Influence of photoperiod on hormones, behavior, and immune function

Human immune and metabolic biomarker levels, and stress-biomarker associations, differ by season: Implications for biomedical health research

Although seasonal changes in physiology are well documented, little is known about how human immune and metabolic markers vary across seasons, and no studies have examined how stress → health biomarker associations differ across the year. To investigate these issues, we analyzed data from 2118 participants of the Midlife in the United States (MIDUS) study to determine whether there were differences in (a) levels of 19 immune and metabolic markers, and (b) the association between perceived stress and each biomarker across the year. Results of component-wide boosted generalized additive models revealed seasonal patterning for most biomarkers, with immune proteins generally peaking when days were shorter. Moreover, whereas levels of hemoglobin A1C rose from late fall to spring, triglycerides were elevated in the summer and fall, and high-density lipoprotein decreased steadily from January to December. Urinary cortisol and cortisone exhibited opposite patterns, peaking at the beginning and end of the year, respectively. Most critically, we found that the effects of perceived stress on 18 of the 19 health biomarkers assessed varied by month of measurement. In some cases, these differences involved the magnitude of the stress → biomarker association but, in other cases, it was the direction of the effect that changed. Studies that do not account for month of biomarker assessment may thus yield misleading or unreproducible results.

Mitochondrial stress in the spaceflight environment

Space is a challenging environment that deregulates individual homeostasis. The main external hazards associated with spaceflight include ionizing space radiation, microgravity, isolation and confinement, distance from Earth, and hostile environment. Characterizing the biological responses to spaceflight environment is essential to validate the health risks, and to develop effective protection strategies. Mitochondria energetics is a key mechanism underpinning many physiological, ecological and evolutionary processes. Moreover, mitochondrial stress can be considered one of the fundamental features of space travel. So, we attempt to synthesize key information regarding the extensive effects of spaceflight on mitochondria. In summary, mitochondria are affected by all of the five main hazards of spaceflight at multiple levels, including their morphology, respiratory function, protein, and genetics, in various tissues and organ systems. We emphasize that investigating mitochondrial biology in spaceflight conditions should become the central focus of research on the impacts of spaceflight on human health, as this approach will help resolve numerous challenges of space health and combat several health disorders associated with mitochondrial dysfunction.

Characterizing the relationship between gonadotropin releasing hormone (GnRH), kisspeptin, and RFamide related peptide 3 (RFRP-3) neurons in the equine hypothalamus across the estrous cycle and in the anovulatory seasons

To understand better the role that kisspeptin plays in regulating seasonal and estrous cycle changes in the mare, this study investigated the number, location and interactions between GnRH, kisspeptin and RFRP-3 neurons in the equine hypothalamus. Hypothalami were collected from mares during the non-breeding season, vernal transition and various stages of the breeding season. Fluorescent immunohistochemistry was used to label the neuropeptides of interest. GnRH cells were observed primarily in the arcuate nucleus (ARC), while very few labeled cells were identified in the pre-optic area (POA). Kisspeptin cells were identified primarily in the ARC, with a small number of cells observed dorsal to the ARC, surrounding the third ventricle (3V). The mean number of kisspeptin cells varied between animals and typically showed no pattern associated with season or stage of estrous cycle, but a seasonal difference was identified in the ARC population. Small numbers of RFRP-3 cells were observed in the ARC, ventromedial hypothalamus (VMH) and dorsomedial hypothalamus (DMH). The mean number of RFRP-3 cells appeared higher in pre-ovulatory animals compared to all other stages. The percentage of GnRH cell bodies with kisspeptin appositions did not change with season or stage of estrous cycle. The percentage of kisspeptin cells receiving inputs from RFRP-3 fibers did not vary with season or stage of estrous cycle. These interactions suggest the possibility of the presence of an ultra-short loop feedback system between these three peptides. The changes in RFRP-3 neurons suggest the possibility of a role in the regulation of reproduction in the horse, but it is unlikely to be as a gonadotropin inhibitory factor.

