Imaging system for three-dimensional mapping of cerebrocortical capillary networks in vivo

A personal computer-based image analysis system was developed for the three-dimensional mapping of cerebrocortical capillary networks from intravital video recordings. Capillary circulation in the parietal cortex of anesthetized rats was visualized to 70 microns depth using a closed cranial window preparation and epi-fluorescent, intensified video microscopy. The circulation was video recorded during slow (0.1 micron/frame) scanning of the focal plane (depth of field = 10 microns) through regions of interest. Capillary networks were traced from still video images of several microscope fields recorded at different X, Y, and Z stage coordinates. The length of vessel segments from five networks ranged between 10 and 178 microns and was best approximated by the Gamma distribution. Vessel diameter (2.5 to 8.7 microns) was best fitted by the lognormal distribution. A specific capillary network contained 51 segments and five anastomosing loops with circumferences between 575 and 1226 microns. Velocity of fluorescently labeled red blood cells ranged from 0.77 to 2.22 mm/sec within the capillary loops. The study demonstrates the feasibility of reconstructing capillary networks from intravital video recordings as deep as 70 microns within the cerebral cortex and finds an anastomosing pattern and heterogeneous red blood cell velocity in the capillary network.