Nocturnal Hot Flashes, but Not Serum Hormone Concentrations, as a Predictor of Insomnia in Menopausal Women: Results from the Midlife Women's Health Study.

Background: Sleep disruptions are among the most common symptoms experienced during menopause and can be associated with depression, hot flashes, and fluctuating hormones. However, few studies have examined how such risk factors influence sleep in midlife women in a network-based approach that will establish the complex relationship between variables. Materials and Methods: We used a Bayesian network (BN) to examine the relationship between multiple factors known to influence sleep and depression in midlife women, including hormone concentrations, hot flashes, and menopause status among participants of the longitudinal Midlife Women's Health Study. In year 1, 762 women (45-54 years of age) answered questions regarding the frequency of insomnia, hot flashes, and depression; 389 of the same women answered similar questions at year 4. We measured serum hormones and calculated free estradiol index, free testosterone index, and ratios of estradiol:progesterone, and estradiol:testosterone. For our model, we calculated the change in frequency of insomnia, depression, and covariates (body mass index, menopause status, hot flashes at night, and present quality of life) from year 1 to 4. Results: Using a BN, we found that self-reported hot flashes at night, and no other factors, were direct predictors of self-reported insomnia in year 1. Surprisingly, we did not identify an association between hormone concentrations and self-reported insomnia. Frequency of insomnia in year 4 was only predicted by frequency of insomnia in year 1, whereas frequency of depression in year 4 was predicted by year 4 insomnia and frequency of depression in year 1. No other factors were direct predictors of insomnia or depression in our model. Conclusions: Therefore, hot flashes at night, previous insomnia, and depression are stronger predictors of how women will self-report frequency of sleep disruptions and treatment may reduce menopausal sleep complaints.

Preliminary findings reveal that phthalate exposure is associated with both subjective and objective measures of sleep in a small population of midlife women.

Phthalates are endocrine-disrupting chemicals that influence endogenous hormones. Few studies have examined the link between phthalates and menopause. A recent secondary analysis revealed that phthalates were associated with self-reported sleep measures in perimenopausal women. However, the associations between phthalate exposure and additional measures of sleep remain unknown. We recruited a population of 27 midlife women (aged 45-54) to study the relationship between phthalate exposure and both subjective and objective measures of sleep. Preliminary results indicate that women with higher phthalate exposure have reduced sleep quality, more frequent sleep disruptions, and more restless sleep compared to women with lower exposure.

Association of phthalate exposure and endogenous hormones with self-reported sleep disruptions: results from the Midlife Women's Health Study.

OBJECTIVE: Follicle-stimulating hormone and estradiol (E2) have been associated with sleep in midlife women, however, few studies have examined the association of other hormones or environmental chemical exposure such as phthalates, with self-reported sleep quality. We assessed the relationship of self-reported sleep with hormones and phthalates. METHODS: In total, 762 women (aged 45-54 y, 459 premenopausal, and 303 perimenopausal) from the Midlife Women's Health Study answered self-reported questions regarding the frequency of sleep disturbances, insomnia, and restless sleep. Serum E2, progesterone, testosterone, serum hormone binding globulin, free E2 index, free testosterone index, E2:progesterone, and E2:testosterone were measured. Summary measures of phthalate mixtures, including the phthalates from plastic sources (sumPLASTIC), personal care products (sumPCP), di-(2-ethyhexyl) phthalate (sumDEHP), anti-androgenic phthalates (sumAA), and all phthalate metabolites measured (sumALL), were calculated from urinary phthalate metabolites. Ordinal logistic regression was used to fit each outcome sleep measure with all hormones and summary phthalates. RESULTS: Progesterone and testosterone were significantly negatively associated with the frequency of sleep disturbances and insomnia. Free testosterone index was also negatively associated with insomnia frequency. E2:progesterone was positively associated with frequency of sleep disturbances and restless sleep in self-reported nonsmokers. SumPCP and sumALL were significantly negatively associated with frequency of sleep disturbances, insomnia, and restless sleep. SumDEHP and sumPLASTIC were negatively associated with insomnia frequency. Further, the direction of association between phthalates and sleep appears to be dependent on the quartile of phthalate exposure. All significant associations between phthalates and sleep were in self-reported nonsmokers or former smokers. CONCLUSIONS: Our study supports previous literature that hormones beyond follicle-stimulating hormone and E2 are associated with sleep disruptions in menopause. Further, we are among the first to show that phthalate exposure is associated with sleep disruptions in midlife women.

