Pericytes Are Not Associated With Reduced Capillary Perfusion After Experimental Subarachnoid Hemorrhage

BACKGROUND: Subarachnoid hemorrhage (SAH) is characterized by an acute reduction of cerebral blood flow and subsequent cortical infarcts, but the underlying mechanisms are not well understood. Since pericytes regulate cerebral perfusion on the capillary level, we hypothesize that pericytes may reduce cerebral perfusion after SAH. METHODS: Pericytes and vessel diameters of cerebral microvessels were imaged in vivo using NG2 (neuron-glial antigen 2) reporter mice and 2-photon microscopy before and 3 hours after sham surgery or induction of SAH by perforating the middle cerebral artery with an intraluminal filament. Twenty-four hours after, SAH pericyte density was assessed by immunohistochemistry. RESULTS: SAH caused pearl-string-like constrictions of pial arterioles, slowed down blood flow velocity in pial arterioles by 50%, and reduced the volume of intraparenchymal arterioles and capillaries by up to 70% but did not affect pericyte density or induce capillary constriction by pericytes. CONCLUSIONS: Our results suggest that perfusion deficits after SAH are not induced by pericyte-mediated capillary constrictions.