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通信。这个单一的突触携带有关频率、强度和时间的信息，CNS使用这些信息来提取听觉通道提供的所有信息。突触专门用于在一个宽的频率范围内工作，以线性方式对分级刺激做出反应。突触保持较高的释放率，不会疲劳，对通常低于1 mV的受体电位很敏感。这项提议的目标是描述这些不寻常的突触特性背后的机制。我们将研究突触前和突触后的机制。具体目标1涉及突触前问题，有三个子目标：确定囊泡释放和运输的钙依赖成分，确定释放的动力学同时确定运输和释放的限速步骤，以及阐明释放特性的调控性差异，表征调节释放的钙稳态机制，确定释放和运输的磷酸化依赖调节。具体目的2研究突触后的处理有三个目标：第一，确定传入电特性是否存在可能有助于提高频率选择性的变异性，如电压依赖性过程的动力学和幅度；第二，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，研究与多室释放相关的机制。结构、免疫细胞化学、光学、电生理学和理论工具包括几项新技术，以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的任何突触传递缺陷都会导致听觉障碍，识别新的机制可能为干预提供独特的途径。与公共健康相关所有发生在听觉外周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。任何导致该突触失去保真度的行为都会导致听力损失和耳聋。这种突触的要求相当苛刻，并导致了几个独特的特化，包括：对刺激的分级和线性反应，面对持续且往往很高的释放率和突触后放电率时令人惊讶的不疲倦，以及跨几个数量级频率的锁相能力。这些特殊特性背后的机制尚不清楚，但应该为干预和预防噪音引起的甚至耳毒性引起的听力损失提供场所。这项工作的主要目标是识别和描述这些机制。

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.