Ultrastructural observations on human cerebral capillaries in organ culture.

The use of an organotypic-in the strictly literal meaning of the word, nervous tissue culture device has allowed the identification and ultrastructural study of various types of developing capillaries in human cerebellum and olfactory bulb in vitro. Most capillaries were similar to those already described by other authors or by us, in human or animal embryos and fetuses. Large Type I Capillaries. Their luminal diameters were greater than 8 microns. The basement membranes were thin and discontinous. Numerous interendothelial junctions were either plate-like attachments or contained pentalaminar zones. Type II Capillaries. Their lumina were between 2 and 8 microns in diameter. The basement membranes were wider than those of type I capillaries and were sometimes continuous. The interendothelial junctional complexes of type II capillaries included pentalaminar portions. Many simple or complex vascular sprouts (type IV and V capillaries) had small or non-patent lumina. Their basement membranes were absent or very thin and discontinuous. Their interendothelial junctions were similar to those of type I capillaries. Some of the less frequently encountered capillary types seen in developing human nervous tissue were absent in culture. Some pathological features were seen-especially in long-term cultures-in type I and II capillaries containing degenerating blood cells or processes sometimes obviously related to histiocytic cells. They consisted mainly of an accumulation of microfilaments and modifications of the rough endoplasmic reticulum in the endothelial cells. These pathological changes did not modify the main characteristics of the capillaries. The origin of the vascular sprouts, the exact nature of the interendothelial junctions and the significance of the pathological changes are discussed. This model may prove useful for the study of cerebral vasculogenesis, the development of the blood-brain barrier and the physiological or pathological properties of the human brain capillaries in tissue culture.