Integrating Circadian and Reproductive Rhythms in Mood Regulation

a regular menstrual cycle is important for women's psychological and physiological health beyond its reproductive role.However, the rhythmic structure of modern environments is often disrupted by nighttime exposure to artificial light, irregular shift work, and frequent jet lag, which disturb endogenous circadian rhythms.These disruptions disproportionately affect women and increase their susceptibility to mood disorders, including depression and bipolar disorder, with menstrual cycle disruption sometimes preceding mood symptoms [1].Although lithium remains a primary mood stabilizer and is widely prescribed for bipolar disorder in women, its known effects on ovarian cycles raise concerns [2,3].The ovarian cycle emerges from the interaction between biological oscillators operating on distinct timescales.A slow, infradian timer within the hypothalamic-pituitary-gonadal (HPG) axis integrates hormonal signals, notably estrogen (E2), and maintains a cycle of 28-29 days in humans and 4 days in rodents, while a system of circadian clocks in the hypothalamus and ovaries regulates the pulsatile release of gonadotropins on a much shorter timescale [4].Both systems rely on feedback mechanisms, and despite cycle-to-cycle variability, the ovarian cycle functions as a longterm, highly precise clock [5].These clocks of differing timescales interact in as-yet incompletely understood ways to maintain robust but adaptable physiological regulation over environmental and hormonal fluctuations.The circadian circuit that mediates adaptation to jet lag also en-