FLASH protects against eNOS-induced blood vessel dilation compared to CONV irradiation after one month (10 Gy) in the hippocampus. Animals were injected with tomato lectin 30 min prior to sacrifice and volumetric analysis was performed. Panel A: Quantification of lectin volume at one month postirradiation show that CONV dose rates cause an increase in lectin volume after 10 Gy that is not observed after FLASH ultra-high dose rates. Panel B: Colocalization of eNOS within 5 µm of lectin shows that FLASH does not induce an increase in immunoreactivity while CONV does. Blood vessel volume data shown are the mean ± SEM (n = 4 per group, four images analyzed per animal). eNOS data shown are the mean ± SEM (n = 6 per group, two images analyzed per animal). *P ≤ 0.05, ***P ≤ 0.001 (ANOVA with Bonferroni's multiple comparisons test).