Abstract
Neuronal activity in the brain depends on mostly aerobic generation of energy equivalents and thus on a constant O2 supply. Oxygenation of the vertebrate brain has been optimized during evolution by species-specific uptake and transport of O2 that originally derives from the phototrophic activity of prokaryotic and eukaryotic organisms in the environment. Here, we employed a concept that exploits transcardial injection and vascular distribution of unicellular green algae or cyanobacteria in the brain of Xenopus laevis tadpoles. Using oxygen measurements in the brain ventricle, we found that these microorganisms robustly produce sizable amounts of O2 upon illumination. In a severe hypoxic environment, when neuronal activity has completely ceased, the photosynthetic O2 reliably provoked a restart and rescue of neuronal activity. In the future, phototrophic microorganisms might provide a novel means to directly increase oxygen levels in the brain in a controlled manner under particular eco-physiological conditions or following pathological impairments.