Presynaptic GABA-A receptor activation in auditory brainstem axon terminals

描述(申请人提供)：听觉脑干中外侧上橄榄(LSO)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进行的，这导致了兴奋性的谷氨酸能投射到LSO。从对侧耳朵投射到对侧耳蜗核，然后通过斜方体内侧核(MNTB)，一组神经元将谷氨酸能信号转换为抑制性的甘氨酸能投射。来自两只耳朵的输入的组合决定了LSO神经元计算声音在头部周围空间位置的能力。在发育早期，MNTB神经元还会释放神经递质GABA和谷氨酸。这些神经递质在两只耳朵神经元的正常结构发育中的作用还不是很清楚。如果MNTB神经元中没有谷氨酸，已经证明两只耳朵中编码相同频率的神经元模式不正确地细化到单个LSO神经元上。关于GABA在这些突触中的作用，人们知之甚少，但已有研究表明，GABA的释放可以引起LSO神经元内钙的升高，这可能对神经元之间突触的形成起重要作用。这项建议旨在研究GABA在制定从MNTB到LSO的预测中的作用。实验将在含有MNTB神经元及其向LSO神经元的投射的小鼠脑片上进行。技术将包括全细胞电生理学和双光子成像，以测量当GABA信号被药物改变时神经元的活动模式。将使用包括荧光染料在内的工具来测量钙信号的变化(指示细胞活动)，以及允许使用激光刺激单个神经元的光遗传工具。该建议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。这项研究也将对研究其他大脑区域的GABA信号产生影响。对编码声音定位的神经元回路的正确形成的研究对于更好地理解听觉至关重要，无论是在动物身上还是在人类身上。了解神经元在发育阶段是如何正确连接的，有助于理解在正常听力因发育异常或损伤而受损的情况下，会出现什么问题。对声音感知的复杂性的充分理解将指导听力障碍的精细化治疗。

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.