Molecular and Functional Mechanisms of the aging auditory neuron

摘要 在发育过程中，耳蜗毛细胞（HC）和神经元必须正确，定性， 数量上。这些包括连接到脑干耳蜗核（CN）的特定听觉传入神经元（AN）。 HC的活动维持AN的数量、大小和功能。以前的研究表明，衰老可能 导致特定AN亚型的优先丢失。 我们假设ARHL是由于超快传入反应的丧失，伴随着神经元的重塑。 中枢听觉回路和功能-导致锁相反应功能缺陷的变化 在老年人中。 我们建议使用三种敲入小鼠模型来检查不同AN中与年龄相关的变化：钙视网膜蛋白 （Calb2）-eGFP、钙结合蛋白（Calb1）-mCherry、Pou4f1和（brn3a）-CFP，以及光遗传学和药物遗传学 小鼠模型。这项工作将侧重于以下方面的纵向变化： 1)从HC到脑干核（CN）的结构（解剖学）投射， 2)传入神经元亚型分布和功能，以及 3)确定AN传入中离子电导的年龄依赖性 目的1将追踪从耳蜗到CN的传入神经元亚型特异性投射，并确定年龄- 依赖性变化来识别潜在的解剖可塑性。我们将测量年龄相关的听觉功能， 听性脑干反应（ABR）和畸变产物耳声发射（DPOAE）。我们将评估 并与年龄相关的听觉表型的变化并行进行这些研究。目标2： 确定区域和传入神经元亚型的反应特性和年龄依赖性的变化 变化我们将评估的规律性的峰间期，同步参数，包括向量 强度（VS），缠绕比（k）和电流注入的敏感性，使用实验和生理 刺激.最后，对于目标3，我们将确定三组中离子电导的年龄依赖性， 传入神经元我们将使用膜片钳分析的动力学，电压依赖性，药理学， 电导在年轻和老年神经元，以确定潜在的机制，反应的差异 使用计算分析的三种神经元亚型的特性。 因此，我们将讨论解剖投影和信号处理的复杂性以及随后的年龄- 依赖性变化，这是开发ARHL治疗所必需的。

Abstract During development, cochlear hair cells (HCs) and neurons must be wired correctly, qualitatively, and quantitatively. These include specific auditory afferent neurons (AN) wired to the brainstem cochlear nuclei (CN). The activity of HCs maintains the number, size, and functions of ANs. Previous studies suggest that aging may result in preferential loss of specific AN subtypes. We hypothesize that ARHL arises from a loss of ultrafast afferent responses, accompanied by remodeling of central auditory circuits and functions—changes that result in deficiencies in phase-locked response functions in older adults. We propose to examine age-related changes in distinct AN using three knockin mouse models: calretinin (Calb2)-eGFP, calbindin (Calb1)-mCherry, Pou4f1 and (brn3a)-CFP, and optogenetic and pharmacogenetic mouse models. The work will focus on longitudinal changes in: 1) structural (anatomic) projections from HCs to the brainstem nuclei (CN), 2) afferent neuron subtype distributions and functions, and 3) Identify the age dependence of ionic conductances in AN afferents Aim 1 will trace afferent neuron subtype-specific projections from the cochlea to the CN and determine the age- dependent changes to identify potential anatomic plasticity. We will measure age-dependent auditory function, auditory brainstem responses (ABR), and distortion product otoacoustic emissions (DPOAE). We will evaluate and perform these studies in parallel with changes in age-related auditory phenotype. For Aim 2, we will determine regional and afferent neuron subtype variations in the response properties and the age-dependent changes. We will evaluate the regularity of inter-spike intervals, synchronization parameters, including vector strength (VS), winding ratio (k), and sensitivity to current injection, using experimental and physiological stimulation. Finally, for Aim 3, we will identify the age dependence of ionic conductances in three groups of afferent neurons. We will use patch-clamp analyses of the kinetics, voltage-dependence, pharmacology, and conductance in young and aged neurons to determine the underlying mechanisms for the differences in response properties of three neuronal subtypes, using computational analyses. Thus, we will address the complexity of anatomic projections and signal processing and subsequent age- dependent changes, which are necessary for developing a treatment for ARHL.