Diffusion of Substances Through the Brain

描述(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)扩散。ECS是大脑中将一个细胞与另一个细胞分开的狭窄缝隙(约30-50 nm)。这个缝隙包含一种类似脑脊液的溶液和一种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图案化扩散中的作用。这项工作的主要工具将是使用Mcell软件的蒙特卡罗模拟，这将得到使用集成光学成像(IOI)方法测量大鼠脑片细胞外扩散的实验的支持。该项目有三个目标。第一个目标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。这种束在扩散张量成像的磁共振技术中起着重要作用。探针离子四甲基铵在细胞外扩散的测量已经在三个轴上进行过，分别在胼胝体和小脑的分子层。这些测量揭示了这两个地区的分量值之间的悖论，这表明几何形状和扩散之间的关系比迄今所认为的更复杂。由实验支持的建模将确定细胞外基质和几何因素在解释差异中的作用。第二个目标将决定如何通过与细胞外基质结合来改变生长因子的扩散。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力因素，在发育过程中至关重要。它们弥漫在ECS中，正在作为治疗药物进行试验，以缓解帕金森氏症和其他慢性病。细胞外基质与生长因子结合，并可作为生长因子的局部储存场所，这些过程被ECS几何结构的扩散性质所改变，但对这些过程的定量了解很少。对成纤维细胞生长因子-2的建模和实验将确定结合、扩散和几何参数的组合，这些参数将解释观察数据。第三个目标是提高IOI方法的分辨率，该方法基于对扩散分子云的成像，这些分子云通过先前附着的荧光染料而变得可见。目前，分子的来源是通过压力从微管注入少量的分子来实现的，但在这个项目中，将开发一种高度受控的离子导入源来释放分子。在某些情况下，光散射可能会限制IOI的分辨率，并将对此进行修正。 与公共健康相关：该项目重点关注细胞外基质(一种长的复杂分子的缠结)在阻止物质(包括潜在药物)在脑细胞之间狭窄空间中移动时的扩散所起的作用。对富含纤维的脑区的扩散研究将改善扩散张量成像(DTI)磁共振技术的基础，研究生长因子的扩散和结合将有助于将治疗药物输送到大脑。荧光分子成像技术的发展将为测量药物在脑组织中的扩散提供一种相对廉价的方法。

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.