Imaging visual plasticity in vivo

描述(申请人提供)：在发育过程中通过视觉经验重建皮质网络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致专一性回避了它们是如何实现的问题。令人惊讶的是，我们最近表明，小胶质细胞，即来自骨髓的神经免疫细胞，可能在这一过程中起着关键作用。传统上，小胶质细胞被认为是唯一的免疫功能，在健康的大脑中以静止状态存在。相反，我们假设小胶质细胞是大脑回路的组成部分，对正常的大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(经常监视突触裂隙)，并且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、弱的和暂时性的结构，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-突触相互作用的改变，同时小胶质细胞吞噬作用显著增加，吞噬细胞包涵体包含非常类似突触的结构。重要的是，我们的初步数据显示，在活体中，视皮层小胶质功能的破坏会减弱视觉驱动的可塑性。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其结构，而且实际上通过吞噬过程移除不需要的突触，所有这些都是以活动依赖的方式进行的，这是可塑性的重要部分。这些结果是诱人的，并引入了一种新的思维方式，即视觉皮质中活动驱动的可塑性机制，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)。我们还将探索一个可能的分子信号的作用，该信号可以将突触的活动与定向的小胶质细胞-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在功能可塑性和突触重塑中的作用，方法是将小胶质细胞从视皮层中迅速消除，并改变小胶质细胞-突触通讯通路(Aim3)。这些目标的成功完成将决定突触与小胶质细胞相互作用的分子机制，并建立神经可塑性基础上的小胶质细胞功能。由于许多神经发育和神经退行性疾病的特征是突触丢失和神经炎症(小胶质细胞激活)，实现这些目标不仅将为脑可塑性提供新的机制见解，还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.