Direct in vivo measurement of glycine and the neurochemical profile in the rat medulla oblongata

The medulla oblongata (MO) contains a high density of glycinergic synapses and a particularly high concentration of glycine The aims of this study were to measure directly in vivo the neurochemical profile, including glycine, in MO using a spin-echo-based H-1 MRS sequence at TE = 2 8 ms and to compare it with three other brain regions (cortex, striatum and hippocampus) in the rat Glycine was quantified in MO at TE = 2 8 ms with a Cramer-Rao lower bound (CRIB) of approximately 5% As a result of the relatively low level of glycine in the other three regions, the measurement of glycine was performed at TE = 20 ms, which provides a favorable J-modulation of overlapping myo-inositol resonance The other 14 metabolites composing the neurochemical profile were quantified in vivo in MO with CRLBs below 25% Absolute concentrations of metabolites in MO, such as glutamate, glutamine, gamma-aminobutyrate, taurine and glycine, were in the range of previous in vitro quantifications in tissue extracts Compared with the other regions, MO had a three-fold higher glycine concentration, and was characterised by reduced (p < 0 001) concentrations of glutamate (-50 +/- 4%), glutamine (-54 +/- 3%) and taurine (-78 +/- 3%) This study suggests that the functional specialisation of distinct brain regions is reflected in the neurochemical profile Copyright (C) 2010 John Wiley & Sons, Ltd