On the other hand, low NPY levels are found in the cerebrospinal fluid of depressed patients (Westrin et al., 1999; Heilig et al., 2004; Ozsoy et al., 2016) and in genetic- (Caberlotto et al., 1998, 1999), lesion- (Goyal et al., 2009), and stress-induced animal models of depression (Sergeyev et al., 2005). This evidence concerns the gene NPY and major depressive disorder.