Increased brain capillaries in chronic hypoxia

The effect of chronic hypobaric hypoxia (28 days, 455 Torr) on the organiza tion of brain vessels was studied in Balb/c mice. In comparison to age-matc hed controls kept at sea level, emulsion-perfused capillaries in hypoxic mi ce showed marked dilation in all brain areas studied. Capillary length per unit volume of tissue (L-v) was increased in the cerebellar granular layer, the caudate nucleus, the globus pallidus, the substantia nigra, the superi or colliculus, and the dentate gyrus. There was a selective increase oft, i n the hippocampus (CA1 strata pyramidale and lacunosum and CA3 strata pyram idale and oriens) and in somatosensory cortex layers V and VI, motor cortex layers II, III, V, and VI, and auditory cortex layers II and III. An incre ase in capillary surface area per unit volume of tissue was also determined in several brain areas, including layer IV of somatosensory cortex, where L-v was not significantly increased. The O-2 diffusion conductance and PO2 in the tissues were estimated with a mathematical model. The remodeling of capillary diameter and length during chronic hypoxia accounts for the signi ficant increase of O-2 conductance to neural tissues. Also the estimated ti ssue Pot in chronic brain hypoxia is markedly increased in the caudate nucl eus and the substantia nigra compared with acute hypoxia. These results sug gest that formation of new capillaries is an important mechanism to restore the O-2 deficit in chronic brain hypoxia and that local rates of energy ut ilization may influence angiogenesis in different areas of the brain.