Abstract
Objective: To test the hypothesis that adenosine can increase capillary densities in developing brain tissue.
Methods: Transparent tadpoles of albino Xenopus laevis were exposed to adenosine agonists, mainly 5′-N-ethylcarboxamidoadenosine (NECA), and to antagonists, mainly 8-phenyltheophylline (8PT) in aquarium water. After 2 weeks in drugs, networks of blood vessels on the dorsal surface of the optic tectum were scanned in vivo by videomicroscopy. Densities of surface capillaries and venules, of deep branches, and of deep perfused capillaries were calculated.
Results: NECA initially dilated brain blood vessels and chronically increased blood flow by a simple subjective index. 8PT diminished diameters and prevented the subjective flow increase. Chronic 3 μM NECA significantly increased densities of total deep branches from pial vessels into the tectum.
Conclusions: In an in vivo amphibian assay, NECA dilated brain capillaries and venules and increased their flow and density. Adenosine was present chemically and increased during metabolic stress. These results are consistent with adenosine as a metabolic signal for growth of blood vessels during brain development. In addition, it appeared that short-term dilation and flow increase in tectal capillaries in acute NECA was followed over a period of weeks in chronic NECA by vascular remodeling and return of diameters to normal.
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