Synaptic specialization of auditory hair cells

描述（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交流。这个单一的突触携带有关频率、强度和时间的信息，这些信息被中枢神经系统用来提取由听觉模态提供的所有信息。突触是专门在一个广泛的频率范围内运作，以线性方式对分级刺激作出反应。突触保持高释放率，不疲劳，对通常低于1mv的受体电位敏感。这项提议的目的是描述这些不寻常的突触特性背后的机制。突触前和突触后机制将被研究。具体目标1解决突触前问题，有三个子目标；鉴定囊泡释放和运输的Ca2+依赖成分，确定释放动力学，同时确定运输和释放的限速步骤，并阐明释放特性的tonotopic差异，表征Ca2+调节释放的稳态机制，并鉴定磷酸化依赖的释放和运输调节。特异性目的2研究突触后加工的三个目标；首先，确定传入电特性是否存在张力异位变化，这可能有助于提高频率选择性，如电压依赖性过程的动力学和幅度；其次，表征不同位置的突触传递，以确定受体类型和数量的差异；第三，研究与多泡释放相关的机制。包括结构、免疫细胞化学、光学、电生理和理论工具在内的一些新技术，使我们能够更好地研究这些问题。鉴于毛细胞传入纤维突触突触传递的任何缺陷都会导致听觉障碍，确定新的机制可能为干预提供独特的途径。所有发生在听觉周围的信号处理都是通过毛细胞传入纤维突触传递给中枢神经系统的。任何导致该突触失去保真度的行为都会导致听力丧失和耳聋。对这个突触的要求是相当高的，并导致了几个独特的专业化，包括：对刺激的分级和线性反应，面对持续且经常高的释放率和突触后放电率时惊人的缺乏疲劳，以及在几个数量级的频率上锁相的能力。这些特殊特性的机制尚不清楚，但应该为干预和预防噪音诱发甚至耳毒性诱发的听力损失提供了场所。这项工作的主要目标是确定和描述这些机制。

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.