Ion channels and presynaptic function of an auditory synapse

描述（由申请人提供）：听觉脑干回路需要突触传递的可靠性和精确性，以便以亚毫秒精度编码时间。突触传递是由神经末梢不同离子通道的互补完善的，它决定了脉冲阈值和形状，以及支持高频放电的能力。这项研究的长期目标是了解促成这些功能的突触机制。最近，一项免疫组织化学研究表明，一种不寻常的K+通道亚型KCNQ5存在于听觉脑干的所有兴奋性末梢。KCNQ （Kv7）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，尽管体细胞KCNQ通道的功能已经在各种细胞类型中得到了广泛的研究，但对突触的关注却很少，部分原因是神经末梢的小尺寸通常阻碍了它们的直接测量。Held的花萼，其大尺寸允许全细胞膜片钳记录，是一种特殊的制备，允许我们直接分析突触前KCNQ通道。我们发现KCNQ5通道是主要的K+通道，负责设置花萼的静息特性。通道的调制控制静息特性、阈下电活动和发射机释放概率。通道的阻断对突触前兴奋性也有深远的影响。在这个应用中，我们的目的是确定KCNQ通道如何控制听觉突触的突触前兴奋性。首先，我们将结合免疫组织化学、电生理学和双光子成像来验证KCNQ5的抑制导致Held花萼因轴突和轴突末端离子通道（Kv1和NaV）失活而改变spike放电的假设。然后将结果纳入突触前的传播和激发的完整模型，以解释KCNQ的作用。通过对关键突触前通道部分阻断的实验结果进行预测，对模型数据进行验证。由于KCNQ5是下听系统所有兴奋性终末的组成部分，我们还将研究KCNQ在耳蜗核终末的作用，其功能与耳蜗花萼有很大的不同。初步数据表明，KCNQ通道阻断抑制颗粒细胞平行纤维向侧翻细胞的胞吐，提示它们可能需要维持完整的突触前尖峰波形。我们将研究KCNQ在控制耳蜗核末端递质释放中的作用。这项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有重要意义，可以丰富我们对突触前离子通道的认识，进而了解KCNQ通道在神经系统中的生理作用，而且对公共卫生也有重要意义，可以为了解KCNQ相关疾病提供可能。

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.