In an animal model, fecal microbiota from patients with MDD was transferred to mice, resulting in depressive-like behavior, decreased levels of hippocampal neurotransmitters, and increased levels of Adrenocorticotropic hormone (ACTH), Corticotropin-releasing hormone (CRH), and serum pro-inflammatory cytokines [85]. This evidence concerns the gene POMC and major depressive disorder.