TNF and major depressive disorder: Published data have linked the activation of TNF‐α signalling to multiple brain disorders, such as the development of narcolepsy, depression, neurodegenerative diseases such as AD and PD, and multiple sclerosis.17, 18, 19, 20 Published data have implicated a role of TNF‐α in sleep and wakefulness cycle, as well as fatigue, during infections.21 Our previous study has demonstrated that TNF‐α regulates hypocretin system in vitro in cultured cells.22 The role of TNF‐α in the regulation of hypocretin system in vivo and the molecular mechanism involved are unknown to the field.