A randomized controlled trial to compare the effects of time-restricted eating versus Mediterranean diet on symptoms and quality of life in bipolar disorder

BACKGROUND

The primary objective of this randomized controlled trial (RCT) is to establish the effectiveness of time-restricted eating (TRE) compared with the Mediterranean diet for people with bipolar disorder (BD) who have symptoms of sleep disorders or circadian rhythm sleep-wake disruption. This work builds on the growing evidence that TRE has benefits for improving circadian rhythms. TRE and Mediterranean diet guidance will be offered remotely using self-help materials and an app, with coaching support.

METHODS

This study is an international RCT to compare the effectiveness of TRE and the Mediterranean diet. Three hundred participants will be recruited primarily via social media. Main inclusion criteria are: receiving treatment for a diagnosis of BD I or II (confirmed via DIAMOND structured diagnostic interview), endorsement of sleep or circadian problems, self-reported eating window of ≥ 12 h, and no current mood episode, acute suicidality, eating disorder, psychosis, alcohol or substance use disorder, or other health conditions that would interfere with or limit the safety of following the dietary guidance. Participants will be asked to complete baseline daily food logging for two weeks and then will be randomly allocated to follow TRE or the Mediterranean diet for 8 weeks, during which time, they will continue to complete daily food logging. Intervention content will be delivered via an app. Symptom severity interviews will be conducted at baseline; mid-intervention (4 weeks after the intervention begins); end of intervention; and at 6, 9, and 15 months post-baseline by phone or videoconference. Self-rated symptom severity and quality of life data will be gathered at those timepoints, as well as at 16 weeks post baseline. To provide a more refined index of whether TRE successfully decreases emotional lability and improves sleep, participants will be asked to complete a sleep diary (core CSD) each morning and complete six mood assessments per day for eight days at baseline and again at mid-intervention.

DISCUSSION

The planned research will provide novel and important information on whether TRE is more beneficial than the Mediterranean diet for reducing mood symptoms and improving quality of life in individuals with BD who also experience sleep or circadian problems.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT06188754.

Neural substrates underlying rhythmic coupling of female reproductive and thermoregulatory circuits

Coordinated fluctuations in female reproductive physiology and thermoregulatory output have been reported for over a century. These changes occur rhythmically at the hourly (ultradian), daily (circadian), and multi-day (ovulatory) timescales, are critical for reproductive function, and have led to the use of temperature patterns as a proxy for female reproductive state. The mechanisms underlying coupling between reproductive and thermoregulatory systems are not fully established, hindering the expansion of inferences that body temperature can provide about female reproductive status. At present, numerous digital tools rely on temperature to infer the timing of ovulation and additional applications (e.g., monitoring ovulatory irregularities and progression of puberty, pregnancy, and menopause are developed based on the assumption that reproductive-thermoregulatory coupling occurs across timescales and life stages. However, without clear understanding of the mechanisms and degree of coupling among the neural substrates regulating temperature and the reproductive axis, whether such approaches will bear fruit in particular domains is uncertain. In this overview, we present evidence supporting broad coupling among the central circuits governing reproduction, thermoregulation, and broader systemic physiology, focusing on timing at ultradian frequencies. Future work characterizing the dynamics of reproductive-thermoregulatory coupling across the lifespan, and of conditions that may decouple these circuits (e.g., circadian disruption, metabolic disease) and compromise female reproductive health, will aid in the development of strategies for early detection of reproductive irregularities and monitoring the efficacy of fertility treatments.

S-Cone Photoreceptors Regulate Daily Rhythms and Light-Induced Arousal/Wakefulness in Diurnal Grass Rats (Arvicanthis niloticus)

Beyond visual perception, light has non-image-forming effects mediated by melanopsin-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs). The present study first used multielectrode array recordings to show that in a diurnal rodent, Nile grass rats (Arvicanthis niloticus), ipRGCs generate rod/cone-driven and melanopsin-based photoresponses that stably encode irradiance. Subsequently, two ipRGC-mediated non-image-forming effects, namely entrainment of daily rhythms and light-induced arousal, were examined. Animals were first housed under a 12:12 h light/dark cycle (lights-on at 0600 h) with the light phase generated by a low-irradiance fluorescent light (F12), a daylight spectrum (D65) stimulating all photoreceptors, or a narrowband 480 nm spectrum (480) that maximized melanopsin stimulation and minimized S-cone stimulation (λ_max 360 nm) compared to D65. Daily rhythms of locomotor activities showed onset and offset closer to lights-on and lights-off, respectively, in D65 and 480 than in F12, and higher day/night activity ratio under D65 versus 480 and F12, suggesting the importance of S-cone stimulation. To assess light-induced arousal, 3-h light exposures using 4 spectra that stimulated melanopsin equally but S-cones differentially were superimposed on F12 background lighting: D65, 480, 480 + 365 (narrowband 365 nm), and D65 - 365. Compared to the F12-only condition, all four pulses increased in-cage activity and promoted wakefulness, with 480 + 365 having the greatest and longest-lasting wakefulness-promoting effects, again indicating the importance of stimulating S-cones as well as melanopsin. These findings provide insights into the temporal dynamics of photoreceptor contributions to non-image-forming photoresponses in a diurnal rodent that may help guide future studies of lighting environments and phototherapy protocols that promote human health and productivity.

Continuous body temperature as a window into adolescent development

Continuous body temperature is a rich source of information on hormonal status, biological rhythms, and metabolism, all of which undergo stereotyped change across adolescence. Due to the direct actions of these dynamic systems on body temperature regulation, continuous temperature may be uniquely suited to monitoring adolescent development and the impacts of exogenous reproductive hormones or peptides (e.g., hormonal contraception, puberty blockers, gender affirming hormone treatment). This mini-review outlines how traditional methods for monitoring the timing and tempo of puberty may be augmented by markers derived from continuous body temperature. These features may provide greater temporal precision, scalability, and reduce reliance on self-report, particularly in females. Continuous body temperature data can now be gathered with ease across a variety of wearable form factors, providing the opportunity to develop tools that aid in individual, parental, clinical, and researcher awareness and education.

Female mice exhibit less overall variance, with a higher proportion of structured variance, than males at multiple timescales of continuous body temperature and locomotive activity records

Despite recent work demonstrating that female rodents and humans do not show greater variance in behavior and physiology than males due to ovulatory cycles, many researchers still default to using males in their investigations. Although government funding agencies now require inclusion of female subjects where applicable, the erroneous belief that the study of males reduces overall data variance continues to result in male subject bias. Recently, we reported the first direct experimental refutation of this belief by examining continuous body temperature and locomotor activity in male and female mice. These findings revealed that males exceeded female variance within and across individuals over time, showing greater variance within a day than females do across an entire estrous cycle. However, the possibility remains that male variance within a day is impacted by ultradian rhythms, analogous to the influence of infradian estrous cycles on female variance, and both sexes show predictable, structured variance across the day. If structures underlying variance can be predicted, then the variance can be statistically accounted for, reducing experimental error and increasing precision of measurements. Here we assess these continuous body temperature and activity data for the contributions of structured and unstructured variance to overall variance within and across individuals at ultradian, circadian, and infradian timescales. In no instance do females exceed male variance, and in most instances male variance exceeds female variance. Additionally, more female variance is accounted for by temporal structure. In conclusion, even when estrous cycles are not controlled for, females show less variability than males, and this advantage can be further capitalized upon by inclusion of known temporal patterns to control for previously unknown but structured sources of variance.

Circadian Regulation of Hormonal Timing and the Pathophysiology of Circadian Dysregulation

Circadian rhythms are endogenously generated, daily patterns of behavior and physiology that are essential for optimal health and disease prevention. Disruptions to circadian timing are associated with a host of maladies, including metabolic disease and obesity, diabetes, heart disease, cancer, and mental health disturbances. The circadian timing system is hierarchically organized, with a master circadian clock located in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus and subordinate clocks throughout the CNS and periphery. The SCN receives light information via a direct retinal pathway, synchronizing the master clock to environmental time. At the cellular level, circadian rhythms are ubiquitous, with rhythms generated by interlocking, autoregulatory transcription-translation feedback loops. At the level of the SCN, tight cellular coupling maintains rhythms even in the absence of environmental input. The SCN, in turn, communicates timing information via the autonomic nervous system and hormonal signaling. This signaling couples individual cellular oscillators at the tissue level in extra-SCN brain loci and the periphery and synchronizes subordinate clocks to external time. In the modern world, circadian disruption is widespread due to limited exposure to sunlight during the day, exposure to artificial light at night, and widespread use of light-emitting electronic devices, likely contributing to an increase in the prevalence, and the progression, of a host of disease states. The present overview focuses on the circadian control of endocrine secretions, the significance of rhythms within key endocrine axes for typical, homeostatic functioning, and implications for health and disease when dysregulated. © 2022 American Physiological Society. Compr Physiol 12: 1-30, 2022.

