ADCYAP1 and major depressive disorder: In humans, the dysregulation of PACAP and the PAC1 receptor has been associated with schizophrenia, depression, and post-traumatic stress disorder (PTSD) (Hashimoto et al., 2007, 2010; Ressler et al., 2011; Mercer et al., 2016; Ross et al., 2020).