Modeling of Calcium Dynamics in Spines

这个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)和长时抑制(LTD)的配对方案中涉及的关键时间窗口。这需要对树突棘中的树突状钙动力学进行详细的分析，并对神经活动启动的钙离子介导的信号转导通路进行研究。该模型将利用本提案中其他项目的实验数据，这些数据涉及脊柱的结构和重要分子的位置(项目2：Weinberg)、钙离子流入后在脊柱中发生的生化反应(项目3：Kennedy)以及使用双光子显微镜直接测量钙动力学(项目4：Svoboda)。这些测量值将被合并到蒙特卡洛的Mceli中 一种计算机程序，通过跟踪可扩散分子之间的随机行走和相互作用来模拟亚细胞信号。三个具体目标将同时实现。首先，我们将重建一个体积为5_MX、5_m、5_m的小鼠海马区CA1区神经纤维，作为模拟的解剖基础。这将使神经递质在细胞外空间的释放和扩散的模拟得以准确建模。其次，我们将使用该模型来估计小功能微域中的[Ca2+]， 比如突触后的密度。由于重建可能包含大约100个形状和大小不同的脊椎，我们还将获得系统中的可变性估计。该模型将能够测量钙调素(CAM)在EPSP和/或动作电位发生时的激活情况，然后允许激活的CaM与CaMKII结合并激活CaMKII。第三，我们将从理论上检查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。我们将开发一种对随机模型的解析近似来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 一段树突与树突棘和PSD的简化模型中的谷氨酸能突触。由于这种信号转导级联意味着多个可扩散物种之间的相互作用，因此在核心设施1中提出的Mcell的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.