In Vivo Microdialysis for Measurement of Oxidative Metabolism in the Living Brain

Microdialysis allows for measurement of multiple compounds dissolved in the interstitial fluid of the rat brain, including carbon dioxide, if a radioactive tracer is included. Upon introduction of a ¹⁴ C-labeled compound into the interstitial fluid of the brain, the compound is transported into cells and metabolized into various products including CO₂ . The ¹⁴ C-metabolites, including ¹⁴ CO₂ released to the interstitial fluid, equilibrate with fluid in the microdialysis probe and can be collected in the microdialysis effluent. The described methodology allows determination of the rate of oxidative metabolism of potential substrates for brain energy metabolism. Inclusion of nonradioactive competitive substrates provides additional information on oxidative pathways. Our laboratory has utilized microdialysis to measure changes in oxidative metabolism in the brains of adult rats and of 8-day-old rat pups subjected to ischemia/hypoxia.