Increased brain capillaries in chronic hypoxia

Abstract

The effect of chronic hypobaric hypoxia (28 days, 455 Torr) on the organization of brain vessels was studied in Balb/c mice. In comparison to age-matched controls kept at sea level, emulsion-perfused capillaries in hypoxic mice showed marked dilation in all brain areas studied. Capillary length per unit volume of tissue (Lv) was increased in the cerebellar granular layer, the caudate nucleus, the globus pallidus, the substantia nigra, the superior colliculus, and the dentate gyrus. There was a selective increase of Lv in the hippocampus (CA1 strata pyramidale and lacunosum and CA3 strata pyramidale 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 increase in capillary surface area per unit volume of tissue was also determined in several brain areas, including layer IV of somatosensory cortex, where Lv was not significantly increased. The O2 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 significant increase of O2 conductance to neural tissues. Also the estimated tissue PO2 in chronic brain hypoxia is markedly increased in the caudate nucleus and the substantia nigra compared with acute hypoxia. These results suggest that formation of new capillaries is an important mechanism to restore the O2 deficit in chronic brain hypoxia and that local rates of energy utilization may influence angiogenesis in different areas of the brain.

Liver X receptors in the central nervous system: From lipid homeostasis to neuronal degeneration

“…Similar findings have been reported in brains of mice after chronic hypoxia (35). Because the ventricles are closed, many changes observed in the brain of LXR␣ Ϫ/Ϫ ␤ Ϫ/Ϫ mice could be due to hypoxia.…”

Cerebral Oxygenation in Awake Rats during Acclimation and Deacclimation to Hypoxia: AnIn VivoElectron Paramagnetic Resonance Study

“…One variable will be the depth of measurement in the cortex. The capillary density, which has an effect on Pto 2 , varies by as much as 50% between layers II and VI in the cortex (Boero et al, 1999). It is unlikely that the chronically implanted sensors were consistent to less than 200 mm in depth.…”

“…High oxygen was not used during study 2 to eliminate the chance that repeated exposure to high O 2 would alter the time course for acclimation. Harik et al, 1996;Boero et al, 1999). Modeling studies indicate that changes in arterial Po 2 , capillarity, and hematocrit are not enough to account for the measured change in Pto 2 (Grinberg et al, 2005), indicating that more information is needed to understand this regulation.…”

Pepsin pretreatment allows collagen IV immunostaining of blood vessels in adult mouse brain

“…Vessels have been identified using standard histological stains such as silver (Gallyas, 1970) or toluidine blue (Manoonkitiwongsa et al, 2001), histochemical assays for enzymes enriched in blood vessels (Lee et al, 2005;Bell et al, 1984) as well as immunohistochemistry for vascular associated antigens. In animals, the cerebrovasculature has also been labeled in vivo by perfusion with photographic emulsions (Boero et al, 1999;D'Andrea, 2004), India ink (Shimada et al, 1992) or lectins .…”