Molecular and Functional Mechanisms of the aging auditory neuron

摘要 在发育过程中，耳蜗毛细胞(HCs)和神经元必须正确、定性和 从数量上讲。这些包括连接到脑干耳蜗核(CN)的特定听觉传入神经元(AN)。 HCS的活动维持ANS的数量、大小和功能。先前的研究表明，衰老可能会 导致特定AN亚型的优先损失。 我们假设ARHL源于超快传入反应的丧失，并伴随着 中枢听觉回路和功能--导致锁相反应功能缺陷的改变 在老年人身上。 我们建议使用三种敲击小鼠模型来研究不同年龄的AN的相关变化：Calretinin (Calb2)-EGFP、Calbindin(Calb1)-mCherry、Pou4f1和(Brn3a)-CFP，以及光遗传学和药物遗传学 老鼠模型。这项工作将侧重于以下方面的纵向变化： 1)Hcs向脑干核团(CN)的结构(解剖)投射； 2)传入神经元亚型分布和功能 3)确定传入神经中离子电导的年龄相关性 目标1将追踪传入神经元亚型特定的投射从耳蜗到中央核，并确定年龄- 依赖改变以识别潜在的解剖可塑性。我们将测量与年龄相关的听觉功能， 听性脑干反应(ABR)和失真产物耳声发射(DPOAE)。我们将评估 并在与年龄相关的听觉表型变化的同时进行这些研究。对于目标2，我们将 确定局部和传入神经元亚型在反应特性和年龄相关性中的差异 改变。我们将评估脉冲间期、同步参数，包括向量的规律性 强度(Vs)、绕组比(K)和对电流注入的灵敏度，使用实验和生理学方法 刺激。最后，对于目标3，我们将确定以下三组离子电导的年龄相关性 传入神经元。我们将使用膜片钳分析动力学、电压依赖性、药理学和 年轻神经元和老年神经元的电导以确定反应差异的潜在机制 三种神经元亚型的特性，使用计算分析。 因此，我们将解决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，这对于开发ARHL的治疗方法是必要的。

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.