Synaptic mechanisms underlying auditory function and dysfunction

描述（由申请人提供）：由基因突变或自身免疫性疾病（例如多发性硬化症，MS）引起的中枢神经系统脱髓鞘导致听力障碍，如突发性听力损失、无法定位声音和/或耳鸣。这种缺陷通常归因于伴随轴突脱髓鞘的传导速度和时间保真度的降低。然而，在听觉神经系统中，脱髓鞘对突触功能参数，包括突触前兴奋性、神经递质释放和突触可塑性的直接影响在很大程度上是未知的。与脱髓鞘相关的突触功能缺陷在多大程度上导致听力障碍？本研究的目的是探讨髓鞘鞘化对听觉通路中Held突触萼功能和结构成熟的作用。我们已发表的和初步的研究表明，在听觉脑干中，浓缩髓鞘形成的损失增加了突触传递的时间错误和失败。在髓鞘缺陷大鼠体内听觉脑干反应测试中，单个突触水平的变化与听觉通路沿着延迟和退化的信号传递相关。基于初步的数据，我们假设，轴突髓鞘形成所需的半节点和突触前终端的离子通道的正确位置，在短期的可塑性和开发一个紧密的突触结构的发射机释放的精度。为了验证这一假设，我们将使用Long-Evans Shaker大鼠，其完全缺乏中央髓鞘形成，排除与炎症因子相关的混杂效应。我们将进行膜片钳记录突触前末梢，突触后神经元和星形胶质细胞，沿着Na+和Ca 2+成像。在目的1中，我们将测试的假设，缺乏髓鞘破坏的Na+和K+通道的表达模式，并导致突触前末梢的脉冲定时错误和故障。在目标2中，我们将测试缺乏髓鞘形成通过增加突触前Ca 2+积累和引起突触信号的延迟来降低突触功效的假设。在目标3中，我们将测试缺乏髓鞘时空破坏突触-星形胶质细胞通讯，并导致过度谷氨酸介导的轴突和突触变性的假设。这些研究将对我们理解中枢脱髓鞘后受损的听觉处理产生重大影响，并有助于改善MS和听神经病中听力障碍的治疗。此外，在突触水平上对中枢脱髓鞘后果的进一步理解将对整个神经退行性疾病领域具有广泛的意义。

DESCRIPTION (provided by applicant): Demyelination in the central nervous system, resulting from genetic mutations or autoimmune disease (e.g. multiple sclerosis, MS), causes hearing impairments such as sudden hearing loss, inability to localize sound and/or tinnitus. Such deficits are generally attributed to the decrements in conduction velocity and temporal fidelity that accompany axon demyelination. However, the direct impact of demyelination on synapse functional parameters, including presynaptic excitability, neurotransmitter release and synaptic plasticity, is largely unknown in the auditory nervous system. To what extent do deficits in synapse function associated with demyelination contribute to hearing impairments? The objective of this proposal is to investigate the role of myelin ensheathment on the functional and structural maturation of the calyx of Held synapse in the auditory pathway. Our published and preliminary studies show that the loss of condensed myelination increases timing errors and failures in synaptic transmission at the calyx synapses in the auditory brainstem. Changes at the level of individual synapses are associated with delayed and degraded signal transmission along the auditory pathway in an in vivo auditory brainstem response test in myelin-deficient rats. Based on the preliminary data, we hypothesize that axon myelination is required for the proper location of ion channels at hemi-nodes and presynaptic terminals, for precision of transmitter release involved in short-term plasticity and for development of a tight synaptic structure. To test this hypothesis, we will use the Long-Evans Shaker rat, which completely lacks central myelination, excluding confounding effects associated with inflammatory factors. We will perform patch-clamp recordings of presynaptic terminals, post-synaptic neurons and astrocytes, along with Na+ and Ca2+ imaging. In Aim 1, we will test the hypothesis that lack of myelination disrupts the expression pattern of Na+ and K+ channels and leads to impulse timing errors and failures at presynaptic terminals. In Aim 2, we will test the hypothesis that lack of myelination decreases synaptic efficacy by increasing presynaptic Ca2+ accumulation and causing asynchrony of synaptic signals. In Aim 3, we will test the hypothesis that lack of myelin spatiotemporally disrupts synapse-astrocyte communication and leads to excessive glutamate-mediated axonal and synaptic degeneration. These studies will have a significant impact on our understanding of damaged auditory processing following central demyelination, and contribute to improve treatment of hearing disorders in MS and auditory neuropathy. Furthermore, an improved understanding the consequences of central demyelination at the synaptic level will have broad relevance for the entire field of neurodegenerative diseases.