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

描述(由申请人提供)：听觉脑干或皮质中突触传递的缺陷可能会导致中枢听觉处理障碍，大脑无法正确处理声音。研究听觉脑干中支配听力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。这项拟议研究的长期目标是确定控制听觉脑干突触(称为Hold的花瓣)短期可塑性的机制，并确定该突触的可塑性对声音定位的功能重要性。Hold的花冠是听觉脑干中的一个巨大的谷氨酸能突触，其功能是作为声音定位的快速兴奋性突触。花萼表现出一种被称为强直性后增强(PTP)的短期可塑性，这种可塑性可由高频(强直性)刺激诱导，并依赖于突触前残余钙离子浓度的升高。具体地说，突触前Ca~(2+)的增加激活了Ca~(2+)依赖的蛋白激酶C亚型(PKCCa)。虽然长期以来，人们一直将花萼作为突触的模型进行研究，但还没有人探讨PTP在花萼中的生理意义。花盏是谷氨酸突触，投射到斜方体内侧核(MNTB)的主要神经元上。最近发现MNTB？LSO突触在突触形成前的突触精化过程中共同释放谷氨酸/GABA/甘氨酸。Calyceal PTP被认为是为了调节MNTB放电的保真度和时间精度，并增加MNTB？LSO突触的释放概率，以利于谷氨酸能传递。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方面发挥重要作用。本研究的具体目的是：(1)确定Hold的花萼在生理条件下PTP的动态变化；(2)研究PTP在脑干声音定位通路中的功能作用；(3)分析PTP的分子级联，选择性地改变花萼的短期可塑性。实现这些目标的主要技术包括全细胞电生理记录、大量突触前钙离子在脑片中的负载以及对钙瞬变的双光子成像。这项提案的完成将为PTP的职能角色提供相当大的洞察力 听觉脑干中的关键突触。韦德·雷格尔博士的专业知识和哈佛医学院的环境为我提供了完成目标所必需的电生理学和成像技术方面的广泛培训。

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.