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Title: [Inner hair cells loss by carboplatin and the changes of cochlear compound action potential in chinchillas].
Author: Yuan F, Ding DL, Wang J, Cao YT, Salvi RJ, Qi WD.
Journal: Zhonghua Er Bi Yan Hou Tou Jing Wai Ke Za Zhi; 2020 May 07; 55(5):506-513. PubMed ID: 32842367.
Abstract:
Objective: To measure the cochlear compound action potential (CAP) and the densities of hair cells (HCs) along the whole length of the basilar membrane (BM) in adult chinchillas. And to investigate the relationship between the severity of inner hair cells (IHCs) loss and the changes of CAP by using carboplatin-cochlear lesion model. Methods: Totally 18 chinchillas were recruited after ontological evaluation. They were randomly divided into three groups (with 6 subjects in each), A: control, B and C: legion groups treated with one or two shot(s) of carboplatin respectively (76 mg/kg in one shot, i.p., one-week interval between the two shots). Endpoint tests were performed 30 days after the carboplatin treatment in groups B and C, and matched time in group A. A sliver-ball electrode was placed into round window niche via hypotympanic approach in anesthetized chinchilla. CAP was measured in response to clicks and tone burst of 0.5, 1, 2, 4, 8, 16 kHz respectively under anesthesia. CAP amplitudes and thresholds were measured and compared across the groups. After the recording, the whole cochlea surface preparation was made and the HCs were stained in histochemistry against substrate of succinate dehydrogenase (SDH). Images were taken with high-resolution digital camera under light microscope and across the whole cochlea. The length of the basilar membrane (BM) and the number of both IHCs and OHCs were counted. The HC density was calculated as the number of HCs per 10% BM length. Results: The CAP thresholds were (7.1±2.6), (25.4±5.0), (24.6±5.4), (10.4±5.0), (0.4±1.4), (4.2±6.3) and (17.1±14.1) dB SPL (from 6 subjects in group A, n=12 ears) corresponding to stimuli of Click and 0.5, 1, 2, 4, 8, 16 kHz tone bursts respectively. The total number of cochlear HCs were measured as (8 936±643) (x±s) and the average length of the BMs was (17.73±1.012) mm from the six subjects in the group A (n=12 ears). The HC density was found to be varied slightly across the BM. There was no significant CAP threshold difference between the control (group A) and the group B, which received one shot of carboplatin. However, the maximal CAP amplitude was reduced by 40% in the group B and compared with group A. Correspondingly, approximately 40% loss of IHCs were seen. In contrast, a significant CAP threshold shift was seen in subjects receiving two shots of carboplatin (group C), which was accompanied by a loss of 90% IHCs. Conclusions: The CAP thresholds of adult chinchillas show typical open-V shape with the lowest values at 2, 4, and 8 kHz. IHC loss by carboplatin in certain degree is well correlated with CAP amplitude reduction, but does not change the threshold when inner hair cell loss reaches 40%, however, if inner hair cell loss exceeds 80%, the threshold shift of CAP will be inevitable. 目的： 通过卡铂耳蜗损伤模型，观察成年南美栗鼠耳蜗听神经复合动作电位（compound action potential，CAP）及其基底膜内、外毛细胞密度，探讨内毛细胞损害程度与CAP振幅、阈值改变的关系。 方法： 18只成年南美栗鼠经耳科学检查后按随机数字表法分为3组（每组6只）：A组为对照组，B组和C组分别接受1次和2次卡铂注射（76 mg/kg，腹腔注射，2次注射间隔1周）。B组和C组动物在卡铂注射后30 d、A组在相应时间行终点功能测试。经下鼓室径路将记录电极安放到麻醉后南美栗鼠的圆窗龛，记录短声（click）及0.5、1、2、4、8、16 kHz短纯音刺激下的CAP。测试结束后处死动物。耳蜗基底膜铺片经琥珀酸脱氢酶组织化学染色标记毛细胞，在光学显微镜下对全耳蜗基底膜铺片连续高清拍摄，统计毛细胞数量及基底膜长度，计算10%基底膜长度内耳蜗内、外毛细胞的数量作为毛细胞密度。采用GraphPad 6软件进行统计学处理。 结果： A组成年南美栗鼠click及0.5、1、2、4、8、16 kHz短纯音声刺激CAP阈值分别为（7.1±2.6）、（25.4±5.0）、（24.6±5.4）、（10.4±5.0）、（0.4±1.4）、（4.2±6.3）和（17.1±14.1）dB SPL（x±s，n=12）。A组单个耳蜗毛细胞总数为（8 936±643）个（x±s，n=7），全耳蜗基底膜长度为（17.73±1.01）mm（n=12）。与A组相比，B组动物CAP阈值未见明显变化，但CAP饱和振幅降低了40%并伴有约40%的内毛细胞缺失。C组动物CAP明显升高并损失了近90%的内毛细胞。 结论： 成年南美栗鼠短纯音CAP阈值在2、4、8 kHz最低，在低频或高频时阈值略有升高。卡铂造成的部分内毛细胞损伤与CAP振幅改变有良好的对应关系，但在内毛细胞损失40%时并不改变CAP的阈值，当内毛细胞缺失超过80%时，CAP阈值的升高不可避免。.

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