Melatonin is a key hormone involved in the photoperiodic signaling pathway. In both teleosts
and mammals, melatonin produced in the pineal gland at night is released into the blood
and cerebrospinal fluid, providing rhythmic information to the whole organism. Melatonin
acts via specific receptors, allowing the synchronization of daily and annual physiological
rhythms to environmental conditions. The pituitary gland, which produces several hormones
involved in a variety of physiological processes such as growth, metabolism, stress and …

Our environment is constantly changing. While some variations are fast and unpredictable
(eg meteorological phenomena), others, such as solar cycles, moon phases, and seasons
follow regular patterns. Photoperiod, the alternation of light and darkness, is the most
reliable (noise-free, characterized by predictable rhythms over a long period of time) signal,
allowing animals to synchronize their biological rhythms with both daily and seasonal
changes. Photoperiod is conveyed by two types of signal: a neural message from …