Subchronic 17alpha-ethinyl estradiol differentially affects subtypes of sleep and wakefulness in ovariectomized rats

On the basis of sex and sleep: the influence of the estrous cycle and sex on sleep-wake behavior

The recurrent hormonal fluctuations within reproductive cycles impact sleep-wake behavior in women and in rats and mice used in preclinical models of sleep research. Strides have been made in sleep-related clinical trials to include equal numbers of women; however, the inclusion of female rodents in neuroscience and sleep research is lacking. Female animals are commonly omitted from studies over concerns of the effect of estrus cycle hormones on measured outcomes. This review highlights the estrous cycle's broad effects on sleep-wake behavior: from changes in sleep macroarchitecture to regionally specific alterations in neural oscillations. These changes are largely driven by cycle-dependent ovarian hormonal fluctuations occurring during proestrus and estrus that modulate neural circuits regulating sleep-wake behavior. Removal of estrous cycle influence by ovariectomy ablates characteristic sleep changes. Further, sex differences in sleep are present between gonadally intact females and males. Removal of reproductive hormones via gonadectomy in both sexes mitigates some, but not all sex differences. We examine the extent to which reproductive hormones and sex chromosomes contribute to sex differences in sleep-wake behavior. Finally, this review addresses the limitations in our understanding of the estrous cycle's impact on sleep-wake behavior, gaps in female sleep research that are well studied in males, and the implications that ignoring the estrous cycle has on studies of sleep-related processes.

Is sleep deficit associated with infertility and recurrent pregnancy losses? Results from a prospective cohort study

INTRODUCTION

Biological rhythms, the innate cycle of changes in the body's physiological functions, are circadian if they have a 24-hour period. It is known that sleep is a key feature of human circadian rhythm but the relation between sleep and female fertility is largely unknown. This paucity of research is surprising given that circadian rhythms are paramount to human physiology and sleep is related to major female reproductive events. This study was designed to investigate whether there is a difference between the sleep and activity parameters of women with poor reproductive outcome compared with healthy, fertile parous women (comparator group) using subjective (questionnaires) and objective (actigraphy and light exposure) measures.

MATERIAL AND METHODS

A prospective cohort study in a tertiary in vitro fertilization referral center in the UK; composed of three study groups: women diagnosed with recurrent implantation failure, women with recurrent miscarriage (RM) and a comparison group (fertile women without endometrial pathology). Comparison women were selected gynecology patients without endometrial disease (ie perineal complaints or altruistic egg donors). Primary outcome was differences in objective length of sleep in each of the participant groups using actigraphy. Secondary outcomes were subjective sleep quality and quantity, using participant questionnaires, light exposure, and the feasibility of machine learning in activity-pattern interpretation.

RESULTS

Women with recurrent implantation failure slept daily on average for 7 hours 35 minutes (± 57 min), 53 minutes less than the comparison group (P = .03), although quality of their objective sleep, and quantity of their subjective sleep, were not significantly different. Women with recurrent miscarriage slept less that the comparison women (36 minutes less/night) but more than women with recurrent implantation failure (17 minutes more/night). No difference in light exposure was found between recurrent miscarriage and the recurrent implantation failure and comparison groups.

CONCLUSIONS

This study demonstrates an objective observation of sleep time reduction in women with subfertility, although it is not yet clear if this association is casual. Given our increased understanding of the internal body clock and circadian rhythm on fertility, our observation warrants further investigation.

Sex differences in age-related changes in the sleep-wake cycle

Age-related changes in sleep and circadian regulation occur as early as the middle years of life. Research also suggests that sleep and circadian rhythms are regulated differently between women and men. However, does sleep and circadian rhythms regulation age similarly in men and women? In this review, we present the mechanisms underlying age-related differences in sleep and the current state of knowledge on how they interact with sex. We also address how testosterone, estrogens, and progesterone fluctuations across adulthood interact with sleep and circadian regulation. Finally, we will propose research avenues to unravel the mechanisms underlying sex differences in age-related effects on sleep.

