SLC6A4 and major depressive disorder: Molecular alterations observed in animal models exposed to prenatal maternal stress include: turnover of serotonin (5HIAA/5-HT ratio, (5-hydroxyindoleacetic acid/serotonin)) in the hippocampus, increased TPH (tryptophan hydroxylase) expression, and serotonin level in the dorsal raphe nuclei, increase the 5-HT1A receptor (serotonin 1A receptor) in the hippocampus, and the decrease in SERT (serotonin transporter or 5HTT) levels in the offspring who may have a manifestation of depression in later life (reviewed in St-Pierre et al., 2016) [89].