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

Abstract

We have used 1H homonuclear double-resonance difference spectroscopy at 360.13 MHz to resolve specific metabolite resonances in the brains of intact rats. Metabolite resonances resolved include previously obscured proton resonances of alanine, γ-aminobutyric acid (GABA), glutamate, and taurine. The γ-aminobutyric acid α- and γ-CH2 proton resonances were observed in the living rat in the difference spectrum obtained upon irradiation of the β-CH2 proton resonance at 1.91 ppm. A 3-fold increase in the intensity of the α- and γ-CH2 resonances of γ-aminobutyric acid was observed 30 min after death. The α-CH and γ-CH2 resonances of glutamate were also resolved in vivo by selective irradiation of the β-CH2 protons to which they are spin-coupled. In addition, this technique was used to observe the β-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 β-CH3 resonance.