Fisetin (25 mg/kg) was given by gavage and the characteristic emission peak of fisetin was detected strongly in the blood vessels and more weakly in the brain parenchyma within 40 min after administration (b, c). Within 120 min (d), fisetin fluorescence was detectable in blood vessels (asterisks), the adjacent brain parenchyma and also in individual neuronal cells (arrows). No emission at 550 nm was seen in prior to fisetin administration (a, c). Spectral measurements were taken before (3, 4) and 40 min after (1, 2) oral administration at the blood vessel (1, 3) and adjacent parenchymal area (2, 4) on ROIs. FOV was 225 μm × 225 μm in all experiments.