[Study of the brain capillaries and their surrounding tissues at various stages of development in mice (author's...

The development of the brain capillaries and their surrounding tissues from fetuses to adult mice were studied ultrastructurally. 1. The intracerebral blood vessels on day 10 of gestation showed sinusoid characteristics. 2. The interendothelial junctional complex on day 15 of gestation showed the zonula occludens like in the case of adult. 3. The anlage of pericyte was observed already on day 15 of gestation. 4. The endothelium decreased prominently in its complexity and thickness till the 8th day of age. 5. Sprouting of the intracerebral capillaries were observed on the 8th day of age. 6. The BM-material was observed continuously near the corresponding plasma membranes of the endothelium on the first day of age. The perivascular clefts surrounding the blood vessels were partly open and had direct contact with the extracellular space till 8 days of age. 7. The large extracellular space which was observed from the fetuses to the first day of age became remarkably narrower after 4 days and it was observed that there were interrelations between the development of neuropils and narrowing of the extracellular space. This study shows that several capillaries with different permeabilities coexist over a long period of time in the cereberum. The latter seems to play an important role in the formation of the blood-brain barrier.