Diffusion of Substances Through the Brain

描述（由申请人提供）：长期目标是了解脑细胞外空间（ECS）物质扩散的生物物理学。在生物医学上，这一建议将加强对药物在大脑中的传递障碍和影响ECS化学信号的因素的理解。ECS包括脑细胞间狭窄间隙的集合，并包含长链糖基化分子的细胞外基质（ECM）。ECS中的扩散障碍由复合参数扭曲度表征，包括a)几何路径长度的增加，b)死区微域，c)阻塞和间隙粘度，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。这些因素将通过荧光大分子的综合光学成像结合四甲基铵和其他离子在体内和脑切片中的实时离子电泳来探索物质的扩散。

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