The role of short-term plasticity at the calyx of Held for auditory processing

描述（由申请人提供）：听觉脑干或皮层突触传递缺陷可导致中枢听觉处理障碍，即大脑不能正确处理声音。研究听觉脑干中控制听觉过程的突触机制将有助于更好地理解人类听力障碍的病因。本研究的长期目标是确定听觉脑干突触（称为Held花萼）的短期可塑性的控制机制，并确定该突触的可塑性对声音定位的功能重要性。赫尔德花萼是听觉脑干中一个巨大的谷氨酸能突触，在声音定位中起快速兴奋性突触的作用。花萼表现出一种短期可塑性，称为破伤风后增强（PTP），它可以由高频（破伤风）刺激诱导，并依赖于突触前残余Ca2+浓度的升高。具体来说，突触前Ca2+的增加激活了蛋白激酶C （PKCCa）的Ca2+依赖亚型。虽然花萼作为一种模式突触已经被研究了很长时间，但花萼上PTP的生理意义尚未被探索。花萼是投射到梯形体内侧核主要神经元上的谷氨酸突触。MNTB ？最近发现LSO突触在听力发作前的突触完善期共同释放谷氨酸/GABA/甘氨酸。据推测，花萼PTP可以调节MNTB发射的保真度和时间精度，并增加MNTB的释放概率。LSO突触有利于谷氨酸能的传递。因此，像PTP这样的短期可塑性形式可能在形成声音定位脑干回路中发挥重要作用。本研究计划的具体目的是：(1)确定生理条件下花萼PTP的动态，(2)研究花萼PTP在脑干声音定位通路中的功能作用，(3)解剖PTP分子级联以选择性地改变花萼的短期可塑性。用于实现这些目标的主要技术包括全细胞电生理记录，脑切片中大量突触前Ca2+负载，以及Ca2+瞬态的双光子成像。该提案的完成将对PTP在a中的功能角色提供相当深入的了解

DESCRIPTION (provided by applicant): Defects in synaptic transmission in the auditory brainstem or cortex can give rise to central auditory processing disorders where the brain cannot correctly process sound. Investigating the synaptic mechanisms governing the processes of hearing in the auditory brainstem will allow for a better understanding of the etiology of human hearing disorders. The long-term objectives of the proposed research are to define the mechanisms that govern short-term plasticity at the auditory brainstem synapse called the calyx of Held, and to determine the functional importance of plasticity at this synapse for sound localization. The calyx of Held is a giant glutamatergic synapse in the auditory brainstem that functions as a fast excitatory synapse for sound localization. The calyx displays a form of short-term plasticity called post-tetanic potentiation (PTP), which can be induced by high-frequency (tetanic) stimulation and is dependent on elevations in presynaptic residual Ca2+ concentrations. Specifically, increases in presynaptic Ca2+ activate Ca2+-dependent isoforms of protein kinase C (PKCCa). While the calyx has long been studied as a model synapse, the physiological significance of PTP at the calyx has not been explored. Calyces are glutamatgeric synapses that project onto principal neurons of the medial nucleus of the trapezoid body (MNTB). The MNTB ?LSO synapse has been recently discovered to co-release glutamate/GABA/glycine during the period of synaptic refinement prior to hearing onset. Calyceal PTP is hypothesized to modulate the fidelity and temporal precision of MNTB firing remains unknown, and to increase release probability at the MNTB?LSO synapse to favor glutamatergic transmission. Thus, forms of short-term plasticity like PTP could play a major role in shaping the sound localization brainstem circuit. The specific aims of this research proposal are to (1) determine the dynamics of PTP under physiological conditions at the calyx of Held, (2) investigate the functional role of calyceal PTP in the brainstem sound localization pathway, and (3) dissect the PTP molecular cascade to selectively alter short-term plasticity at the calyx. The primary techniques used to achieve these aims include whole-cell electrophysiology recordings, bulk presynaptic Ca2+ loading in brain slices, and two-photon imaging of Ca2+ transients. The completion of this proposal will provide considerable insight into the functional roles of PTP at a key synapse in the auditory brainstem. The expertise of Dr. Wade Regehr and the environment of Harvard Medical School provide me with extensive training in electrophysiology and imaging techniques necessary to complete my goals.