MMP9 and infection: Consistent with the results in cerebrum tissues, the expression of Mmp9, Vegf, Ang-2, and Et-1 genes in GPS-infected bEnd.3 cells were significantly increased (p < 0.05), whereas quercetin decreased the upregulation of Mmp9, Vegf, Ang-2, and Et-1 induced by GPS infection in bEnd.3 cells (p < 0.05, Figure 10A–D), indicating that quercetin could improve the BBB permeability induced by GPS.