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.