Findings show that AdipoR1 is present in serotonin neurons in the dorsal raphe nucleus, where deletion of AdipoR1 in these area leads to reduced expression of the serotonin synthesis enzyme Tryptophan Hydroxylase 2 (TPH2), decreased serotonin levels and altered Serotonin Transporter (SERT) expression, resulting in impaired serotonin transmission and depression-like behaviours [110]. This evidence concerns the gene TPH2 and major depressive disorder.