A Novel Method to Demonstrate Capillary Geometry and Perfusion Patterns in Rat Brain from the Same Histological Section

Abstract

The geometry of the microvascular bed as well as its perfusion pattern are important determinants of oxygen transport to tissues. In the present study, we analyzed capillary geometry in the rat parietal cortex using discriminative morphometric methods. Specifically, we labeled arteriolar capillary (i.e. the proximal portion of the capillary bed, AC) and venular capillary (i.e. the distal portion of the capillary bed, VC) endothelium with different colors. While the geometry of the capillary bed sets the surface area for diffusion of oxygen, the pattern of perfusion within the capillary bed under in vivo conditions provides information as to regional conditions for oxygen diffusion. Accordingly, we used a highly concentrated colloidal gold solution as a plasma label, to identify capillaries perfused with plasma under controlled conditions. While gold particles may be directly visualized on electron micrographs, they require enhancement with silver to make them visible at the light microscopic level. To our knowledge, this is the first study where these methods have been combined within the same histological section, i.e. enzymatic labeling of the capillary endothelium as well as delineation of capillary perfusion with silver enhanced colloidal gold particles.