Increase in Evans blue dye extravasation into the brain in the late developmental stage

The development of the blood–brain barrier (BBB) against permeability to inert tracers, such as Evans blue dye (EBD), occurs quite early on at embryonic stages (before E13–E15), and the BBB remains resistant to EBD between E15 and early adulthood (P20–P30). Here, we aimed to examine the changes in EBD permeability at a later stage in development, specifically comparing young rats (P20) with adult rats (P86). We found markedly higher EBD extravasation into the forebrains of adult rats compared with those of the young rats (P=0.0132; Student’s t-test). In contrast, there was no difference in EBD extravasation to the liver, suggesting no change in vascular permeability in peripheral tissues. Furthermore, EBD extravasation into the cerebellum was less prominent than that into the forebrain, suggesting that the disruption of the BBB was brain-region specific. In conclusion, we found a specific increase in EBD extravasation in the mature forebrain, and the protocol that we used may be a good template for studying developmental disruption of the BBB.