Differential permeability of blood microvasculatures in various sympathetic ganglia of rodents.

The ultrastructure of capillaries and their permeability to lanthanum ion and horseradish peroxidase (HRP) in various rodent sympathetic ganglia were investigated in this study. Electron microscopic observation revealed that most capillaries surrounding the principal neurons in these ganglia were of the continuous (non-fenestrated) type, while the fenestrated capillaries were consistently associated with the small granule-containing (SGC) cells in rat and hamster superior cervical ganglia and the coeliac-mesenteric ganglia (CMG) complex. Both of the capillaries surrounding the principal neurons and adjacent to SGC cells in various gerbil sympathetic ganglia or in rat and hamster thoracic ganglia were of the non-fenestrated type. After lanthanum perfusion, lanthanum tracer was limited to the blood-vessel lumen but was apparently obstructed by the tight junctions of capillaries. No lanthanum was visible in the extravascular space surrounding the principal neurons of rodent superior cervical and thoracic ganglia. By contrast, lanthanum extravasation was observed in the luminal, abluminal and perivascular surface of capillaries in the CMG complex and near SGC cells in the superior cervical ganglion. Injecting HRP showed that all blood vessels in various sympathetic ganglia were impermeable to HRP. HRP-DAB reaction product was limited to the lumen of capillaries, blocked by tight junctions and obstructed by fenestral diaphragms of fenestrated capillaries close to SGC cells. We conclude that: (1) the capillaries surrounding the principal neurons in rodent superior cervical and thoracic ganglia are more restrictive to HRP and lanthanum ion than those anywhere in the CMG complex or in regions containing SGC cells of superior cervical ganglia; (2) according to the results of lanthanum and HRP experiments, the existence of different blood-barrier properties are present among different rodent sympathetic ganglia or within the same ganglion.