Department of Neuroscience, School of Medicine and Health Science, Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany.
Cluster of Excellence "Hearing4all", Carl von Ossietzky Universität Oldenburg, 26129 Oldenburg, Germany.
Int J Mol Sci. 2024 Feb 27;25(5):2738. doi: 10.3390/ijms25052738.
In mammalian hearing, type-I afferent auditory nerve fibers comprise the basis of the afferent auditory pathway. They are connected to inner hair cells of the cochlea via specialized ribbon synapses. Auditory nerve fibers of different physiological types differ subtly in their synaptic location and morphology. Low-spontaneous-rate auditory nerve fibers typically connect on the modiolar side of the inner hair cell, while high-spontaneous-rate fibers are typically found on the pillar side. In aging and noise-damaged ears, this fine-tuned balance between auditory nerve fiber populations can be disrupted and the functional consequences are currently unclear. Here, using immunofluorescent labeling of presynaptic ribbons and postsynaptic glutamate receptor patches, we investigated changes in synaptic morphology at three different tonotopic locations along the cochlea of aging gerbils compared to those of young adults. Quiet-aged gerbils showed about 20% loss of afferent ribbon synapses. While the loss was random at apical, low-frequency cochlear locations, at the basal, high-frequency location it almost exclusively affected the modiolar-located synapses. The subtle differences in volumes of pre- and postsynaptic elements located on the inner hair cell's modiolar versus pillar side were unaffected by age. This is consistent with known physiology and suggests a predominant, age-related loss in the low-spontaneous-rate auditory nerve population in the cochlear base, but not the apex.
在哺乳动物的听力中，I 型传入听觉神经纤维构成传入听觉通路的基础。它们通过特化的带状突触与耳蜗内毛细胞相连。不同生理类型的听觉神经纤维在其突触位置和形态上略有不同。低自发性率听觉神经纤维通常连接在内毛细胞的蜗轴侧，而高自发性率纤维通常位于支柱侧。在衰老和噪声损伤的耳朵中，这种听觉神经纤维群体之间的精细平衡可能会被打破，其功能后果目前尚不清楚。在这里，我们使用免疫荧光标记突触前带和突触后谷氨酸受体斑，研究了与年轻成年人相比，在衰老沙鼠耳蜗的三个不同音位位置上突触形态的变化。安静的老年沙鼠显示出约 20%的传入带突触丢失。虽然在耳蜗顶部的低频位置，丢失是随机的，但在基底高频位置，它几乎只影响蜗轴侧的突触。位于内毛细胞蜗轴侧和支柱侧的突触前和突触后元素的体积差异不受年龄影响。这与已知的生理学一致，表明在耳蜗基部，与年龄相关的低自发性率听觉神经群体的丢失更为明显，而不是在耳蜗顶部。
