OXT and psychiatric disorder: For example, lower plasma OT levels and higher AVP levels have been linked with several psychiatric disorders, including major depressive disorders (Londen et al., 1997; de Winter et al., 2003) and posttraumatic stress disorder (De Kloet et al., 2008), that have been characterized as involving increased amygdala activation (Siegle et al., 2002; Etkin and Wager, 2007).