Pharmacological challenges examining the underlying mechanism of altered response inhibition and attention due to circadian disruption in adult Long-Evans rats.

Endogenous circadian rhythms govern behavior and physiology, while circadian disruption is an environmental factor that impacts cognition by altering the circadian clock at a molecular level. We modeled the effects of 2 sources of circadian disruption - activity occurring during typical rest periods and untimely light exposure - to evaluate the effects of circadian disruption on behavior and underlying neurochemistry. Firstly, adult Long-Evans rats of both sexes were maintained on a 12 h:12 h light:dark cycle and tested using a 5-choice serial reaction time task (5-CSRTT) under 3 conditions: 4 h into the dark phase with no exposure to ambient light during testing (control), 4 h into the dark phase with exposure to ambient light during testing, and 4 h into the light phase. Both models resulted in impulsive behavior and reduced attention compared to control. We established that changes in the diurnal expression pattern occur in the clock gene Period 2 (Per2) in the light phase-tested model. Choline acetyltransferase (Chat) and Dopamine receptor 1 (Drd1) showed rhythmic expression with peak expression during the dark phase regardless of light-testing condition. Next, we performed drug challenges in a new rat cohort to examine the interaction between the cholinergic and dopaminergic neurotransmitter systems in regulating the behavioral changes caused by circadian disruption. We administered the cholinergic agonist nicotine and either the dopamine-1 receptor (DR1) antagonist SCH23390 or the DR2 antagonist eticlopride under the 3 circadian conditions to identify differential drug responses between treatment groups. Rats in both models demonstrated increased sensitivity to nicotine as compared to control, while SCH23390 and eticlopride ameliorated the effect of nicotine on 5-CSRTT performance in both models. Our study is the first to identify detrimental effects of both models of circadian disruption on impulsive behavior, and that the effects of circadian disruption are mediated by an interaction between cholinergic and dopaminergic systems.

Modulation of circadian rhythms through estrogen receptor signaling.

Circadian rhythms are physiological and behavioral processes that exhibit a 24-hr cycle. These daily rhythms are essential for living organisms to align their behavior and physiology with the environment to increase the likelihood of survival. In mammals, circadian rhythms synchronize with the environment primarily by the suprachiasmatic nucleus, a hypothalamic brain region that integrates exogenous and endogenous timing cues. Sex steroid hormones, including estrogens, are thought to modulate sexually dimorphic behaviors through developmental programming of the brain (i.e., organization), as well as acute receptor signaling during adulthood (i.e., activation). Importantly, there are known sex differences in the expression of circadian locomotor activity and molecular organization of the suprachiasmatic nucleus, likely due, in part, to the actions of circulating estrogens. Circadian locomotor rhythms, which are coordinated by the suprachiasmatic nucleus, have been shown to be regulated by developmental and adult levels of circulating estrogens. Further, increasing evidence suggests that estrogens can modulate expression of circadian clock genes that are essential for orchestration of circadian rhythms by the suprachiasmatic nucleus. In this review, we will discuss the organizational and activational modulation of the circadian timekeeping system by estrogens through estrogen receptor signaling.

Exposure to di-(2-ethylhexyl) phthalate transgenerationally alters anxiety-like behavior and amygdala gene expression in adult male and female mice.

