Blood vessels in the central nervous system (CNS) have strong barrier functions called blood brain barrier (BBB), which enables the CNS-specific pharmacokinetics and homeostasis.  Recent studies have clarified that the surrounding astrocytes and microglia actively regulate the formation and maturation of BBB.  However, the precise spatiotemporal changes and the underlying mechanisms for respective cell types remain to be elucidated.
In this study, we investigated the period of cerebrovascular BBB formation in rat brains using Evans Blue, which has already been accepted not to penetrate into mature BBB. We found that rat cerebrovascular BBB was formed between day 4 and day 15 after birth.  By 2D and 3D image analysis of the immunohistochemical data using IMARIS (Oxford Instruments), we clarified the cell number, three-dimensional structure, and coverage rate of astrocytes and microglia in the process of BBB maturation. Of interest, microglia directly contacted with the capillaries and the coverage rate reached the maximum at day 15 after birth, which is correlated with BBB maturation. We are currently analyzing the spatiotemporal dynamics specific to respective cell types. Our study strongly suggests that both of astrocytes and microglia directly contact with brain microvasculature and play important roles in BBB maturation.