[Early development of cerebral blood vessels: on the morphological changes in endothelial cells during the fetal period in the rat brain].

Developmental changes of cerebral blood vessels in the rat fetal brain from the embryonic day 11 (E 11) to E 21 were chronologically observed with light and electron microscopes. Based on the fine structures the development of the blood vessels was divided into three successive stages: Stage I (from E 11 to E 21). The neural groove fused at the dorsal portion and transferred to the neural tube. Endothelial cells located only around the neural tissue, and showed a primitive nature in their cellular structures, such as immature nucleus and intracytoplasmic organelles. There were many pores at the thin portion of the cytoplasmic processes. Stage II (from E 13 to E 16). Matrix cells in the neural tube began to produce neuroblasts. These neuroblasts migrated from the matrix layer and were recognized as the migrating zone just outside the matrix layer. The formation of the migrating zone started at the ventrolateral portion and successively spread to the lateral neopallium and then to the medial one of the cerebrum. Perineural vessels invaded into the neural tissue at the ventrolateral portion and were distributed in the migrating zone and the matrix layer. It was the first appearance of the intraneural blood vessels, and the next invading seemed to follow the area which formed the migrating zone. The endothelial cells at this stage became to increase their cytoplasmic thickness and simultaneously to protrude many cell processes to the luminal and abluminal sides. Numerous large vesicles in the cytoplasm were also observed. Being associated with the vesicle formation the pores in the cytoplasm were rapidly decreased. Pericytes were recognized around the endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)