Galanin is a 29–30 amino acid neuropeptide originally isolated from the small intestine of pigs that has been implicated in feeding, pain, stress responses, depression, and substance use disorders.108, 109, 110 It is expressed in most (∼80%) rodent LC neurons and a smaller but still significant proportion of nonhuman primate and human LC neurons.111, 112, 113, 114, 115, 116 There are also galaninergic inputs to the LC originating from as yet unidentified sources.117. Here, GAL is linked to major depressive disorder.