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

描述(申请人提供)：神经科学中的一个主要挑战是了解神经元网络是如何通过经验修改的，以及蛋白质/基因如何对电路修改做出贡献。神经回路在发育过程中通过依赖活动的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是必不可少的，例如长时程增强(LTP)和抑制(LTD)。识别这些形式可塑性背后的分子的努力已经揭示了一组针对兴奋性突触的基因。其中，Arc与神经元回路中信息的行为编码联系最紧密。ARC通过直接与内吞机制相互作用，对表面AMPA型谷氨酸受体(AMPAR)进行稳态调节。然而，人们对Arc在神经元回路水平上的功能或其在体内调节信息存储的确切作用知之甚少。视觉皮层是探索这些问题的理想准备，因为视觉体验可以被调节来诱导神经元活动的总体变化。这项提议的总体目标是研究Arc在改变神经回路以响应视觉经验方面所起作用的机制，以及这些过程在神经障碍中是如何被破坏的。在以前的实验中，我们发现Arc在小鼠视皮层(V1)的经验依赖性可塑性中起着重要作用。Arc基因敲除的小鼠表现出眼睛优势可塑性的缺陷，以及一种新发现的依赖经验的可塑性，刺激特异性反应增强。我们还发现了一个经验和弧形依赖成分来建立对侧与同侧的比率。Arc是如何调节视皮层的经验依赖性可塑性的？目标1的目的是利用V1脑片的脑片电生理学研究这些表型的机制，并研究Arc在三种不同类型的突触可塑性中的作用：LTD，LTP和突触伸缩。体内电生理学为评估依赖经验的可塑性提供了强有力的工具，但很难识别单个细胞的特定网络。目标2的目标是利用体内的双光子钙成像在单细胞水平上研究Arc在经验依赖性可塑性中的作用，该成像可以空间精确地测量多个细胞中的神经元活动。Aim 3将直接测试Arc是否通过其在AMPAR贩运中的作用来调节可塑性。最后，Aim 4打算测试Arc水平对正常突触动态平衡至关重要，以及Arc水平异常导致神经疾病中观察到的突触功能障碍的想法，包括阿尔茨海默病、脆性X综合征和Angelman综合征。 与公共健康相关：这项提议的总体目标是在分子和细胞水平上了解体验如何塑造和修改大脑。我们将研究活动依赖基因Arc在小鼠视皮层突触和经验依赖信息存储中的作用。我们还将测试这一假设，即正常的Arc水平对大脑功能至关重要，并且Arc表达的异常调节导致在神经疾病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.