Microglia-dependent mechanisms governing neural circuit plasticity

这项提议的目标是确定小胶质细胞和感觉体验如何整合到 将突触重塑为精确的、有功能的脑图。数以万亿计的突触形成非常精确的 大脑中代表身体各个部位的地形图。这些地图由以下人员塑造和维护 感觉体验(视觉、触觉等)，包括消除不太活跃的突触和形成 其他突触的维持。尽管有50多年的研究，但其潜在的机制 经验表明，移除或维持特定突触仍然是一个悬而未决的问题。我们做了 最初兴奋和意外的观察到小胶质细胞，驻留的中枢神经系统巨噬细胞，吞噬和 消除了发育中的视网膜原系统中不太活跃的突触的子集。进一步，减少 小胶质细胞介导的突触吞噬50%(补体受体3KO)导致持续 视黄素生成的突触数量增加。这项工作为突触建立了一种新的思维方式 重塑和引发了几个重要的新问题：小胶质细胞介导的突触重塑 是实现功能电路所必需的吗？小胶质细胞会重塑成人大脑中的突触吗？何以 神经活动调节小胶质细胞介导的突触重构？视网膜原化系统是有限的 来解决这些问题。我们需要一个强大的系统来研究突触重塑 整个生命中突触的可塑性，测量功能的简便方法，以及地形排列 具有较高的时空分辨率。小鼠桶状皮质符合所有这些标准，并将使我们能够测试 经验调节小胶质细胞将发育和成熟的悬液塑造成功能性的假说 大脑回路。我们新的初步数据首次显示小胶质细胞吞噬兴奋性丘脑皮质 (TC)发育中的桶状皮质和感觉剥夺(胡须去除)后的突触 刚出生的。此外，小胶质细胞(集落刺激因子1受体KO；CSF1R KO)缺陷的小鼠也有缺陷 在适当的桶结构和TC输入的发展中，去除胡须之后 在小胶质细胞特异性趋化因子受体(Fractalkine Receptor K0， CX3CR1 KO)。我们现在将使用高分辨率静态和功能成像和分子成像的组合 生物学在小鼠桶状皮质：1)确定小胶质细胞是否雕刻成发育中的皮质环路 功能脑图(目标1)。2)确定小胶质细胞是否调节经验依赖的可塑性 新生儿和成人的皮质地形图(目标2)。3)确定小胶质细胞如何重塑突触以响应 神经活动的变化(目标3)。答案将揭示调节感官体验的新机制 调节结构和功能脑图的发展，将确定实现可塑性的新方法 并将为突触如何在多种背景下重塑提供新的机制洞察力 (发育、学习和记忆、疾病等)。

The goal of this proposal is to determine how microglia and sensory experience integrate to remodel synapses into precise, functional brain maps. Trillions of synapses form highly precise topographic maps in the brain representing each part of the body. These maps are shaped and maintained by sensory experience (vision, touch, etc.), including elimination of less active synapses and formation and maintenance of other synapses. Despite over 50 years of research, the underlying mechanisms by which experience dictates removal or maintenance of specific synapses still remains an open question. We made the initial exciting and unexpected observation that microglia, the resident CNS macrophages, engulfed and eliminated a subset of less active synapses in the developing retinogeniculate system. Further, reducing microglia-mediated engulfment of synapses by 50% (complement receptor 3 KO) resulted in sustained increases in retinogeniculate synapse number. This work established a new way of thinking about synaptic remodeling and inspired several important new questions: Is microglia-mediated synaptic remodeling necessary for achieving functional circuits? Do microglia remodel synapses in the adult brain? How does neural activity regulate microglia-mediated synaptic remodeling? The retinogeniculate system was limiting for addressing these questions. We required a robust system for studying synaptic remodeling that involved plasticity of synapses throughout life, tractable assays for measuring function, and a topographic arrangment with high spatial and temporal resolution. The mouse barrel cortex fit all these critera and will enable us to test the hypothesis that experience regulates microglia to shape developing and mature syanpses into functional brain circuits. Our new preliminary data show for the first time that microglia engulf excitatory thalamocortical (TC) synapses in the developing barrel cortex and following sensory deprivation (whisker removal) in the neonate. Further, mice deficient in microglia (colony stimulating factor 1 receptor KO; CSF1R KO) have defects in the development of approriate barrel architecture and TC input elimination following whisker deprivation is completely blocked in mice deficient in a microglia-specific chemokine receptor (fractalkine receptor KO, CX3CR1 KO). We will now use a combination of high resolution static and functional imaging and molecular biology in the mouse barrel cortex to: 1) Determine whether microglia sculpt developing cortical circuits into functional brain maps (Aim 1). 2) Determine whether microglia regulate experience-dependent plasticity of cortical maps in the neonate and adult (Aim 2). 3) Identify how microglia remodel synapses in response to changes in neural activity (Aim 3). Answers will uncover new mechanisms regulating how sensory experience regulates the development of structural and functional brain maps, will identify new ways to achieve plasticity in the adult brain, and will provide new mechanistic insight into how synapses remodel in multiple contexts (development, learning and memory, disease, etc.).