Homonuclear 1H double-resonance difference spectroscopy of the rat brain in vivo.

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Abstract
1H homonuclear double-resonance difference spectroscopy at 360.13 MHz was used to resolve specific metabolite resonances in the brains of intact rats. Metabolite resonances resolved include previously obscured proton resonances of Ala, GABA, Glu and Tau. The GABA .alpha.- and .gamma.-CH2 proton resonances were observed in the living rat in the difference spectrum were observed in the living rat in the difference spectrum obtained upon irradiation of the .beta.-CH2 proton resonance at 1.91 ppm. A 3-fold increase in the intensity of the .alpha.- and .gamma.-CH2 resonances of GABA was observed 30 min after death. The .alpha.-CH and .gamma.-CH2 resonances of Glu were also resolved in vivo by selective irradiation of the .beta.-CH2 protons to which they are spin-coupled. This technique was used to observe the .beta.-CH3 protons of lactate through the intact scalp of a rat. Large lipid signals arising from scalp tissue were eliminated in the difference spectrum, revealing the lactate .beta.-CH3 resonance.