Synaptic Homeostasis in Neocortical Neurons and Circuits

 描述(由申请人提供)：稳态突触伸缩是一种重要的可塑性形式，被认为是维持神经回路发育中稳定功能所必需的。突触伸缩将神经元的所有兴奋性突触强度沿正确的方向向上或向下“缩放”，以稳定神经元的放电率。突触重量的这些稳态调节在很大程度上是通过含有GluA2的AMPAR在突触上的突触积累的变化来完成的，并且似乎是对给定神经元上的所有兴奋性突触输入进行操作，以响应神经元自身放电的变化。尽管最近引起了人们的极大兴趣，但在突触伸缩过程中实现AMPAR丰度的动态平衡调节的分子和生物物理机制仍然知之甚少，而且这种突触伸缩模型背后的许多假设(如其全球性)在很大程度上仍未得到检验。在这项提议中，我们旨在阐明在放大过程中导致突触AMPAR丰度增加的机制，并测试这种形式的可塑性作用于所有兴奋性输入以稳定体内神经元放电的想法。这一建议是基于或最近的观察结果，即AMPAR结合蛋白GRIP1对于在放大过程中突触AMPAR丰度的调节增加是必不可少的，并且这一过程需要GRIP1和GluA2之间的直接相互作用。在这里，我们建议通过使用各种尖端成像方法来确定(在生物物理水平上)GluA2-GRIP1之间的这种受调控的相互作用如何导致突触AMPAR丰度的增加。我们将测试两种替代模型：第一，GRIP1与AMPAR一起与突触通信，并增强突触对受体的捕获；第二，GRIP1增强对突触支架具有增强亲和力的修饰AMPAR的突触递送。此外，我们将使用我们通过这些体外研究产生的工具来选择性地干扰在体内突触放大过程中的AMPAR运输，以探索在完整的新皮质环路中突触放大的机制和功能。

 DESCRIPTION (provided by applicant): Homeostatic synaptic scaling is an important form of plasticity thought to be essential for maintaining stable function in developing neural circuits. Synaptic scaling "scales" the strength of all of a neuron's excitatory synaptic strengths up or down in the correct direction to stabilize neuronal firing rates. These homeostatic adjustments in synaptic weights are accomplished in large part through changes in the synaptic accumulation of GluA2-containing AMPAR at synapses, and appear to operate on all excitatory synaptic inputs onto a given neuron in response to changes in the neuron's own firing. Despite great recent interest, the molecular and biophysical mechanisms that enable this homeostatic adjustment of AMPAR abundance during synaptic scaling are still poorly understood, and many of the assumptions underlying this model of synaptic scaling (such as its global nature) remain largely untested. In this proposal we aim to illuminate the mechanisms that lead to enhanced synaptic AMPAR abundance during scaling up, and to test the idea that this form of plasticity acts on all excitatory inputs to stabilize neuronal firing in vivo. This proposal is built around or recent observation that the AMPAR-binding protein GRIP1 is essential for the regulated increase in synaptic AMPAR abundance during scaling up, and that this process requires direct interactions between GRIP1 and GluA2. Here we proposed to determine how (at the biophysical level) this regulated interaction between GluA2-GRIP1 drives an increase in synaptic AMPAR abundance, by using a variety of cutting edge imaging approaches. We will test two alternative models: first, that GRIP1 traffics to synapses along with AMPAR and enhances synaptic capture of the receptor, and second, that GRIP1 enhances synaptic delivery of modified AMPAR that have an enhanced affinity for synaptic scaffolds. Further, we will use the tools we have generated through these in vitro studies to selectively disrupt AMPAR trafficking during synaptic scaling up in vivo, in order to probe the mechanism and function of synaptic scaling within intact neocortical circuits.