Presynaptic GABA-A receptor activation in auditory brainstem axon terminals

描述（由申请人提供）：听觉脑干中外侧上级橄榄（LSO）的神经元接收来自双耳的声音信息。来自同侧耳的输入是通过耳蜗核的，其引起到LSO的兴奋性、神经元能投射。来自对侧耳的输入投射到对侧耳蜗核，然后通过斜方体内侧核（MNTB），这是一组神经元，将神经元能信号转换为抑制性甘氨酸能投射。来自两只耳朵的输入组合决定了LSO神经元计算声音在头部周围空间中的位置的能力。在发育早期，MNTB神经元也释放神经递质GABA和谷氨酸。这些神经递质在双耳神经元正常结构发育中的作用还不是很清楚。如果谷氨酸在MNTB神经元中不存在，则已经表明存在对来自两个耳朵的神经元的模式的不适当的细化，其将相同的频率编码到单个LSO神经元上。关于GABA在这些突触中的功能知之甚少，但已显示GABA释放可引起LSO神经元中的钙升高，这对于神经元之间的突触形成可能是重要的。本提案旨在研究GABA在从MNTB到LSO的投射发展中的作用。实验将在来自含有MNTB神经元及其向LSO神经元的投射的小鼠的脑切片中进行。技术将包括全细胞电生理学和双光子成像，以测量当GABA信号被改变时神经元的活动模式。将使用包括测量钙信号传导（指示细胞活性）变化的荧光染料和允许使用激光刺激单个神经元的“光遗传学”工具的工具。该提案还包括电子显微镜实验，以研究MNTB和LSO神经元之间突触的亚细胞结构，以测量GABA受体如何参与MNTB和LSO之间突触的正确形成。这项研究也将对其他大脑区域的GABA信号研究产生影响。研究编码声音定位的神经元回路的正确形成对于更好地理解动物和人类的听觉至关重要。了解神经元在发育阶段如何正确连接，可以指导我们了解在异常发育或损伤导致正常听力受损的情况下可能出现的问题。对声音感知的复杂性的充分理解将指导治疗听力障碍的精细疗法。

DESCRIPTION (provided by applicant): The neurons of the lateral superior olive (LSO) in the auditory brainstem receive sound information from both ears. Inputs from the ipsilateral ear are via the cochlear nucleus, which gives rise to an excitatory, glutamatergic projection to the LSO. Inputs from the contralateral ear project to the contralateral cochlear nucleus, then through the medial nucleus of the trapezoid body (MNTB), a group of neurons that convert the glutamatergic signal to an inhibitory, glycinergic projection. The combination of inputs from the two ears determines the ability of LSO neurons to compute the location of sound in space around the head. Early in development the MNTB neurons also release the neurotransmitters GABA and glutamate. The purpose of these neurotransmitters in the proper structural development of neurons from the two ears is not very well understood. If glutamate is absent from the MNTB neurons, it has been shown that there is an improper refinement of patterns of neurons from the two ears that encode the same frequency onto a single LSO neuron. Less is known about the function of GABA in these synapses, but it has been shown that GABA release can cause a calcium rise in the LSO neurons, which may be important for formation of synapses between the neurons. This proposal aims to study the role of GABA in development of the projections from the MNTB to the LSO. Experiments will be performed in brain slices from mice containing both MNTB neurons and their projections to LSO neurons. Techniques will include whole-cell electrophysiology and 2-photon imaging to measure the patterns of activity in neurons when GABA signaling is altered pharmacologically. Tools including fluorescent dyes that measure changes in calcium signaling (indicative of cellular activity) and 'optogenetic' tools that allow stimulation of individual neurons using laser light will be used. The proposal also includes electron microscopy experiments to investigate the subcellular structures at the synapses between MNTB and LSO neurons in order to measure how GABA receptors are involved in the proper formation of synapses between the MNTB and LSO. This research will also have implications for investigation of GABA signaling in other brain regions. Research into the proper formation of neuronal circuits that encode sound localization is crucial for a greater understanding of hearing, both in animals and in humans. Understanding how neurons properly connect in developmental stages guides understanding of what can go wrong in situations in which normal hearing is compromised through aberrant development or through injury. A full understanding of the complexity of the perception of sound will guide refined therapies for treatment of hearing disorders.