Auditory coding at the hair cell ribbon synapse

毛细胞带状突触的听觉编码

• 批准号: 7713083
• 负责人: Geng-Lin Li
• 金额: $ 8.97万
• 依托单位: OREGON HEALTH & SCIENCE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-07-02 至 2011-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7713083
• 关键词: AMPA Receptors; Acoustic Nerve; Adult; Affinity; Aging; Algorithms; Auditory; Auditory system; Buffers; Cells; Charge; Chemical Synapse; Child; Cochlea; Cochlear Implants; Code; Dependence; Dialysis procedure; Dyes; Electric Capacitance; Electrodes; Endocytosis; Ensure; Fiber; Fire - disasters; Hair Cells; Hearing; Image; Measurement; Measures; Membrane; Membrane Potentials; Microscope; Microscopy; Monitor; Nerve Fibers; Patients; Phase; Photons; Principal Investigator; Protocols documentation; Recycling; Refractory; Resistance; Resolution; Rest; Retinal; Retrieval; Sensory; Signal Transduction; Simulate; Site; Source; Stimulus; Synapses; Synaptic Cleft; Synaptic Transmission; Synaptic Vesicles; Testing; Time; Ultraviolet Rays; United States; Variant; Vesicle; auditory pathway; depressed; flash photolysis; improved; patch clamp; postsynaptic; presynaptic; response; ribbon synapse; sound; transmission process; voltage

DESCRIPTION (provided by applicant): Hair cells in the cochlea connect to auditory afferent fibers via ribbon synapses. Presynaptic graded potentials are converted here into postsynaptic spikes. The long-term objective of this study is to investigate the strategies for auditory signal encoding at this synapse. It has been suggested that hair cells tend to release more than one synaptic vesicle at a time (multivesicular release: MVR). However, the cellular mechanisms underlying MVR are poorly understood and its functional advantages are not known. Our first hypothesis is that MVR occurs when [Ca2+]j in hair cells crosses a threshold that triggers neighboring vesicles on a ribbon to pre-fuse with each other and release all their contents into the synaptic cleft simultaneously. We will determine the quantal response size (i.e., excitatory postsynaptic current (EPSC) amplitude evoked by a single vesicle fusion) and use this to quantify EPSC quantal content. We will find out if vesicles in MVR are from a single ribbon and investigate the Ca2+-dependence of MVR (i.e. determine its Ca2+ threshold). The second hypothesis concerns the function of MRV and has two parts. One part is that MVR can charge and discharge the membrane of afferent fibers more rapidly, helping them to fire spikes with higher temporal precision for phase-locking. The second part is that MRV provides a necessary varying factor on EPSC amplitudes evoked by repeated sinusoidal depolarizations of hair cells. This allows afferent fibers to avoid firing spikes at every sinusoidal cycle and the timing of spikes will not deteriorate due to spike refractory periods. We will measure EPSCs in response to a sinusoidal presynaptic depolarization and then simulate these EPSCs to either substitute MVR with evenly distributed single vesicle releases within a time window (e.g. 0.1 ms), or limit the variation of EPSC amplitudes within the variation of quantal responses (removing thus the variation in their quantal content). These simulated EPSCs will then be experimentally injected into afferent fibers under current-clamp to determine to what extent the phase-locking of spikes becomes deteriorated when MVR is absent. The third hypothesis to be tested is that fused synaptic vesicles can be recycled through fast endocytosis following MVR. We will use a 2-photon microscope to visualize FM1-43 dye loading to monitor vesicle recycling, and we will also make cell-attached capacitance measurements on hair cells to study vesicle recycling by monitoring capacitance changes with a time resolution of 50 ps or higher. RELEVANCE: In the United States, roughly 23,000 adults and 15,500 children have received cochlear implants, which restore part of their hearing by directly stimulating auditory nerve fibers with electrodes. However, the algorithms to stimulate the fibers according to the sound signal have been determined only empirically. The fundamental studies of afferent fiber spiking proposed here will provide guidance for significantly improving these algorithms, especially for adult patients whose auditory systems are fully developed and may thus have lost some of their plasticity and adaptability to different stimulus protocols.

描述（由申请人提供）：耳蜗中的毛细胞通过色带突触连接到听觉传入纤维。突触前分级电位在此转化为突触后尖峰。这项研究的长期目的是研究该突触时的听觉信号的策略。有人提出，毛细胞一次倾向于一次释放多个突触囊泡（多重释放：MVR）。但是，MVR的细胞机制知之甚少，其功能优势尚不清楚。我们的第一个假设是，当毛细胞中的[Ca2+] j越过阈值时，MVR发生，该阈值会触发带有带有的囊泡的相邻囊泡以彼此预融合并同时释放其所有内容物。我们将确定数量响应大小（即，单个囊泡融合引起的兴奋性突触后电流（EPSC）振幅）并使用它来量化EPSC量子含量。我们将找出MVR中的囊泡是否来自单个色带，并研究MVR的Ca2+依赖性（即确定其Ca2+阈值）。第二个假设涉及MRV的功能，并具有两个部分。一个部分是MVR可以更快地为传入纤维的膜充电并排放膜，从而帮助他们以更高的时间精度发射尖峰以进行相锁定。第二部分是MRV在毛细胞的重复正弦去极化引起的EPSC振幅上提供了必要的不同因素。这允许传入纤维避免在每个正弦周期发射尖峰，并且由于尖峰的耐火周期，尖峰的时机不会恶化。我们将测量EPSC，以响应正弦突触前去极化，然后模拟这些EPSC在一个时间窗口内（例如0.1 ms）内用均匀分布的单个囊泡释放的MVR替换MVR，或限制EPSC的变化在定量响应的变化范围内（恢复其定量含量的变量）内。然后，这些模拟EPSC将在电流夹下进行实验注射到传入纤维中，以确定当缺乏MVR时，尖峰的相锁定在多大程度上会恶化。要测试的第三个假设是，MVR后可以通过快速内吞作用来回收融合的突触囊泡。我们将使用2光子显微镜可视化FM1-43染料载荷来监测囊泡回收，并且我们还将对毛细胞的细胞跟踪电容测量进行测量，以通过使用时间分辨率为50 PS或更高的时间分辨率来监测电容的变化来研究囊泡回收。 相关性：在美国，大约有23,000名成年人和15,500名儿童接受了人工耳蜗的植入物，这些植入物通过直接刺激带有电极的听觉神经纤维来恢复其听力的一部分。但是，根据声信号刺激纤维的算法仅通过经验确定。对此处提出的传入纤维尖峰的基本研究将为显着改善这些算法提供指导，尤其是对于成年患者的听觉系统的发展，并因此可能失去了对不同刺激方案的一些可塑性和适应性。