Melatonin receptors are specialized proteins found in various tissues throughout the body that respond to the hormone melatonin. This hormone is primarily produced by the pineal gland in the brain and helps regulate sleep-wake cycles, also known as circadian rhythms. There are two main types of melatonin receptors, known as MT1 and MT2, which play different roles in mediating the effects of melatonin on sleep and other physiological processes. These receptors are located in areas of the brain that control sleep, mood, and reproductive functions. When melatonin binds to these receptors, it signals the body that it is time to sleep, promoting relaxation and drowsiness. Additionally, melatonin receptors are also found in other organs, influencing functions such as immune response and seasonal reproduction in some animals.