Fan Liqiang, Zhang Zhen, Wang Hui, Li Chunyan, Xing Yazhi, Yin Shankai, Chen Zhengnong, Wang Jian
Department of Otolaryngology-Head and Neck Surgery, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, Shanghai, China.
Otolaryngology Institute of Shanghai Jiao Tong University, Shanghai, China.
Front Syst Neurosci. 2020 May 12;14:25. doi: 10.3389/fnsys.2020.00025. eCollection 2020.
The auditory sensory organs appear to be less damaged by exposure to high-level noise that is presented after exposure to non-traumatizing low-level noise. This phenomenon is known as the toughening or conditioning effect. Functionally, it is manifested by a reduced threshold shift, and morphologically by a reduced hair cell loss. However, it remains unclear whether prior exposure to toughening noise can mitigate the synaptic loss induced by exposure to damaging noise. Since the cochlear afferent synapse between the inner hair cells and primary auditory neurons has been identified as a novel site involved in noise-induced cochlear damage, we were interested in assessing whether this synapse can be toughened. In the present study, the synaptic loss was induced by a damaging noise exposure (106 dB SPL) and compared across Guinea pigs who had and had not been previously exposed to a toughening noise (85 dB SPL). Results revealed that the toughening noise heavily reduced the synaptic loss observed 1 day after exposure to the damaging noise. Although it was significant, the protective effect of the toughening noise on permanent synaptic loss was much smaller. Compared with cases in the control group without noise exposure, coding deficits were seen in both toughened groups, as reflected in the compound action potential (CAP) by signals with amplitude modulation. In general, the pre-exposure to the toughening noise resulted in a significantly reduced synaptic loss by the high-level noise. However, this morphological protection was not accompanied by a robust functional benefit.
与暴露于非致伤性低水平噪声后再暴露于高水平噪声相比，听觉感觉器官似乎受其损伤更小。这种现象被称为强化或适应效应。在功能上，它表现为阈值偏移减小，在形态学上表现为毛细胞损失减少。然而，预先暴露于强化噪声是否能减轻由暴露于损伤性噪声引起的突触损失仍不清楚。由于内毛细胞与初级听觉神经元之间的耳蜗传入突触已被确定为噪声性耳蜗损伤的一个新的相关部位，我们感兴趣的是评估这种突触是否可以被强化。在本研究中，通过暴露于损伤性噪声（106 dB SPL）诱导突触损失，并在先前暴露于强化噪声（85 dB SPL）和未暴露于强化噪声的豚鼠之间进行比较。结果显示，强化噪声大大减少了暴露于损伤性噪声1天后观察到的突触损失。虽然这种保护作用显著，但强化噪声对永久性突触损失的保护作用要小得多。与未暴露于噪声的对照组相比，两个强化组均出现编码缺陷，这在复合动作电位（CAP）中表现为具有幅度调制的信号。总体而言，预先暴露于强化噪声可显著减少高水平噪声导致的突触损失。然而，这种形态学上的保护并没有伴随着强大的功能益处。