Phthalates are industrial plasticizers and stabilizers commonly found in polyvinyl chloride plastic and consumer products, including food packaging, cosmetics, medical devices, and children's toys. Di-(2-ethylhexyl) phthalate (DEHP), one of the most commonly used phthalates, exhibits endocrine-disrupting characteristics and direct exposure leads to reproductive deficits and abnormalities in anxiety-related behaviors. Importantly, increasing evidence indicates that the impacts of DEHP exposure on reproduction and social behavior persist across multiple generations. In this study, we tested the hypothesis that transgenerational DEHP exposure alters anxiety-like behavior and neural gene expression in both male and female mice. Pregnant CD-1 mice were orally dosed daily with either tocopherol-stripped corn oil or DEHP (20 or 200 µg/kg/day; 500 or 750 mg/kg/day) from gestational day 10.5 until birth to produce the F1 generation. Females from each generation were bred with untreated, unrelated CD-1 males to produce subsequent generations. Behavior and gene expression assays were performed with adult, intact F3 males and females. Transgenerational DEHP exposure increased time spent in the open arm in the elevated plus maze for adult females (750 mg/kg/day lineage), but not males. In adult females, we observed a down-regulation of mRNA expression of estrogen receptor 1 in the 200 µg/kg/day and 500 mg/kg/day treatment lineages, mineralocorticoid receptor in the 200 µg/kg/day lineage, and dopamine receptor 2 in the 20 µg/kg/day and 750 mg/kg/day lineages. In adult males, we found an up-regulation of estrogen receptor 2 in the 20 and 200 µg/kg/day lineages, and dopamine receptor 1 in the 20 µg/kg/day and 750 mg/kg/day lineages. No hippocampal gene expression modifications were observed in response to treatment. These results implicate dose-specific transgenerational effects on behavior and neural gene expression in adult male and female mice.

Factors associated with poor sleep during menopause: results from the Midlife Women's Health Study.

BACKGROUND: Poor sleep is one of the most common problems reported during menopause, and is known to vary throughout the menopause transition. The objective of this study was to describe the dynamics of poor sleep among participants of the Midlife Women's Health Study and to identify risk factors associated with poor sleep during the menopausal transition. METHODS: Annual responses to surveys that included questions about the frequency of sleep disturbances and insomnia were analyzed to determine the likelihood of persistent poor sleep throughout the menopausal transition and the correlation of responses to the different sleep-related questions, including frequency of restless sleep during the first year of the study. Responses to questions about a large number of potential risk factors were used to identify risk factors for poor sleep. RESULTS: Poor sleep in premenopause was not predictive of poor sleep in perimenopause, and poor sleep in perimenopause was not predictive of poor sleep in postmenopause. Frequencies of each of the measures of poor sleep were highly correlated. For all sleep outcomes, high frequency of depression was related to a high frequency of poor sleep. Vasomotor symptoms were also significantly related with a higher frequency of all poor sleep outcomes. A history of smoking was also associated with higher frequencies of insomnia and sleep disturbances. CONCLUSIONS: The risk factors identified for poor sleep, depression and vasomotor symptoms, were consistently associated with poor sleep throughout the menopausal transition. The likelihood of these risk factors changed from premenopause, through perimenopause, and into postmenopause, however, which could explain changes in sleep difficulties across the menopausal transition. Treatment of these risk factors should be considered when addressing sleep difficulties in menopausal women.

Circadian disruption affects initial learning but not cognitive flexibility in an automated set-shifting task in adult Long-Evans rats.

A sizeable percent of adults are subject to circadian disturbances such as shift work, which involves misalignment of time of light exposure, activity periods, sleep, and eating. Chronic adherence to disruptive circadian schedules can negatively impact cognitive functioning. Developing preclinical models of circadian disruption allow investigation of the relationship and underlying mechanisms between circadian disruption and cognitive functioning. We placed adult Long-Evans rats of both sexes on a 12:12h light:dark schedule in which rats performed an automated operant-behavior task for 3months, with daily testing occurring either 4h after lights-on or lights-off. At the end of this period, rats were tested on an automated set-shifting task to compare the effects of the 2 testing schedules on cognitive flexibility, which is the focus of this report. Over the initial 3-month period, day-tested rats shifted to a diurnal activity schedule, with males shifting more effectively than females, while night-tested rats remained nocturnal. Upon beginning the set-shifting task, night-tested rats took longer to reach criterion performance in the initial, visual-cue detection stage as compared to day-tested rats. The groups did not differ in performance on subsequent egocentric-cue based and reversal phases. Sex-related differences in task performance unrelated to testing schedule, particularly longer latencies to lever press in females, were also detected. One possible explanation for our findings is that the night-tested rats also experienced a form of circadian disruption when they were exposed to ambient light during the daily testing sessions, and that the form they experienced was more detrimental to initial acquisition of the task than testing during the light phase. Subsequent experiments will incorporate a night-tested group that is not exposed to ambient light in order to better understand the effect seen in the night-tested rats in the current study.

