Diffusion of Substances Through the Brain

描述(申请人提供)：长期目标是了解物质在脑细胞外空间(ECS)扩散的生物物理学。在生物医学方面，这一建议将加强对药物在大脑中传递的障碍以及影响ECS中化学信号的因素的了解。ECS由脑细胞之间狭窄的间隙组成，并含有由长链糖基化分子组成的细胞外基质(ECM)。ECS中扩散的阻碍由一个复合参数曲折来表征，该参数包括a)几何路径长度的增加，b)死隙微区，c)阻碍和间隙粘度，d)与ECM的特异性结合和e)与ECM上固定负电荷的非特异性相互作用。这些因素将通过在体内和脑切片中使用荧光大分子的集成光学成像结合四甲基铵和其他离子的实时离子导入来探索物质的扩散。 目标1：可以穿越ECS的最大分子或粒子是什么？初步实验表明，直径为40 nm的大分子可以在体内扩散。进一步的分子大小范围将在正常和渗透修饰的ECS中进行探索。 目标2：特定的ECM结合在多大程度上阻碍了生物重要分子的扩散？自然产生的模型蛋白乳铁蛋白的扩散将检测与ECM的硫酸乙酰肝素蛋白多糖的特异性结合。 目标3：ECS中是否存在收费歧视？这一目标将研究扩散的单价和多价离子以及生物胺与ECM的固定负电荷之间的非特异性相互作用。 目的4：模拟死区微区、结合和电荷相互作用及统一软件。将开发用于数据分析的模型和算法，并统一定制软件，以方便外部用户

DESCRIPTION (provided by applicant): The long-term goal is to understand the biophysics of substance diffusion in brain extracellular space (ECS). Biomedically, this proposal will enhance understanding of impediments to drug delivery in brain and factors that affect chemical signaling in the ECS. The ECS comprises the ensemble of narrow interstitial spaces between brain cells and harbors an extracellular matrix (ECM) of long chain glycosylated molecules. Hindrance to diffusion in the ECS is characterized by a composite parameter, the tortuosity, that includes a) increase in geometric path-length, b) dead-space microdomains, c) obstruction and interstitial viscosity, d) specific binding to ECM and e) nonspecific interaction with fixed negative charges on the ECM. These factors will be explored through the diffusion of substances using integrative optical imaging of fluorescent macromolecules combined with realtime iontophoresis of tetramethylammonium and other ions both in vivo and in brain slices. Aim 1: What is the largest molecule or particle that can traverse the ECS? Preliminary experiments show that macromolecules with 40 nm diameter can diffuse in vivo. A further range of molecular sizes will be explored in normal and osmotically modified ECS. Aim 2: How much does specific ECM binding hinder diffusion of biologically important molecules? Diffusion of the naturally occurring model protein, lactoferrin, will assay specific binding with heparan sulfate proteoglycans of the ECM. Aim 3: Is there charge discrimination in the ECS? This aim will study the non-specific interaction of diffusing mono- and multivalent ions and biogenic amines with the fixed negative charges of the ECM. Aim 4: Model dead-space microdomains, binding and charge interaction and unify software. Models and algorithms for data analysis will be developed and the custom software unified to facilitate outside users