Fine structure of basement membranes of the capillary endothelium and perivascular astrocyte in some circumventricular organs by three-dimensional SEM.

The three components of the basement membrane, the lamina lucida, lamina basalis, and lamina reticularis, were examined stereoscopically with a high-resolution scanning electron microscope. Brains of 12 rats and 3 guinea pigs were used. In the lamina reticularis, microfibrils connect to collagen fibrils with one end and anchor to the external surface of the lamina basalis with the other. Their helical substructure, the pitch of helices 70-80 nm and maximum width 15-20 nm on scanning electron micrographs, was reconfirmed. In the lamina lucida, short cross-bridge filaments spanned the basal lamina and the applied plasma membrane. They measured 10-15 nm in diameter, 30-90 nm in length, and were distributed with a regular spacing fo 40-60 nm. It is discussed that the basement membrane serves as the anchorage of the microfibrils and of the cross-bridge filaments and mediates the interconnection between the plasma membrane and extracellular connective tissue elements.