Changes in brain metabolites measured with magnetic resonance spectroscopy in antidepressant responders with comorbid major depression and posttraumatic stress disorder

In a present pilot study, performed on 11 subjects, we studied proton magnetic resonance spectroscopy (1H-MRS) changes in early to intermediate (3-6 weeks) responders to antidepressant treatment with selective serotonin reuptake inhibitors (SSRIs). All subjects had diagnosis of major recurrent depression comorbid to posttraumatic stress disorder (PTSD). Magnetic spectroscopy was done in the region of dorsolateral prefrontal cortex on a 3T MRI-unit. Participants were selected out of the larger sample due to an early response to antidepressant treatment within 3-6 weeks, measured with Beck Depression Inventory (BDI). We measured levels of neuronal marker N-acetyl-aspartate (NAA), choline (CHO) and creatine (Cr). There was no difference in NAA/Cr ratios between the first and the second spectroscopic scans (p= 0.751). However, CHO/Cr ratios showed increasing trend with mean value at the first scan of 1.09 (SD =0.22) while mean value at second scan was 1.25 (SD=0.24), displaying statistically significant difference (p=0.015). In conclusion, significant increase in choline to creatine ratio from the first to the second spectroscopic scan during the antidepressant treatment, compared to almost identical values of NAA to creatine ratio, suggests increased turnover of cell membranes as a mechanism of the early response to the antidepressant drug therapy.