Sleep regulation and sex hormones exposure in men and women across adulthood

This review aims to discuss how endogenous and exogenous testosterone exposures in men and estrogens/progesterone exposures in women interact with sleep regulation. In young men, testosterone secretion peaks during sleep and is linked to sleep architecture. Animal and human studies support the notion that sleep loss suppresses testosterone secretion. Testosterone levels decline slowly throughout the aging process, but relatively few studies investigate its impact on age-related sleep modifications. Results suggest that poorer sleep quality is associated with lower testosterone concentrations and that sleep loss may have a more prominent effect on testosterone levels in older individuals. In women, sex steroid levels are characterized by a marked monthly cycle and reproductive milestones such as pregnancy and menopause. Animal models indicate that estrogens and progesterone influence sleep. Most studies do not show any clear effects of the menstrual cycle on sleep, but sample sizes are too low, and research designs often inhibit definitive conclusions. The effects of hormonal contraceptives on sleep are currently unknown. Pregnancy and the postpartum period are associated with increased sleep disturbances, but their relation to the hormonal milieu still needs to be determined. Finally, studies suggest that menopausal transition and the hormonal changes associated with it are linked to lower subjective sleep quality, but results concerning objective sleep measures are less conclusive. More research is necessary to unravel the effects of vasomotor symptoms on sleep. Hormone therapy seems to induce positive effects on sleep, but key concerns are still unresolved, including the long-term effects and efficacy of different hormonal regimens.

Sex chromosomes regulate nighttime sleep propensity during recovery from sleep loss in mice

Sex differences in spontaneous sleep amount are largely dependent on reproductive hormones; however, in mice some sex differences in sleep amount during the active phase are preserved after gonadectomy and may be driven by non-hormonal factors. In this study, we sought to determine whether or not these sex differences are driven by sex chromosome complement. Mice from the four core genotype (FCG) mouse model, whose sex chromosome complement (XY, XX) is independent of phenotype (male or female), were implanted with electroencephalographic (EEG) and electromyographic (EMG) electrodes for the recording of sleep-wake states and underwent a 24-hr baseline recording followed by six hours of forced wakefulness. During baseline conditions in mice whose gonads remained intact, males had more total sleep and non-rapid eye movement sleep than females during the active phase. Gonadectomized FCG mice exhibited no sex differences in rest-phase sleep amount; however, during the mid-active-phase (nighttime), XX males had more spontaneous non-rapid eye movement (NREM) sleep than XX females. The XY mice did not exhibit sex differences in sleep amount. Following forced wakefulness there was a change in the factors regulating sleep. XY females slept more during their mid-active phase siestas than XX females and had higher NREM slow wave activity, a measure of sleep propensity. These findings suggest that the process that regulates sleep propensity is sex-linked, and that sleep amount and sleep propensity are regulated differently in males and females following sleep loss.

Ovarian hormones promote recovery from sleep deprivation by increasing sleep intensity in middle-aged ovariectomized rats

Sleep disturbances are commonly associated with menopause. Hormone replacement therapy is often used to treat various menopausal symptoms, but its efficacy for improving sleep is a matter of debate. We addressed this question by using a rodent model of ovarian hormone loss and replacement in midlife. Middle-aged female rats were ovariectomized and implanted with capsules containing estradiol with or without progesterone, or oil. After two weeks, sleep/wake states were recorded polygraphically during a 24-h baseline period, followed by 6h of sleep deprivation in the second half of the light phase, and a 24-h recovery period. During the baseline dark phase, hormone treatments increased wakefulness, and decreased non-rapid eye movement sleep (NREMS) by shortening NREMS episodes; however, NREMS EEG delta power or energy (cumulative power) was unaffected by combined hormones. Following sleep deprivation, all the groups showed NREMS and rapid eye movement sleep (REMS) rebounds, with similar relative increases from respective baseline levels. The increases in NREMS EEG delta power/energy during recovery were enhanced by combined hormones. These results from middle-aged ovariectomized rats indicate that replacement with estrogen with or without progesterone reduces baseline NREMS without affecting sleep intensity, particularly during the dark (active) phase, whereas following sleep deprivation the same hormone treatments do not affect the ability to increase NREMS or REMS, but treatment with both hormones, in particular, enhances the intensity of recovery sleep. These results support the usefulness of ovariectomized middle-aged rats as a model system to study the biological effects of hormone replacement on sleep regulation.

Female reproductive hormones alter sleep architecture in ovariectomized rats

STUDY OBJECTIVES

Treating ovariectomized rats with physiological levels of estradiol and/or progesterone affects aspects of both baseline (24 h) sleep and recovery (18 h) sleep after 6 h of sleep deprivation. We have extended the analysis of these effects by examining several additional parameters of sleep architecture using the same data set as in our previous study (Deurveilher et al. SLEEP 2009;32(7):865-877).

DESIGN

Sleep in ovariectomized rats implanted with oil, 17 β-estradiol and/or progesterone capsules was recorded using EEG and EMG before, during, and after 6 h of sleep deprivation during the light phase of a 12/12 h light/dark cycle.

