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）处，“模拟”声音信息在听觉神经纤维处被转换为动作电位的“数字”模式并被传输到大脑。动作电位序列中每个尖峰的相对时间携带着重要的信息，需要在听觉通路中如实地表示出来。时间编码的一个很好的表征形式是锁相：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双耳的微小时间差来定位声源所必需的。耳间延迟可以小到10微秒，强调听觉周边的时间编码的精度。该提案的目标是研究允许IHC带状突触以高精度和长时间释放神经递质的机制。在急性切除的大鼠耳蜗制备物中，将从IHC和听觉神经纤维的突触后末梢进行同步膜片钳记录。最近，我们已经表明，短期易化发生在这个突触，不仅增加了释放，但也减少了潜伏期。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，通过控制其传播与特定的缓冲液，并通过监测其衰减时间过程与荧光染料。还将通过释放胞质空间中的Ca2+来研究促进作用。其次，锁相突触反应的潜在机制将被调查。初步实验表明，在IHC带状突触的突触反应锁相周期性刺激。这一特点将进一步探讨通过施加具有可变幅度的刺激，并通过测试是否保存的首选相位。这些实验将与单步去极化的反应进行比较。我们将评估短期便利化的作用 以及在建立锁相时的凹陷。最后，将研究IHC带状突触以高精度连续发出信号的能力。已经表明，响应于稳定的IHC去极化，该突触表现出短期抑制。将评估耗尽刺激后突触反应性恢复的时间过程。考虑到神经同步是复杂任务（如语音清晰度）所必需的，本研究的结果有望为人工耳蜗设计的潜在改进和更好地理解源于IHC传入突触的听力缺陷提供基础。这项研究将主要在阿根廷与Juan Goutman博士合作在Instituto de Investigaciones en Ingenier <$a Gen <$tica y Biolog <$a Molecular（INGEBI）进行，伴随基金为R01 DC 006476，01 - 01 - 2004至11 - 29 - 2013。

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.