Ionic Cell Signaling in Small Spaces

描述（由申请人提供）：突触神经元之间的通信发生在分子数量较少的小空间中，在未混合的体积中远非平衡。如果没有精确的亚细胞超微结构模型，以及所有相关分子（包括神经递质受体、转运体、结合蛋白、降解酶和其他信号靶标）的位置和动力学速率常数的详细知识，很难估计微域中化学反应的动力学。例如，常见的信号制剂，如钙，根据它们进入细胞的位置和它们的靶标所在的位置，有不同的效果。如果细胞的空间组织是重要的，那么仅仅重建信号转导通路的反应网络是不够的。显然，为了研究和理解这些信号通路的行为，必须获得这些通路的精确三维（3-D）解剖重建；也就是说，将信号通路置于其自然环境中，包括细胞超微结构和生化分子的三维分布。在这里，我们利用MCell蒙特卡罗计算建模程序和神经组织的高分辨率三维重建，我们提出探索突触信号的三个组成部分：1)大鼠海马CA3区锥体细胞突触前钮扣的钙动力学，2)鸟睫状神经节突触后萼状突触配体门控离子通道附近的钙微结构域，3)大鼠小脑皮质肾小球的细胞外谷氨酸动力学。这三个系统的特征足以进行定量建模，并将使我们能够探索钙进入突触前末端后神经递质释放的机制，以及释放位点之间的相互作用，钙进入突触后细胞的影响，以及神经递质在突触间隙中的扩散和细胞外空间中向邻近突触的溢出。由这些mccell模型提供的对这些系统的详细理解将提供可能适用于许多其他突触的新见解，特别是应该有助于阐明信号微域的功能障碍如何导致神经和精神病理。公共卫生相关性：神经元通过突触进行交流，突触前神经元释放的化学物质与突触后神经元上的受体结合，并在离子流过的膜上打开通道。我们将使用一个叫做MCell的计算机模型来研究这个过程的每一个方面，这个模型模拟了突触信号传导过程中每个重要的分子和它们之间的化学相互作用。这些研究将帮助我们了解突触是如何工作的，以及它们在神经和精神病理学中的功能障碍。

DESCRIPTION (provided by applicant): The communication between neurons at synapses occurs in small spaces with small numbers of molecules, far from equilibrium in unmixed volumes. The dynamics of chemical reactions in microdomains is difficult to estimate without having an accurate model of sub-cellular ultrastructure as well as detailed knowledge of the locations and kinetic rate constants of all the relevant molecules, including the neurotransmitter receptors, transporters, binding proteins, degradative enzymes, and other signaling targets. For example, common signaling agents such as calcium have different effects depending on where they enter the cell, and where their targets are located. If the spatial organization of the cell is important, then it is not enough to reconstruct the reaction network of signal transduction pathways. Clearly, to study and understand the behavior of these signaling pathways it is essential to obtain accurate three-dimensional (3-D) anatomical reconstructions of the pathways; that is, to place the signaling pathways within their natural context, which includes the cellular ultrastructure and 3-D distributions of the biochemical molecules. Here, using the MCell Monte Carlo computational modeling program and high-resolution 3-D reconstructions of neural tissue, we propose to explore three components of synaptic signaling: 1) calcium dynamics in the presynaptic boutons from area CA3 pyramidal cells in the rat hippocampus, 2) calcium microdomains in the vicinity of ligand-gated ion channels in postsynaptic calyciform synapses of the avian ciliary ganglion, and 3) extracellular glutamate dynamics in glomeruli from rat cerebellar cortex. These three systems are sufficiently well characterized for quantitative modeling and will allow us to explore the mechanisms underlying the release of neurotransmitter following the entry of calcium into the presynaptic terminal and cross-talk between release sites, the effects of calcium entry into the postsynaptic cell, and the diffusion of neurotransmitter in the synaptic cleft and spillover to neighboring synapses in extracellular space. The detailed level of understanding of these systems afforded by these MCell models will provide new insights that may be applicable to many other synapses, and in particular should help to elucidate how dysfunctions in signaling microdomains may contribute to neurological and psychiatric pathology. PUBLIC HEALTH RELEVANCE: Neurons communicate at synapses, where chemicals released by the presynaptic neuron bind to receptors on the postsynaptic neuron and open channels in the membrane that ions flow through. We will study every aspect of this process using a computer model, called MCell, which simulates every important molecule and chemical interaction between them during synaptic signaling. These studies will help us understand how synapses work and how they dysfunction in neurological and psychiatric pathology.