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Augmentation of cytoskeletons in fetal capillary endothelial cells is one of the well known pathologic changes in toxemic placentae. But we can find very few reports on these filaments in placentae, especially on their ontogeny. An ultrastructural study on human chorionic villi from 55 normal and 25 toxemic pregnancies, covering all periods of gestation, revealed that endothelial cells already had a small amount of intermediate filaments and microfilaments from 6 weeks' gestation and that they gradually increased as pregnancy progresses. In toxemic cases, intermediate filaments were markedly augmented, occasionally forming bundles, to occupy the cytoplasm of endothelial cells, so that there was often no space for cytoplasmic organelles. Intermediate filaments were predominant in thinner parts of endothelial cells; both intermediate filaments and microfilaments were easily recognized in thicker parts. These filaments seemed to determine the arrangement of organelles such as rough endoplasmic reticulum and mitochondria. Immunohistochemical and immunoelectron microscopic studies with monoclonal antibodies proved that endothelial cells contained vimentin and actin, not cytokeratin and desmin. In toxemic placentae, augmentation of intermediate filaments may disturb normal movements of endothelial cells, and may cause an increase in vascular resistance to placental microcirculation and intrauterine growth retardation in the fetus.

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.