In the current study, we reveal a potential non-invasive therapeutic approach for enhancement of BBB permeability to facilitate CNS drug delivery, systemic pre-injection of VEGF. This result is consistent with an in vitro study showing that VEGF dose-dependently and reversibly enhanced permeability through cultured Sipeimine endothelial cell layers. In contrast, others have reported that systemic application of VEGF only increases the permeability of already compromised BBA. For example, VEGF increased the BBB permeability around the ischemic region of a mouse stroke model but not in the contralateral hemisphere. However, our study demonstrates that VEGF can indeed enhance the permeability of the intact BBB in healthy mice in vivo. Moreover, this effect was observed at relatively low concentrations and was not associated with severe edema. These lower concentrations have also been shown to increase BBB permeability without induction of vascular proliferation, but continuous infusion led to retraction of astrocyte endfeet, monocyte infiltration, and neuroinflammation. We suggest that a single low dose of VEGF may transiently enhanced BBB permeability without disrupting neural homeostasis for safe CNS Forsythin delivery of neurotherapeutics. The absence of enhanced BBB permeability in some brain regions, which made MR images appear multifocal rather than homogeneous, may be due to the lag phase phenomenon, where local VEGF concentration fails to reach a threshold concentration due to its relatively brief plasma half-life. Previous studies also revealed that most VEGF receptors are located on the abluminal side of the BBB, which may limit access to systemic VEGF in some brain regions. While the identification of VEGF as an enhancer of BBB permeability represents the first step toward possible use for CNS drug delivery, much work remains to be done to elucidate the molecular mechanism. It was reported that VEGF can upregulate the mRNA expression of both VEGF and its receptors Flt-1 and Flk-1 in endothelial cells, possibly initiating a positive feedback cycle leading to enhanced BBB permeability. It is known that VEGF is a heparin-binding endothelial cell mitogen and angiogenic factor in vivo. Since angiogenesis depends on the migration of endothelial and peripheral cells, sprouting of new vessels might be linked to the reconstruction of existing vessels. Tissue reorganization requires activation of matrix metalloproteinases and VEGF enhances MMP-9 activity of in vivo ischemia models and in vitro BBB models. In addition, the endothelial nitric-oxide synthase pathway may also mediate transient opening of the BBB. It was reported that systemic administration of the selective eNOS inhibitor cavtratin in mice abrogated VEGF-induced BBB disruption and protected against neurologic deficits in the MS model system. Previous studies also highlighted a role for the src-suppressed C-kinase substrate in the regulation of BBB permeability. SSeCKS decreased VEGF expression by downregulating AP-1 and stimulating expression of angiopoietin-1. The contribution of these signaling mechanisms obviously depends on their sensitivity to serum VEGF concentration and duration of receptor interaction.