Short-term plasticity & temporal precision at the inner hair cell ribbon synapse

描述（由申请人提供）：在内毛细胞（IHC）带状突触，听觉通路中的第一个突触，“模拟”声音信息被转换成听觉神经纤维动作电位的“数字”模式并传输到大脑。动作电位序列中每个脉冲的相对时间携带着重要的信息，这些信息需要在听觉通路中忠实地表现出来。时间编码的一个很好的特征形式是锁相：听觉神经元能够在低频刺激的每个周期内的特定时间放电。这种现象是通过计算声波到达两耳的时间差来定位声源所必需的。耳间延迟可以小到10微秒，强调了听觉外围时间编码的准确性。本研究的目的是研究IHC带状突触长时间高精度释放神经递质的机制。在急性切除的大鼠耳蜗制备中，将同时从ihc和听神经纤维的突触后末端进行膜片钳记录。最近，我们已经表明，短期促进发生在这个突触，不仅产生释放增加，而且减少延迟。我们的第一个目标是研究这种现象背后的机制。我们将研究残留的细胞内Ca2+浓度的作用，通过控制其扩散与特定的缓冲液，并通过监测其衰变时间过程与荧光染料。促进作用也将通过释放细胞质空间中的Ca2+来研究。其次，锁相突触反应的潜在机制将被研究。初步实验表明，IHC带状突触的突触反应对周期性刺激具有锁相性。这一特征将通过应用可变振幅的刺激和测试优选相位是否守恒来进一步探讨。这些实验将与单步去极化的响应进行比较。我们将评估短期便利的作用

DESCRIPTION (provided by applicant): At the inner hair cell (IHC) ribbon synapse, the first synapse in the auditory pathway, 'analog' sound information is converted into a 'digital' pattern of action potentials at auditory nerve fibers and transmitted to the brain. The relative time of each spike within a train of action potentials carries important information that needs to be faithfully represented in the auditory pathway. A well characterized form of temporal coding is phase locking: auditory neurons are capable of firing at a particular time within each cycle of a low-frequency stimulus. This phenomenon is required for localizing a sound source by computing the small difference in time at which the wave arrives at the two ears. Interaural delays can be as small as 10 microseconds, emphasizing the precision of temporal coding by the auditory periphery. The goal of this proposal is to investigate the mechanisms that allow the IHC ribbon synapse to release neurotransmitter with high precision and over long periods of time. In acutely excised rat cochlear preparations, simultaneous patch-clamp recordings will be performed from IHCs and postsynaptic terminals of auditory nerve fibers. Recently, we have shown that short-term facilitation occurs at this synapse, producing not only an increase in release but also a reduction in latency. Our first aim is to investigate the mechanisms underlying this phenomenon. We will study the role of the residual intracellular Ca2+ concentration by controlling its spread with specific buffers, and by monitoring its decay time course with fluorescent dyes. Facilitation will also be studied by uncaging Ca2+ in the cytosolic space. Secondly, the underlying mechanisms of phase-locked synaptic responses will be investigated. Preliminary experiments show that synaptic responses at the IHC ribbon synapse phase-lock to periodic stimuli. This feature will be further explored by applying stimuli with variable amplitude and by testing whether the preferred phase is conserved. These experiments will be compared with responses to single step depolarizations. We will evaluate the role of short-term facilitation and depression in establishing phase-locking. Finally, the ability of the IHC ribbon synapse to signal continuously with high precision will be studied. It has been shown that in response to steady IHC depolarization, this synapse exhibits short-term depression. The time course of recovery of synaptic responsiveness following a depleting stimulus will be evaluated. Given that neural synchrony is required for complex tasks such as speech intelligibility, the outcome of this study will hopefully provide the basis for potential improvements in cochlear implant design and a better understanding of hearing deficits that originate at the IHC afferent synapse. This research will be done primarily in Argentina, at the Instituto de Investigaciones en Ingenier¿a Gen¿tica y Biolog¿a Molecular (INGEBI) in collaboration with Dr. Juan Goutman, with the companion grant being R01 DC006476, 01-01-2004 to 11-29-2013.