豚鼠内淋巴积水早期低频听力损失的形态学变化

Morphological changes associated with low-tone hearing loss in guinea pig models of early endolymphatic hydrops

本研究旨在观察豚鼠内淋巴积水模型早期的耳蜗功能改变与形态变化之间的关系。选用白化豚鼠30只,随机分为3组:10只假手术对照组(仅暴露乙状窦);20只制备耳蜗内淋巴积水的动物模型,其中积水4周组10只,积水8周组10只。采用经枕后入路骨蜡堵塞内淋巴囊和管的方法制备耳蜗积水动物模型。对造模手术前、对照组、4周组和8周组豚鼠行耳蜗电图测试(鼓膜电极记录)、听觉脑干诱发电位(auditory brainstem response,ABR)测试,观察豚鼠听力改变。测试结束后,每组5只动物耳蜗标本做火棉胶切片观察耳蜗形态学改变,另5只动物耳蜗进行扫描电镜图像分析观察毛细胞改变。结果显示,4周组和8周组的最大中阶面积(scala media area,SMA)比值分别为2.64±0.10、3.54±0.13,显著大于对照组(1.06±0.08)。4周组和8周组的耳蜗电图总和电位(summating potential,SP)/复合动作电位(compound action potential,AP)比值分别为0.33±0.14、0.43±0.14,显著高于对照组(0.07±0.06)。最大SMA比值与SP/AP比值之间有正相关(r=0.86)。造模组豚鼠听力损失主要出现在2kHz和4kHz两个较低频率,而毛细胞损伤主要出现在顶回和第三回。以上结果表明,SP/AP比值增大可以作为一个早期判断豚鼠内淋巴积水的指标;内淋巴积水早期出现低频听力损失,可能与积水早期耳蜗顶回和第三回外毛细胞静纤毛损伤有关。

The present study was to explore the functional and morphological changes in cochleas of guinea pig models of early endolymphatic hydrops. Thirty albino guinea pigs were randomly divided into three groups： control, 4-week model and 8-week model groups. For each group, n = 10. Model groups were operated on the right ears to result in endolymphatic hydrops with the method of slight destruction of endolymphatic sac and duct from extradural posterior cranial fossa approach, and the animals in control group were sham operated. Electrocochleogram recorded by trans-tympanic approach and auditory brainstem response （ABR） were tested in preoperative model groups, control group, 4-week model group and 8-week model group to assess the hearing changes. Histologic morphometry was used to quantify hydrops by testing scala media area （SMA） ratio. Scanning electron microscope was used to assess the changes of cochlea hair cells. The results showed that the summating potential/compound action potential （SP/AP） ratio of electrocochleogram in 4-week model group （0.33 ± 0.14） and 8-week model group （0.43 ± 0.14） increased significantly, compared with that in control group （0.07 ± 0.06）. The maximum SMA ratio in 4-week model group （2.64 ± 0.10） and 8-week model group （3.54 ± 0.13） increased significantly, compared with that in control group （1.06 ± 0.08）. The results of maximum SMA ratio correlated with SP/AP ratio of electrocochleogram （r = 0.86）. The results of hearing threshold of ABR revealed that the operated ears of model groups were higher than the preoperative results at frequencies of 2 kHz and 4 kHz. And the damage of cochlea hair cells in operated ears occurred in apical and subapical turns. These results suggest the increased SP/AP ratio of electrocochleogram can indicate early endolymphatic hydrops. There is low-tone hearing loss in guinea pig models of early endolymphatic hydrops, and it may be associated with the abnormalities of the stereocilia among the outer hair cells in operated ears which occurs in apical and subapical turns.