Ultracytochemical studies of vesicular and canalicular transport structures in the injured mammalian blood-brain barrier

Abstract

An ultracytochemical investigation was performed to study the origin of pinocytic vesicles and canalicular structures within endothelial cells (EC) of the injured mammalian blood-brain barrier (BBB). To accomplish this goal, two electron-dense tracers, native ferritin (NF) and horseradish peroxidase (HRP), were used in conjunction with the detection of alkaline phosphatase (AP) activity, a known marker of EC plasmalemma of brain micro-blood vessels. Brain ECs from (1) mice subjected to crude leptomeningeal damage for 1, 2, or 3 days and (2) cats subjected to cold lesion injury for 1, 4, or 24h were evaluated for tracer transport and AP activity. Fine structural analysis of leaking segments of micro-blood vessels from damaged cerebral cortex or basal ganglia demonstrated pinocytic vesicles, deep invaginations of the luminal plasmalemma and elongated, tubular profiles, all containing tracer. Because we observed in ECs from both experimental models of brain injury a positive reaction for AP activity in the luminal plasmalemma, in its deep invaginations, in deliminating membranes of pinocytic vesicles, and in tubulo-canalicular structures, we conclude that all types of transport structures derive from the same 100Å thick exoplasmic plasmalemmal membranes. Further, besides the pinocytic vesicular transport system (PTS), the canalicular transport system (CTS) appears to serve as an additional important mechanism for macromolecular transport across the damaged mammalian BBB.