Water permeabilities of neural cells and capillaries in brain : Using claudin-5 knocked out mice and H-1 MRI

用Claudin-t基因敲除小鼠和H-1MRI分析脑内毛细血管和神经细胞的水通透性。血脑屏障(BBB)的解剖学基础在于脑内皮细胞的紧密连接(TJ)，以及它们有限的跨细胞作用。Claudin-5是脑内皮细胞中主要的TJ细胞黏附分子。用三种松弛试剂(约700Da-17 kDa)测定小鼠神经元/神经胶质细胞和血脑屏障的透水性。正常小鼠的纵向松弛速率(1/T_1)变化很小(~lt；0.1 S)，甚至血液水分的1/T_1加快40 S~(-1)以上。说明正常的BBB具有很低的透水性。在claudin-5基因敲除的小鼠中，Gd-DTPA^&lt；2-gt；可以通过修饰的BBB。根据Gd-DTPA的剂量依赖关系，检测到神经元/神经胶质细胞的水外排速率，相当于弥漫性水分通透性为1.5-1.0 cm S。松弛试剂(大于2 kDa)不能通过改性血脑屏障。根据松弛试剂的剂量依赖关系，检测到BBB的水外排速率对应于适度范围的扩散水渗透性。这些发现为了解血脑屏障的分子生物学提供了新的视角，也代表了该方法在监测转基因动物的生理参数方面的有效性。

The water permeability of capillaries and neural cells in the brain were analyzed by using claudin-t knocked out mice and H-1 MRI. The anatomic basis for blood-brain barrier (BBB) resides in tight junctions (TJs) of brain endothelial cells in addition to their limited transcytosis. The claudin-5 was identified as a major TJ cell adhesion molecule in brain endothelial cells. Three relaxation reagents (ca. 700Da - 17kDa) were applied to estimate water permeability of the neurons/glia cells and BBB in mice. In the intact mice, the longitudinal relaxation rates (1/T_1) showed minimal changes (<0.1 s^<-1>) even the 1/T_1 of blood water was accelerated more than 40 s^<-1> by using the 3 reagents. It is suggested that the normal BBB have very low water permeability. In the claudin-5 knocked out mice, Gd-DTPA^<2-> can pass through the modified BBB. From the dose-dependency of Gd-DTPA, a water efflux rate from the neurons/glia cells was detected which is corresponding to a diffusional water permeability of 1.5-1.0cm s^<-1>. The relaxation reagents (bigger than 2kDa) could not pass through the modified BBB. From the dose-dependency of a relaxation reagent, a water efflux rate from the BBB was detected which is corresponding to a moderate range of diffusional water permeability. These findings provide a new insight on the molecular biology of BBB, and also represent usefulness of this method to monitor physiological parameters of genetically modified animals.