Venous microvasculature of the pineal body and choroid plexus in the rat.

Rats were perfused from aorta with Ringer's solution and with Karnovsky's fixative, and injected from the right atrium with Mercox resin. Specimens were properly taken, observed under LM, TEM, SEM, and stereo-photographed. Fenestrated endothelial cells of the pineal capillary were observed to contain plenty of microtubules running parallel to the long axis of the vessel. The endothelial basal lamina appeared anchored by microfibrils onto fine collagen fibrils and onto the basal lamina of the perivascular cells. These findings indicate resistance of the capillary endothelium against compression by perivascular hydrostatic pressure, and strongly suggest that the perivascular cerebrospinal fluid is absorbed into the capillary lumen. Resin cast of the pineal venous system looked like a glomerule with two longer collecting veins on the ventral surface and with shorter ones on the dorsal side all emptying into the straight sinus and the confluence of sinuses. Resin cast of the choroid plexus venous system tended to lobulate and looked like a vine with a spiral collecting vein emptying into the great vein. Two veins were found connecting the great vein to the confluence and to the transverse sinuses. These could be effective collaterals in case of occlusion of Galen's vein.