Glycine Tissue Level in Medulla Oblongata Measured in vivo with H MRS at 9.4 T in Rat Brain

Introduction: In the central nervous system, glycine has a dual role as inhibitory neurotransmitter activating glycine receptors [1] and as co-agonist for glutamate excitatory transmission through N-methyl-D-aspartate receptors [2]. The medulla oblongata (MO) is the part of the brainstem which regulates autonomic functions, such as heart beat, breathing and blood pressure. In the MO, glycine is present in particularly high concentration [3], but it has never been quantified in vivo and in a noninvasive way. Recently, detection of glycine in rat brain in vivo has been reported, using a spin echo coherence excitation with the optimized echo time (TE) of 20 ms [4]. The aim of the present investigation was i) to measure the in vivo neurochemical profile in the MO by localized H NMR spectroscopy, with particular focus on glycine quantification, and ii) to compare the neurochemical profile in MO with that in hippocampus, striatum and cortex.