Diffusion of flexible random-coil dextran polymers measured in anisotropic brain extracellular space by integrative optical imaging.
Diffusion of flexible random-coil dextran polymers measured in anisotropic brain extracellular space by integrative optical imaging.
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DOI：
10.1529/biophysj.107.124743
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发表时间：
2008-08
影响因子：
3.4
通讯作者：
F. Xiao;C. Nicholson;J. Hrabe;S. Hrabetova
中科院分区：
文献类型：
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作者：
F. Xiao;C. Nicholson;J. Hrabe;S. Hrabetova
有有限数量的方法可用于量化各向异性脑区域中大分子的细胞外扩散，例如，一个包含许多排列的纤维的区域，其中沿纤维的扩散沿着比跨纤维的扩散快。我们应用集成光学成像方法来测量荧光团Alexa Fluor 488的扩散（分子量（MW）547）和荧光团标记的柔性无规卷曲葡聚糖聚合物（dex3，MW 3000; dex75，MW 75，000; dex282，MW 282，000; dex 525，MW 525，000）在分离的龟小脑的各向异性分子层的细胞外间隙（ECS）中。对于所有的分子，二维图像获得了一个椭圆形的长轴和短轴取向沿着和跨，分别无髓平行纤维。有效扩散系数，D*（主要）和D*（次要），随着分子尺寸的减小。对于Alexa Fluor 488至dex 75，扩散各向异性比（DAR = D*（主要）/D*（次要））增加，但随后意外地达到平台。我们认为，dex 282和dex 525接近ECS的宽度和变形扩散。为了支持这一概念，标度理论表明dex 282和dex 525的扩散行为与向爬行状态的转变一致，并估计平均ECS宽度约为31 nm。这些发现对分子和药物的间质转运以及异位释放和溢出过程中神经递质扩散的建模具有重要意义。
There are a limited number of methods available to quantify the extracellular diffusion of macromolecules in an anisotropic brain region, e.g., an area containing numerous aligned fibers where diffusion is faster along the fibers than across. We applied the integrative optical imaging method to measure diffusion of the fluorophore Alexa Fluor 488 (molecular weight (MW) 547) and fluorophore-labeled flexible random-coil dextran polymers (dex3, MW 3000; dex75, MW 75,000; dex282, MW 282,000; dex525, MW 525,000) in the extracellular space (ECS) of the anisotropic molecular layer of the isolated turtle cerebellum. For all molecules, two-dimensional images acquired an elliptical shape with major and minor axes oriented along and across, respectively, the unmyelinated parallel fibers. The effective diffusion coefficients, D*(major) and D*(minor), decreased with molecular size. The diffusion anisotropy ratio (DAR = D*(major)/D*(minor)) increased for Alexa Fluor 488 through dex75 but then unexpectedly reached a plateau. We argue that dex282 and dex525 approach the ECS width and deform to diffuse. In support of this concept, scaling theory shows the diffusion behavior of dex282 and dex525 to be consistent with transition to a reptation regime, and estimates the average ECS width at approximately 31 nm. These findings have implications for the interstitial transport of molecules and drugs, and for modeling neurotransmitter diffusion during ectopic release and spillover.