Estradiol signaling in the medial preoptic nucleus: a lifespan framework for female sleep regulation

Dear Editor, Sleep disturbances are pervasive across the female lifespan, emerging at puberty, fluctuating through the reproductive years, and becoming increasingly common during the menopausal transition. These patterns strongly suggest that ovarian hormones, particularly estradiol (E2), exert a significant influence on the neural circuits that regulate sleep and arousal. Yet, despite the evidence linking hormonal changes to sleep quality, our mechanistic understanding of sleep physiology in females remains limited, including which of the numerous sleep-regulatory regions mediate the E2’s effects on sleep. The study by Kruk et al. [1] offers an important advance by providing direct mechanistic evidence that E2 acts within a specific sleep-regulatory nucleus, the median preoptic nucleus (MnPO), to shape sleep architecture in adult female rats. Interpreting the relationship between circulating estrogens and sleep is complicated by hormonal fluctuations across a woman’s life. During the reproductive years, cyclic changes in ovarian steroids can coincide with shifts in sleep onset and continuity, with some women experiencing sleep fragmentation during periods of high or rapidly changing estradiol. In contrast, as women transition into menopause, the progressive loss of estrogens becomes associated with difficulty staying asleep, increased nighttime awakenings, and reductions in restorative sleep [2–4]. These different patterns across the lifespan underscore how sensitive sleep-regulatory circuits are to both the presence and absence of estradiol. Understanding where and how E2 interacts with sleep circuits is, therefore, critical to understanding the fluctuations in clinical presentations.