Synaptic physiology of unipolar brush cells in the dorsal cochlear nucleus

耳蜗背核单极刷细胞的突触生理学

• 批准号: 8313320
• 负责人: Carolina Borges-Merjane
• 金额: $ 4.22万
• 依托单位: OREGON HEALTH & SCIENCE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-06-30 至 2015-06-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8313320
• 关键词: Acoustic Nerve; Action Potentials; Affect; Affinity; Auditory; Auditory system; Brain Stem; Brush Cell; Cell Nucleus; Cells; Cellular Structures; Characteristics; Cleaved cell; Coupled; Cytoplasmic Granules; Data; Dendrites; Disease; Disinhibition; Event; Exocytosis; Fiber; Foundations; Functional disorder; Glutamates; Goals; Head and neck structure; Hearing; Hyperactive behavior; Image; Interneurons; Lead; Measures; Mediating; Methods; Microscopy; Modeling; Mus; Neurotransmitters; Output; Photons; Physiologic pulse; Physiological; Physiology; Positioning Attribute; Presynaptic Terminals; Probability; Process; Property; Proprioception; Research Training; Signal Transduction; Site; Sound Localization; Structure; Synapses; Synaptic Cleft; Synaptic Receptors; Synaptic Transmission; Testing; Time; Tinnitus; Vesicle; auditory stimulus; base; dorsal cochlear nucleus; granule cell; hearing impairment; innovation; insight; mossy fiber; mouse model; multisensory; patch clamp; postsynaptic; research study; response; sound; synaptic depression; synaptic function; transmission process

DESCRIPTION (provided by applicant): The dorsal cochlear nucleus (DCN) is one of the initial structures in the mammalian brainstem that processes sound, integrating multisensory and auditory nerve input. Multisensory modulation of auditory input is a basic feature of the DCN and may be a critical contributor to tinnitus, a common hearing impairment disorders characterized by the perception of sound without exterior auditory stimulus. Although multisensory modulation of auditory input in the DCN has been shown to be important for DCN function, the synaptic and cellular mechanisms underlying synaptic transmission from multisensory fibers to its primary targets within the DCN circuitry are not well known. Multisensory input to the DCN is relayed by mossy fibers (MF), whose primary synaptic targets are granule cells (GrCs). However, a large subset of GrCs receives input through an excitatory interneuron called unipolar brush cells (UBCs). UBCs have a single short dendrite that terminates in a brush-like structure and interdigitates with a single pre-synaptic terminal, formin an unusually large excitatory synaptic contact. A previous model suggests that prolonged entrapment of glutamate in the irregular synaptic cleft underlies the characteristic slow-decaying post-synaptic current (EPSC) of UBCs. The goal of this proposal is to investigate whether UBCs temporally amplify input from MF to GrCs for further integration with auditory input, and if so, what synaptic specializations promote such amplification. We propose that multivesicular release from MF terminals contributes to prolonged glutamate in the cleft and allows UBCs to provide temporal amplification of signals to GrCs. Aim 1 will determine the physiological postsynaptic response of GrCs to UBC mediated input These experiments will directly test for the first time the effect of UBCs input to GrCs using combined imaging and electrophysiological approaches in a GFP-tagged UBC mouse through 2- photon microscopy and patch-clamp recordings from connected UBC-GrC pairs. Aim 2 will determine the mode of exocytosis at the MF-UBC synapse. Preliminary data shows low variance in amplitude of evoked EPSCs in UBC upon MF stimulation with consistent synaptic depression, therefore suggesting a high probability of release the MF-UBC synapse. The proposed experiments will investigate the mode of release at these synapses with patch-clamp recordings and the analysis of the non-equilibrium inhibition of the post- synaptic receptors by low-affinity competitive antagonists coupled to multiple-probability fluctuation analysis. Through these methods the quantal size, the number of independent release sites and the probability of release at each site can be calculated. By investigating synaptic transmission through the main structure relaying multisensory input to the DCN, and the impact of UBCs to GrC activity, this proposal will provide the foundation for understanding how the DCN early processing of multisensory input affects integration with auditory input at the principal output cells. This will characterize the first cellular contributor pertaining to the modulation and triggers of somatic tinnitus at the DCN. PUBLIC HEALTH RELEVANCE: Enhancement of multisensory input modulation of auditory input to the dorsal cochlear nucleus (DCN) can lead to disinhibition and subsequent hyperactivity of this nucleus, an event highly associated with tinnitus onset. This proposal seeks to characterize early processing of multisensory input relayed by mossy fibers at the DCN, by focusing on one of their primary cell targets, the unipolar brush cells. A better understanding of the impact of unipolar brush cells to their synaptic targets activity and underlying synaptic specializations that allows them to execute their function can provide insight into multisensory modulation and trigger of somatic tinnitus at the DCN.

描述（申请人提供）：耳蜗背核（DCN）是哺乳动物脑干中处理声音的初始结构之一，整合多感觉和听觉神经输入。听觉输入的多感觉调节是DCN的一个基本特征，可能是耳鸣的关键因素，耳鸣是一种常见的听力障碍，其特征是在没有外部听觉刺激的情况下感知声音。虽然DCN中听觉输入的多感觉调节已被证明对DCN功能很重要，但DCN回路中多感觉纤维突触传递到主要目标的突触和细胞机制尚不清楚。多感觉输入通过苔藓纤维（MF）传递到DCN，其主要突触靶点是颗粒细胞（GrCs）。然而，大部分GrCs通过称为单极刷细胞（ubc）的兴奋性中间神经元接受输入。ubc有一个短的树突，末端呈刷状结构，并与一个突触前末端交叉，形成一个异常大的兴奋性突触接触。先前的一个模型表明，不规则突触间隙中谷氨酸的长时间滞留是ubc典型的慢衰减突触后电流（EPSC）的基础。本提案的目的是研究ubc是否会暂时放大从MF到GrCs的输入，以便与听觉输入进一步整合，如果是的话，是什么突触特化促进了这种放大。我们认为，MF末端的多泡释放有助于延长裂缝中的谷氨酸，并允许ubc向GrCs提供时间放大信号。这些实验将首次在gfp标记的UBC小鼠中，通过双光子显微镜和膜片钳记录连接的UBC- grc对，使用联合成像和电生理方法直接测试UBC输入对GrCs的影响。目的2将确定MF-UBC突触的胞吐模式。初步数据显示，在中频刺激下，UBC中诱发的EPSCs振幅变化较小，突触持续抑制，因此表明中频-UBC突触释放的可能性很大。本实验将通过膜片钳记录研究这些突触的释放模式，并结合多概率波动分析分析低亲和力竞争拮抗剂对突触后受体的非平衡抑制。通过这些方法可以计算出量子大小、独立释放点的数量以及每个释放点的释放概率。通过研究将多感觉输入传递到DCN的主要结构的突触传递，以及ubc对GrC活动的影响，本研究将为理解DCN对多感觉输入的早期处理如何影响主要输出细胞与听觉输入的整合提供基础。这将表征第一个细胞贡献者有关的调制和触发的躯体耳鸣在DCN。