Evidence for a blood‐ganglion barrier in the superior cervical ganglion of the rat

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Abstract
The permeability of the blood vessels in the superior cervical ganglion of the rat was tested by intravenous injection of horseradish peroxidase (HRP).By light microscopy, peroxidase activity was found in three locations: in the capsule of the ganglion, in the lumina of the blood vessels, and within macrophages. Electron microscopy revealed that virtually all ganglionic blood vessels contained HRP 5 minutes following its administration. The intensity of peroxidase activity declined over the period of 15 minutes. The enzyme was localized on the luminal surface of the endothelial cells, attaching to the glycocalyx. Endothelial microvilli, projecting into the vessel lumen, were also covered with peroxidase. Micropinocytotic vesicles on the luminal surface of the endothelium contained reaction product. Some of these vesicles were free within the cytoplasm of the endothelium but none was observed on the abluminal surface. Peroxidase activity was not detected in the extracellular space even after 15 minutes.The majority of blood vessels in the superior cervical ganglion possess a continuous endothelium with tight junctions; features associated with the blood‐brain barrier of the central nervous system and peripheral nerves. It is proposed that these vessels perform a barrier function between the capillary circulation and the superior cervical ganglion.