Sex Differences in Pubertal Circadian and Ultradian Rhythmic Development Under Semi-naturalistic Conditions

Biological rhythms in core body temperature (CBT) provide informative markers of adolescent development under controlled laboratory conditions. However, it is unknown whether these markers are preserved under more variable, semi-naturalistic conditions, and whether CBT may therefore prove useful in a real-world setting. To evaluate this possibility, we examined fecal steroid concentrations and CBT rhythms from pre-adolescence (p26) through early adulthood (p76) in intact male and female Wistar rats under natural light and climate at the Stephen Glickman Field Station for the Study of Behavior, Ecology and Reproduction. Despite greater environmental variability, CBT markers of pubertal onset and its rhythmic progression were comparable with those previously reported in laboratory conditions in female rats and extend actigraphy-based findings in males. Specifically, sex differences emerged in CBT circadian rhythm (CR) power and amplitude prior to pubertal onset and persisted into early adulthood, with females exhibiting elevated CBT and decreased CR power compared with males. Within-day (ultradian rhythm [UR]) patterns also exhibited a pronounced sex difference associated with estrous cyclicity. Pubertal onset, defined by vaginal opening, preputial separation, and sex steroid concentrations, occurred later than previously reported under lab conditions for both sexes. Vaginal opening and increased fecal estradiol concentrations were closely tied to the commencement of 4-day oscillations in CBT and UR power. By contrast, preputial separation and the first rise in testosterone concentration were not associated with adolescent changes to CBT rhythms in male rats. Together, males and females exhibited unique temporal patterning of CBT and sex steroids across pubertal development, with tractable associations between hormonal concentrations, external development, and temporal structure in females. The preservation of these features outside the laboratory supports CBT as a strong candidate for translational pubertal monitoring under semi-naturalistic conditions in females.

Multi-Timescale Rhythmicity of Blood Glucose and Insulin Delivery Reveals Key Advantages of Hybrid Closed Loop Therapy

BACKGROUND

Blood glucose and insulin exhibit coordinated daily and hourly rhythms in people without diabetes (nonT1D). Although the presence and stability of these rhythms are associated with euglycemia, it is unknown if they (1) are preserved in individuals with type 1 diabetes (T1D) and (2) vary by therapy type. In particular, Hybrid Closed Loop (HCL) systems improve glycemia in T1D compared to Sensor Augmented Pump (SAP) therapies, but the extent to which either recapitulates coupled glucose and insulin rhythmicity is not well described. In HCL systems, more rapid modulation of glucose via automated insulin delivery may result in greater rhythmic coordination and euglycemia. Such precision may not be possible in SAP systems. We hypothesized that HCL users would exhibit fewer hyperglycemic event, superior rhythmicity, and coordination relative to SAP users.

METHODS

Wavelet and coherence analyses were used to compare glucose and insulin delivery rate (IDR) within-day and daily rhythms, and their coordination, in 3 datasets: HCL (n = 150), SAP (n = 89), and nonT1D glucose (n = 16).

RESULTS

Glycemia, correlation between normalized glucose and IDR, daily coherence of glucose and IDR, and amplitude of glucose oscillations differed significantly between SAP and HCL users. Daily glucose rhythms differed significantly between SAP, but not HCL, users and nonT1D individuals.

CONCLUSIONS

SAP use is associated with greater hyperglycemia, higher amplitude glucose fluctuations, and a less stably coordinated rhythmic phenotype compared to HCL use. Improvements in glucose and IDR rhythmicity may contribute to the overall effectiveness of HCL systems.

Impact of Chronic Prenatal Stress on Maternal Neuroendocrine Function and Embryo and Placenta Development During Early-to-Mid-Pregnancy in Mice

Psychological stress, both leading up to and during pregnancy, is associated with increased risk for negative pregnancy outcomes. Although the neuroendocrine circuits that link the stress response to reduced sexual motivation and mating are well-described, the specific pathways by which stress negatively impacts gestational outcomes remain unclear. Using a mouse model of chronic psychological stress during pregnancy, we investigated 1) how chronic exposure to stress during gestation impacts maternal reproductive neuroendocrine circuitry, and 2) whether stress alters developmental outcomes for the fetus or placenta by mid-pregnancy. Focusing on the stress-responsive neuropeptide RFRP-3, we identified novel contacts between RFRP-3-immunoreactive (RFRP-3-ir) cells and tuberoinfundibular dopaminergic neurons in the arcuate nucleus, thus providing a potential pathway linking the neuroendocrine stress response directly to pituitary prolactin production and release. However, neither of these cell populations nor circulating levels of pituitary hormones were affected by chronic stress. Conversely, circulating levels of steroid hormones relevant to gestational outcomes (progesterone and corticosterone) were altered in chronically-stressed dams across gestation, and those dams were qualitatively more likely to experience delays in fetal development. Together, these findings suggest that, up until at least mid-pregnancy, mothers appear to be relatively resilient to the effects of elevated glucocorticoids on reproductive neuroendocrine system function. We conclude that understanding how chronic psychological stress impacts reproductive outcomes will require understanding individual susceptibility and identifying reliable neuroendocrine changes resulting from gestational stress.

Hypothalamic Overexpression of Neurosecretory Protein GL Leads to Obesity in Male C57BL/6J Mice

INTRODUCTION

The mechanisms underlying obesity are not fully understood, necessitating the creation of novel animal models for the investigation of metabolic disorders. We have previously found that neurosecretory protein GL (NPGL), a newly identified hypothalamic neuropeptide, is involved in feeding behavior and fat accumulation in rats. However, the impact of NPGL on obesity remains unclear in any animal model. The present investigation sought to elucidate whether NPGL causes obesity in the obesity-prone mouse strain C57BL/6J.

METHODS

We overexpressed the NPGL-precursor gene (Npgl) in the hypothalamus using adeno-associated virus in male C57BL/6J mice fed normal chow (NC) or a high-calorie diet (HCD). After 9 weeks of Npgl overexpression, we measured adipose tissues, muscle, and several organ masses in addition to food intake and body mass. To assess the effects of Npgl overexpression on peripheral tissues, we analyzed mRNA expression of lipid metabolism-related genes by quantitative RT-PCR. Whole body energy consumption was assessed using an O2/CO2 metabolism measurement before an apparent increase in body mass.

RESULTS

Npgl overexpression increased food intake, body mass, adipose tissues and liver masses, and food efficiency under both NC and HCD, resulting in obesity observable within 8 weeks. Furthermore, we observed fat accumulation in adipose tissues and liver. Additionally, mRNA expression of lipid metabolism-related factors was increased in white adipose tissue and the liver after Npgl overexpression. Npgl overexpression inhibited energy expenditure during a dark period.

CONCLUSION

Taken together, the present study suggests that NPGL can act as an obesogenic factor that acts within a short period of time in mice. As a result, this Npgl overexpression-induced obesity can be widely applied to study the etiology of obesity from genes to behavior.

Adolescent Development of Biological Rhythms in Female Rats: Estradiol Dependence and Effects of Combined Contraceptives

Adolescence is a period of continuous development, including the maturation of endogenous rhythms across systems and timescales. Although, these dynamic changes are well-recognized, their continuous structure and hormonal dependence have not been systematically characterized. Given the well-established link between core body temperature (CBT) and reproductive hormones in adults, we hypothesized that high-resolution CBT can be applied to passively monitor pubertal development and disruption with high fidelity. To examine this possibility, we used signal processing to investigate the trajectory of CBT rhythms at the within-day (ultradian), daily (circadian), and ovulatory timescales, their dependence on estradiol (E2), and the effects of hormonal contraceptives. Puberty onset was marked by a rise in fecal estradiol (fE2), followed by an elevation in CBT and circadian power. This time period marked the commencement of 4-day rhythmicity in fE2, CBT, and ultradian power marking the onset of the estrous cycle. The rise in circadian amplitude was accelerated by E2 treatment, indicating a role for this hormone in rhythmic development. Contraceptive administration in later adolescence reduced CBT and circadian power and resulted in disruption to 4-day cycles that persisted after discontinuation. Our data reveal with precise temporal resolution how biological rhythms change across adolescence and demonstrate a role for E2 in the emergence and preservation of multiscale rhythmicity. These findings also demonstrate how hormones delivered exogenously in a non-rhythmic pattern can disrupt rhythmic development. These data lay the groundwork for a future in which temperature metrics provide an inexpensive, convenient method for monitoring pubertal maturation and support the development of hormone therapies that better mimic and support human chronobiology.

