AFFERENT SYNAPTIC TRANSMISSION IN THE MAMMALIAN COCHLEA

项目摘要 这项研究的首要目标是基本发现耳蜗信号传导机制。这 这些知识将有助于确定未来治疗干预的新细胞和分子靶点。 内毛细胞（inner hair cells，IHC）与Ⅰ型听神经纤维（type I auditory nerve fibers，ANFs）之间的突触是听神经系统发育的第一站。 编码声音信号的听觉通路。听觉神经对声音的编码依赖于 ANF的性质，由其不同的自发放电率（SR），声学阈值和 动态范围在这里，我们调查，如何ANF自发和诱发放电的形状的属性， 单个IHC传入突触（Aim 1）。哺乳动物的听觉系统有许多系统， 并行操作，以调整听觉神经纤维（ANF）的动态范围，并防止由于 声音曝光传出外侧橄榄耳蜗（olivoccolear，OPN）神经元可能在IHC传入突触中发挥这一作用。 脑干神经元起源于脑干，它们在耳蜗中的突触位于关键位置， 一个不同的神经递质队列到无髓鞘ANF树突，提供直接 调节ANF中毛细胞诱导的突触后活性。因此，纤维是理想的候选人， 调节ANF的动态范围，并保护IHC传入突触免受声音损伤 exposure.在这里，我们确定，如何横向传出输入调节ANF放电的细胞水平（目的2）， 专注于多巴胺能和胆碱能传递。最后，我们调查，神经元如何响应 声音暴露和调整他们的调制ANF发射（目标3）。 我们将使用电生理学方法，并测量突触后活动，自发和诱发放电， 4-6周龄小鼠离体耳蜗组织中的ANF。我们将使用特定的小鼠模型和光遗传学， 刺激离体耳蜗组织中的IHC、ANF或ERF纤维。其次，我们将使用声音曝光 实验和免疫标记技术，以系统地研究外周和 中枢神经元对一系列声音暴露条件的反应。我们将特别 设计合理的暴露条件，诱导可测量的纤维变化，使我们能够研究 用电生理学的方法探讨这种变化的潜在机制。

Project Summary The overarching goal of this research is basic discovery of fundamental cochlear signaling mechanisms. This knowledge will help to identify new cellular and molecular targets for future therapeutic intervention. The synapse between inner hair cells (IHCs) and type I auditory nerve fibers (ANFs) is the first station in the auditory pathway to code the sound signal. Coding of sound in the auditory nerve depends on the diverse properties of ANFs, described by their different spontaneous firing rates (SRs), acoustic thresholds and dynamic ranges. Here we investigate, how ANF spontaneous and evoked firing is shaped by properties of individual IHC afferent synapses (Aim 1). The mammalian auditory system has a number of systems that operate in parallel to adjust the dynamic ranges of auditory nerve fibers (ANFs) and to prevent damage due to sound exposure. Efferent lateral olivocochlear (LOC) neurons may serve this role at the IHC afferent synapse. LOC neurons originate in the brainstem, and their synapses in the cochlea are strategically located to release a diverse cohort of neurotransmitters onto the unmyelinated ANF dendrites, providing the ability to directly modulate the hair cell induced postsynaptic activity in ANFs. Therefore, LOC fibers are ideal candidates for adjusting the ANF's dynamic range, and for protecting the IHC afferent synapse from damage due to sound exposure. Here we determine, how lateral efferent inputs modulate ANF firing on the cellular level (Aim 2), focusing on dopaminergic and cholinergic transmission. Finally, we investigate, how LOC neurons respond to sound exposure and adjust their modulation of ANF firing (Aim 3). We will use electrophysiological methods, and measure postsynaptic activity, spontaneous and evoked firing of ANFs in excised cochlear tissue of 4-6 week old mice. We will use specific mouse models and optogenetics to stimulate IHCs, ANFs or LOC fibers in excised cochlear tissue. Secondly, we will use sound exposure experiments and immunolabeling techniques to systematically investigate changes in the peripheral and central components of LOC neurons in response to a range of sound exposure conditions. We will specifically design sound exposure conditions that induce measurable changes in LOC fibers and allow us to investigate the underlying mechanisms of such changes with electrophysiological methods.