Immunohistochemical localization of adherens junction components in blood-brain barrier microvessels of the rat

The morphology and molecular composition of intercellular adherens junctions have most frequently been described in epithelial cells and the fascia adhaerens of the intercalated disc. A group of cytoplasmic molecules is known to be associated with adherens junctions. The intercellular bond is mediated by cadherins which bridge the cells by homophilic binding. Recently, endothelial cells have also been shown to form intercellular junctions of the adherens-type. However, they are morphologically less distinct and little is known about their molecular components. In this study we report the localization of some adherens junction components in intact microvessels of the blood-brain barrier in the rat. We used antibodies raised against alpha-actinin, vinculin, zyxin, cadherin (antipan-cadherin antibody) and A-CAM (N-cadherin) in immunohistochemical experiments at light and electron microscopical levels. Microvessel walls reacted positively for all antigens throughout postnatal development. All antigens were localised, though not necessarily exclusively, to interendothelial junctions. At the ultrastructural level, pan-cadherin reactivity was present throughout the entire length of the cleft. These results could mean that in blood-brain barrier endothelial cells the complex tight junction is embedded in an adherens junction which occupies the entire length of the cleft.