Imaging visual plasticity in vivo

描述（由申请人提供）：在发育过程中，视觉经验对皮层网络的重塑依赖于突触结构和功能的快速变化。这些活动驱动的突触变化的精细特异性回避了它们是如何实现的问题。令人惊讶的是，我们最近发现，来自骨髓的神经免疫细胞小胶质细胞可能在这一过程中起关键作用。传统上，小胶质细胞被认为只具有免疫功能，在健康的大脑中处于静止状态。相反，我们假设小胶质细胞是脑回路的一个组成部分，对正常的脑功能和可塑性起着至关重要的作用。事实上，在过去的两年里，我们已经证明了小胶质细胞动态地接触突触元件（经常监测突触间隙），这些小胶质细胞的接触导致突触结构的改变，这一现象与突触强度的变化有关。更令人惊讶的是，小胶质细胞区分不同的突触类型，并优先接触小的、弱的和短暂的结构，这表明小胶质细胞和突触之间的相互作用具有显著的特异性。此外，视觉剥夺导致这些小胶质细胞-突触相互作用的变化，同时小胶质细胞吞噬作用显著增加，吞噬包涵体包含与突触非常相似的结构。重要的是，我们的初步数据表明，视觉皮层中小胶质细胞功能的破坏会减弱体内视觉驱动的可塑性。因此，我们的数据表明，小胶质细胞不仅针对突触亚型并改变它们的结构，它们实际上通过吞噬过程去除不需要的突触，所有这些都是以活动依赖的方式进行的，这是可塑性的重要组成部分。这些结果是诱人的，并引入了一种新的方式来思考活动驱动的可塑性在视觉皮层的机制，也可能延伸到其他大脑区域和功能。在这个更新应用中，我们将研究突触活动如何影响小胶质细胞-突触相互作用（Aim1）。我们还将探讨一个假定的分子信号的作用，该信号可以将突触活动与定向小胶质细胞突触相互作用（Aim2）联系起来。最后，我们将直接分析小胶质细胞对功能可塑性和突触重塑的贡献，通过从视觉皮层中急性清除小胶质细胞，以及通过改变参与小胶质细胞-突触通信的小胶质细胞通路（Aim3）。这些目标的成功完成将确定突触与小胶质细胞相互作用的分子机制，并确定小胶质细胞在神经可塑性基础上的功能。由于许多神经发育和神经退行性疾病的特征是突触丧失和神经炎症（小胶质细胞激活），完成这些目标不仅将为大脑可塑性提供新的机制见解，而且可能为此类疾病的治疗途径的发展提供信息。

DESCRIPTION (provided by applicant): Remodeling of cortical networks by visual experience during development relies on rapid changes in synaptic structure and function. The exquisite specificity of these activity-driven synaptic changes begs the question of how they are implemented. Surprisingly we have recently shown that microglia, neuroimmune cells derived from bone marrow, may be critical in this process. Traditionally, microglia are considered to serve an exclusively immune function and exist in a quiescent state in the healthy brain. Instead, we posit that microglia are an integral part of brain circuitry and contribute critically o normal brain function and plasticity. Indeed, over the past two years we have shown that microglia dynamically contact synaptic elements (frequently surveilling the synaptic cleft), and that these microglial contacts result in alterations of synapse structure, a phenomenon linked to changes in synapse strength. Even more surprisingly, microglia discriminate different synaptic types and preferentially contact small, weak and transient structures, showing that interactions between microglia and synapses have remarkable specificity. Furthermore, visual deprivation leads to changes in these microglia- synapse interactions along with a striking increase in microglial phagocytosis, and phagocytic inclusions contain structures that strongly resemble synapses. Importantly, our preliminary data show that disruption of microglial function in the visual cortex attenuates visually-driven plasticity in vivo. Thus, our data suggest that microglia not only target synaptic subtypes and alter their structure, they actually remove unwanted synapses through a phagocytic process, all in an activity-dependent manner, and that this is a vital part of plasticity. These results are tantalizing and introduce a new way of thinking about mechanisms of activity-driven plasticity in the visual cortex that may also extend to other brain regions and functions. In this renewal application, we will examine how synaptic activity influences microglia-synapse interactions (Aim1). We will also explore the role of a putative molecular signal that could link activity at synapses with directed microglia-synapse interactions (Aim2). Lastly we will directly assay the contribution of microglia to functional plasticity and synaptic remodeling by acutely eliminating microglia from the visual cortex, as well as by altering microglial pathways involved in microglia-synapse communication (Aim3). The successful completion of these aims will determine the molecular mechanisms by which synapses interact with microglia, and establish microglial functions underlying neural plasticity. Because many neurodevelopmental and neurodegenerative disorders are characterized by synapse loss and neuroinflammation (microglial activation), accomplishing these aims will not only provide new mechanistic insights into brain plasticity but may also inform the development of treatment avenues for such diseases.