Prokopová S, Vargová L, Syková E
Department of Neuroscience, Institute of Experimental Medicine AS CR, Prague, Czech Republic.
Neuroreport. 1997 Nov 10;8(16):3527-32. doi: 10.1097/00001756-199711100-00022.
Extrasynaptic transmission is mediated by the diffusion of transmitters, through the extracellular space (ECS) to receptors on neurons and glia. The three-dimensional diffusion of tetramethylammonium (mol. wt 74.1 kDa) was investigated in the isolated rat spinal cord at postnatal days 4-20. The diffusion parameters of the ECS, volume fraction alpha, tortuosity lambda (lambda2 = free/apparent diffusion coefficient in tissue) and nonspecific uptake k', were different in gray and white matter. In both gray and white matter, alpha decreased with neuronal development and gliogenesis by about 15% while lambda significantly increased. Diffusion in gray matter remained isotropic (lambda = 1.65), while in white matter it became anisotropic, i.e. easier along the fibers (lambda = 1.38) than across the fibers (lambda = 1.80). Anisotropy increased in the second postnatal week, during pronounced myelination. In myelinated tissue, preferential diffusion of neuroactive substances occurs along the axons.
突触外传递是由递质通过细胞外空间（ECS）扩散至神经元和神经胶质细胞上的受体介导的。在出生后4 - 20天的离体大鼠脊髓中研究了四甲基铵（分子量74.1 kDa）的三维扩散。ECS的扩散参数，体积分数α、曲折度λ（λ2 = 组织中自由/表观扩散系数）和非特异性摄取k'，在灰质和白质中有所不同。在灰质和白质中，α随着神经元发育和神经胶质生成而降低约15%，而λ显著增加。灰质中的扩散保持各向同性（λ = 1.65），而白质中的扩散变为各向异性，即沿纤维方向（λ = 1.38）比跨纤维方向（λ = 1.80）更容易。在出生后第二周明显髓鞘形成期间，各向异性增加。在有髓组织中，神经活性物质沿轴突优先扩散。
