Developmental study of ultrastructural and biochemical changes in isolated chick brain microvessels.

The morphology of the endothelial junctions, the expression of the alkaline phosphatase (ALKP) and gamma-glutamyltranspeptidase (GGT) activities, and the transport systems for neutral amino acids (NAA) and for d-glucose were studied in parallel in isolated microvessels from the brains of 9-, 12-, and 21-day chick embryos and 30-day chickens using freeze-fracturing and biochemical techniques. In the 9-day embryos, the endothelium junctional plasma membranes show alignments of discrete intramembrane particles (Imps) on the replica P-faces. In the 12-day embryos, the junctional membranes show short fibrils of loosely interconnected fused Imps.