Intercellular Communication in Retinal Development

描述(申请人提供)：神经元的输出不仅受兴奋的影响，还受神经递质、γ-氨基丁酸(GABA)和甘氨酸介导的抑制的幅度和时间的影响。在神经系统的许多疾病中，当兴奋没有通过抑制得到适当的控制时，回路就会变得功能失调。我们对组装和维持适当抑制性连接的细胞相互作用的理解远远落后于我们对兴奋回路的了解。在这个项目中，我们建议显著提高对控制兴奋性神经递质从轴突释放的抑制性连接的发展和功能维持的知识。我们将重点研究视网膜双极细胞轴突终末的抑制性突触。这些神经元是将视觉信号从光感受器传递到视网膜神经节细胞所必需的。来自这些细胞的传输至少由两种不同类型的抑制性突触形成。在目标1中，我们将在基因上标记调节同一轴突抑制的离子型GABAA和GABAC受体，但具有不同的动力学。我们将使用相关荧光成像和连续块面部扫描电子显微镜来绘制不同类型突触的连接模式。利用GABA受体亚基特异的条件性基因敲除小鼠，我们将确定携带Alpha1 GABAA受体亚基的成熟GABA能突触是否需要在发育过程中短暂丰富的Alpha3亚基的存在。在目标2中，我们将使用成像、电生理分析和抑制性传递受扰的突变小鼠来确定神经传递在建立双极细胞轴突上抑制性突触类型的适当组合中的作用。在目标3中，我们将区分在双极细胞的不同细胞区段中用于调节GABA能突触的途径，轴突和树突。我们将使用分子和遗传方法来改变细胞内的氯离子通量 尤其是在这些神经元中。我们的结果将极大地促进对细胞 通过并行处理感觉信号的电路来调节突触前抑制的发展和维持的机制。

DESCRIPTION (provided by applicant): The output of a neuron is shaped not only by excitation but also by the magnitude and timing of inhibition mediated by the neurotransmitters, gamma-aminobutyric acid (GABA) and glycine. Circuits become dysfunctional as found in many diseases of the nervous system when excitation is not controlled properly by inhibition. Our understanding of the cellular interactions that assemble and maintain appropriate inhibitory connections lags far behind our knowledge about excitatory circuits. In this project, we propose to significantly advance knowledge of the development and functional maintenance of inhibitory connections that control the release of excitatory neurotransmitters from axons. We will focus on inhibitory synapses on the axon terminals of retinal bipolar cells. These neurons are essential for relaying visual signals from photoreceptors to the retinal ganglion cells. Transmission from these cells is shaped by at least two different types of inhibitory synapses. In Aim 1, we will genetically label ionotropic GABAA and GABAC receptors that regulate inhibition onto the same axon, but with different kinetics. We will use correlative fluorescence imaging and serial block face scanning electron microscopy to map connectivity patterns of the different synapse types. Using GABA receptor subunit specific conditional knockout mice, we will determine whether mature GABAergic synapses bearing alpha1 GABAA receptor subunits require the presence of alpha3 subunits that are transiently abundant during development. In Aim 2, we will employ imaging, electrophysiological assays, and mutant mice with perturbed inhibitory transmission to ascertain the role of neurotransmission in establishing the appropriate combination of inhibitory synapse types on bipolar cell axons. In Aim 3, we will distinguish the pathways that are employed to regulate GABAergic synapses in distinct cell compartments, axon versus dendrite, of bipolar cells. We will use molecular and genetic approaches to alter intracellular chloride flux specifically in these neurons. Our results will significantly advance understanding of the cellular mechanisms that regulate the development and maintenance of presynaptic inhibition across circuits that act in parallel to process sensory signals.