The crosstalk between photoperiod and early mild stress on juvenile oscar (Astronotus ocellatus) after acute stress

Early mild stress (EMS) is like preparedness and might help fish deal with stress appropriately. This study investigated how EMS and photoperiod changes can impact growth, haematology, blood biochemistry, immunological response, antioxidant system, liver enzymes, and stress response of oscar (Astronotus ocellatus; 7.29 ± 0.96 g) before and after acute confinement stress (AC stress). Ten experimental treatments included five different photoperiods 8L16D (08:16 light to dark), 12L12D (12:12 light to dark), 16L8D (16:08 light to dark), 20L4D (20:04 light to dark), and 24L0D (24:00 light to dark), and these five photoperiod schedules were conducted in an EMS condition. After 9 weeks, no significant differences were found in growth parameters, survival rate, and body composition. At the end of the experiment and after AC stress, fish farmed in 24 light hours had the lowest haematocrit, white blood cells, total protein, blood performance, lysozyme, immunoglobulin M, complement C3, superoxide dismutase, and catalase. Fish that experienced EMS had significantly higher survival rates than those farmed in normal conditions (80.67% vs 61.33%). In conclusion, considering all measured parameters, 8-h light can be suggested as an optimum photoperiod for this fish species. Under 24L0D (no EMS) conditions, there were many negative effects apparent. In addition, a positive effect of EMS was evident in terms of survival after AC stress. AC stress decreased some health parameters under 24-h light treatment, while these results were not observed in EMS-exposed fish. Therefore, the EMS schedule can be a useful tool in preventing the negative effects of stress.

Negative photoperiod induces an increase in the number of ovulations in dairy cattle

This study sought to examine the impact of negative photoperiod on the incidence of multiple ovulations and pregnancies in dairy cattle. The study population consisted of 5,373 pregnant cows in their third or greater lactation that experienced their first post-partum pregnancy after spontaneous estrus. The positive photoperiod (increasing day-length) extends from December 22 to June 21, whereas the negative photoperiod (decreasing day-length) extends from June 22 to December 21. The odds ratios (ORs) for multiple ovulations and pregnancies in cows that became pregnant during the negative photoperiod and the remaining cows that became pregnant during the positive photoperiod were 1.4 and 1.3 (P < 0.0001), respectively. The ORs for cows that became pregnant ≥ 90 days in milk and the remaining cows that became pregnant < 90 days in milk were 4.3 and 4.1 (P < 0.0001), respectively. No significant differences were detected in the monthly rates of multiple ovulations or pregnancies during positive and negative photoperiods. Thus, the present study demonstrates that the ovarian function in cows is related to changes in day-length, with decreasing day-length being associated with greater multiple ovulation and pregnancy rates. The present study also shows that positive and negative photoperiods exhibit different trends. The results of this study are consistent with a growing body of work demonstrating the effects of photoperiod patterns on the reproductive physiology of cows, with clear implications for twin pregnancy prevention.

Causal associations between modifiable risk factors and isolated REM sleep behavior disorder: a mendelian randomization study

Objectives

This Mendelian randomization (MR) study identified modifiable risk factors for isolated rapid eye movement sleep behavior disorder (iRBD).

Methods

Genome-wide association study (GWAS) datasets for 29 modifiable risk factors for iRBD in discovery and replication stages were used. GWAS data for iRBD cases were obtained from the International RBD Study Group. The inverse variance weighted (IVW) method was primarily employed to explore causality, with supplementary analyses used to verify the robustness of IVW findings. Co-localization analysis further substantiated causal associations identified via MR. Genetic correlations between mental illness and iRBD were identified using trait covariance, linkage disequilibrium score regression, and co-localization analyses.

Results

Our study revealed causal associations between sun exposure-related factors and iRBD. Utilizing sun protection (odds ratio [OR] = 0.31 [0.14, 0.69], p = 0.004), ease of sunburn (OR = 0.70 [0.57, 0.87], p = 0.001), childhood sunburn occasions (OR = 0.58 [0.39, 0.87], p = 0.008), and phototoxic dermatitis (OR = 0.78 [0.66, 0.92], p = 0.003) decreased iRBD risk. Conversely, a deep skin color increased risk (OR = 1.42 [1.04, 1.93], p = 0.026). Smoking, alcohol consumption, low education levels, and mental illness were not risk factors for iRBD. Anxiety disorders and iRBD were genetically correlated.

Conclusion

Our study does not corroborate previous findings that identified smoking, alcohol use, low education, and mental illness as risk factors for iRBD. Moreover, we found that excessive sun exposure elevates iRBD risk. These findings offer new insights for screening high-risk populations and devising preventive measures.

