GLUL and major depressive disorder: Autopsy studies of brain samples from major depressive disorder (MDD) patients show a reduced density and a changed morphology of glial cells [14–19] and a decreased expression of astrocytic markers such as glial fibrillary acidic protein (GFAP) [20–23], excitatory amino acid transporters (EAATs), and glutamine synthetase (GS) in several brain regions [20, 24], particularly in the prefrontal cortex (PFC) and hippocampus.