Dependency on hemodynamic responses on vessel segments determined by vessel-branch-based analysis of vascular network in rat cortex

The blood flow regulatory system is of great interest for understanding of energy demand and supply homeostasis in the brain. To probe vessel-by-vessel flow regulatory system, we developed a new method, vessel-branch-based analysis of spatiotemporal flow structures. Time-lapse images of flow structures were obtained in the rat somatosensory cortex, while a cocktail of fluorescently-labeled plasma and red blood cells (RBC) was injected from the external carotid artery. All vessels obtained were segmented into 6 groups, i.e. small, medium, and large arteries and veins, and diameter and transit time of both plasma and RBC flows were determined at each segment. Global and local perturbations were induced with systemic administration of sodium nitroprusside (SNP, vasodilator) and electrical forepaw stimulation, respectively, and then changes from baseline were measured. Under SNP administration, RBC flow was more dilated than plasma flow at all segments. The transit time of RBC and plasma flows were prolonged. The transit time of plasma was more prolonged than that of RBC flow. The difference in diameter between RBC and plasma flows was maximum at medium artery segment (from 25 to 50 um in diameter). Upon the forepaw stimulation, plasma flow was unchanged in diameter and slightly shortened in transit time at most of segments, except for small artery segment (less than 25 um in diameter) which unchanged in transit time but increased in diameter for both plasma and RBC. These results suggest that independent global and local flow regulatory system may exist depending on the vessel segment. In conclusion, we developed a vessel-branch-based analysis method for spatiotemporal blood flow structures, which allows us independent evaluation of vessel-by-vessel flow regulation system. Our approach will be further applicable to the analysis of flow structures in various disease models.GRC 2010, Brain Energy Metabolism & Blood Flo