Maternal stress during pregnancy alters fetal cortico-cerebellar connectivity in utero and increases child sleep problems after birth

Child sleep disorders are increasingly prevalent and understanding early predictors of sleep problems, starting in utero, may meaningfully guide future prevention efforts. Here, we investigated whether prenatal exposure to maternal psychological stress is associated with increased sleep problems in toddlers. We also examined whether fetal brain connectivity has direct or indirect influence on this putative association. Pregnant women underwent fetal resting-state functional connectivity MRI and completed questionnaires on stress, worry, and negative affect. At 3-year follow-up, 64 mothers reported on child sleep problems, and in the subset that have reached 5-year follow-up, actigraphy data (N = 25) has also been obtained. We observe that higher maternal prenatal stress is associated with increased toddler sleep concerns, with actigraphy sleep metrics, and with decreased fetal cerebellar-insular connectivity. Specific mediating effects were not identified for the fetal brain regions examined. The search for underlying mechanisms of the link between maternal prenatal stress and child sleep problems should be continued and extended to other brain areas.

Ultradian rhythms in heart rate variability and distal body temperature anticipate onset of the luteinizing hormone surge

The menstrual cycle is characterized by predictable patterns of physiological change across timescales. Although patterns of reproductive hormones across the menstrual cycle, particularly ultradian rhythms, are well described, monitoring these measures repeatedly to predict the preovulatory luteinizing hormone (LH) surge is not practical. In the present study, we explored whether non-invasive measures coupled to the reproductive system: high frequency distal body temperature (DBT), sleeping heart rate (HR), sleeping heart rate variability (HRV), and sleep timing, could be used to anticipate the preovulatory LH surge in women. To test this possibility, we used signal processing to examine these measures in 45 premenopausal and 10 perimenopausal cycles alongside dates of supra-surge threshold LH and menstruation. Additionally, urinary estradiol and progesterone metabolites were measured daily surrounding the LH surge in 20 cycles. Wavelet analysis revealed a consistent pattern of DBT and HRV ultradian rhythm (2-5 h) power that uniquely enabled anticipation of the LH surge at least 2 days prior to its onset in 100% of individuals. Together, the present findings reveal fluctuations in distal body temperature and heart rate variability that consistently anticipate the LH surge, suggesting that automated ultradian rhythm monitoring may provide a novel and convenient method for non-invasive fertility assessment.

The Impact of Di-2-Ethylhexyl Phthalate on Sperm Fertility

A growing number of studies point to reduced fertility upon chronic exposure to endocrine-disrupting chemicals (EDCs) such as phthalates and plasticizers. These toxins are ubiquitous and are often found in food and beverage containers, medical devices, as well as in common household and personal care items. Animal studies with EDCs, such as phthalates and bisphenol A have shown a dose-dependent decrease in fertility and embryo toxicity upon chronic exposure. However, limited research has been conducted on the acute effects of these EDCs on male fertility. Here we used a murine model to test the acute effects of four ubiquitous environmental toxins: bisphenol A (BPA), di-2-ethylhexyl phthalate (DEHP), diethyl phthalate (DEP), and dimethyl phthalate (DMP) on sperm fertilizing ability and pre-implantation embryo development. The most potent of these toxins, di-2-ethylhexyl phthalate (DEHP), was further evaluated for its effect on sperm ion channel activity, capacitation status, acrosome reaction and generation of reactive oxygen species (ROS). DEHP demonstrated a profound hazardous effect on sperm fertility by producing an altered capacitation profile, impairing the acrosome reaction, and, interestingly, also increasing ROS production. These results indicate that in addition to its known chronic impact on reproductive potential, DEHP also imposes acute and profound damage to spermatozoa, and thus, represents a significant risk to male fertility.

MON-016 Neural Circuits and Hormonal Mechanisms Underlying the Negative Impact of Stress on Pregnancy Outcomes

Despite numerous findings detailing the negative impact of stress on female reproductive health, the means by which stress acts on the CNS and periphery to compromise reproductive success remains poorly understood. As a result, the current study sought to clarify the neuroendocrine mechanisms by which stress acts on the brain to deleteriously influence pregnancy outcomes. Reproduction is regulated by the hypothalamo-pituitary-gonadal (HPG) axis, with hypothalamic gonadotropin-releasing hormone (GnRH) neurons representing the final, common pathway of this axis. Cells expressing the inhibitory neuropeptide, RFamide-related peptide-3 (RFRP-3), lie upstream of the GnRH system and are markedly regulated by environmental and psychosocial factors, including stress. In the present study, we asked whether RFRP-3 neurons mediate the effects of stress on pregnancy outcomes through the regulation of prolactin secretion, as prolactin is critical for pregnancy maintenance. More specifically, because specialized hypothalamic dopaminergic neurons, namely tubero-infundibular dopaminergic (TIDA) neurons, are major regulators of prolactin secretion, we hypothesized that RFRP-3 neurons directly target TIDA cells to negatively influence fetal development. To test this possibility, we subjected pregnant mice to chronic restraint stress for the first half of pregnancy and performed a broad screen of hypothalamic neuroendocrine function compared to non-stressed controls. Stressed mice exhibited elevated baseline concentrations of corticosterone that remained high at least 6 days after the final exposure to stress. Whereas progesterone concentrations were reduced by stress early in pregnancy, stressed mice recovered typical progesterone secretion during late gestation. These early, stressful experiences resulted in persistent developmental delays, reduced embryo weight, and abnormal placental histology. Significantly, a small percentage of TIDA cells receive close contacts from RFRP-3 axons, providing a mechanism for the control of prolactin secretion by stress. However, contrary to expectation, the percentage of TIDA neurons receiving input from RFRP-3 cells was not impacted by stress. Together, these findings identify a potential pathway of control for the impact of stress on neuroendocrine factors critical to pregnancy success, although further work using more sensitive approaches is needed to examine the putative role of RFRP-3 on stress-induced pregnancy outcomes.

Neurosecretory protein GL induces fat accumulation in mice

We recently discovered a novel gene encoding a small secretory protein, neurosecretory protein GL (NPGL), which stimulates feeding behavior in mice following acute administration. These findings suggest that dysregulation of NPGL contributes to obesity and metabolic disease. To explore this possibility, we investigated the impact of prolonged exposure to NPGL through 13 days of chronic intracerebroventricular (i.c.v.) infusion and examined feeding behavior, body composition, expressions of lipid metabolic factors, respiratory metabolism, locomotor activity, and food preference. Under standard chow diet, NPGL increased white adipose tissue (WAT) mass without affecting feeding behavior and body mass. In contrast, when fed a high-calorie diet, NPGL stimulated feeding behavior and increased body mass concomitant with marked fat accumulation. Quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that mRNA expressions for key enzymes and related factors involved in lipid metabolism were increased in WAT and liver. Likewise, analyses of respiratory metabolism and locomotor activity revealed that energy expenditure and locomotor activity were significantly decreased by NPGL. In contrast, selective feeding of macronutrients did not alter food preference in response to NPGL, although total calorie intake was increased. Immunohistochemical analysis revealed that NPGL-containing cells produce galanin, a neuropeptide that stimulates food intake. Taken together, these results provide further support for NPGL as a novel regulator of fat deposition through changes in energy intake and locomotor activity.

Time-of-day-dependent sensitivity of the reproductive axis to RFamide-related peptide-3 inhibition in female Syrian hamsters

In spontaneously ovulating rodent species, the timing of the luteinising hormone (LH) surge is controlled by the master circadian pacemaker in the suprachiasmatic nucleus (SCN). The SCN initiates the LH surge via the coordinated control of two opposing neuropeptidergic systems that lie upstream of the gonadotrophin-releasing hormone (GnRH) neuronal system: the stimulatory peptide, kisspeptin, and the inhibitory peptide, RFamide-related peptide-3 (RFRP-3; the mammalian orthologue of avian gonadotrophin-inhibitory hormone [GnIH]). We have previously shown that the GnRH system exhibits time-dependent sensitivity to kisspeptin stimulation, further contributing to the precise timing of the LH surge. To examine whether this time-dependent sensitivity of the GnRH system is unique to kisspeptin or a more common mechanism of regulatory control, we explored daily changes in the response of the GnRH system to RFRP-3 inhibition. Female Syrian hamsters were ovariectomised to eliminate oestradiol (E₂ )-negative-feedback and RFRP-3 or saline was centrally administered in the morning or late afternoon. LH concentrations and Lhβ mRNA expression did not differ between morning RFRP-3-and saline-treated groups, although they were markedly suppressed by RFRP-3 administration in the afternoon. However, RFRP-3 inhibition of circulating LH at the time of the surge does not appear to act via the GnRH system because no differences in medial preoptic area Gnrh or RFRP-3 receptor Gpr147 mRNA expression were observed. Rather, RFRP-3 suppressed arcuate nucleus Kiss1 mRNA expression and potentially impacted pituitary gonadotrophs directly. Taken together, these findings reveal time-dependent responsiveness of the reproductive axis to RFRP-3 inhibition, possibly via variation in the sensitivity of arcuate nucleus kisspeptin neurones to this neuropeptide.

