title: Brain energy metabolism measured by (13)C magnetic resonance spectroscopy in vivo upon infusion of [3-(13)C]lactate.
abstract: The brain uses lactate produced by glycolysis as an energy source. How lactate originated from the blood stream is used to fuel brain metabolism is not clear. The current study measures brain metabolic fluxes and estimates the amount of pyruvate that becomes labeled in glial and neuronal compartments upon infusion of [3-(13)C]lactate. For that, labeling incorporation into carbons of glutamate and glutamine was measured by (13)C magnetic resonance spectroscopy at 14.1 T and analyzed with a two-compartment model of brain metabolism to estimate rates of mitochondrial oxidation, glial pyruvate carboxylation, and the glutamate-glutamine cycle as well as pyruvate fractional enrichments. Extracerebral lactate at supraphysiological levels contributes at least two-fold more to replenish the neuronal than the glial pyruvate pools. The rates of mitochondrial oxidation in neurons and glia, pyruvate carboxylase, and glutamate-glutamine cycles were similar to those estimated by administration of (13)C-enriched glucose, the main fuel of brain energy metabolism. These results are in agreement with primary utilization of exogenous lactate in neurons rather than astrocytes.
authors.affiliation: Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: João M N
authors.initials: JM
authors.lastname: Duarte
authors.affiliation: Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Freya-Merret
authors.initials: FM
authors.lastname: Girault
authors.affiliation: Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.|Department of Radiology, University of Lausanne, Lausanne, Switzerland.|Department of Radiology, University of Geneva, Geneva, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Gruetter
mesh_terms: D000818:Animals; D001784:Blood Gas Analysis; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects / Q000378:metabolism*; D002247:Carbon Isotopes / Q000008:administration & dosage / Q000378:metabolism; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000008:administration & dosage / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D011877:Radionuclide Imaging; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002247:Carbon Isotopes; D005973:Glutamine; D019344:Lactic Acid; D018698:Glutamic Acid
keywords: 13C MRS; brain; lactate; metabolism