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Healthy aging is associated with a decline in cognitive function, and is a major risk factor for many neurodegenerative diseases. Although, there are several evidence that brain mitochondrial function is altered with aging its significance at the cellular level is elusive. In this study, we have investigated mitochondrial TCA cycle and neurotransmitter cycle fluxes associated with glutamatergic, GABAergic neurons and astroglia in the cerebral cortex and hippocampus of young (6 months) and aged (24 months) C57BL6 mice by using 1H‐[13C]‐NMR spectroscopy together with timed infusion of 13C‐labeled glucose and acetate. The ratio VCyc/VTCA was determined from a steady‐state [2‐13C]acetate experiment. Metabolic fluxes were obtained by fitting a three‐compartment metabolic model to 13C turnover of amino acids from glucose. Levels of glutamate, aspartate and taurine were reduced in the cerebral cortex, while glutamine and choline were elevated in the hippocampus of aged mice. Interestingly, the rate of acetate oxidation increased in the cerebral cortex, while the flux of mitochondrial TCA cycle of glutamatergic neurons decreased in the cerebral cortex (P < .0001) and hippocampus (P = .025) of aged mice. The glutamate‐glutamine neurotransmitter cycle flux was reduced in the cerebral cortex (P < .0001). The GABAergic TCA cycle flux was reduced in the cerebral cortex (P = .0008), while GABA‐glutamine neurotransmitter cycling flux was also reduced in the cerebral cortex (P = .011) and hippocampus (P = .042) of aged brain. In conclusion, the reduction in excitatory and inhibitory neurotransmitter activity of glutamatergic and GABAergic neurons in the cerebral cortex and hippocampus correlates qualitatively with declined cognitive function in aged mice. [ABSTRACT FROM AUTHOR]

Purpose: Recently, we introduced a quantum coherence based method (ge‐HSQC) for indirect 13C‐MRS in the liver to track 13C‐labeled lipids into the hepatic lipid pool in vivo. This approach is more robust in case of respiratory motion, however, inherently leads to a signal loss of 50% when compared with a conventional J‐difference editing technique (JDE). Here, we intend to improve the robustness of a regular JDE (STEAM‐ACED) with the use of a BIlinear Rotation Decoupling (BIRD) filter to achieve 100% higher signal gain when compared with ge‐HSQC. Methods: To determine the efficiency of the BIRD filter 1H‐[13C] lipid spectra were acquired on 3T from a peanut oil phantom, with three different MR sequences: ge‐HSQC, STEAM‐ACED, and the BIRD filter together with STEAM‐ACED (BIRD‐STEAM‐ACED). Finally, our proposed method is tested in vivo in five healthy volunteers with varying liver fat content. In these subjects we quantified the 1H‐[13C]‐signal from the hepatic lipid pool and determined 13C enrichment, which is expected to be 1.1% according to the natural abundance of 13C. Results: The application of the proposed BIRD filter reduces the subtraction artifact of 1H‐[12C] lipid signal efficiently in JDE experiments, which leads to a signal gain of 100% of 1H‐[13C]‐lipid signals when compared with the ge‐HSQC. Phase distortions in vivo were minimal with the use of BIRD compared with STEAM‐ACED, which enabled us to robustly quantify the 13C‐enrichment in all five subjects. Conclusion: The BIRD‐STEAM‐ACED sequence is an efficient and promising tool for 13C‐tracking experiments in the human liver in vivo. [ABSTRACT FROM AUTHOR]