Microangioarchitecture of rat parietal cortex with special reference to vascular "sphincters". Scanning electron microscopic and dark field microscopic study.

Microangioarchitecture of the rat parietal cortex was studied by means of scanning electron microscopy and dark field microscopy. The richest supply of blood vessels in the parietal cortex was found in layer III + IV and layer V, where 2 isolated plexuses of microvessels were prominent. The appearance of the plexuses was quite different between motor and sensory areas. In the motor area the capillary plexuses were narrow and compact, while in sensory area the plexuses were wide and diffuse. Characteristic ring formations, called ring-shaped-compressions in the present study, were frequently observed at branching sites of arterioles. The ring-shaped-compression probably corresponds to the precapillary sphincter. A similar structure was also seen in capillaries and venules and, therefore, it is likely that not only arterioles, but also capillaries and even venules, can actively change diameter to control cerebral blood flow.