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

描述(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”声音信息在听觉神经纤维处被转化为“数字”动作电位模式，并传输到大脑。一系列动作电位中每个峰的相对时间携带着重要的信息，需要在听觉通路中忠实地表现出来。时间编码的一种很好的特征形式是相位锁定：听神经元能够在低频刺激的每个周期内的特定时间放电。通过计算波到达两只耳朵的微小时间差来定位声源时，需要这种现象。耳间延迟可以小到10微秒，强调听觉外周时间编码的精确度。这项提议的目标是研究允许IHC带状突触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准备中，将从IHC和听神经纤维的突触后终末同时进行膜片钳记录。最近，我们已经证明在这个突触上发生了短期的易化，不仅产生了释放的增加，而且潜伏期的减少。我们的第一个目标是研究这种现象背后的机制。我们将通过使用特定的缓冲液控制细胞内残余钙浓度的扩散，并通过荧光染料监测其衰减时间过程来研究细胞内剩余钙浓度的作用。此外，还将通过去除胞质间隙中的钙离子来研究促进作用。其次，我们将探讨锁相突触反应的潜在机制。初步实验表明，IHC带状突触对周期性刺激的反应是相位锁定的。这一特征将通过施加可变幅度的刺激和测试首选相位是否保守来进一步探索。这些实验将与单步去极化的反应进行比较。我们将评估短期促进的作用 以及在建立锁相过程中的抑制。最后，将研究IHC带突触持续高精度信号传递的能力。已有研究表明，对稳定的IHC去极化的反应，该突触表现出短期的抑制。将评估在耗尽刺激后突触反应性恢复的时间进程。鉴于语音清晰度等复杂任务需要神经同步，这项研究的结果有望为人工耳蜗设计的潜在改进提供基础，并更好地理解源于IHC传入突触的听力障碍。这项研究将主要在阿根廷与胡安·古特曼博士合作在阿根廷生物分子研究所(INGEBI)进行，附带赠款为R01 DC006476,2004年1月1日至2013年11月29日。

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.