ABSTRACT
The objective of this chapter is to provide a general overview of the physiological role of seasonality in reproduction, which allows mammals to con£ne their breeding activity to a time of the year when it is most likely to be successful. In the £rst part, information is provided about the environmental factors that control seasonality of reproduction in humans and various animal species, with photoperiod being the main one. Next, the mode of action of photoperiod on seasonal breeding is analyzed, with two main pathways being investigated: a. the transduction of the light/dark cycle into an endocrine signal which is the circadian secretion of melatonin produced by the pineal gland and b. the regulation of the hypothalamic-pituitary-gonadal axis activity by melatonin secretion from puberty to adulthood, in both sexes. Finally, some novel physiological activities of melatonin (antioxidative, myometrium contractility) that could be considered for new therapeutic strategies in the pathophysiology of the reproductive system are discussed.
