AFFERENT SYNAPTIC TRANSMISSION IN THE MAMMALIAN COCHLEA

项目摘要 本研究的首要目标是基本发现基本的耳蜗信令机制。这 知识将有助于为未来的治疗干预确定新的细胞和分子靶点。 内毛细胞(IHC)和I型听神经纤维(ANF)之间的突触是 对声音信号进行编码的听觉通路。听觉神经中声音的编码依赖于不同的 ANF的性质，用它们不同的自发放电率(SRS)、声阈值和 动态范围。在这里，我们研究ANF自发和诱发放电是如何由 单个IHC传入突触(目标1)。哺乳动物的听觉系统有许多系统， 并行操作以调整听神经纤维(ANF)的动态范围，并防止因 声音暴露。传出外侧橄榄耳蜗(LOC)神经元可能在IHC传入突触中起这种作用。 LoC神经元起源于脑干，它们在耳蜗处的突触被战略性地定位为释放 一组不同的神经递质进入无髓鞘ANF树突，提供了直接 调节毛细胞诱导的ANF突触后活动。因此，LOC纤维是理想的候选材料 调节ANF的动态范围，保护IHC传入突触免受声音的损害 曝光。在这里，我们确定了侧向传出输入如何在细胞水平上调制ANF的激发(目标2)， 专注于多巴胺能和胆碱能传递。最后，我们研究LOC神经元如何对 声音暴露并调整其对ANF发射的调制(目标3)。 我们将使用电生理方法，并测量突触后活动，自发和诱发的放电 4-6周龄小鼠耳蜗组织中ANF的含量。我们将使用特定的小鼠模型和光遗传学来 刺激切除的耳蜗组织中的IHC、ANF或LOC纤维。其次，我们将使用声音暴露 实验和免疫标记技术系统地研究外周和外周血的变化 LOC神经元的中枢成分对一系列声音暴露条件的反应。我们将具体地 设计声音暴露条件，使LOC纤维发生可测量的变化，并允许我们研究 用电生理学方法研究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.