Loss of Fertility in the Absence of Progesterone Receptor Expression in Kisspeptin Neurons of Female Mice.

Ovarian steroids, estradiol and progesterone, play central roles in regulating female reproduction by acting as both positive and negative regulators of gonadotropin-releasing hormone (GnRH) secretion in the hypothalamus. Recent studies have identified kisspeptin neurons of the hypothalamus as the target of estrogenic regulation of GnRH secretion. In this study, we aimed to determine the significance of progesterone receptor (PGR) expression in the kisspeptin neurons. To this end, the Pgr gene was selectively ablated in mouse kisspeptin neurons and the reproductive consequence assessed. The hypothalamus of the Pgr deficient female mouse expressed kisspeptin, the pituitary released LH in response to GnRH stimulation, and the ovary ovulated when stimulated with gonadotropins. However, the mutant mouse gradually lost cyclicity, was unable to generate a LH surge in response to rising estradiol, and eventually became infertile. Taken together, these results indicate that the loss of PGR impairs kisspeptin secretory machinery and therefore that PGR plays a critical role in regulating kisspeptin secretion.

Changes in estrogen receptor signaling alters the timekeeping system in male mice.

Circadian rhythms are modulated by steroid hormones; however, the mechanisms of this action are not fully understood, particularly in males. In females estradiol regulates activity level, pattern of expression, and free running period (tau). We tested the hypothesis that activity level and distribution in male mice includes both classical and "non-classical" actions of estrogens at the estrogen receptor subtype 1 (ESR1). We used transgenic mice with mutations in their estrogen response pathways: ESR1 knock-out (ERKO) mice lack the ability to respond to estrogens via ESR1. "Non-classical" estrogen receptor knock-in (NERKI) mice have an inserted ESR1 receptor with a mutation in the estrogen-response-element binding domain, allowing activation via non-genomic and second messenger pathways. Gonadectomized male NERKI, ERKO, and wildtype (WT) littermates were given oil, or low or high dose estradiol and daily activity parameters were quantified. Estradiol shortened the ratio of activity in the light relative to dark (LD ratio), shortened tau, advanced the time of activity onset, and altered responsiveness to light cues administered in the late subjective night, suggesting modulation by an ESR1-independent mechanism. Estradiol treatment in NERKI but not WT males altered the timing of activity onset, LD ratio, and the behavioral response to light cues. These results may represent disruptions in the balance of genomic/nongenomic or ESR1/ESR2 signaling pathways. We also found a significant genotype effect on total activity, LD ratio, tau, and activity duration. These data provide new information about the role of ESR1-dependent and independent signaling pathways on the timekeeping system in male mice.

Estrogen receptor 1 modulates circadian rhythms in adult female mice.

Estradiol influences the level and distribution of daily activity, the duration of the free-running period, and the behavioral phase response to light pulses. However, the mechanisms by which estradiol regulates daily and circadian rhythms are not fully understood. We tested the hypothesis that estrogens modulate daily activity patterns via both classical and "non-classical" actions at the estrogen receptor subtype 1 (ESR1). We used female transgenic mice with mutations in their estrogen response pathways; ESR1 knock-out (ERKO) mice and "non-classical" estrogen receptor knock-in (NERKI) mice. NERKI mice have an ESR1 receptor with a mutation in the estrogen-response-element binding domain, allowing only actions via "non-classical" genomic and second messenger pathways. Ovariectomized female NERKI, ERKO, and wildtype (WT) mice were given a subcutaneous capsule with low- or high-dose estradiol and compared with counterparts with no hormone replacement. We measured wheel-running activity in a light:dark cycle and constant darkness, and the behavioral phase response to light pulses given at different points during the subjective day and night. Estradiol increased average daily wheel-running, consolidated activity to the dark phase, and shortened the endogenous period in WT, but not NERKI and ERKO mice. The timing of activity onset during entrainment was advanced in all estradiol-treated animals regardless of genotype suggesting an ESR1-independent mechanism. We propose that estradiol modifies period, activity level, and distribution of activity via classical actions of ESR1 whereas an ESR1 independent mechanism regulates the phase of rhythms.

