SCANNING AND TRANSMISSION ELECTRON-MICROSCOPIC STUDIES OF MICROVASCULAR PATHOLOGY IN THE OSMOTICALLY IMPAIRED BLOOD-BRAIN-BARRIER

The present investigation focused on the structural events occurring i n endothelial cells lining the lumina of brain microvessels in rats su bjected to a single intracarotid injection of hypertonic 1.8 M L (-) a rabinose solution with or without intravenous injection of horseradish peroxidase. Blood vessels from cerebral cortex and thalamus were eval uated by transmission and scanning electron microscopy. After short-te rm exposure (10-12 min) there was widespread flooding of peroxidase in to the brain neuropil of the ipsilateral hemisphere. Peroxidase tracer was frequently observed within vesiculo-tubular profiles, and occasio nally within widened interendothelial junctional clefts. Partially fra gmented, necrotic endothelial cells appeared to be in the process of d esquamation. Individual endothelial cells appeared to be shrunken with widened interendothelial spaces. Some healthy endothelial cells appea red to be involved in repair processes, manifested by the extension of thin cellular processes towards the area of vessel injury. Other path ological alterations included a conspicuous increase in the number of endothelial cell microvilli, large crater-like invaginations of the en dothelial plasma membranes and muscular blood vessels in the process o f spasm. We also observed a platelet reaction with or without endothel ial cell necrosis and attached microthrombi in some arterial segments.