AVP is the primary activator of the HPA axis and a vasoconstrictor as well as an antidiuretic that is also being actively studied as a stress biomarker.56,57 Additionally, AVP has a behavioral role and is a neural regulator of numerous social behaviors, including affiliation, aggression, and pair bonding.58 De Kloet et al. previously identified an elevated concentration of plasma AVP in human patients with post-traumatic stress disorder compared to both traumatized and healthy non-traumatized controls.59 This evidence concerns the gene AVP and post-traumatic stress disorder.