Neurosecretory Protein GL Induces Fat Accumulation in Chicks

We recently found a previously unidentified cDNA in chicken hypothalamus which encodes the precursor for neurosecretory protein GL (NPGL). A previous study showed that intracerebroventricular (i.c.v.) infusion of NPGL caused body mass gain in chicks. However, it was not clear which part(s) of the body gained mass. In the present study, we investigated which tissues increased in mass after chronic i.c.v. infusion of NPGL in chicks. We found that NPGL increased the masses of the liver, abdominal fat, and subcutaneous fat, while NPGL did not affect the masses of muscles, including pectoralis major, pectoralis minor, and biceps femoris. Oil Red O staining revealed that fat deposition had occurred in the liver. In addition, the size of the lipid droplets in the abdominal fat increased. Furthermore, we found an upregulation of lipogenesis and downregulation of lipolysis in the abdominal fat, but not in the liver. These results indicate that NPGL is involved in fat storage in chicks.

Functional Implications of RFRP-3 in the Central Control of Daily and Seasonal Rhythms in Reproduction

Adaptation of reproductive activity to environmental changes is essential for breeding success and offspring survival. In mammals, the reproductive system displays regular cycles of activation and inactivation which are synchronized with seasonal and/or daily rhythms in environmental factors, notably light intensity and duration. Thus, most species adapt their breeding activity along the year to ensure that birth and weaning of the offspring occur at a time when resources are optimal. Additionally, female reproductive activity is highest at the beginning of the active phase during the period of full oocyte maturation, in order to improve breeding success. In reproductive physiology, it is therefore fundamental to delineate how geophysical signals are integrated in the hypothalamo-pituitary-gonadal axis, notably by the neurons expressing gonadotropin releasing hormone (GnRH). Several neurochemicals have been reported to regulate GnRH neuronal activity, but recently two hypothalamic neuropeptides belonging to the superfamily of (Arg)(Phe)-amide peptides, RFRP-3 and kisspeptin, have emerged as critical for the integration of environmental cues within the reproductive axis. The goal of this review is to survey the current understanding of the role played by RFRP-3 in the temporal regulation of reproduction, and consider how its effect might combine with that of kisspeptin to improve the synchronization of reproduction to environmental challenges.

Circadian Control of Neuroendocrine Function: Implications for Health and Disease

The circadian timing system orchestrates daily rhythms in physiology and behavior via the suprachiasmatic nucleus (SCN), the master brain clock. Because endocrine secretions have far-reaching influence on the brain and periphery, circadian regulation of hormones is essential for normal functioning and disruptions to circadian timing (e.g., irregular sleep patterns, limited exposure to sunlight, jet lag, nighttime light exposure) have detrimental health consequences. Herein, we provide an overview of circadian timing in three major endocrine axes, the hypothalamo-pituitary-gonadal (HPG), hypothalamo-pituitary-adrenal (HPA) and hypothalamo-pituitary-thyroid (HPT) axes, and then consider the negative health consequences of circadian disruptions in each of these systems. For example, disruptions to HPG axis circadian timing lead to a host of negative reproductive outcomes such as irregular menstrual cycles, low sperm density and increased rates of miscarriages and infertility. Dysregulation of HPA axis timing is associated with obesity and metabolic disease, whereas disruptions to the HPT axis are associated with dysregulated metabolic gene rhythms in the heart. Together, this overview underscores the significance of circadian endocrine rhythms in normal health and disease prevention.

Pregnancy stage determines the effect of chronic stress on ovarian progesterone synthesis

Although stress-induced glucocorticoid release is thought to be a primary driver by which maternal stress negatively impacts pregnancy outcomes, the downstream neuroendocrine targets mediating these adverse outcomes are less well understood. We hypothesized that stress-induced glucocorticoid secretion inhibits pituitary hormone secretion, resulting in decreased ovarian progesterone synthesis. Using a chronic restraint model of stress in mice, we quantified steroid hormone production, pituitary hormones, and expression of ovarian genes that support progesterone production at both early ( day 5) and midpregnancy ( day 10). Females subjected to daily restraint had elevated baseline glucocorticoids during both early and midpregnancy; however, lower circulating progesterone was observed only during early pregnancy. Lower progesterone production was associated with lower expression of steroidogenic enzymes in the ovary of restrained females during early pregnancy. There were no stress-related changes to luteinizing hormone (LH) or prolactin (PRL). By midpregnancy, circulating LH decreased regardless of treatment, and this was associated with downregulation of ovarian steroidogenic gene expression. Our results are consistent with a role for LH in maintaining steroidogenic enzyme expression in the ovary, but neither circulating PRL nor LH were associated with the stress-induced inhibition of ovarian progesterone production during early pregnancy. We conclude that chronic stress impacts endocrine networks differently in pregnant and nonpregnant mammals. These findings underscore the need for further studies exploring dynamic changes in endocrine networks participating in pregnancy initiation and progression to elucidate the physiological mechanisms that connect stress exposure to adverse pregnancy outcomes.

Chronic subcutaneous infusion of neurosecretory protein GM increases body mass gain in chicks

Recently we discovered a small hypothalamic protein in the chicken, named neurosecretory protein GL (NPGL), which is associated with body growth and energy metabolism in birds and rodents. Genome database analysis suggested that the NPGL gene has a paralogous gene in vertebrates, named neurosecretory protein GM (NPGM). However, the biological action of NPGM remains unclear. In this study, we investigated whether NPGM affects body growth in chicks. We found that subcutaneous infusion of NPGM for six days increased body mass gain in a dose-dependent manner. Despite the observed increase in body mass, infusion of NPGM did not alter food and water intake. Of note, we observed tendency of mass increase of several peripheral tissues, specifically. When we compared several tissue types, NPGM seemed to induce the largest growth increase in white adipose tissue mass. These results suggest that NPGM may accelerate fat accumulation and body growth. In addition, we analyzed whether NPGM increases body growth through the action of pituitary hormones. However, we observed no significant changes in mRNA expression of pituitary hormones or plasma levels of growth hormone in NPGM-treated chicks. This is the first report describing the biological action of NPGM in vertebrates.

Evidence for a Coupled Oscillator Model of Endocrine Ultradian Rhythms

Whereas long-period temporal structures in endocrine dynamics have been well studied, endocrine rhythms on the scale of hours are relatively unexplored. The study of these ultradian rhythms (URs) has remained nascent, in part, because a theoretical framework unifying ultradian patterns across systems has not been established. The present overview proposes a conceptual coupled oscillator network model of URs in which oscillating hormonal outputs, or nodes, are connected by edges representing the strength of node-node coupling. We propose that variable-strength coupling exists both within and across classic hormonal axes. Because coupled oscillators synchronize, such a model implies that changes across hormonal systems could be inferred by surveying accessible nodes in the network. This implication would at once simplify the study of URs and open new avenues of exploration into conditions affecting coupling. In support of this proposed framework, we review mammalian evidence for (1) URs of the gut-brain axis and the hypothalamo-pituitary-thyroid, -adrenal, and -gonadal axes, (2) UR coupling within and across these axes; and (3) the relation of these URs to body temperature. URs across these systems exhibit behavior broadly consistent with a coupled oscillator network, maintaining both consistent URs and coupling within and across axes. This model may aid the exploration of mammalian physiology at high temporal resolution and improve the understanding of endocrine system dynamics within individuals.

Gonadotrophin-inhibitory hormone and its mammalian orthologue RFamide-related peptide-3: Discovery and functional implications for reproduction and stress

At the turn of the millennium, a neuropeptide with pronounced inhibitory actions on avian pituitary gonadotrophin secretion was identified and named gonadotrophin-inhibitory hormone (GnIH). Across bird species, GnIH acts at the level of the pituitary and the gonadotrophin-releasing hormone (GnRH) neuronal system to inhibit reproduction. Subsequent to this initial discovery, orthologues of GnIH have been identified and characterised across a broad range of species. In many vertebrates, the actions of GnIH and its orthologues serve functional roles analogous to those seen in birds. In other cases, GnIH and its orthologues exhibit more diverse actions dependent on sex, species, season and reproductive condition. The present review highlights the discovery and functional implications of GnIH across species, focusing on research domains in which the significance of this neuropeptide has been explored most.

Neural Versus Gonadal GnIH: Are they Independent Systems? A Mini-Review

Based on research in protochordates and basal vertebrates, we know that communication across the first endocrine axes likely relied on diffusion. Because diffusion is relatively slow, rapid responses to some cues, including stress-related cues, may have required further local control of axis outputs (e.g., steroid hormone production by the gonads). Despite the evolution of much more efficient circulatory systems and complex nervous systems in vertebrates, production of many "neuro"transmitters has been identified outside of the hypothalamus across the vertebrate phylogeny and these neurotransmitters are known to locally regulate endocrine function. Our understanding of tissue-specific neuropeptide expression and their role coordinating physiological/behavioral responses of the whole organism remains limited, in part, due to nomenclature and historic dogma that ignores local regulation of axis output. Here, we review regulation of gonadotropin-inhibitory hormone (GnIH) across the reproductive axis in birds and mammals to bring further attention to context-dependent disparities and similarities in neuropeptide production by the brain and gonads. We find that GnIH responsiveness to cues of stress appears conserved across species, but that the response of specific tissues and the direction of GnIH regulation varies. The implications of differential regulation across tissues remain unclear in most studies, but further work that manipulates and contrasts function in different tissues has the potential to inform us about both organism-specific function and endocrine axis evolution.

