Although the
neurotransmitters/modulators
glutamate and, more recently,
glycine have been implicated in the development and maintenance of
Alcohol Use Disorder (AUD) in preclinical research, human
proton magnetic resonance spectroscopy (1H-MRS) studies have focused solely on the measurement of
glutamate. The purpose of the present analysis was to examine the relative associations of brain
glutamate and
glycine levels with recent heavy drinking in 41 treatment naïve individuals with AUD using 1H-MRS. The present study is the first that we are aware of to report in vivo brain
glycine levels from an investigation of addiction. Dorsal Anterior Cingulate Cortex (dACC)
glutamate and
glycine concentration estimates were obtained using Two-Dimensional J-Resolved Point Resolved Spectroscopy at 3 Tesla, and past 2-week summary estimates of alcohol consumption were assessed via the Timeline Followback method.
Glutamate (β = -0.44, t = -3.09, p = 0.004) and
glycine (β = -0.68, t = -5.72, p < 0.001) were each significantly, inversely associated with number of heavy drinking days when considered alone. However, when both variables were simultaneously entered into a single regression model, the effect of
glutamate was no longer significant (β = -0.11, t = -0.81, p = 0.42) whereas the effect of
glycine remained significant (β = -0.62, t = -4.38, p < 0.001). The present study extends the literature by demonstrating a unique, inverse association of brain
glycine levels with recent heavy drinking in treatment naïve individuals with AUD. If replicated and extended, these data could lead to enhanced knowledge of how glycinergic systems change with alcohol consumption and AUD progression leading to pharmacological interventional/preventative strategies that modulate brain
glycine levels.