We use an Olympus Fluoview1000 two-photon microscope (BX61W1-FV1000, Olympus, Ltd., Tokyo, Japan) with an excitation source of a Spectra-Physics MaiTai HP DeepSee femtosecond Ti:Sa laser. To acquire images (either stacks or single focal planes) from GFP-positive vessels, a long-working-distance (2 mm) water-immersion objective (× 25, NA 1.05) was used for line-scan measurements. The images were taken at 12-bit depth with resolution of 1024×1024 pixels. We chose a scanning rate of 10μs/pixel and 2000 lines in total to follow the velocity of RBCs. The average RBC velocity speed has been reported [8 (link), 15 (link)]. In vivo vessel diameters were measured manually using ImageJ [16 (link)]. RBC velocity and flux were calculated with an automated image-processing algorithm using MATLAB software (The MathWorks Inc., Natick, Massachusetts) [8 (link), 15 (link)].