Localization and function of neurosecretory protein GM, a novel small secretory protein, in the chicken hypothalamus

Recently, we discovered a novel cDNA encoding the precursor of a small secretory protein, neurosecretory protein GL (NPGL), in the hypothalamic infundibulum of chickens. NPGL plays an important role in the regulation of growth and feeding. A database search indicated that the NPGL gene has a paralogous gene: neurosecretory protein GM (NPGM), also in chickens. We identified cDNA encoding the NPGM precursor in chickens. Morphological analysis showed that NPGM-containing cells are specifically localized in the medial mammillary nucleus (MM) and infundibular nucleus (IN) in the hypothalamus. In addition, we found that NPGM and NPGL are co-localized, especially in the MM. The expression levels of NPGM mRNA gradually decreased during post-hatch development, in contrast to those of NPGL mRNA. Moreover, we investigated the relationship between NPGM and other known factors. NPGM was found to be produced in histaminergic neurons in the MM. NPGM and histidine decarboxylase, a histamine-producing enzyme, displayed similar expression patterns during post-hatch development. Acute intracerebroventricular injection of NPGM decreased food intake, similar to the effect of histamine. To our knowledge, this is the first report of the localization and function of NPGM in the brain of vertebrates. These results will further advance the understanding mechanisms underlying energy homeostasis.

Effects of chronic intracerebroventricular infusion of neurosecretory protein GL on body mass and food and water intake in chicks

Recently, we discovered a novel cDNA encoding the precursor of a small secretory protein, neurosecretory protein GL (NPGL), in the chicken mediobasal hypothalamus. In this study, immunohistochemical analysis revealed that NPGL was produced in the infundibular and medial mammillary nuclei of the mediobasal hypothalamus, with immunoreactive fibers also detected in the hypothalamus and the median eminence. As it is known that these regions are involved in feeding behavior in chicks, we surveyed the effects of chronic intracerebroventricular infusion of NPGL on feeding behavior and body mass for a period of two weeks. NPGL stimulated food and water intake, with a concomitant increase in body mass. However, NPGL did not influence mRNA expression of several hypothalamic ingestion-related neuropeptides. Our data suggest that NPGL may be a novel neuronal regulator involved in growth processes in chicks.

RFamide-related Peptide-3 and the Trade-off between Reproductive and Ingestive Behavior

Ingestive and sex behaviors are important for individual survival and reproductive success, but when environmental energy availability is limited, individuals of many different species make a trade-off, forfeiting sex for ingestive behavior. For example, food-deprived female Syrian hamsters (Mesocricetus auratus) forego vaginal scent marking and lordosis (sex behaviors) in favor of foraging, hoarding, and eating food (ingestive behavior). Reproductive processes tend to be energetically costly, and individual survival requires homeostasis in metabolic energy. Thus, during energetic challenges, the chances of survival are enhanced by decreasing the energy expended on reproductive processes. The entire hypothalamic-pituitary-gonadal (HPG) system is inhibited by severe energetic challenges, but comparatively little is known about the effects of mild energetic challenges. We hypothesized that (1) a trade-off is made between sex and ingestive behavior even when the level of food restriction is insufficient to inhibit the HPG system; (2) mild energetic challenges force a trade-off between appetitive ingestive and sex behaviors, but not consummatory versions of the same behaviors; and (3) the trade-off is orchestrated by ovarian steroid modulation of RFamide-related peptide 3 (RFRP-3). In other species, RFRP-3, an ortholog of avian gonadotropin-inhibitory hormone, is implicated in control of behavior in response to energetic challenges and stressful stimuli. In support of our three hypotheses, there is a "dose-response" effect of food restriction and re-feeding on the activation of RFRP-3-immunoreactive cells in the dorsomedial hypothalamus and on appetitive behaviors (food hoarding and sexual motivation), but not on consummatory behaviors (food intake and lordosis), with no significant effect on circulating levels of estradiol or progesterone. The effect of food restriction on the activation of RFRP-3 cells is modulated at the time of estrus in gonadally-intact females and in ovariectomized females treated with progesterone alone or with estradiol plus progesterone. Intracerebral treatment with RFRP-3 results in significant decreases in sexual motivation and results in significant but small increases in food hoarding in hamsters fed ad libitum. These and other results are consistent with the idea that ovarian steroids and RFRP-3 are part of a system that orchestrates trade-offs in appetitive behaviors in environments where energy availability fluctuates.

The effect of social rank feedback on risk taking and associated reward processes in adolescent girls

The onset of adolescence is associated with an increased tendency to engage in risky behaviors and a developmental shift toward peers that contributes to increased prioritization for learning about and achieving social status. There is relatively little understanding about the specific links between these adolescent-typical phenomena, particularly regarding their neural underpinnings. Based on existing models that suggest the role of puberty in promoting adolescent status-seeking and risk-taking tendencies, we investigated the relation of pubertal hormones with behavioral and neural responses to status-relevant social information in the context of risk taking. We used a probabilistic decision task in which 11- to 13-year-old girls chose to take a risk, or not, while receiving either social rank or monetary performance feedback. While feedback type did not differentially influence risk-taking behavior, whole-brain imaging results showed that activation in the anterior insula was increased for risk taking in the social rank feedback condition compared to the monetary feedback condition. This heightened activation was more pronounced in girls with higher estradiol levels. These findings suggest that brain processes involved in adolescent risky decisions may be influenced by the desire for social-status enhancement and provide preliminary evidence for the role of pubertal hormones in enhancing this adolescent-typical social sensitivity.

The Preoptic Area and the RFamide-Related Peptide Neuronal System Gate Seasonal Changes in Chemosensory Processing

Males of many species rely on chemosensory information for social communication. In male Syrian hamsters (Mesocricetus auratus), as in many species, female chemosignals potently stimulate sexual behavior and a concurrent, rapid increase in circulating luteinizing hormone (LH) and testosterone (T). However, under winter-like, short-day (SD) photoperiods, when Syrian hamsters are reproductively quiescent, these same female chemosignals fail to elicit behavioral or hormonal responses, even after T replacement. It is currently unknown where in the brain chemosensory processing is gated in a seasonally dependent manner such that reproductive responses are only displayed during the appropriate breeding season. The goal of the present study was to determine where this gating occurred by identifying neural loci that respond differentially to female chemosignals across photoperiods, independent of circulating T concentrations. Adult male Syrian hamsters were housed under either long-day (LD) (reproductively active) or SD (reproductively inactive) photoperiods with half of the SD animals receiving T replacement. Animals were exposed to either female hamster vaginal secretions (FHVSs) diluted in mineral oil or to vehicle, and the activational state of chemosensory processing centers and elements of the neuroendocrine reproductive axis were examined. Components of the chemosensory pathway upstream of hypothalamic centers increased expression of FOS, an indirect marker of neuronal activation, similarly across photoperiods. In contrast, the preoptic area (POA) of the hypothalamus responded to FHVS only in LD animals, consistent with its role in promoting expression of male sexual behavior. Within the neuroendocrine axis, the RF-amide related peptide (RFRP), but not the kisspeptin neuronal system responded to FHVS only in LD animals. Neither response within the POA or the RFRP neuronal system was rescued by T replacement in SD animals, mirroring photoperiodic regulation of reproductive responses. Considering the POA and the RFRP neuronal system promote reproductive behavior and function in male Syrian hamsters, differential activation of these systems represents a potential means by which photoperiod limits expression of reproduction to the appropriate environmental context.

Neurosecretory protein GL stimulates food intake, de novo lipogenesis, and onset of obesity

Mechanisms underlying the central regulation of food intake and fat accumulation are not fully understood. We found that neurosecretory protein GL (NPGL), a newly-identified neuropeptide, increased food intake and white adipose tissue (WAT) in rats. NPGL-precursor gene overexpression in the hypothalamus caused increases in food intake, WAT, body mass, and circulating insulin when fed a high calorie diet. Intracerebroventricular administration of NPGL induced de novo lipogenesis in WAT, increased insulin, and it selectively induced carbohydrate intake. Neutralizing antibody administration decreased the size of lipid droplets in WAT. Npgl mRNA expression was upregulated by fasting and low insulin levels. Additionally, NPGL-producing cells were responsive to insulin. These results point to NPGL as a novel neuronal regulator that drives food intake and fat deposition through de novo lipogenesis and acts to maintain steady-state fat level in concert with insulin. Dysregulation of NPGL may be a root cause of obesity.

