Spontaneous activity in the developing auditory system

项目摘要 发育中的听觉系统中的神经元在发病前经历高度刻板的突发性活动 感官体验。当无感觉的内部支持细胞时，这种活动在耳蜗内启动 释放三磷酸腺苷，触发一系列事件，最终在螺旋神经节诱导一连串的动作电位 传播到整个听觉系统的神经元(SGN)。三磷酸腺苷触发物的空间受限释放 在以后将对相似频率的声音进行编码的SGN组中相互关联的发射，提供了一种方法 在听力前诱导大脑中声音处理回路的依赖活动的成熟和精炼 开始了。尽管在这一关键的发展时期，模式化活动非常突出，但它在 听觉系统的成熟仍然知之甚少，部分原因是不能选择性地干扰 在保留耳蜗声传导的同时进行自发活动。在这里，我们建议新的杠杆化 开发的小鼠模型允许选择性地干扰耳蜗内的自发活动 细胞仍然保留了耳蜗结构和听神经的完整性。我们将显式测试 一种假说认为，听觉神经元的爆发式放电是启动脑组织结构和功能成熟的关键。 新生的声音处理电路。这些研究将利用两个基因P2ry1和TMEM16A的遗传中断 耳蜗支持细胞产生自发活动所需的成分，在体内具有广阔的视野和 神经元活动的双光子成像、RNA表达谱和听觉功能的行为分析 来严格检验这一假说。我们将扩展我们最近的发现，下丘中的星形胶质细胞 在自发事件中，听前小鼠的(IC)与周围神经元共同激活，提供了一种 协调三部分突触的空间和时间成熟的手段(兴奋性突触被 星形胶质细胞)。目标1将重点放在耳蜗上，确定P2RY1和TMEM16A的缺失如何影响 SGN的性质和发展轨迹。目标2将定义耳蜗和 听皮层(AC)的耳蜗外自发活动，决定了耳蜗源性的干扰 自发活动改变IC和AC内神经元激活的空间模式并最终影响 听觉辨别。目标3将定义诱导钙升高所需的神经元活动模式 并确定选择性基因干扰星形胶质细胞mGluR5的表达，这是 检测神经元爆发式放电所必需的，影响星形胶质细胞的成熟和进行性细化 声音在活体中的声调表现。这些研究将使我们更深入地了解 用于定义处理声音信息的电路并建立框架以探索 早期生命中的基因突变、创伤和接触耳毒性药物会改变脑细胞的加工能力 中枢听觉回路。从这些研究中获得的信息最终可能有助于制定新的战略 弥补耳蜗机能输出的发育障碍，提高耳蜗机能 植入物。

Project Summary Neurons in the developing auditory system experience highly stereotyped bursts of activity prior to the onset of sensory experience. This activity is initiated within the cochlea when non-sensory inner supporting cells release ATP, triggering a cascade of events that ultimately induces trains of action potentials in spiral ganglion neurons (SGNs) that propagate throughout the auditory system. The spatially restricted release of ATP triggers correlated firing in groups of SGNs that will later encode similar frequencies of sound, providing a means to induce activity-dependent maturation and refinement of sound processing circuits in the brain prior to hearing onset. Despite the prominence of patterned activity during this critical developmental period, its role in maturation of the auditory system remains poorly understood, in part, due to an inability to selectively disrupt spontaneous activity while preserving sound transduction in the cochlea. Here, we propose to leverage newly developed mouse models that allow selective disruption of spontaneous activity within cochlear supporting cells yet preserve cochlear structure and the integrity of the auditory nerve. We will explicitly test the hypothesis that burst firing of auditory neurons is critical to initiate structural and functional maturation of nascent sound processing circuits. These studies will leverage genetic disruption of P2ry1 and Tmem16a, two components required to generate spontaneous activity in cochlear supporting cells, with in vivo widefield and two photon imaging of neuronal activity, RNA expression profiling and behavioral analyses of auditory function to rigorously test this hypothesis. We will extend our recent discovery that astrocytes in the inferior colliculus (IC) of pre-hearing mice are co-activated with surrounding neurons during spontaneous events, providing a means to coordinate spatial and temporal maturation of tripartite synapses (excitatory synapses ensheathed by astrocytes). Aim 1 will focus on the cochlea, determining how loss of P2RY1 and TMEM16A influence the properties and developmental trajectory of SGNs. Aim 2 will define the relationship between cochlear and extra-cochlear spontaneous activity in auditory cortex (AC), determine how disruption of cochlea-derived spontaneous activity alters spatial patterns of neuronal activation in the IC and AC and ultimately influence auditory discrimination. Aim 3 will define the patterns of neuronal activity required to induce calcium elevation in astrocytes and determine how selective genetic disruption of astrocyte mGluR5 expression, which is necessary to detect neuronal burst firing, influences astrocyte maturation and progressive refinement of tonotopic representation of sounds in vivo. These studies will provide greater insight into the fundamental mechanisms used to define circuits that process sound information and establish a framework to explore how genetic mutations, trauma and exposure to ototoxic drugs during early life alter the processing capabilities of central auditory circuits. Information gained from these studies may ultimately help establish new strategies to compensate for developmental disruptions in cochlear output and improve the performance of cochlear implants.