低气压噪声环境对豚鼠耳蜗谷氨酸免疫反应及听阈的影响

Changes of glutamate immunoreactivity and hearing function in cochlea of guinea pig with hearing loss induced by noise in hypobaric environment

目的观察低气压噪声暴露后不同时间豚鼠耳蜗内毛细胞(IHCs)谷氨酸免疫反应(Glu-IR)及听阈的变化。方法按照暴露条件的不同分为四组:低压噪声组、低压组、噪声组和正常对照组。其中,低压噪声组又根据暴露后不同时间点随机分为5小组,即出舱后即刻、8h、1d、3d、7d组,每组动物9只;其余三组各设受试动物9只。豚鼠分组暴露于5500m低气压环境,120dB声压级(SPL)白噪声持续刺激8h。观察暴露后不同时间各组听性脑干反应(ABR)阈的改变,耳蜗IHCs中Glu-IR阳性产物的光密度值。结果低压噪声组和噪声组出舱后8h组ABR阈移最大,与对照组相比有统计学差异(P<0.01),此后两组ABR阈移逐渐恢复,但仍较对照组显著升高(P<0.01)。低压组仅在出舱后即刻出现暂时阈移,此后迅速恢复。低压噪声组出舱即刻IHCs中Glu-IR阳性产物光密度值明显高于对照组(P<0.01),出舱后8h其IHCs内Glu-IR产物光密度值较对照组降低且有统计学差异(P<0.01),出舱后1d、3d和7d组与对照组间无统计学差异。结论低气压可协同噪声环境导致听觉损伤。低气压噪声暴露后,耳蜗IHCs内Glu-IR经过一个增强-减弱-恢复的动态变化过程。低气压噪声环境所致听力损伤可能与IHCs内Glu的变化有关。

Objective To investigate the changes of glutamate immunoreactivity(Glu-IR) and the hearing function in cochlea of guinea pig with hearing loss induced by noise in hypobaric environment.Methods Normal guinea pigs were randomly divided into four groups(hypobaric-noise group,hypobaric group,noise group and control group).All the animals were exposed to 120 dB SPL white noise in hypobaric chamber to reproduce a low pressure environment of 5500 m altitude for 8 h,and the hypobaric-noise group was distributed into five subgroups according to their different periods after exposure(0 h,8 h,1 d,3 d and 7 d subgroups,respectively).Acoustic brainstem response(ABR),the immunohistochemical stains and image quantitative analysis were utilized to evaluate the changes of hearing thresholds and immune reaction to glutamate in cochlea.Results The ABR thresholds were obviously elevated in the hypobaric-noise group and noise group compared with the normal control(P<0.01),although they had a tendency to recover.The greatest threshold shifts were observed in the 8-hour subgroup.The hypobaric group only had temporary threshold shift just after exposure(0 h).The optical density of the Glu-IR positive substances in IHCs increased obviously just after exposure in 0 h subgroup compared with the normal control(P<0.01).However,the density of the Glu-IR substances reduced obviously in 8 h subgroup after exposure(P<0.01).There was no difference between 1 d,3 d or 7 d subgroup and the normal control.Conclusions The acute hypobaric environment combined with noise can induce hearing loss.The Glu-IR in IHCs has dynamic changes after exposure to noise in hypobaric environment.The mechanism of the hearing loss induced by noise in hypobaric environment may be associated with the over-release of glutamate in IHCs after exposure.