Heterogeneity of feed-forward inhibition in the dorsal cochlear nucleus

描述（由申请人提供）：听觉脑干中的神经元回路专门用于提取和表示声学信息的特定方面。抑制性神经元在这些回路中发挥着重要作用，但抑制如何促进听觉处理尚不清楚。哺乳动物耳蜗背核（DCN）是听觉神经纤维的主要目标之一，被认为处理用于定位声源的单耳信号。被称为垂直细胞的甘氨酸能神经元对DCN主细胞的前馈抑制被认为对这一功能有重要贡献，然而，确定垂直细胞中活性如何被募集以及这些神经元对其目标的影响的具体机制尚未被确定。该建议的目的是通过直接研究垂直细胞和突触特性来阐明垂直细胞在DCN中的作用。全细胞膜片钳技术，结合解剖和免疫组织化学分析，将用于验证至少两种功能不同的垂直细胞亚型解释DCN主神经元的体内行为的假设。为了在脑干切片制备中记录垂直细胞，本研究将利用最近开发的转基因小鼠，其中甘氨酸能神经元表达绿色荧光蛋白。在Specific Aim 1中，垂直细胞将使用电生理和解剖学标准分类为不同的功能亚型。特异性目标2将解决垂直细胞亚类的活性由γ -氨基丁酸介导的抑制差异调节的假设。Specific Aim 3的实验将使用双全细胞膜片钳记录垂直细胞和主神经元之间的突触连接对，以研究来自垂直细胞的亚型特异性抑制输入是否有助于DCN主细胞的特征性反应特性。这些目标的成功完成将有助于深入了解DCN功能的基本机制，并可能揭示DCN中垂直细胞介导的抑制的异质性。

DESCRIPTION (provided by applicant): Neuronal circuits in the auditory brainstem are specialized to extract and represent specific aspects of acoustic information. Inhibitory neurons feature prominently in these circuits, but how inhibition contributes to auditory processing is not well understood. The mammalian dorsal cochlear nucleus (DCN), one of the principal targets of auditory nerve fibers, is thought to process monaural cues used to localize sound sources. Feed-forward inhibition onto DCN principal cells from glycinergic neurons known as vertical cells is believed to contribute importantly to this function, yet the specific mechanisms that determine how activity in vertical cells is recruited and what effect these neurons have on their targets have not previously been identified. The objective of this proposal is to clarify the role of vertical cells in the DCN by directly investigating their cellular and synaptic properties. Whole-cell patch-clamp techniques, in combination with anatomical and immunohistochemical analysis, will be used to test the hypothesis that at least two functionally distinct subtypes of vertical cells account for the in vivo behavior of DCN principal neurons. To target recordings of vertical cells in a brainstem slice preparation, this study will take advantage of recently developed transgenic mice in which glycinergic neurons express green fluorescent protein. In Specific Aim 1, vertical cells will be categorized into different functional subtypes using electrophysiological and anatomical criteria. Specific Aim 2 will address the hypothesis that activity in vertical cell subclasses is differentially modulated by inhibition mediated by gamma-aminobutyric acid. Experiments in Specific Aim 3 will use dual whole-cell patch-clamp recordings between synaptically connected pairs of vertical cells and principal neurons to investigate whether subtype-specific inhibitory input from vertical cells contributes to the characteristic response properties of DCN principal cells. Successful completion of these aims will provide insight into the basic mechanisms underlying DCN function and may reveal previously unappreciated heterogeneity of vertical cell-mediated inhibition within the DCN. Public Health Relevance: Some forms of tinnitus (persistent ringing in the ears) are thought to arise from noise-induced or aging-related loss of vertical cell activity. Understanding the basic mechanisms underlying normal vertical cell function should provide insight into how loss of activity in these neurons may contribute to the pathophysiology of tinnitus and could suggest avenues for therapeutic intervention.