Cristina Cudalbu1, Bernard Lanz2, Paul R. Vasos3, Yves Pilloud2, Vladimr Mlynrik2, Rolf Gruetter2,4
1Laboratory for Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fdrale de Lausanne (EPFL) , Lausanne, Switzerland; 2Laboratory for Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fdrale de Lausanne (EPFL), Lausanne, Switzerland; 3Laboratory for Biomolecular Magnetic Resonance, Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland; 42Departments of Radiology, Universities of Lausanne and Geneva, Switzerland
15N MRS is an alternative approach to 13C MRS in studying glutamate-glutamine metabolism and can provide a more straightforward interpretation. For this study we developed a new pulse sequence in order to simultaneously measure [5-15N]Gln and [2-15N]Gln+Glu for a direct measurement of the net glutamine synthesis rate (Vsyn-Vnt), Vsyn and VGDH under 15N-labeled ammonia infusion in the rat brain, using in vivo localized 15N MRS interleaved with 1H MRS. We obtained from the 1H data a net synthesis flux (Vsyn-Vnt)=0.0350.001mol/min/g. By fitting the in vivo 5-15N Gln and 2-15N Glu+Gln time courses, Vsyn=0.240.03mol/min/g, VGDH=0.0300.001mol/min/g. Finally, the apparent neurotransmission rate, Vnt=0.210.03mol/min/g.