PMCH and major depressive disorder: Besides being a key regulator of feeding behavior and energy metabolism—and affecting reward, addiction, stress-responses, anxiety and depression—the MCH system is also known to influence learning and memory (as previously noted) (Adamantidis and de Lecea, 2009; Sherwood et al., 2012; Izawa et al., 2019), social and maternal behaviors (Alachkar et al., 2016; Phan et al., 2020; Sanathara et al., 2021), and nociception/pain (Jang et al., 2018).