Synaptic mechanisms underlying auditory function and dysfunction

描述(申请人提供)：中枢神经系统脱髓鞘，由基因突变或自身免疫性疾病(如多发性硬化症，MS)引起，可导致听力损伤，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而来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的直接影响，包括突触前兴奋性、神经递质释放和突触可塑性，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会导致听力障碍？本研究的目的是探讨髓鞘在听觉通路中突触被膜的功能和结构成熟中的作用。我们已发表的和初步的研究表明，浓缩的髓鞘形成的丢失增加了听性脑干中花冠突触的计时误差和突触传递的失败。在体内髓鞘缺陷大鼠的听觉脑干反应测试中，单个突触水平的变化与沿听觉通路的信号传递延迟和退化有关。根据初步数据，我们推测轴突髓鞘是半结节和突触前终末离子通道正确定位所必需的，是参与短期可塑性的递质释放的精确度所必需的，也是形成紧密突触结构所必需的。为了验证这一假设，我们将使用Long-Evans Shaker大鼠，它完全缺乏中枢髓鞘，不包括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终末、突触后神经元和星形胶质细胞，以及Na+和Ca~(2+)成像。在目标1中，我们将检验这一假说，即缺乏髓鞘会扰乱Na+和K+通道的表达模式，并导致突触前终末的脉冲计时错误和失败。在目标2中，我们将检验这一假说，即缺乏髓鞘作用会增加突触前钙的积累，导致突触信号的不同步，从而降低突触的有效性。在目标3中，我们将检验这一假说，即缺乏髓鞘会在时空上扰乱突触-星形胶质细胞的通讯，并导致谷氨酸介导的轴突和突触过度变性。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听力障碍和听神经病的治疗。此外，更好地理解中枢脱髓鞘在突触水平的后果将对整个神经退行性疾病领域具有广泛的相关性。

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.