MEASUREMENTS AND RESULTS

During the baseline dark, but not light, phase, treatments with estradiol alone or combined with progesterone decreased the mean duration of non-rapid eye movement sleep (NREMS) episodes and the number of REMS episodes, while also increasing brief awakenings, consistent with the previously reported lower baseline NREMS and REMS amounts. Following sleep deprivation, the hormonal treatments caused a larger percentage increase from baseline in the mean durations of NREMS and REMS episodes, and a larger percentage decrease in brief awakenings, consistent with the previously reported larger increase in recovery REMS amount. There were no hormonal effects on NREMS and REMS EEG power values, other than on recovery NREMS delta power, as previously reported.

CONCLUSIONS

Physiological levels of estradiol and/or progesterone in female rats modulate sleep architecture differently at baseline and after acute sleep loss, fragmenting baseline sleep while consolidating recovery sleep. These hormones also play a role in the diurnal pattern of NREMS maintenance.

Estradiol replacement enhances sleep deprivation-induced c-Fos immunoreactivity in forebrain arousal regions of ovariectomized rats

To understand how female sex hormones influence homeostatic mechanisms of sleep, we studied the effects of estradiol (E2) replacement on c-Fos immunoreactivity in sleep/wake-regulatory brain areas after sleep deprivation (SD) in ovariectomized rats. Adult rats were ovariectomized and implanted subcutaneously with capsules containing 17β-E2(10.5 μg; to mimic diestrous E2levels) or oil. After 2 wk, animals with E2capsules received a single subcutaneous injection of 17β-E2(10 μg/kg; to achieve proestrous E2levels) or oil; control animals with oil capsules received an oil injection. Twenty-four hours later, animals were either left undisturbed or sleep deprived by “gentle handling” for 6 h during the early light phase, and killed. E2treatment increased serum E2levels and uterus weights dose dependently, while attenuating body weight gain. Regardless of hormonal conditions, SD increased c-Fos immunoreactivity in all four arousal-promoting areas and four limbic and neuroendocrine nuclei studied, whereas it decreased c-Fos labeling in the sleep-promoting ventrolateral preoptic nucleus (VLPO). Low and high E2treatments enhanced the SD-induced c-Fos immunoreactivity in the laterodorsal subnucleus of the bed nucleus of stria terminalis and the tuberomammillary nucleus, and in orexin-containing hypothalamic neurons, with no effect on the basal forebrain and locus coeruleus. The high E2treatment decreased c-Fos labeling in the VLPO under nondeprived conditions. These results indicate that E2replacement modulates SD-induced or spontaneous c-Fos expression in sleep/wake-regulatory and limbic forebrain nuclei. These modulatory effects of E2replacement on neuronal activity may be, in part, responsible for E2's influence on sleep/wake behavior.

Effect of 17alpha-ethinyl estradiol on active phase rapid eye movement sleep microarchitecture

Estrogen treatment decreases active phase rapid eye movement (REM) sleep in ovariectomized rats. Here we explored further the effect of 17alpha-ethinyl estradiol (17alpha-EE) on active phase REM sleep in ovariectomized rats by analyzing spectral properties and the number and length of REM sleep bouts. The greatest suppression of REM sleep occurred on day 4 of 17alpha-EE treatment, was due to decreases in bout length, and was accompanied by decreased EEG theta power. These results further elucidate 17alpha-EE's effects on REM sleep and provide greater understanding of the mechanisms by which estrogens alter sleep-wakefulness patterns.

Estradiol suppresses rapid eye movement sleep and activation of sleep-active neurons in the ventrolateral preoptic area

Studies from multiple species, including humans, suggest that gonadal hormones, and ovarian hormones in particular, influence the physiology of sleep, but the mechanisms by which these hormones influence sleep behaviors are unknown. Previously, we demonstrated a 50% reduction in lipocalin-prostaglandin D synthase (L-PGDS) transcript levels, following estradiol treatment, at the level of the ventrolateral preoptic area (VLPO), a putative sleep-active nucleus. Catalytic activity of L-PGDS produces prostaglandin D(2) (PGD(2)), an endogenous somnogen. Based on our previous studies, we hypothesized that estradiol is acting via PGD(2) to suppress neuronal activity in the VLPO of females. To begin to test whether this is true, we quantified the number of Fos-immunopositive cells in hormonally manipulated male and female rats. We found that in females during the light phase, estradiol suppressed Fos expression in VLPO neurons. Interestingly, protein expression of L-PGDS followed the same pattern. Surprisingly, changes in the hormonal milieu of males had no effect. Using telemetry to record electroencephalograms from gonadally intact females, we found, in the light phase of proestrus when estradiol levels are high, a marked reduction in rapid eye movement (REM) sleep compared with the other days of the estrous cycle. However, during the dark phase of proestrus when estrogen and progesterone levels are elevated, significantly less time was spent in both non-REM and REM sleep. Thus, it seems that hormones in females play a major role in the regulation of sleep and arousal via activation of neurons in key sleep and arousal centers.