Enhanced vesicular transport of exogenous peroxidase across cerebral vessels, induced by serotonin

Previous studies have revealed that the endothelial cells of cerebral vessels are linked by tight junctions preventing an intercellular passage of exogenous peroxidase. However, under normal conditions, vesicular transport of the tracer has been demonstrated in parts of cerebral vessels, especially in arterioles with a diameter of 30-100 mu. Solutions, containing 50-800 mug of buffered 5-hydroxytryptamine sulphate (serotonin), were perfused through the cerebral ventricles on mice after intravenous injection of horseradish peroxidase. Usually, the biogenic amine enhanced the vesicular transport of exogenous peroxidase. The serotonin-induced increased transport was observed in vessels on the surface of the brain as well as in vessels located in the parenchyma. No cell damage was observed. Increased transport was observed in arterioles, venules, and in capillaries. Therefore, it is not likely that the serotonin effect is a constriction of smooth muscle cells causing an opening of the tight junctions followed by an intercellular movement of tracer. The most reasonable assumption behind the mechanism is that serotonin affects the plasmamembrane of endothelial cells resulting in an enhanced production and transfer of cytoplasmic vesicles.