Diffusion of Substances Through the Brain

描述（由申请人提供）：这项工作的长期目标是了解物质如何在脑细胞外空间（ECS）中扩散。ECS是大脑中一个细胞与另一个细胞之间的狭窄间隙（约30 - 50纳米）。这个间隙包含一种类似脑脊液的溶液和由复杂的长链碳水化合物分子组成的细胞外基质。这个项目的重点是细胞外基质在阻碍和模式扩散中的作用。这项工作的主要工具将是使用MCell软件进行蒙特卡罗模拟，并将通过使用综合光学成像（IOI）方法测量大鼠脑切片的细胞外扩散的实验来支持。该项目有三个目标。第一个目的是确定由排列的纤维束引起的各向异性扩散的细胞外成分的来源。这种束在磁共振扩散张量成像技术中起着重要的作用。探测离子四甲基铵的细胞外扩散的测量已经在胼胝体和小脑分子层的三个轴上进行过。这些测量结果揭示了两个地区成分值的悖论，表明几何和扩散之间的关系比迄今为止所假设的更为复杂。由实验支持的模型将决定细胞外基质和几何因素在解释差异中的作用。第二个目标将确定生长因子的扩散是如何通过与细胞外基质结合而改变的。生长因子是一种内源性蛋白质，是促进成人脑细胞可塑性的有效药物，在发育过程中是必不可少的。它们在ECS中扩散，并作为治疗帕金森氏症和其他慢性疾病的药物进行试验。细胞外基质结合生长因子，并可能作为它们的局部存储位点，这些过程被ECS几何结构的扩散特性所改变，然而对这些过程的定量理解很少。用FGF-2生长因子进行建模和实验将确定结合和扩散的组合以及解释观测数据的几何参数。第三个目标是提高IOI方法的分辨率，IOI方法是基于对扩散的分子云进行成像，这些分子云通过事先附着荧光染料而可见。目前，分子的来源是通过从微移液管中注入少量的压力来实现的，但在这个项目中，将开发一种高度控制的离子渗透源来释放分子。在某些情况下，光散射可能会限制IOI的分辨率，对此将制定一个修正。

DESCRIPTION (provided by applicant): The long term goal of this work is to understand how substances diffuse in the brain extracellular space (ECS). The ECS is the narrow gap (about 30 - 50 nm) that separates one cell from another in brain. This gap contains a solution that resembles cerebrospinal fluid and an extracellular matrix made up of complex long chain carbohydrate molecules. This project focuses on the role of the extracellular matrix in hindering and patterning diffusion. The major tool for this work will be Monte Carlo simulation using the MCell software and this will be supported by experiments using the integrative optical imaging (IOI) method to measure extracellular diffusion in rat brain slices. The project has three Aims. The first Aim is to determine the origin of the extracellular components of anisotropic diffusion arising from aligned fiber bundles. Such bundles play a major role in the magnetic resonance technique of diffusion tensor imaging. Measurements of the extracellular diffusion of the probe ion tetramethylammonium have been made previously in three axes in both corpus callosum and in the molecular layer of the cerebellum. These measurements reveal paradoxes in the component values in both regions that suggest a more complex relation between geometry and diffusion than hitherto assumed. Modeling supported by experiments will determine the role of extracellular matrix and geometrical factors in accounting for the discrepancies. The second Aim will determine how the diffusion of growth factors is modified by binding to extracellular matrix. Growth factors are endogenous proteins that are potent agents that promote brain cell plasticity in adults and are essential during development. They diffuse in the ECS and are being trialed as therapeutic agents to relieve Parkinson's Diseases and other chronic illnesses. The extracellular matrix binds growth factors and may act as a local storage site for them and these processes are modified by the diffusion properties of the ECS geometry, however there is little quantitative understanding of these processes. Modeling and experiments with the FGF-2 growth factor will determine combinations of binding and diffusion and geometric parameters that will account for observed data. The third Aim is to improve the resolution of the IOI method which is based on imaging a cloud of diffusing molecules that are made visible by prior attachment of a fluorescent dye. Presently, the source of molecules is achieved by pressure injecting a small amount from a micropipette but in this project a highly controlled iontophoretic source will be developed to release the molecules. In some conditions, light scattering may limit the resolution of IOI and a correction for this will be formulated. PUBLIC HEALTH RELEVANCE: This project focuses on the role of the extracellular matrix (an entanglement of long complex molecules) in hindering diffusion of substances, including potential drugs, as they move in the narrow spaces between brain cells. Diffusion studies in fiber-rich brain regions will improve the basis for the magnetic resonance technique of diffusion tensor imaging (DTI) and investigations on the diffusion and binding of growth factors will facilitate therapeutic delivery to the brain. Development of an imaging technique for fluorescent molecules will provide a relatively inexpensive method for measuring diffusion of drugs in brain tissue.