Photic phase-response curve in 2 strains of mice with impaired responsiveness to estrogens.

Steroid hormones including estrogens modulate the expression of daily activity and circadian rhythms, including free-running period, phase angle of activity onset, and response to light. The mechanisms underlying these effects, however, are not fully understood. We tested the hypothesis that estrogen signaling is required for photic responsiveness of the circadian timing system. We used estrogen receptor subtype 1 (ESR1) knock-out mice (ERKO) and nonclassic estrogen receptor knock-in mice (NERKI). ERKO animals are unable to respond to estrogen at ESR1, and NERKI animals lack the ability to respond to estrogens via estrogen response element-mediated transcription but still respond via nonclassical mechanisms. We analyzed behavioral shifts in activity onset in response to 1-h light pulses given across the subjective 24-h day in gonadally intact male and female NERKI, ERKO, and wild-type (WT) littermates. We also examined Fos protein expression in the suprachiasmatic nucleus, the site of the master circadian pacemaker, at 2 times of day. We found a significant effect of genotype on phase shifts in response to light pulses given in the subjective night. Female WT mice had a significantly larger phase response than ERKO females during the early subjective night (phase shift of 98 min and 58 min, respectively; p < 0.05). NERKI females were intermediate to WT and ERKO females, suggesting a contribution of nonclassical estrogen signaling on circadian timekeeping functions. This genotype effect is not observed in males; they did not have a difference in phase shifts following a light pulse at any time point. WT males, however, shifted an average of 47 min less than did females at zeitgeber time (ZT) 16 (ZT 0 lights-on and ZT 12 lights-off). These data indicate that estrogens modify the response of the circadian timekeeping system to light via classical and nonclassical signaling pathways.

Genetic polymorphisms in the aryl hydrocarbon receptor-signaling pathway and sleep disturbances in middle-aged women.

OBJECTIVE: We aimed to determine if selected genetic polymorphisms in the aryl hydrocarbon receptor (AHR)-signaling pathway and circadian locomotor output cycles kaput (CLOCK) are associated with insomnia and early awakening in middle-aged women. METHODS: Women aged 45 to 54years (n=639) were recruited into a middle-aged health study and agreed to complete questionnaires and donate blood samples. Questionnaires were used to assess sleep outcomes. Blood samples were processed for genotyping for the selected polymorphisms: AHR (rs2066853), AHR repressor (AHRR) (rs2292596), aryl hydrocarbon nuclear translocator (ARNT) (rs2228099), and CLOCK (rs1801260). Data were analyzed using multivariable logistic regression. RESULTS: Women heterozygous for the AHRR alleles (GC) had decreased odds of insomnia compared to women homozygous for the AHRR_C allele (adjusted odds ratio [aOR], 0.69; 95% confidence interval [CI], 0.49-0.96). Women with at least one of the AHRR_G or CLOCK_C alleles had significantly decreased odds of insomnia compared to women homozygous for the AHRR_C and CLOCK_T alleles (aOR, 0.64; 95% CI, 0.43-0.96). Additionally, women homozygous for the AHRR_G and CLOCK_C alleles had significantly decreased odds of insomnia compared to women homozygous for the AHRR_C and CLOCK_T alleles (aOR, 0.56; 95% CI, 0.35-0.89). None of the selected single nucleotide polymorphisms (SNPs) or combinations of SNPs were significantly associated with early awakening. CONCLUSIONS: Selected genetic polymorphisms in the AHR-signaling pathway (i.e., AHRR) and CLOCK may play a role in decreasing the risk for experiencing insomnia during the menopausal transition.

A retrospective study of circadian and seasonal presentations of dogs with congestive heart failure: 119 cases (1997-2009).

OBJECTIVES: To test the hypothesis that there is a daily or seasonal rhythm in the presentation of congestive heart failure (CHF) in dogs. DESIGN: Retrospective case series from 1997 to 2009. SETTING: Small animal veterinary teaching hospital. ANIMALS: One hundred and nineteen dogs with 126 acute presentations of CHF. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Medical records from a veterinary teaching hospital were searched for the occurrence of CHF. The effect of admission time, weekday, month, and season were analyzed separately using chi-square tests. CHF presentations were largely confined to Monday and Tuesday (57%) and between 9 am and 11:59 am (55%). CHF was more common during September, October, and November (37%). CONCLUSIONS: Information from this study may assist veterinarians in educating clients about the timing of clinical signs, and enable veterinary hospitals to anticipate CHF cases during certain times of the day and year.

