Role of the MT1 and MT2 melatonin receptors in mediating depressive- and anxiety-like behaviors in C3H/HeN mice.

Melatonin is a neurohormone primarily synthesized by the pineal gland following a circadian rhythm with a high level during the night and a low level during the day. Alterations in the synthesis and secretion of melatonin have been reported in various mood disorders, including major depressive disorder. However, the role of endogenous melatonin in the pathophysiology of depressive disorder is unclear. Melatonin primarily acts through two G protein-coupled receptors, termed MT1 and MT2 . The present study investigated the effect of genetic deletion of the MT1 and/or MT2 receptors on tests associated with depression- and anxiety-like behaviors in C3H/HeN mice. Deletion of the MT1 and/or MT2 receptors caused a deficit in hedonic and social interaction behavior, and increased anxiety-like behavior. It is likely that dysregulations of the MT1 and/or MT2 melatonin receptors could be involved in the pathophysiology of depression and anxiety.