Capillary perfusion of the rat brain cortex: An in vivo confocal microscopy study

Abstract

Confocal laser-scanning microscopy was used to visualize subsurface cerebral microvessels labeled with intravascular fluorescein in a closed cranial window model of the anesthetized rat. In noninvasive optical sections up to 250 μm beneath the brain surface, plasma perfusion and blood cell perfusion of individual capillaries were studied. Under resting conditions, in all cerebral capillaries the presence of plasma flow was demonstrated by the appearance of an intravenously injected fluorescent tracer within 20 seconds after injection. Plasma flow was verified even in capillaries that contained stationary erythrocytes or leukocytes; 91.1% of the capillaries contained flowing blood cells, 5.2% contained stationary blood cells, and no blood cells were seen in 3.6%. Mean blood cell velocity was 498.3±443.9 μm/s, and the mean blood cell supply rate was 35.75±28.01 cells per second. When capillaries were continuously observed for 1 minute, 'on' and 'off' periods of blood cell flow were noted. During hypercapnia (increase of PCO2 from 33.25 to 50.26 mm Hg), mean blood cell flux increased from 38.6±17.2 to 55.5±12.2 per second (P <40 per second) decreased from 59.2% to 22.4%. Capillary diameter increased from 5.33±0.25 to 5.66±0.29 μm (P