Dually supplied t-junctions in arteriolo-arteriolar anastomosis in mice: Key to local hemodynamic homeostasis in normal and ischemic states?

Background and Purpose-: The functional role of arteriolo-arteriolar anastomosis (AAA) between the middle cerebral artery (MCA) and anterior cerebral artery in local hemodynamics is unknown, and was investigated here. Methods-: Blood flow in AAAs was examined using fluorescein isothiocyanate-labeled red blood cells (RBCs) as a flow indicator in 16 anesthetized C57BL/6J mice before and after MCA occlusion up to 7 experimental days. Results-: We observed paradoxical flow in AAAs; labeled RBCs entered from both the MCA and anterior cerebral artery sides and the opposing flows met at a branching T-junction, where the flows combined and passed into a penetrating arteriole. The dually fed T-junction was not fixed in position, but functionally jumped to adjacent T-junctions in response to changing hemodynamic conditions. On MCA occlusion, RBC flow from the MCA side immediately stopped. After a period of "hesitation," blood started to move retrogradely in one of the MCA branches toward the MCA stem. The retrograde blood flow was statistically significantly (P<0.05), serving to feed blood to other MCA branches after a lag period. In capillaries, MCA occlusion induced immediate RBC disappearance in the ischemic core and to a lesser extent in the marginal zone near AAAs. At day 3 after ischemia, we recognized the beginning of remodeling with angiogenesis centering on AAAs. Conclusions-: AAAs appear to play a key role in local hemodynamic homeostasis, both in the normal state and in the development of collateral channels and revascularization during ischemia.