Maximal number of pre-synaptic ribbons are formed in cochlear region corresponding to middle frequency in mice

Abstract

Objective: To investigate whether there are more quantitative pre-synaptic ribbons formed in the cochlear region corresponding to middle-frequency in cochlea of mice.

Methods: Counts of pre-synaptic ribbons were performed using immunostaining and laser confocal microscopy. Hearing thresholds and function of ribbon synapses were estimated by auditory brain response (ABR) and compound action potential (CAP). Cochlear mapping has been achieved to match the frequencies and corresponding regions along the cochlear spiral.

Results: The number of pre-synaptic ribbons in per inner hair cell (IHC) has been found to increase gradually from the base turn, the maximal quantity appeared at the region of 50–70% from the apex. Next, ABR thresholds showed that there was the lowest ABR threshold in the frequency around 8–16 kHz, corresponding to the region of 50–70% from the apex according to the cochlear mapping. Further, CAP amplitudes were estimated, and the maximal value identified at the same frequency (8–16 kHz).

Conclusions: Maximal number of pre-synaptic ribbons is formed in the cochlear region of middle frequency in mice, coupling with the lowest ABR threshold and highest CAP amplitudes. Our study shows that the middle frequency (8–16 kHz) could be the most sensitive region to sound stimuli in mice.

Chinese abstract

目的：探讨小鼠耳蜗区域是否因耳蜗内中频而形成更多的前突触带。

方法：使用免疫染色和激光共聚焦显微镜进行前突触计数。通过听觉脑反应（ABR）和复合动作电位（CAP）估计听觉阈值和突触带的功能。已经完成了耳蜗定位, 将沿耳蜗螺旋的频率与相应区域对应。

结果：发现每个内毛细胞（IHC）中的突触前丝带数量从基线逐渐增加, 最大量出现在从顶点的50-70%的区域。接下来, ABR阈值表明, 在频率为8-16kHz左右处存在最低的ABR阈值, 根据耳蜗定位, 对应于从顶点50-70%的区域。此外, 估计了CAP幅度, 并且在相同频率（8-16kHz）处识别出最大值。

结论：在小鼠中频耳蜗区域有最大数量的前突触带形成, 与最低ABR阈值和最高CAP幅度耦合。我们的研究表明, 中频（8-16 kHz）可能是小鼠声音刺激最敏感区域。

Keywords:

• ABR threshold
• cochlear frequency
• inner hair cells
• ribbon synapse
• mice

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

National Natural Science Foundation of China10.13039/5011000018093104003881572666

Beijing Natural Science Foundation10.13039/5011000048265122040

National Basic Research Program of China2012CB967900

China Postdoctoral Science Foundation10.13039/50110000285820100377920100470103This work was supported by the National Natural Science Foundation of China [grant number: 31040038], Beijing Natural Science Foundation (5122040). Additionally, this work was also supported by the grant from the National Basic Research Program of China (973Program; 2012CB967900), the grants from the China Postdoctoral Science Foundation [grant number: 201003779;20100470103].