DOI:http://dx.doi.org/10.7554/eLife.28527.001

Throughout history, our ancestors needed to accumulate fat to survive during times when food sources were scarce. However, for most people in the modern age, food is abundant and eating too much is a major cause of weight gain, obesity and diseases affecting the metabolism. Obesity in particular, can lead to diseases such as diabetes and heart disease.

Hunger and appetite are regulated by proteins and other chemicals that act as messengers, for example insulin, and a region of the brain called the hypothalamus. However, the full mechanisms that regulate these sensations remain unclear. Only recently, a protein called NPGL was discovered in a part of the hypothalamus of birds and mammals. However, it was not known if NPGL plays a role in regulating eating habits and weight gain.

Iwakoshi-Ukena et al. have now discovered that NPGL is found in the hypothalamus of rats and is regulated by diet and insulin. When the gene for NPGL was manipulated to produce too much of the protein, rats fed a high calorie diet started to eat more, and gained more weight and body fat. Adding additional NPGL to their brains had the same effect. When the animals were fed a normal diet, NPGL only moderately affected how much they ate, but it substantially increased how much fat they produced. Iwakoshi-Ukena et al. also observed that when animals were starved and insulin levels were low, the rats started to produce more NPGL. These results suggest that NPGL plays a role in fat storage when energy sources are limited, and can contribute to obesity when too much NPGL is produced in animals on a high calorie diet.

These findings indicate that NPGL could be an additional brain chemical that regulates hunger and fat storage in mammals. A next step will be to reveal the specific mechanisms by which NPGL regulates overeating and fat accumulation. These findings will further advance the study and treatment of obesity and obesity-related diseases.

DOI:http://dx.doi.org/10.7554/eLife.28527.002

Food restriction-induced changes in motivation differ with stages of the estrous cycle and are closely linked to RFamide-related peptide-3 but not kisspeptin in Syrian hamsters

We tested the hypothesis that the effects of food restriction on behavioral motivation are mediated by one or both of the RFamide peptides, RFamide-related peptide-3 (RFRP-3) and kisspeptin (Kp) in female Syrian hamsters (Mesocricetus auratus). Female hamsters fed ad libitum and given a choice between food and adult male hamsters are highly motivated to visit males instead of food on all four days of the estrous cycle, but after 8days of mild food restriction (75% of ad libitum intake) they shift their preference toward food every day of the estrous cycle until the day of estrus, when they shift their preference back toward the males. In support of a role for RFRP-3 in these behavioral changes, the preference for food and the activation of RFRP-3-immunoreactive (Ir) cells in the dorsomedial hypothalamus (DMH) showed the same estrous cycle pattern in food-restricted females, but no association was observed between behavior and the activation of Kp cells in the hypothalamic arcuate nucleus or preoptic area. Next, we tested the hypothesis that food-restriction-induced activation of RFRP-3-Ir cells is modulated by high levels of ovarian steroids at the time of estrus. In support of this idea, on nonestrous days, mild food restriction increased activation of RFRP-3-Ir cells, but failed to do so on the day of estrus even though this level of food restriction did not significantly decrease circulating concentrations of estradiol or progesterone. Furthermore, in ovariectomized females, food-restriction-induced increases in activation of RFRP-3-Ir cells were blocked by systemic treatment with progesterone alone, estradiol plus progesterone, but not estradiol alone. Central infusion with RFRP-3 in ad libitum-fed females significantly decreased sexual motivation and produced significant increases in 90-minute food hoarding, in support of the hypothesis that elevated central levels of RFRP-3 are sufficient to create the shift in behavioral motivation in females fed ad libitum. Together, these results are consistent with the hypothesis that high levels of ingestive motivation are promoted during the nonfertile phase of the estrous cycle by elevated activation of RFRP-3-Ir cells, and RFRP-3-Ir cellular activation is modulated by ovarian steroids around the time of estrus, thereby diverting attention away from food and increasing sexual motivation.

Neurosecretory Protein GL, a Hypothalamic Small Secretory Protein, Participates in Energy Homeostasis in Male Mice

We have recently identified from the avian hypothalamus a complementary DNA encoding a small secretory protein termed neurosecretory protein GL (NPGL). In chicks, NPGL increases body weight gain without affecting food intake. A database search reveals that NPGL is conserved throughout vertebrates. However, the central distribution and functional role of NPGL remains to be elucidated in mammals. In this study, we identified the precursor complementary DNA encoding NPGL from the mouse hypothalamus. Quantitative reverse transcription polymerase chain reaction and morphological analyses revealed that NPGL precursor messenger RNA is robustly expressed in the mediobasal hypothalamus with NPGL neurons specifically localized to the lateroposterior part of the arcuate nucleus in the hypothalamus. NPGL-immunoreactive fibers were observed in close anatomical contact with pro-opiomelanocortin neurons in the rostral region of the arcuate nucleus. NPGL messenger RNA expression was elevated by 24-hour fasting and reduced by feeding of a high-fat diet for 5 weeks. Furthermore, intracerebroventricular injection of mature NPGL increased food intake, pointing to an important role in feeding. Taken together, these findings report on the distribution of NPGL in the mammalian brain and point to an important role for this neuropeptide in energy homeostasis.

Sex differences in variability across timescales in BALB/c mice

BACKGROUND

Females are markedly underinvestigated in the biological and behavioral sciences due to the presumption that cyclic hormonal changes across the ovulatory cycle introduce excess variability to measures of interest in comparison to males. However, recent analyses indicate that male and female mice and rats exhibit comparable variability across numerous physiological and behavioral measures, even when the stage of the estrous cycle is not considered. Hormonal changes across the ovulatory cycle likely contribute cyclic, intra-individual variability in females, but the source(s) of male variability has, to our knowledge, not been investigated. It is unclear whether male variability, like that of females, is temporally structured and, therefore, quantifiable and predictable. Finally, whether males and females exhibit variability on similar time scales has not been explored.

METHODS

These questions were addressed by collecting chronic, high temporal resolution locomotor activity (LA) and core body temperature (CBT) data from male and female BALB/c mice.

RESULTS

Contrary to expectation, males are more variable than females over the course of the day (diel variability) and exhibit higher intra-individual daily range than females in both LA and CBT. Between mice of a given sex, variability is comparable for LA but the inter-individual daily range in CBT is greater for males. To identify potential rhythmic processes contributing to these sex differences, we employed wavelet transformations across a range of periodicities (1-39 h).

CONCLUSIONS

Although variability in circadian power is comparable between the sexes for both LA and CBT, infradian variability is greater in females and ultradian variability is greater in males. Thus, exclusion of female mice from studies because of estrous cycle variability may increase variance in investigations where only male measures are collected over a span of several hours and limit generalization of findings from males to females.

A System for In Vivo Imaging of Hepatic Free Fatty Acid Uptake

Alterations in hepatic free fatty acid (FFA) uptake and metabolism contribute to the development of prevalent liver disorders such as hepatosteatosis. However, detecting dynamic changes in FFA uptake by the liver in live model organisms has proven difficult. To enable noninvasive real-time imaging of FFA flux in the liver, we generated transgenic mice with liver-specific expression of luciferase and performed bioluminescence imaging with an FFA probe. Our approach enabled us to observe the changes in FFA hepatic uptake under different physiological conditions in live animals. By using this method, we detected a decrease in FFA accumulation in the liver after mice were given injections of deoxycholic acid and an increase after they were fed fenofibrate. In addition, we observed diurnal regulation of FFA hepatic uptake in living mice. Our imaging system appears to be a useful and reliable tool for studying the dynamic changes in hepatic FFA flux in models of liver disease.

Risky decision-making in adolescent girls: The role of pubertal hormones and reward circuitry

Adolescence is a developmental period characterized by a greater tendency to take risks. While the adult literature has shown that sex steroids influence reward-related brain functioning and risk taking, research on the role of these hormones during puberty is limited. In this study, we examined the relation between pubertal hormones and adolescent risk taking using a probabilistic decision-making task. In this task, participants could choose on each trial to play or pass based on explicit information about the risk level and stakes involved in their decision. We administered this task to 58 11-to-13-year-old girls while functional MRI images were obtained to examine reward-related brain processes associated with their risky choices. Results showed that higher testosterone levels were associated with increased risk taking, which was mediated by increased medial orbitofrontal cortex activation. Furthermore, higher estradiol levels were associated with increased nucleus accumbens activation, which in turn related to decreased risk taking. These findings offer potential neuroendocrine mechanisms that can explain why some adolescent girls might engage in more risk taking compared to others.