Sleep, rhythms, and the endocrine brain: influence of sex and gonadal hormones.

While much is known about the mechanisms that underlie sleep and circadian rhythms, the investigation into sex differences and gonadal steroid modulation of sleep and biological rhythms is in its infancy. There is a growing recognition of sex disparities in sleep and rhythm disorders. Understanding how neuroendocrine mediators and sex differences influence sleep and biological rhythms is central to advancing our understanding of sleep-related disorders. While it is known that ovarian steroids affect circadian rhythms in rodents, the role of androgen is less understood. Surprising findings that androgens, acting via androgen receptors in the master "circadian clock" within the suprachiasmatic nucleus, modulate photic effects on activity in males point to novel mechanisms of circadian control. Work in aromatase-deficient mice suggests that some sex differences in photic responsiveness are independent of gonadal hormone effects during development. In parallel, aspects of sex differences in sleep are also reported to be independent of gonadal steroids and may involve sex chromosome complement. This a summary of recent work illustrating how sex differences and gonadal hormones influence sleep and circadian rhythms that was presented at a Mini-Symposium at the 2011 annual meeting of the Society for Neuroscience.

Estradiol deficiency during development modulates the expression of circadian and daily rhythms in male and female aromatase knockout mice.

Gonadal steroids modify the phase, amplitude and period of circadian rhythms. To further resolve the role of estradiol, we examined daily patterns of activity, circadian free running period and behavioral responses to light pulses using aromatase deficient (ArKO) mice. These animals lack the enzyme necessary to produce estradiol. We hypothesized that circulating estrogens during development and adulthood modulate the amount of activity, the temporal relationship of activity patterns relative to a light:dark cycle, and the free running period. Intact and gonadectomized male and female ArKO and wildtype (WT) littermates were used. WT males, but not ArKO males, retained the ability to respond to steroid hormones; the time of activity onset, free running period in constant darkness, and total daily activity were significantly different in gonadectomized compared to intact males. In contrast, gonadectomy did not alter the expression of these variables in ArKO males. ArKO females had a longer free running period in constant darkness compared to WT females regardless of gonadal state. Ovariectomized ArKO females had a significantly delayed activity onset when compared to intact ArKO females and ovariectomized WT females, despite all 3 groups being estrogen deficient. Phase shifts in response to light pulses given at different times of the day revealed an interaction between genotype, sex, and circulating steroids. These results from ArKO animals strongly suggest an organizational effect of estradiol during a critical period of development on the expression of biological rhythms.

Characterization of the estrous cycle in Octodon degus.

We characterized the reproductive cycle of Octodon degus to determine whether reproductive maturation is spontaneous in juveniles and if ovarian cyclicity and luteal function are spontaneous in adults. Laboratory-reared prepubertal and adult females were monitored for vaginal patency and increased wheel-running. Sexual receptivity was assessed by pairing adult females with a male 1) continuously, 2) at the time of vaginal patency, or 3) following estradiol treatment. Blood samples were assayed for estradiol and progesterone concentrations on Days 1, 4, 8, and 16 relative to vaginal opening. Ovarian tissues were collected 6 and 16 days after behavioral estrus and 6 days after copulation for histology. In juveniles, the onset of cyclic vaginal patency and increased wheel-running activity was spontaneous, occurred in the absence of proximal male cues, and appeared at regular intervals (17.5 ± 1.4 days). In adults, vaginal patency and increased wheel-running occurred cyclically (21.2 ± 0.6 days) in the absence of proximal male cues, and these traits predicted the time of sexual receptivity. Corpora lutea develop spontaneously and are maintained for 12-14 days. The ovaries had well-developed corpora lutea 6 days after mating and 6 days after estrus without mating. Progesterone concentrations were highest in the second half of the cycle when corpora lutea were present and estradiol concentrations peaked on the day of estrus. Thus, female degus appear to exhibit a spontaneous reproductive cycle consistent with other Hystricognathi rodents. Octodon degus is a novel model with which to examine the mechanisms underlying different reproductive cycles.

