Vascular changes in the rat brain during chronic hypoxia in the presence and absence of hypercapnia.

Changes in brain vascularity in adult rats during adaptation to chronic normobaric hypoxia with or without elevated CO(2) were morphometrically investigated. Immunohistochemistry with anti-rat endothelial cell antigen (RECA-1) antibody was carried out for the vascular analysis. After the rats were subjected to hypoxia for 2 to 8 weeks (wks)(10 percent O(2) in N(2)), the total area of blood vessels was measured in 6 brain regions. After 2 wks of hypoxia, the blood vessel area was found to be significantly increased in the frontal cortex, striatum, hippocampus, thalamus, cerebellum, and medulla oblongata, by 44% , 96% , 65% , 50% , 102% and 97% , respectively. The ratio of large vessels with an area &#62; 500 micro m(2) was also increased in all brain regions. Hypoxic adaptation in brain vascularity did not change during 8 wks of hypoxia, and the hypoxia-induced levels measured in the vasculature returned to control levels 2 wks after the termination of hypoxia in areas of the brain other than the cortex and thalamus. In addition, hypoxia-induced changes in terms of the total vascular area and vessel size distribution were significantly inhibited by the elevation in CO(2), whereas chronic hypercapnia without hypoxia had no effect on brain vascularity. These findings suggested that adaptations in brain vascularity in response to hypoxia are rapidly induced, and there are regional differences in the reversibility of such vascular changes. Carbon dioxide is a potent suppressor of hypoxia-induced vascular changes, and may play an important role in vascular remodeling during the process of adaptation to chronic hypoxia.</p

Iteration Method to Derive Exact Rotation Curves from Position-Velocity Diagrams of Spiral Galaxies

We present an iteration method to derive exact rotation curves (RC) of spiral galaxies from observed position-velocity diagrams (PVD), which comprises the following procedure. An initial rotation curve, RC0, is adopted from an observed PV diagram (PV0), obtained by any simple method such as the peak-intensity method. Using this rotation curve and an observed radial distribution of intensity (emissivity), we construct a simulated PV diagram (PV1). The difference between a rotation curve obtained from this PV1 and the original RC (e.g., difference between peak-intensity velocities) is used to correct the initial RC to obtain a corrected rotation curve, RC1. This RC1 is used to calculated another PVD (PV2) using the observed intensity distribution, and to obtain the second iterated RC (RC2). This iteration is repeated until PV$i$ converges to PV0, so that the differences between PV$i$ and PV0 becomes minimum. Finally RC$i$ is adopted as the most reliable rotation curve. We apply this method to some observed PVDs of nearby galaxies, and show that the iteration successfully converges to give reliable rotation curves. We show that the method is powerful to detect central massive objects.Comment: To appear in ApJ.Letters, 5 pages Latex with 4 figure