GLUL and major depressive disorder: In this study, in a mixed population of patients with MDD and BD, we evaluated the relationship between 1H-MRS glutamate in the AC and single-nucleotide polymorphisms (SNPs) of astrocyte-specific genes, GLUL, SLC1A3, and SLC1A2, encoding for glutamine synthetase (GS), excitatory amino acid transporter (EAAT) 1 and EAAT2, respectively, which are known to regulate synaptic or extracellular glutamate levels in the astrocyte.