Ion channels and presynaptic function of an auditory synapse

描述（由申请人提供）：听觉脑干的电路需要突触传输的可靠性和精确性，以便以亚毫秒的精度对计时进行编码。突触传递通过神经末梢上不同离子通道的互补来细化，这决定了尖峰阈值和形状，以及支持高频放电的能力。这项研究的长期目标是了解有助于这些功能的突触机制。最近，一项免疫组织化学研究表明，一个不寻常的K+通道亚型，KCNQ 5，存在于所有的兴奋性终端的听觉脑干。KCNQ（Kv 7）通道与人类神经元和心脏疾病密切相关。在中枢神经系统中，虽然体细胞KCNQ通道的功能已经在各种类型的细胞中得到了广泛的研究，但很少有人关注突触，部分原因是神经末梢的小尺寸通常排除了它们的直接测量。赫尔德的萼，其大尺寸允许全细胞膜片钳记录，是一个特殊的准备，使我们能够直接分析突触前KCNQ通道。我们发现，KCNQ 5通道是主要的K+通道，负责设置的休息性质的花萼。通道的调制控制静息特性、阈下电活动和发射器释放概率。通道的阻断对突触前兴奋性也有深远的影响。在这个应用程序中，我们的目标是确定KCNQ通道如何控制听觉突触的突触前兴奋性。首先，我们将使用免疫组织化学，电生理学和2-光子成像的组合来测试的假设，抑制KCNQ 5导致花萼的Held改变尖峰发射作为轴突和轴突末端离子通道（Kv 1和NaV）的失活的结果。结果将被纳入一个完整的模型的传播和兴奋的突触前占的作用KCNQ。模型数据将通过预测部分阻断关键突触前通道的实验结果来证实。由于KCNQ 5是在较低的听觉系统中的所有兴奋性终端的组成部分，我们也将研究KCNQ在终端的作用，在耳蜗核的功能显着不同的花萼。初步数据表明，KCNQ通道的阻滞抑制颗粒细胞平行纤维的胞吐作用进入侧手翻细胞，这表明它们可能需要维持完整的突触前尖峰波形。我们将研究KCNQ在控制耳蜗核末梢递质释放中的作用。对这一建议的研究将扩展我们对突触前KCNQ功能的理解，这可能对以持续活动为特征的神经系统疾病（如耳鸣或癫痫）有影响。因此，这一应用不仅对基础科学很重要，因为它丰富了我们对突触前离子通道和KCNQ通道在神经系统中的生理作用的认识，而且对公共卫生也很重要，因为它提供了对KCNQ相关疾病的可能见解。

DESCRIPTION (provided by applicant): The reliability and precision of synaptic transmission are required by circuits of the auditory brainstem in order to encode timing with sub-millisecond accuracy. Synaptic transmission is refined by the complement of different ion channels at nerve terminals, which determines spike threshold and shape, and the ability to support high-frequency firing. The long-term goal of this research is to understand the synaptic mechanisms that contribute to these functions. Recently, an immunohistochemical study showed that an unusual K+ channel subtype, KCNQ5, is present at all excitatory terminals of the auditory brainstem. KCNQ (Kv7) channels are tightly associated with human neuronal and heart diseases. In the CNS, although the function of somatic KCNQ channels has been extensively examined in a variety of cell types, little attention has been paid to the synapse, in part because the small size of nerve terminals usually precludes their direct measurement. The calyx of Held, whose large size permits whole-cell patch-clamp recording, is an exceptional preparation that allows us direct analysis of presynaptic KCNQ channels. We found that the KCNQ5 channel is the major K+ channel responsible for setting the resting properties of the calyx. Modulation of the channel controls resting properties, subthreshold electrical activity, and transmitter release probability. Block of the channel also has profound effects on presynaptic excitability. In this application, we aim to determine how KCNQ channel controls the presynaptic excitability of auditory synapses. First, we will use a combination of immunohistochemistry, electrophysiology and 2-photon imaging to test the hypothesis that inhibition of KCNQ5 leads calyx of Held to altered spike firing as a result of inactivation of axonal and axon terminal ion channels (Kv1 and NaV). Results will be then incorporated into a complete model of propagation and excitation of presynaptic to account for the role of KCNQ. The modeling data will be confirmed by predicting the experimental results from partially blocking of key presynaptic channels. Since KCNQ5 is a component of all excitatory terminals in the lower auditory system, we will also examine the role of KCNQ at terminals in the cochlear nucleus whose function differs dramatically from the calyx. Preliminary data indicate that block of KCNQ channels suppresses exocytosis of granule cell parallel fiber into cartwheel cells, suggesting they may be required to maintain a full presynaptic spike waveform. We will examine the role of KCNQ in controlling transmitter release at terminals in the cochlear nucleus. The study of this proposal will extend our understanding of presynaptic KCNQ function, which may have implications for neurological disorders that are characterized by persistent activity, such as tinnitus or epilepsy. Thus, this application is important not only for basic science by enriching our knowledge of presynaptic ion channels and then physiological role KCNQ channel in the nervous system, but also for public health by providing possible insight into KCNQ-related diseases.