Hippocampal metabolic abnormalities at first onset and with recurrent episodes of a major depressive disorder: A proton magnetic resonance spectroscopy study

The neural underpinnings of major depressive disorder (MDD) are unknown but there is evidence for structural alteration in the hippocampus that may become more pronounced over the course of illness. The aim of the present study was to examine metabolite levels of N-acetyl-aspartate (NAA), Myo-inositol (MI), Glutamate-glutamine (Glx) and choline-containing compounds (GPC and GPC + PCh) in patients presenting for first treatment of a depressive episode compared to those with multiple past episodes and age and sex matched controls. We used single voxel proton magnetic resonance spectroscopy (1H-MRS) centered on the hippocampus. Choline-containing compounds were significantly increased in patients with a high past illness burden relative to controls after controlling for hippocampal volume. The group presenting for first treatment had only increases in MI levels compared with matched controls. These results suggest that abnormal membrane turnover in the hippocampus is greater in patients with highly recurrent illness, and provide support for the hypothesis that there are neuronal changes in this region over the course of illness.