Changes in the expression of genes encoding SERT, 5-HT2A, Tph2, DOPA, DDC, BDNF, and GSK-3β in the stressed groups, as shown in the Illumina assay, are in line with previous studies suggesting the role of these molecules in the mechanisms of MDD [77,88,89,90]. This evidence concerns the gene SLC6A4 and major depressive disorder.