The target cells of the hormone melatonin are in the:

Melatonin primarily targets the **suprachiasmatic nucleus (SCN) of the hypothalamus**. The SCN serves as the body’s master circadian clock, regulating sleep-wake cycles and other daily physiological rhythms. By acting on the SCN, melatonin helps signal nighttime to the body, promoting sleep and assisting in maintaining the internal biological clock. **Key Target Areas of Melatonin:** 1. **Suprachiasmatic Nucleus (SCN):** Located in the hypothalamus, the SCN receives information about light exposure from the retina and uses melatonin signals to regulate circadian rhythms. 2. **Pineal Gland:** Melatonin can act in an autocrine or paracrine manner within the pineal gland itself. 3. **Retina:** Melatonin receptors in the retina help modulate visual functions based on the time of day. 4. **Reproductive Tissues:** Melatonin influences reproductive hormones and seasonal breeding behaviors in some animals. 5. **Immune System Cells:** Melatonin has immunomodulatory effects, influencing immune responses. Understanding the primary targets of melatonin helps in comprehending its role in sleep regulation, circadian rhythm maintenance, and its broader physiological effects. **Conclusion:** The main target cells of melatonin are located in the **suprachiasmatic nucleus of the hypothalamus**, where it plays a crucial role in regulating the body’s internal clock and sleep patterns. **Reference:** - Reiter, R. J., & Tan, D. X. (2015). Melatonin as an antioxidant: under promises but over delivers. *Journal of Pineal Research, 58*(1), 13–34. **Answer:** They act on the body’s suprachiasmatic nucleus (SCN) within the hypothalamus as melatonin’s target cells