Melatonin, better known as "the hormone of darkness," is secreted by the pineal gland during the night and helps us fall asleep. Because its internal regulation depends on light, melatonin is part of chronobiology, the study of biological mechanisms and their adaptations to lunar and solar related rhythms (Klein et al. 1991). Therefore, photoperiod changes greatly impact melatonin concentration, influencing changes in neuronal and hormonal mechanisms of the photo neuro-endocrine systems, namely reproduction. Research has shown that a disruption in the circadian rhythm of melatonin due to photoperiod changes detrimentally affects the rhythmic function of the female reproductive cycle. Research from journals, articles, and printed books has shown that both exogenous and endogenous features contribute to the reproductive cycle and that the internal mechanisms are entrained by environmental cues. Photoresponsiveness of the reproductive system is mediated by the internal biological clock, transcriptional factors, period genes, photic input, GnRH (gonadotropin-releasing hormone) neurons, and melatonin secretions. Specifically, melatonin secretions directly affect reproductive function either through stimulatory or inhibitory pathways. Seasonally breeding animals interpret photic information according to melatonin secretions. This clearly points to a relationship of melatonin with photic and reproductive qualities. Research is ongoing with various species of animals in hope of uncovering the mystery of the connection between light, melatonin, and reproduction, which may be helpful in understanding the effects of photoneuroendocrinology on the female human.
Szlafrok, R. (2012). Do Photoperiodic Changes in Melatonin Secretion Detrimentally Affect the Female Reproductive Cycle?. The Science Journal of the Lander College of Arts and Sciences, 6(1). Retrieved from https://touroscholar.touro.edu/sjlcas/vol6/iss1/8