NKCC1小鼠的内耳超微结构观察及其与听觉平衡功能的关系

Ultrastructure of the Inner Ear of NKCC1 Transgenic Mice and Its Association with the Audition and Equilibrium

目的研究不同基因型Na-K-2Cl联合转运子1(NKCC1)小鼠的耳蜗和前庭器官的超微形态特点及其与听觉平衡功能的关系。方法采用电子显微镜对NKCC1+/+野生型鼠、NKCC1+/-杂合子鼠和NKCC1-/-基因敲除鼠的耳蜗基底膜和前庭椭圆囊进行观察,并应用听觉脑干反应(ABR)检测各基因型鼠的听力和观察平衡表现。结果电镜观察显示NKCC1-/-鼠的边缘细胞体积明显缩小,边缘细胞与中间细胞之间空隙扩大成空泡样,并可见前庭膜贴附于边缘细胞的顶膜边缘上。NKCC1-/-鼠外毛细胞呈现为点状缺失,椭圆囊毛细胞仅有少许残留。NKCC1+/+鼠听力和平衡正常,ABR检测的短声阈值为23.13±3.78(dB SPL);NKCC1+/-鼠听力低于NKCC1+/+鼠,ABR短声阈值为38.49±12.29(dB SPL)。NKCC1+/+和NKCC1+/-鼠ABR的阈值在各个频率的差异均有极显著性意义(均P<0.01)。NKCC1-/-鼠呈现全聋并有平衡失调,ABR的各个频率在100 dB SPL均无反应。结论NKCC1基因在内耳表达的不同可以影响小鼠的听觉平衡功能并导致内耳形态改变;内耳形态改变也可作为基因缺失小鼠听觉平衡的形态学基础。

Objective To investigate the ultrastructure of cochlea and vestibule in Na-K-2Cl cotransporter-1(NKCC1) transgenic mice and the role of NKCC1 in auditory and equilibrium functions of the inner ear.Methods Hearing thresholds were measured in the NKCC1^(-/-) mice,NKCC1^(+/-) mice and NKCC1^(+/+) mice by auditory brainstem response(ABR) respectively.The inner ears of the mice were removed and examined morphologically under the electronmicroscopy.Results The transmission electron microscopy(TEM) revealed NKCC1^(-/-) mice exhibited a marked atrophy of volume in marginal cells of the stria vascularis;Reissner's membrane was lain against the edge of marginal cells in stria vascularis;the intercellular spaces between the marginal cell layer and deeper layers of the stria vascularis were wider in mutant than in NKCC1^(+/+) mice ears.The scanning electron microscopy(SEM) showed punctiform absence of outer hair cells in NKCC1^(-/-) cochlea and only a few hair cells present in vestibule.The auditory function of NKCC1^(+/+) mice was normal and the mean value for ABR thresholds in response to click sound stimulus was 23.13±3.78(dB SPL).The auditory function of the NKCC1^(+/-) mice was worse than that of NKCC1^(+/+) mice and the mean value for ABR thresholds in response to click sound stimulus in NKCC1^(+/-) mice was 38.49±12.29(dB SPL).There was significant difference in ABR thresholds at different frequency between NKCC1^(+/+) and NKCC1^(+/-) mice(P<0.01).NKCC1^(-/-) mice were completely deaf and the ABR wave form was not observed for even 100 dB SPL sound stimuli used.NKCC1^(-/-) mice were deaf and demonstrated difficulties in maintaining their balance.Conclusion NKCC1 plays a critical role in the function of the mice inner ear.The morphologic change in cochlea and vestibule was correlated with the absence of NKCC1 and could lead to disorder of the normal auditory function and equilibrium function.