Auditory Coding at the Hair Cell Ribbon Synapse

耳蜗中的毛细胞通过带状突触连接到听觉传入纤维，带状突触将突触前神经元转化为听觉神经元。 Gracied potential（analog signal）Into postsynaptic all-or-none spikes（digital signal）.长期目标 本研究的目的是探讨突触传递机制和听觉编码策略， 这些突触先前，通过测定牛蛙毛细胞带状突触的量子尺寸， 两栖类乳头，我们明确表明，毛细胞可以释放一个以上的突触囊泡 一次（多泡释放，MRV）从单个释放位点（即，ribbon）。研究细胞机制 我们将测量MVR的钙依赖性并确定其钙阈值。到 为了证明MRV的功能优势，我们将首先用窦状隙突触前刺激毛细胞， 模拟体内毛细胞电压响应的去极化，并量化诱发的EPSC中的MVR。 然后，我们模拟了两组EPSC，其中我们或者用均匀分布的单个MVR代替MVR， 囊泡在时间窗内释放（例如，0.1 ms），或固定MVR的量子内容（去除 其量子含量的变化）。我们将原始和模拟的EPSC都喂入传入纤维 在电流钳位下，并找出在什么程度上的尖峰的相位锁定得到恶化。探讨 突触囊泡是如何循环的，我们将使用双光子显微镜来观察FM 1 -43染料负载， 监测囊泡循环，我们还将对毛细胞进行细胞附着电容测量， 通过监测亚毫秒级时间分辨率的电容变化来研究囊泡再循环。

Hair cells in the cochlea connect to auditory afferent fibers via ribbon synapses, which convert presynaptic gracied potentials (analog signal) Into postsynaptic all-or-none spikes (digital signal). The long-term objective of this study is to investigate mechanisms of synaptic transmission and strategies for auditory coding at these synapses. Previously, by determining the quantal size of the hair cell ribbon synapse in bullfrog j amphibian papilla, we demonstrated unequivocally that hair cells can release more than one synaptic vesicle at a time (multivesicular release, MRV) from a single release site (i.e., ribbon). To study cellular mechanisms that control MRV, we will measure the calcium-dependence of MVR and determine its calcium threshold. To demonstrate the functional advantages of MRV, we will first stimulate hair cells with sinusoidal presynaptic depolarizations that mimic hair cell voltage responses in vivo, and quantify MVRs in the evoked EPSCs. Then we simulate two sets of EPSCs in which we either substitute MVRs with evenly distributed single vesicle releases within a time window (e.g., 0.1 ms), or fix the quantal content of MVRs (removing the variation in their quantal contents). We will feed both the original and simulated EPSCs to afferent fibers under current-clamp, and find out to what extent the phase-locking of spikes gets deteriorated. To investigate how synaptic vesicles are recycled, we will use a two-photon microscope to visualize FM1-43 dye loading to monitor vesicle recycling, and we will also make cell-attached capacitance measurement on hair cells to study vesicle recycling by monitoring capacitance changes with a submillisecond time resolution.