Further studies on the blood-brain barrier to low molecular weight substances. An ultrastructural cytochemical study

A high resolution cytochemical study was performed in cats to investigate the cerebral blood vessel permeability to low molecular weight non-liposoluble substances. Sodium ferrocyanide was injected to four adult cats through an intraventricular canula and a copper solution was perfused intravascularly. Electroencephalographic recording throughout the experiments showed no detectable alterations induced by the administered solutions. Brain fragments fixed by intravascular perfusion were processed for electron microscopy. Pineal gland from the same animals and masseter muscle fragments in which ferrocyanide had been directly injected in those animals were studied as controls. A copper ferrocyanide suspension was directly injected into the lateral ventricle to two cats and 15 min later the brains were fixed by perfusion and processed for electron microscopy. An electrondense precipitate was seen in the interstitial and perivascular space, but not into the vessel lumen in these animals. No reaction product was observed in the brain parenchyma of cats injected intraventricularly with sodium ferrocyanide, whereas electron-dense deposits were clearly depicted in the pineal gland and masseter muscle in the same animals. The results further support the thesis that the junctions between the endothelial cells in brain capillaries represent a physical barrier to non-liposoluble substances.