The Pathophysiologic Role of Disrupted Circadian and Neuroendocrine Rhythms in Breast Carcinogenesis

Most physiological processes in the brain and body exhibit daily (circadian) rhythms coordinated by an endogenous master clock located in the suprachiasmatic nucleus of the hypothalamus that are essential for normal health and functioning. Exposure to sunlight during the day and darkness at night optimally entrains biological rhythms to promote homeostasis and human health. Unfortunately, a major consequence of the modern lifestyle is increased exposure to sun-free environments during the day and artificial lighting at night. Additionally, behavioral disruptions to circadian rhythms (ie, repeated transmeridian flights, night or rotating shift work, or sleep disturbances) have a profound influence on health and have been linked to a number of pathological conditions, including endocrine-dependent cancers. Specifically, night shift work has been identified as a significant risk factor for breast cancer in industrialized countries. Several mechanisms have been proposed by which shift work-induced circadian disruptions promote cancer. In this review, we examine the importance of the brain-body link through which circadian disruptions contribute to endocrine-dependent diseases, including breast carcinogenesis, by negatively impacting neuroendocrine and neuroimmune cells, and we consider preventive measures directed at maximizing circadian health.

Detection of Successful and Unsuccessful Pregnancies in Mice within Hours of Pairing through Frequency Analysis of High Temporal Resolution Core Body Temperature Data

Many controllable factors negatively impact fetal development, underscoring the importance of early pregnancy detection and identification of events that reliably predict potential complications. Clinically, core body temperature (CBT) is used to aid family planning and pregnancy detection. However, such temperature data typically are gathered in single, daily measurements. In animal studies, interventions or cell/tissue harvesting at defined stages of fetal development are arduous, requiring timed mating by trained observers. The value of continuous temperature measurements remains largely unexplored, but the advent of small, inexpensive, and increasingly ubiquitous, accurate sensor devices makes continuous measures feasible. Here, using a mouse model, we show that continuous, 1-min resolution CBT measurements reliably allow for the earliest and most accurate detection of pregnancy (100%, within 14 h of initial pairing), without requiring interaction with the animal for data collection. This method also reveals a subset of females that exhibit a pregnancy-like response following pairing that persists for a variable number of days. Application of wavelet analysis that permits frequency analysis while preserving temporal resolution, uncovers significant differences in ultradian frequencies of CBT; these rhythms are significantly increased in the 12 h after the day of pairing for pregnancies carried to term compared to apparent pregnancies that failed. High temporal resolution CBT and wavelet analysis permit strikingly early detection and separation of successful pregnancies and pregnancy-like events.

Aggressive interactions are associated with reductions in RFamide-related peptide, but not kisspeptin, neuronal activation in mice

Aggressive interactions lead to changes in both future behavior and circulating testosterone (T) concentrations in animals across taxa. The specific neural circuitry and neurochemical systems by which these encounters alter neuroendocrine functioning are not well understood. Neurons expressing the inhibitory and stimulatory neuropeptides, RFamide-related peptide (RFRP) and kisspeptin, respectively, project to neural loci regulating aggression in addition to neuroendocrine cells controlling sex steroid production. Given these connections to both the reproductive axis and aggression circuitry, RFRP and kisspeptin are in unique positions to mediate post-encounter changes in both T and behavior. The present study examined the activational state of RFRP and kisspeptin neurons of male C57BL/6 mice following an aggressive encounter. Both winners and losers exhibited reduced RFRP/FOS co-localization relative to handling stress controls. Social exposure controls did not display reduced RFRP neuronal activation, indicating that this effect is due to aggressive interaction specifically rather than social interaction generally. RFRP neuronal activation positively correlated with latencies to display several offensive behaviors within winners. These effects were not observed in the anteroventral periventricular (AVPV) nucleus kisspeptin cell population. Together, these findings point to potential neuromodulatory role for RFRP in aggressive behavior and in disinhibiting the reproductive axis to facilitate an increase in T in response to social challenge.

The Role of RFamide-Related Peptide-3 in Age-Related Reproductive Decline in Female Rats

Reproductive senescence, the point in time when females cease to show estrous cyclicity, is associated with endocrine changes in the hypothalamus, pituitary, and gonads. However, the mechanisms triggering this transition are not well understood. To gain a better understanding of the top-down control of the transition from reproductive competence to a state of reproductive senescence, we investigated middle-aged female rats exhibiting varying degrees of reproductive decline, including individuals with normal cycles, irregular cycles, and complete cessation of cycles. We identified hormonal changes in the brain that manifest before ovarian cycles exhibit any deterioration. We found that females exhibit an increase in RFamide-related peptide-3 (RFRP3) mRNA expression in the hypothalamus in middle age prior to changes in estrous cycle length. This increase is transient and followed by subsequent decreases in kisspeptin (KiSS1) and gonadotropin-releasing hormone (GnRH) mRNA expression. Expression of RFRP3 and its receptor also increased locally in the ovaries with advancing age. While it is well known that aging is associated with decreased GnRH release and downstream disruption of the hypothalamic-pituitary-gonadal (HPG) axis, herein, we provide evidence that reproductive senescence is likely triggered by alterations in a network of regulatory neuropeptides upstream of the GnRH system.

Circadian Control of the Female Reproductive Axis Through Gated Responsiveness of the RFRP-3 System to VIP Signaling

Throughout most of the ovulatory cycle, estrogen negative feedback restrains the GnRH neuronal system. Just before ovulation, however, estrogen negative feedback is removed to permit stimulation of the preovulatory GnRH/LH surge (positive feedback) by the circadian clock in the suprachiasmatic nucleus (SCN). The mammalian ortholog of avian gonadotropin-inhibitory hormone, RFamide-related peptide 3 (RFRP-3), participates in the circadian-timed removal of estrogen negative feedback to permit the LH surge. The present study examined the specific neurochemical means by which the SCN controls RFRP-3 activity and explored whether the RFRP-3 system exhibits time-dependent responsiveness to SCN signaling to precisely time the LH surge. We found that RFRP-3 cells in female Syrian hamsters (Mesocricetus auratus) receive close appositions from SCN-derived vasopressin-ergic and vasoactive intestinal peptide (VIP)-ergic terminal fibers. Central VIP administration markedly suppressed RFRP-3 cellular activity in the evening, but not the morning, relative to saline controls, whereas vasopressin was without effect at either time point. Double-label in situ hybridization for Rfrp-3 and the VIP receptors VPAC1 and VPAC2 revealed that the majority of RFRP-3 cells do not coexpress either receptor in Syrian hamsters or mice, suggesting that SCN VIP-ergic signaling inhibits RFRP-3 cells indirectly. The timing of this VIP-mediated disinhibition is further coordinated via temporally gated responsiveness of RFRP-3 cells to circadian signaling. Together, these findings reveal a novel circadian hierarchy of control coordinating the preovulatory LH surge and ovulation.

Seasonal control of gonadotropin-inhibitory hormone (GnIH) in birds and mammals

Animals inhabiting temperate and boreal latitudes experience marked seasonal changes in the quality of their environments and maximize reproductive success by phasing breeding activities with the most favorable time of year. Whereas the specific mechanisms driving seasonal changes in reproductive function vary across species, converging lines of evidence suggest gonadotropin-inhibitory hormone (GnIH) serves as a key component of the neuroendocrine circuitry driving seasonal changes in reproduction and sexual motivation in some species. In addition to anticipating environmental change through transduction of photoperiodic information and modifying reproductive state accordingly, GnIH is also positioned to regulate acute changes in reproductive status should unpredictable conditions manifest throughout the year. The present overview summarizes the role of GnIH in avian and mammalian seasonal breeding while considering the similarities and disparities that have emerged from broad investigations across reproductively photoperiodic species.

Knockdown of hypothalamic RFRP3 prevents chronic stress-induced infertility and embryo resorption

Whereas it is well established that chronic stress induces female reproductive dysfunction, whether stress negatively impacts fertility and fecundity when applied prior to mating and pregnancy has not been explored. In this study, we show that stress that concludes 4 days prior to mating results in persistent and marked reproductive dysfunction, with fewer successful copulation events, fewer pregnancies in those that successfully mated, and increased embryo resorption. Chronic stress exposure led to elevated expression of the hypothalamic inhibitory peptide, RFamide-related peptide-3 (RFRP3), in regularly cycling females. Remarkably, genetic silencing of RFRP3 during stress using an inducible-targeted shRNA completely alleviates stress-induced infertility in female rats, resulting in mating and pregnancy success rates indistinguishable from non-stress controls. We show that chronic stress has long-term effects on pregnancy success, even post-stressor, that are mediated by RFRP3. This points to RFRP3 as a potential clinically relevant single target for stress-induced infertility.

DOI:http://dx.doi.org/10.7554/eLife.04316.001

Infertility has become alarmingly common in otherwise healthy women and around 15% of healthy couples younger than 30 years old are unable to conceive within the first year of trying. High-stress levels are known to decrease short-term fertility in humans and other animals, which may serve to prevent pregnancy during times when food or other resources are in short supply.

However, it is not clear if exposure to stress has lasting effects on fertility. Previous studies have found that when male rats experience stress, they release a protein called RFRP3. This protein inhibits brain activity, leading to a reduction in the release of reproductive hormones.

