Role of Arc in synaptic/experience-dependent plasticity in mouse visual cortex

描述（由申请人提供）：神经科学的一个主要挑战是了解神经网络如何通过经验被修改，以及蛋白质/基因如何参与电路修改。神经回路在发育过程中通过活性依赖基因和蛋白质的表达而得到完善。类似的大分子合成对于长期形式的突触可塑性如长期增强（LTP）和抑制（LTD）是必不可少的。对这些形式的可塑性的分子的鉴定已经揭示了一组以兴奋性突触为目标的基因。其中，Arc与神经元回路中信息的行为编码联系最为紧密。Arc通过直接与内吞机制相互作用调节表面AMPA型谷氨酸受体（AMPARs）。然而，关于Arc在神经元回路水平上的功能，以及它在体内介导信息存储中的确切作用，我们知之甚少。视觉皮层是探索这些问题的理想准备，因为视觉经验可以被调节以诱导神经元活动的总体变化。本提案的总体目标是研究Arc在改变神经回路以响应视觉体验中的作用以及这些过程如何在神经系统疾病中被破坏的机制。在以往的实验中，我们发现Arc在小鼠视觉皮层（V1）的经验依赖可塑性中起着至关重要的作用。Arc敲除小鼠在眼优势可塑性和新发现的经验依赖可塑性，刺激特异性反应增强方面表现出缺陷。我们还发现了一个经验和弧依赖组件来建立对侧与同侧的比例。Arc如何调节视觉皮层中经验依赖的可塑性？目的1是利用V1皮层切片电生理学研究这些表型的机制，并研究Arc在3种不同类型的突触可塑性中的作用；LTD， LTP和突触尺度。体内电生理学为评估经验依赖的可塑性提供了一个强大的工具，但很难识别单个细胞的特定网络。目的2是利用体内双光子钙成像技术，在单细胞水平上研究Arc在经验依赖可塑性中的作用，该技术可以以空间精度测量许多细胞中的神经元活动。Aim 3将直接测试Arc是否通过其在AMPAR贩运中的作用介导可塑性。最后，目的4旨在验证Arc水平对正常突触稳态至关重要的观点，以及异常的Arc水平导致神经系统疾病（包括阿尔茨海默病、脆性X和Angelman综合征）中观察到的突触功能障碍。

DESCRIPTION (provided by applicant): A major challenge in neuroscience is to understand how neuronal networks are modified through experience and how proteins/genes contribute to circuit modification. Neural circuits are refined during development through activity-dependent gene and protein expression. Similar macromolecular synthesis is essential for long-term forms of synaptic plasticity such as long-term potentiation (LTP) and depression (LTD). Efforts to identify molecules that underlie these forms of plasticity have revealed a set of genes that target to excitatory synapses. Among these, Arc is the most tightly coupled to behavioral encoding of information in neuronal circuits. Arc homeostatically regulates surface AMPA type glutamate receptors (AMPARs) by directly interacting with the endocytic machinery. However, very little is known about Arc's function at the level of neuronal circuits or its precise in vivo role in mediating information storage. The visual cortex is an ideal preparation to probe these questions as visual experience can be modulated to induce gross changes in neuronal activity. The overall goal of this proposal is to investigate the mechanisms that underlie Arc's role in modifying neural circuits in response to visual experience and how these processes are disrupted in neurological disorders. In previous experiments, we find that Arc plays a fundamental role in experience- dependent plasticity in mouse visual cortex (V1). Arc knocks out mice exhibit deficits in ocular dominance plasticity and in a newly discovered form of experience-dependent plasticity, stimulus-specific response potentiation. We also uncover an experience and Arc-dependent component to establishing the contralateral to ipsilateral ratio. How does Arc regulate experience-dependent plasticity in the visual cortex? The goal of aim 1 is to investigate the mechanisms underlying these phenotypes by utilizing slice electrophysiology in V1 cortical slices and investigating the role of Arc in 3 different types of synaptic plasticity; LTD, LTP and synaptic scaling. In vivo electrophysiology provides a powerful tool to assess experience-dependent plasticity, but it is difficult to identify specific networks of individual cells. The goal of aim 2 is to investigate the role of Arc in experience- dependent plasticity at the single cell level using 2-photon calcium imaging in vivo, which can measure neuronal activity in many cells with spatial precision. Aim 3 will directly test whether Arc mediates plasticity through its role in AMPAR trafficking. Finally, aim 4 intends to test the idea that Arc levels are critical for normal synaptic homeostasis and that abnormal Arc levels contribute to the synaptic dysfunction observed in neurological disorders, including Alzheimer's disease, Fragile X and Angelman Syndromes. PUBLIC HEALTH RELEVANCE: The overall goal of this proposal is to understand, at the molecular and cellular level, how experience shapes and modifies the brain. We will investigate the role of the activity-dependent gene Arc in synaptic and experience-dependent information storage in mouse visual cortex. We will also test the hypothesis that normal Arc levels are critical for brain function and that abnormal regulation of Arc expression contributes to the synaptic dysfunction observed in neurological disorders.