Developmental programming: impact of fetal exposure to endocrine-disrupting chemicals on gonadotropin-releasing hormone and estrogen receptor mRNA in sheep hypothalamus.

Bisphenol-A (BPA) and methoxychlor (MXC), two endocrine-disrupting chemicals (EDCs) with estrogenic and antiandrogenic effects, disrupt the reproductive system. BPA has profound effects on luteinizing hormone (LH) surge amplitude, and MXC has profound effects on on LH surge timing in sheep. The neural mechanisms involved in the differential disruption of the LH surge by these two EDCs remain to be elucidated. We tested the hypothesis that the differential effects of BPA and MXC on LH surge system involved changes in hypothalamic gonadotropin-releasing hormone (GnRH) and estrogen receptors (ESR), ESR1 and ESR2, mRNA expression. Pregnant sheep were given daily injections of cottonseed oil (controls), MXC, or BPA (5mg/kg/day) from day 30 to 90 of gestation (term 147d). Offspring from these animals were euthanized as adults, during the late follicular phase following synchronization of estrus with prostaglandin F(2alpha), just before the expected onset of preovulatory LH surge and changes in mRNA expression of hypothalamic GnRH, ESR1, and ESR2 quantified following in situ hybridization. GnRH mRNA expression was significantly lower in both groups of EDC-treated females compared to controls. ESR1 expression was increased in prenatal BPA- but not MXC-treated females in medial preoptic area relative to controls. In contrast, ESR2 expression was reduced in the medial preoptic area of both EDC-treated groups. Differences in expression of ESR1/ESR2 receptors may contribute to the differential effects of BPA and MXC on the LH surge system. These findings provide support that prenatal exposure to EDCs alters the neural developmental trajectory leading to long-term reproductive consequences in the adult female.

Shift work, jet lag, and female reproduction.

Circadian rhythms and "clock gene" expression are involved in successful reproductive cycles, mating, and pregnancy. Alterations or disruptions of biological rhythms, as commonly occurs in shift work, jet lag, sleep deprivation, or clock gene knock out models, are linked to significant disruptions in reproductive function. These impairments include altered hormonal secretion patterns, reduced conception rates, increased miscarriage rates and an increased risk of breast cancer. Female health may be particularly susceptible to the impact of desynchronizing work schedules as perturbed hormonal rhythms can further influence the expression patterns of clock genes. Estrogen modifies clock gene expression in the uterus, ovaries, and suprachiasmatic nucleus, the site of the primary circadian clock mechanism. Further work investigating clock genes, light exposure, ovarian hormones, and reproductive function will be critical for indentifying how these factors interact to impact health and susceptibility to disease.

Daily immediate early gene expression in the suprachiasmatic nucleus of male and female Octodon degus.

Diurnal and nocturnal species have different patterns of general activity, sleep-wake rhythms, and endocrine rhythms, but the mechanisms underlying these differences are not clear. Here, we tested the hypothesis that rhythms in immediate early gene (IEG) products in the suprachiasmatic nucleus (SCN) of a diurnal rodent (Octodon degus) reflect their diurnal chronotype. We also compared male and female degus with respect to temporal patterns of expression of one of these gene products, Fos-related Antigen (FRA). Animals were killed across the light:dark cycle, brains were collected, and sections through the SCN were stained for FRA (females and males) or c-Fos and Calbindin (males only) using immunocytochemistry. An additional set of females placed in constant darkness was pulsed with light (or not) during the subjective day or night. Labeled cells in the SCN were counted in all animals. In males, c-Fos/FRA positive (+) cell counts in the dorsomedial SCN were low after lights-on and peaked around the time of lights-off (ZT 13, ZT 0=lights-on). Effect size analyses indicated that females have a 24 h rhythm in FRA expression that is shifted relative to that of males. Light pulses in the subjective day and night produced area-specific changes in IEG expression in females that differs from that reported for males. Overall, these studies reveal the pattern of immediate early gene expression in the SCN of degus is not the same in males and females, and that it differs from the one seen in other species, both nocturnal and diurnal.