In vivo Time-Resolved Brain Phosphorus Nuclear Magnetic Resonance

Abstract

Methods used to obtain and quantify high-quality time-resolved dog brain phosphorus nuclear magnetic resonance (31P NMR) spectra are described. In eight animals the normoxic dog brain spectra showed 10% of total phosphorus in ATP, 14% in phosphocreatine (PCr), and 38% in brain phospholipids containing phosphodiesters. The chemical shift between PCr and inorganic phosphate, 5.09, corresponded to an intracellular brain pH of 7.2. During hypoxia, PCr declined to 0.5 ± 0.3 (n = 8) of starting levels, prior to any changes in brain ATP. Simultaneous recording of the EEG was obtained in two animals. During hypoxia, progressive PCr depletion was associated with progressive slowing of the EEG, which was essentially silent before significant changes occurred in brain ATP. Finally, the brain 31P NMR spectrum and pH were measured at 90-s intervals, and the sequential changes that followed respiratory arrest were monitored in one dog until high-energy phosphate depletion was complete.