Modeling of Calcium Dynamics in Spines

该项目的长期目标是开发一个模型来解释用于诱导长时程增强（LTP）和长时程抑制（LTD）的配对协议中涉及的关键时间窗口。这将需要详细分析树突棘中的树突状Ca 2+动力学，并调查由神经活动引发的Ca 2+介导的信号转导级联。该模型将利用本提案中其他项目的实验数据，包括脊柱结构和重要分子的位置（项目2：温伯格）、Ca 2+流入后脊柱中发生的生化反应（项目3：肯尼迪）以及使用双光子显微镜直接测量Ca 2+动力学（项目4：Svoboda）。这些测量结果将被纳入MCel I，一个蒙特卡罗 一种计算机程序，通过跟踪可扩散分子之间的随机游走和相互作用来模拟亚细胞信号。将同时实现三个具体目标。第一个是5mx5m？5 μ m体积的小鼠海马CA1区神经元作为模拟的解剖基底。这将允许精确地模拟细胞外空间中的神经递质释放和扩散。其次，我们将使用该模型来估计小功能微区中的[Ca 2+]， 例如在突触后密度中。由于重建可能包含大约100个不同形状和大小的脊柱，我们还将获得系统中可变性的估计。该模型将能够测量在EPSP、动作电位或两者以时间偏移发生后钙调蛋白（CAM）的激活，然后允许激活的CaM结合并激活CaMKII。第三，我们将从理论上研究MCell实施的随机方案预计会产生多大的可变性，以确定需要多少次模拟运行才能获得准确的估计。我们将开发一个分析近似的随机模型，以确定系统动力学的统计分布。在初步研究中，我们使用计算机模拟受体激活和钙动力学， 树突棘和PSD的一段树突的简化模型中的突触。由于这种信号转导级联意味着多个可扩散物质之间的相互作用，因此核心设施1中提出的MCell新建模能力是该项目的先决条件。

The long-term goal of this project is to develop a model to explain the critical time window involved in the pairing protocol used for the induction of long-term potentiation (LTP) and long-term depression (LTD). This will require a detailed analysis of dendritic Ca 2+ dynamics in dendritic spines and an investigation of the Ca2+-mediated signal transduction cascades initiated by neural activity. The model will draw on experimental data from the other projects in this proposal on the structure of the spine and the location of important molecules (Project 2: Weinberg), the biochemical reactions that occur in the spine following the influx of Ca 2+ (Project 3: Kennedy) and the direct measurements of Ca 2+ dynamics using 2-photon microscopy (Project 4: Svoboda). These measurements will be incorporated into MCelI, a Monte Carlo computer program that simulates subcellular signaling by following the random walk and interactions between diffusible molecules. Three specific aims will be pursued in parallel. First a 5 _mx 5 _m ? 5 _m volume of hippocampal area CA1 neuropil from mouse will be reconstructed to serve as the anatomical substrate of the simulations. This will allow simulations of neurotransmitter release and diffusion in the extracellular space to be accurately modeled. Second, we will use the model to estimate [Ca 2+] in small functional microdomains, such as in the postsynaptic density. Since the reconstruction will likely contain around 100 spines of varying shapes and sizes, we will also obtain estimates of variability in the system. The model will be able to measure the activation of calmodulin (CAM) following an EPSP, an action potential, or both occurring with a temporal offset, and to then allow activated CaM to bind to, and activate CaMKII. Third, we will examine theoretically how much variability is expected to result from the stochastic schemes implemented by MCell to determine how many simulation runs will be needed to obtain accurate estimates. We will develop an analytical approximation to the stochastic model to determine the statistical distribution of system dynamics. In preliminary studies, we used computer simulation of receptor activation and calcium dynamics at glutamatergic synapses in a simplified model of a segment of dendrite with dendritic spine and PSD. Since this signal transduction cascade implies interactions between multiple diffusible species, the new modeling capabilities for MCell proposed in Core Facility 1 are prerequisite to this project.