Melatonin regulation of circadian rhythmicity in vertebrates

The pineal hormone, melatonin, influences circadian rhythms in a species-specific manner. Generally, endogenous melatonin is more important for circadian function in nonmammalian vertebrates, while in mammals the impact of melatonin is most clearly seen when exogenous melatonin is administered. The effects of melatonin on circadian rhythms in mammals are often subtle, but even small phase shifts caused by melatonin receptor activation can lead to stable entrainment. Rodent studies to identify molecular mechanisms of melatonin action emphasize the role of the MT1 receptor, but some responses appear due to the MT2 receptor subtype. © 2017 Elsevier Inc. All rights reserved