Proceedings of The Physiological Society

University of York (2002) J Physiol 539P, S019


Cerebrovascular proliferation in simulated sleep apnoea in rats

Louise Spoors, R.N. Kalaria, E.A. Laude*, C.J. Emery*, A. Oakley, G.R. Barer and D.H. Barer

Institute for Ageing and Health, General Hospital, Newcastle upon Tyne and *Department of Medicine, Royal Hallamshire Hospital, Sheffield, UK

Severe sleep apnoea (SA) is common in old age and may cause hypoxia for one-third of the sleep period. We report changes in markers of cerebral vascularity in rats exposed to the level and duration of hypoxia typically experienced in SA. Experiments accorded with UK legislation. Groups of mature Wistar rats (~500 g, n = 3/group) were exposed to: normoxia (N), intermittent hypoxia (IH, 4 h daily in 10 % O2, 56 exposures) and continuous hypoxia (CH, 10 % O2, 8 weeks exposure) in a normobaric environmental chamber (CO2 ~0.02 %). After treatment, under anaesthesia (sodium thiopentone, 100 mg kg-1 I.P.), brains were perfused with formol-saline through the common carotid artery at 120 mmHg pressure. After fixation, three dorsoventral sections of the brain were cut (frontal cortex + accumbens striatal nucleus; temporo-parietal cortex + putamen; hippocampus) and stained by immunocytochemistry for the glucose transporter (GLUT-1, an endothelial cell marker) and vascular endothelial growth factor (VEGF). Antibody staining intensity was assessed in five regions: cortex A, accumbens, cortex B, putamen and hippocampus. In each region density was measured by image analysis (Image Pro) in five haphazardly selected discrete fields. The three groups were compared by 1-way ANOVA with pairwise contrasts within each brain region and for all regions combined.

For GLUT-1 expression: mean % antibody density in all regions rose from 1.59 ± 0.07 (S.E.M.) in N rats to 2.23 ± 0.07 in IH rats and 2.85 ± 0.1 in CH rats (P < 0.0001 for N vs. IH, N vs. CH and IH vs. CH). Thus angiogenesis had occurred in both IH and CH rats.

For VEGF: mean % antibody density in all regions was: 0.94 ± 0.09 for N rats, 2.03 ± 0.16 for IH rats and 0.79 ± 0.07 for CH rats (P < 0.0001 for N vs. IH and IH vs. CH but P > 0.5 for N vs. CH), indicating that vascular growth was continuing in IH but not CH rats.

Our results with GLUT-1 suggest that there had been vascular growth in IH and CH rats, which was greater in the latter, whereas VEGF results suggest that vascular proliferation was continuing in IH but not in CH rats. These results are consistent with the hypothesis of Lauro & LaManna (1997), who calculated that angiogenesis would be sufficient to maintain adequate O2 delivery in rats, after just 3 weeks of continuous hypobaric hypoxia.

Where applicable, experiments conform with Society ethical requirements