A quantitative immunocytochemical analysis of total surface area of blood-brain barrier in developing rat brain

A mouse monoclonal antibody which specifically reacts with putative blood-brain barrier (BBB) competent endothelial cells of rat cerebral capillaries was used to identify barrier competent cells in the central nervous system (CNS). The development of the cerebral capillaries and the BBB was examined and quantified, from day 6 to day 40 postpartum, using immunocytochemical and unbiased stereological techniques.There was a progressive increase in capillary formation postnatally, with collateral branching observed with progressive age. BBB development was confined to individual endothelial cells located at the periphery of the cortex until day 10 postpartum. Antibody binding progressively increased postnatally, contributing 30% of the total capillary surface area by day 20. There was a rapid elevation of reactivity from day 20 to day 40, with a mean of 83% by day 40.The BBB constitutes minimal amounts of brain vascular capillaries before day 10 of life in the rat. There is a slower increase in BBB than in total capillaries between days 10 and 20. There is a reversal of this trend between days 20 and 40.