Hippocampal abnormalities of glutamate/glutamine, N-acetylaspartate and choline in patients with depression are related to past illness burden
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Background: Smaller hippocampal volumes in major depressive disorder (MDD) have been linked with earlier onset, previous recurrences and treatment refractoriness. The aim of our study was to investigate metabolite abnormalities in the hippocampus associated with past depressive illness burden. Methods: Glutamate/glutamine (Glx), N-acetylaspartate (NAA) and choline (Cho), potential markers of glial/ neuronal integrity and membrane turnover, respectively, were measured in adults with depression and healthy controls using a 3 T magnetic resonance spectroscopy scanner. Voxels were placed in the head of the right and left hippocampus. We controlled for systematic differences resulting from volume-of-interest (VOI) tissue composition and total hippocampal volume. Results: Our final sample comprised a total of 16 healthy controls and 52 adult patients with depression in different stages of the illness (20 treatment-resistant/chronic, 18 remittedrecurrent and 14 first-episode), comparable for age and sex distribution. Patients with treatment-resistant/chronic and remitted-recurrent depression had significantly lower levels of Glx and NAA than controls, especially in the right hippocampal region (p ≤ 0.025). Diminished levels of Glx were correlated with longer illness duration (left VOI r = -0.34, p = 0.01). By contrast, Cho levels were significantly higher in patients with treatment-resistant/chronic depression than those with first-episode depression or controls in the right and left hippocampus (up to 19% higher; all p ≤ 0.025) and were consistently related to longer illness duration (right VOI r = 0.30, p = 0.028; left VOI r = 0.38, p=0.004) and more previous episodes (right VOI r = 0.46, p= 0.001; left VOI r = 0.44, p= 0.001). Limitations:The cross-sectional design and the inclusion of treated patients are the main limitations of the study. Conclusion: Our results support that metabolite alterations within the hippocampus are more pronounced in patients with a clinical evolution characterized by recurrences and/or chronicity and add further evidence to the potential deleterious effects of stress and depression on this region. © 2013 Canadian Medical Association.