Geraghty et al. took a closer look at how stress may cause lasting fertility problems in female rats. The researchers exposed female rats to stress by restricting their movements for 3 hr each day over the course of 18 days, which increased the levels of stress hormones in the animals. They allowed the rats to recover for one full reproductive cycle—equivalent to a month in humans—and found that while their stress hormone levels returned to normal, RFRP3 levels in the brain remained high. Even after the recovery period, the females were less likely to mate. Also, the females that did mate were less likely to become pregnant, and the ones that did were more likely to lose some of the embryos. Overall, the level of reproductive success in these rats was only 21%, down from 76% in the control group (who were not exposed to the stress).

Next, Geraghty et al. injected a genetically engineered virus into the brain of the stressed rats to switch off the gene that makes RFRP3 during the stress period. This reduced the levels of the RFRP3 protein and restored the mating, pregnancy, and embryo survival rates to the normal levels seen in unstressed rats.

These results suggest that increased levels of RFRP3 during stress can have lasting negative effects on fertility. In the future, developing therapies that lower RFRP3 levels may help individuals who experience fertility problems.

DOI:http://dx.doi.org/10.7554/eLife.04316.002

Contribution of GnIH Research to the Progress of Reproductive Neuroendocrinology

Since the discovery of gonadotropin-releasing hormone (GnRH) in mammals at the beginning of the 1970s, it was generally accepted that GnRH is the only hypothalamic neuropeptide regulating gonadotropin release in mammals and other vertebrates. In 2000, however, gonadotropin-inhibitory hormone (GnIH), a novel hypothalamic neuropeptide that actively inhibits gonadotropin release, was discovered in quail. Numerous studies over the past decade and a half have demonstrated that GnIH serves as a key player regulating reproduction across vertebrates, acting on the brain and pituitary to modulate reproductive physiology and behavior. In the latter case, recent evidence indicates that GnIH can regulate reproductive behavior through changes in neurosteroid, such as neuroestrogen, biosynthesis in the brain. This review summarizes the discovery of GnIH, and the contributions to GnIH research focused on its mode of action, regulation of biosynthesis, and how these findings advance our understanding of reproductive neuroendocrinology.

Dorsomedial hypothalamic lesions counteract decreases in locomotor activity in male Syrian hamsters transferred from long to short day lengths

The dorsomedial nucleus (DMN) of the hypothalamus has been implicated in seasonal control of reproduction. Syrian hamsters with DMN lesions, unlike control hamsters, do not undergo testicular regression after transfer from a long day length (14 h of light per day; LD) to a short day length (8 h of light per day; SD). SDs also markedly reduce hamster locomotor activity (LMA). To assess whether the DMN is a component of the neural circuitry that mediates seasonal variation in LMA, neurologically intact males (controls) and hamsters that had sustained lesions of the DMN (DMNx) were housed in an LD or SD photoperiod for 26 weeks. DMNx that prevented testicular regression counteracted decreases in LMA during 8 to10 weeks of SD treatment; steroid-independent effects of SDs did not override high levels of LMA in DMNx males. As in previous studies, testosterone (T) restoration increased LMA in LD but not SD castrated control males. In the present study, T also failed to increase LMA in SD-DMNx hamsters. The DMN is not necessary to maintain decreased responsiveness of locomotor activity systems to T in SDs, which presumably is mediated by other central nervous system androgen target tissues. Finally, DMNx did not interfere with the spontaneous increase in LMA exhibited by photorefractory hamsters after 26 weeks of SD treatment. We propose that DMN is an essential part of the substrate that mediates seasonal decreases in LMA as day length decreases but is not required to sustain decreased SD responsiveness to T or for development of refractoriness to SDs.

Effects of Pinealectomy and Short Day Lengths on Reproduction and Neuronal RFRP-3, Kisspeptin, and GnRH in Female Turkish Hamsters

Long days (LDs) stimulate and short days (SDs) inhibit reproduction in photoperiodic rodents by modifying nocturnal pineal melatonin secretion. In LD Turkish hamsters, unlike other rodents, pinealectomy induces reproductive quiescence comparable to that produced by SDs. We assessed whether SDs and pinealectomy induce similar or different patterns of kisspeptin and gonadotropin-inhibitory hormone (also known as RFamide-related peptide-3 [RFRP-3] in mammals) expression, important mediators of seasonal reproductive changes in other species. Brains were harvested from sham-operated female Turkish hamsters maintained in LDs and SDs and LD-pinealectomized (pinx) females, all housed in their respective photoperiods for 12 weeks. Uterine weights were substantially higher in LD-sham than in LD-pinx and SD-sham females. RFRP-3-immunoreactive(-ir) cells in the dorsomedial hypothalamic nucleus were greater in number and size in the reproductively competent LD-sham hamsters than in both reproductively suppressed SD-sham and LD-pinx hamsters. LD-sham hamsters had more kisspeptin-ir cells in the anteroventral periventricular nucleus than did LD-pinx hamsters. Reproductive quiescence, whether induced by short-day lengths or pinealectomy, was generally accompanied by comparable changes in RFRP-3 and kisspeptin, suggesting that long-duration melatonin signaling and withdrawal of melatonin by pinealectomy may act through the same neural substrates to induce gonadal quiescence.

A time to remember: the role of circadian clocks in learning and memory

The circadian system has pronounced influence on learning and memory, manifesting as marked changes in memory acquisition and recall across the day. From a mechanistic perspective, the majority of studies have investigated mammalian hippocampal-dependent learning and memory, as this system is highly tractable. The hippocampus plays a major role in learning and memory, and has the potential to integrate circadian information in many ways, including information from local, independent oscillators, and through circadian modulation of neurogenesis, synaptic remodeling, intracellular cascades, and epigenetic regulation of gene expression. These local processes are combined with input from other oscillatory systems to synergistically augment hippocampal rhythmic function. This overview presents an account of the current state of knowledge on circadian interactions with learning and memory circuitry and provides a framework for those interested in further exploring these interactions.

Circadian rhythms have broad implications for understanding brain and behavior

Circadian rhythms are generated by an endogenously organized timing system that drives daily rhythms in behavior, physiology and metabolism. In mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus is the locus of a master circadian clock. The SCN is synchronized to environmental changes in the light:dark cycle by direct, monosynaptic innervation via the retino-hypothalamic tract. In turn, the SCN coordinates the rhythmic activities of innumerable subordinate clocks in virtually all bodily tissues and organs. The core molecular clockwork is composed of a transcriptional/post-translational feedback loop in which clock genes and their protein products periodically suppress their own transcription. This primary loop connects to downstream output genes by additional, interlocked transcriptional feedback loops to create tissue-specific 'circadian transcriptomes'. Signals from peripheral tissues inform the SCN of the internal state of the organism and the brain's master clock is modified accordingly. A consequence of this hierarchical, multilevel feedback system is that there are ubiquitous effects of circadian timing on genetic and metabolic responses throughout the body. This overview examines landmark studies in the history of the study of circadian timing system, and highlights our current understanding of the operation of circadian clocks with a focus on topics of interest to the neuroscience community.

Central and direct regulation of testicular activity by gonadotropin-inhibitory hormone and its receptor

Gonadotropin-inhibitory hormone (GnIH) was first identified in Japanese quail to be an inhibitor of gonadotropin synthesis and release. GnIH peptides have since been identified in all vertebrates, and all share an LPXRFamide (X = L or Q) motif at their C-termini. The receptor for GnIH is the G protein-coupled receptor 147 (GPR147), which inhibits cAMP signaling. Cell bodies of GnIH neurons are located in the paraventricular nucleus (PVN) in birds and the dorsomedial hypothalamic area (DMH) in most mammals. GnIH neurons in the PVN or DMH project to the median eminence to control anterior pituitary function via GPR147 expressed in gonadotropes. Further, GnIH inhibits gonadotropin-releasing hormone (GnRH)-induced gonadotropin subunit gene transcription by inhibiting the adenylate cyclase/cAMP/PKA-dependent ERK pathway in an immortalized mouse gonadotrope cell line (LβT2 cells). GnIH neurons also project to GnRH neurons that express GPR147 in the preoptic area (POA) in birds and mammals. Accordingly, GnIH can inhibit gonadotropin synthesis and release by decreasing the activity of GnRH neurons as well as by directly inhibiting pituitary gonadotrope activity. GnIH and GPR147 can thus centrally suppress testosterone secretion and spermatogenesis by acting in the hypothalamic-pituitary-gonadal axis. GnIH and GPR147 are also expressed in the testis of birds and mammals, possibly acting in an autocrine/paracrine manner to suppress testosterone secretion and spermatogenesis. GnIH expression is also regulated by melatonin, stress, and social environment in birds and mammals. Accordingly, the GnIH-GPR147 system may play a role in transducing physical and social environmental information to regulate optimal testicular activity in birds and mammals. This review discusses central and direct inhibitory effects of GnIH and GPR147 on testosterone secretion and spermatogenesis in birds and mammals.