In mammals, hair cells and spiral ganglion neurons (SGNs) in the cochlea together are sophisticated "sensorineural" structures that transduce auditory information from the outside world into the brain. Hair cells and SGNs are joined by glutamatergic ribbon-type synapses composed of a molecular machinery rivaling in complexity the mechanoelectric transduction components found at the apical side of the hair cell. The cochlear hair cell ribbon synapse has received much attention lately because of recent and important findings related to its damage (sometimes termed "synaptopathy") as a result of noise overexposure. During development, ribbon synapses between type I SGNs and inner hair cells form in the time window between birth and hearing onset and is a process coordinated with type I SGN myelination, spontaneous activity, synaptic pruning, and innervation by efferents. In this review, we highlight new findings regarding the diversity of type I SGNs and inner hair cell synapses, and the molecular mechanisms of selective hair cell targeting. Also discussed are cell adhesion molecules and protein constituents of the ribbon synapse, and how these factors participate in ribbon synapse formation. We also note interesting new insights into the morphological development of type II SGNs, and the potential for cochlear macrophages as important players in protecting SGNs. We also address recent studies demonstrating that the structural and physiological profiles of the type I SGNs do not reach full maturity until weeks after hearing onset, suggesting a protracted development that is likely modulated by activity.

中文翻译：

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耳蜗带状突触形成的当前概念。


在哺乳动物中，耳蜗中的毛细胞和螺旋神经节神经元 (SGN) 共同构成复杂的“感觉神经”结构，将外界的听觉信息传递到大脑。毛细胞和 SGN 通过谷氨酸带状突触连接，该突触由分子机械组成，其复杂性可与毛细胞顶端发现的机电转导组件相媲美。耳蜗毛细胞带状突触最近受到了广泛关注，因为最近发现了与噪音过度暴露导致的损伤（有时称为“突触病”）相关的重要发现。在发育过程中，I 型 SGN 和内毛细胞之间的带状突触在出生和听力出现之间的时间窗口内形成，并且是与 I 型 SGN 髓鞘形成、自发活动、突触修剪和传出神经支配协调的过程。在这篇综述中，我们重点介绍了有关 I 型 SGN 和内毛细胞突触多样性以及选择性毛细胞靶向的分子机制的新发现。还讨论了带状突触的细胞粘附分子和蛋白质成分，以及这些因素如何参与带状突触的形成。我们还注意到对 II 型 SGN 形态发育的有趣新见解，以及耳蜗巨噬细胞作为保护 SGN 的重要参与者的潜力。我们还讨论了最近的研究表明，I 型 SGN 的结构和生理特征直到听力出现后几周才完全成熟，这表明可能受到活动调节的长期发展。