Physiologic and Characteristic Distributions of Glutamate/Glutamine in Patients with Major Depressive Disorder

Purpose Glutamate is the most abundant neurotransmitter in the brain, and proton magnetic resonance spectroscopy (MRS) allows quantification of glutamate-related metabolites (glutamate/glutamine complex; Glx). In previous findings, Glx has been lower in several brain regions of patients with major depressive disorder than in those of healthy controls. However, the physiologic and characteristic distribution of Glx in the same individual remains unclear. We attempted to clarify which brain regions reflect changes associated with depression.Material and method We measured Glx in 12 patients with depression and 12 healthy controls matched for age and sex in three brain regions (left amygdala, left anterior cingulate cortex, and left dorsolateral prefrontal cortex), and then compared the physiologic and characteristic distribution of Glx between the two groups.Results In comparisons of the distributions, Glx was significantly higher in the amygdala than in other regions. Glx tended to be lower among the patients than the controls, although no significant differences were present between the groups. We could not detect the changes expected from major depressive disorder (reduced Glx) in the amygdala, which regulates emotions and shows higher concentrations of Glx than other regions.Conclusion Previous studies have suggested that the concentration of Glx decreases with age, and this might have influenced our results regarding changes with major depressive disorder. In addition, we could not clarify whether medications affected the patient condition, because treatment for depression increased Glx in previous studies. Further MRS studies are needed to clarify Glx distributions in the specific diagnosis of depression.