these two groups was statistically significant (P<0.05). Western blot analysis revealed stronger AIF expression in the apical turn than in the basal turn in the control group. AIF expression in both apical and basal turns was obviously stronger in the noise-exposure group than in the control group (P<0.05). Conclusions AIF is a proapoptotic factor, but may act as a free radical scavenger in response to noise-induced oxidant stress. Its increased expression may be one of the mechanisms for vulnerability of high-frequency hearing in noise-induced hearing loss, as indicated by the different expression levels in the apical and basal cochlear turns
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