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Abstract: Rapid improvement of depressive symptoms occurs after the administration of the NMDA antagonist ketamine. Ketamine administration is accompanied by an increase in GLX (sum-peak of glutamate, glutamine (GLN) and GABA) and GLN in the brain, as measured by magnetic-resonance (MR) spectroscopy. In healthy subjects, we observed an increase in GLX and GLN levels after total sleep deprivation (TSD), which has a rapid antidepressant effects. We examined, if an increase in GLX or GLN is related to the therapeutic effect of TSD. We examined 13 patients with major depression by means of proton MR spectroscopy (field strength: 1.5T) before and after 24h of TSD. Two anatomical areas (dorsolateral prefrontal cortex (DLPC) and parieto-occipital cortex (POC)) were studied. In the DLPC TSD did not change GLX or its elements, whereas the total creatine and choline signal increased marginally. No change could be observed in the POC. For further exploration we took gender and the presence of vegetative characteristics of melancholic depression into account, i.e. the presence of early morning awakening, appetite and weight loss was taken into account, to define vegetative melancholia (VM). TSD led to an increase in GLX and GLN in the DLPC only of male patients. In patients with VM an increase in GLN occurred in this area. The low field strength limits the accuracy for GLX and GLN estimates. Despite the exploratory nature of the study, it nevertheless supports earlier data on the importance of glutamatergic neurotransmission and furthermore of gender and/or vegetative features in depression. [Copyright &y& Elsevier]