To quantify the solute permeability of rat cerebral microvessels, we measured the apparent permeability (P) of pial microvessels to various sized solutes. The pial microcirculation was observed by a high numerical aperture objective lens through a section of the frontoparietal bone thinned with a micro-grinder (a revised method from Easton and Fraser, 1994, J Physiol. 475:147-157, 1994). Sodium...

Molecular diffusion in the brain extracellular space (ECS) is an important determinant of neural function. We developed a brain surface photobleaching method to measure the diffusion of fluorescently labeled macromolecules in the ECS of the cerebral cortex. The ECS in mouse brain was labeled by exposure of the intact dura to fluorescein-dextrans (M(r) 4, 70, and 500 kDa). Fluorescein-dextran di...

The endothelial cell glycocalyx influences blood flow and presents a selective barrier to movement of macromolecules from plasma to the endothelial surface. In the hamster cremaster microcirculation, FITC-labeled Dextran 70 and larger molecules are excluded from a region extending almost 0.5 μm from the endothelial surface into the lumen. Red blood cells under normal flow conditions are exclude...