Studies in heterozygous mice for the VMAT2 gene have shown that mutant animals exhibit many features of depression, such as a lack of pleasure, motor retardation, and sensitivity to stress, which may be explained by the fact that VMAT2 can have a controlling effect on the secretion of DA, NE, and 5-HT at the synapse [26]. Here, SLC18A2 is linked to major depressive disorder.