Synaptic specialization of auditory hair cells

描述（由申请人提供）：外周听觉系统通过感觉细胞和螺旋神经节神经元之间的突触与中枢神经系统通信。该单个突触携带关于频率、强度和定时的信息，CNS使用该信息来提取由听觉模态提供的所有信息。突触专门在宽频率范围内工作，以线性方式对分级刺激作出反应。突触保持高的释放速率，不疲劳，对受体电位敏感，通常低于1 mV。这个提议的目的是描述这些不寻常的突触特性的机制。将研究突触前和突触后机制。具体目标1解决突触前的问题，并有三个子目标：识别囊泡释放和运输的Ca 2+依赖组件，以确定释放的动力学，同时确定运输和释放的限速步骤，并阐明tonotopic释放特性的差异，表征调节释放的Ca 2+稳态机制，并确定磷酸化依赖的释放和运输的调节。具体目标2研究突触后处理有三个目标;第一，以确定是否有tonotopic的传入电特性的变化，可能有助于提高频率选择性，如动力学和电压依赖性过程的幅度，第二，表征在不同位置的突触传递，以确定受体类型和数量的差异，第三，调查与多泡释放相关的机制。包括结构，免疫细胞化学，光学，电生理和理论工具，包括几个新技术，以更好地使我们能够调查这些问题。鉴于毛细胞传入纤维突触的突触传递的任何缺陷都会导致听觉缺陷，识别新的机制可能会提供独特的干预途径。所有发生在听觉周边的信号处理都通过毛细胞传入纤维突触传递到中枢神经系统。任何导致这种突触失去保真度的行为都会导致听力损失和耳聋。这种突触的要求非常苛刻，并导致了几种独特的专业化，包括：对刺激的分级和线性反应，面对持续且通常高的释放率和突触后放电率时惊人的疲劳感，以及在几个数量级的频率上锁相的能力。这些特殊性质的机制尚不清楚，但应提供干预和预防噪声引起的听力损失，甚至耳毒性引起的听力损失。这项工作的主要目标是确定和表征这些机制。

DESCRIPTION (provided by applicant): The peripheral auditory system communicates with the central nervous system through synapses between the sensory cells and the spiral ganglion neurons. This single synapse carries information regarding frequency, intensity and timing that is used by the CNS for to extract all information provided by the auditory modality. The synapse is specialized to operate across a broad frequency range, to respond to graded stimuli in a linear manner. The synapse maintains high rates of release and does not fatigue and is sensitive to receptor potentials often below 1 mV. The goal of this proposal is to delineate the mechanisms underlying these unusual synaptic properties. Both pre and postsynaptic mechanisms will be investigated. Specific Aim 1 addresses presynaptic issues and has three subaims; to identify the Ca2+ dependent components of vesicle release and trafficking, to determine the kinetics of release while identifying the rate limiting steps of trafficking and release, and to elucidate tonotopic differences in release properties, characterizing Ca2+ homeostatic mechanisms that regulate release and identifying phosphorylation dependent regulation of release and trafficking. Specific Aim 2 investigates postsynaptic processing with three goals; first to determine if there are tonotopic variations in afferent electrical properties that might serve to enhance frequency selectivity such as the kinetics and magnitude of voltage-dependent processes, second to characterize synaptic transmission at different locations to identify differences in receptor types and numbers and third to investigate mechanisms associated with multivesicular release. Structural, immunocytochemical, optical, electrophysiological and theoretical tools including several new technologies are included to better enable us to investigate these issues. Given that any deficits in synaptic transmission at the hair cell afferent fiber synapse results in auditory deficits, identifying novel mechanisms may provide unique avenues for intervention. PUBLIC HEALTH RELEVANCE All of the signal processing that happens at the auditory periphery is communicated to the central nervous system through the hair cell afferent fiber synapse. Any action that results in a loss of fidelity of this synapse leads to hearing loss and deafness. The requirements of this synapse are quite demanding and result in several unique specializations including: a graded and linear response to stimulus, an amazing lack of fatigue in the face of continual and often high release rates and postsynaptic firing rates, and the ability to phase-lock across several orders of magnitude of frequencies. Mechanisms underlying these specialized properties are unknown but should offer sites for intervention and prevention of noise induced and even ototoxic induced hearing loss. The primary goal of this work is to identify and characterize these mechanisms.