Background and Purpose-Vascular endothelial growth factor (VEGF) can induce matrix metalloproteinase (MMP)-9activities and focal angiogenesis. We hypothesized that VEGF activation of cerebral MMP-9 would require nitric oxideparticipation.Methods-We compared the in vivo effects of: (1) NG-monomethyl-L-arginine, a nonspecific nitric oxide synthaseinhibitor; (2) L-N6-(1-iminoethyl)lysine, an inducible nitric oxide synthase selective inhibitor; and (3) doxycycline, aknown nonspecific inhibitor of MMP in the mouse brain, using in situ zymography and endothelial marker CD31.3-nitrotyrosine was used as a surrogate for nitric oxide activity. Inflammatory cell markers CD68 and MPO were usedto confirm leukocyte infiltration.Results-VEGF-stimulated MMP-9 activity expressed primarily around cerebral microvessels. NG-monomethyl-L-argininesuppressed cerebral angiogenesis (P_0.05), especially those microvessels associated with MMP-9 activation (P_0.02)induced by VEGF, comparable to the effect of doxycycline. L-N6-(1-iminoethyl)lysine showed similar inhibitoryeffects. 3-nitrotyrosine confirmed nitric oxide levels in the brain. Compared with the lacZ control, VEGF increasedinflammatory cell infiltration, especially macrophages, in the induced brain angiogenic focuses.Conclusions-Inhibition of nitric oxide production decreased MMP-9 activity and focal angiogenesis in the VEGFstimulatedbrain. Both specific and nonspecific inhibition of nitric oxide synthase resulted in similar reductions,suggesting that VEGF-stimulated cerebral MMP activity and angiogenesis are predominantly mediated throughinducible nitric oxide synthase, a specific nitric oxide synthase isoform mediating inflammatory responses. (Stroke.2009;40:2879-2881.)