MYST family histone acetyltransferases regulate reproductive diapause initiation

Histone acetylation, a crucial epigenetic mechanism, has been suggested to play a role in diapause regulation, but this has not been confirmed through gene loss-of-function studies. In this work, we investigated the involvement of MYST family genes, which are key writers of histone acetylation, in initiating reproductive diapause using the cabbage beetle Colaphellus bowringi as a model. We identified C. bowringi orthologs of MYST, including Tip60, KAT6A, KAT7, and KAT8, from previous transcriptomes. Analyses of phylogenetic trees and protein domains indicated that these MYST proteins are structurally conserved across animal species. Expression of these MYST genes was found to be enriched in heads and ovaries of C. bowringi. Under reproductive photoperiod conditions, RNAi targeting MYST genes, especially KAT8, suppressed ovarian growth and yolk deposition, resembling the characteristics of diapausing ovaries. Additionally, KAT8 knockdown led to the upregulation of diapause-related genes, such as heat shock proteins and diapause protein 1, and the emergence of diapause-like guts. Moreover, KAT8 knockdown reduced the expression of a crucial enzyme involved in juvenile hormone (JH) biosynthesis, likely due to decreased H4K16ac levels. Consequently, our findings suggest that MYST family genes, specifically KAT8, influence the JH signal, thereby regulating the initiation of reproductive diapause.

Exploring the mechanisms and impacts of melatonin on fish colouration

The pineal hormone melatonin is a multi-functional molecule with a recognized role in pigment aggregation in chromatophores, mediating its actions through binding to subtypes of its specific receptors. Since its discovery, melatonin has been known to be responsible for pigment aggregation towards the cell centre in fishes, including their embryos, as an adaptation to reduced light and thus results in pale body colouration. Diversity exists in the sensitivity of melanophores towards melatonin at interspecies, intraspecific levels, seasons, and amongst chromatophores at different regions of the animal body. In most of the fishes, melatonin leads to their skin paling at night. It is indicated that the melatonin receptors have characteristically maintained to show the same aggregating effects in fishes and other vertebrates in the evolutionary hierarchy. However, besides this aggregatory effect, melatonin is also responsible for pigment dispersion in certain fishes. Here is the demand in our review to explore further the nature of the dispersive behaviour of melatonin through the so-called β-melatonin receptors. It is clear that the pigment translocations in lower vertebrates under the effect of melatonin are mediated through the melatonin receptors coupled with other hormonal receptors as well. Therefore, being richly supplied with a variety of receptors, chromatophores and melanocytes can be used as in vitro test models for pharmacological applications of known and novel drugs. In this review, we present diverse effects of melatonin on chromatophores of fishes in particular with appropriate implications on most of the recent findings.

Standardized ileal digestible tryptophan and lysine affects the eating and sleeping behavior of 15-30 kg barrows

The objective of this study was to evaluate the effect of standardized ileal digestible (SID) tryptophan (Trp) and lysine (Lys) levels on eating and sleeping behavior and the respective feed intake of barrows. Sixty-four pigs, averaging 15.00 ± 1.63 kg of initial body weight, were used and distributed in a randomized blocks design, in a 4 × 4 factorial scheme, consisting of four levels of SID Trp (0.155, 0.185, 0.215, 0.245%) and four levels of SID Lys (0.972, 1.112, 1.252, and 1.392%). Behavior evaluation was performed by an instantaneous sampling using 10-min intervals during 24 h, at each 7 days (days 7, 14, and 21), and each day was divided into four times of 6 h each one (08:30-14:20, 14:30-20:20, 20:30-02:20, and 02:30-08:20 h), during all the experimental period, yielding a total of 3 × 24 h behavior recordings (72 h) × 6 10-min intervals, totalizing 432 observations per animal. Data were analyzed by classifying behavior into eating or sleeping. All these behaviors were measured in order to obtain the estimated frequency of the eating and sleeping behaviors. Changes were observed (P<0.05) for all the behavioral parameters during the starting phase. SID Trp and SID Lys showed an interactive positive effect on the estimated frequency of eating behavior, and mainly SID Trp increased the estimated frequency of the sleeping behavior of starting pigs in the nocturnal time. Pig diets with increasing levels of SID Trp and SID Lys until 0.245 and 1.392%, respectively, increased the average daily feed intake, and the interaction of the amino acids increased the estimated frequency of eating behavior during all the starting phase, and mainly the increasing levels of SID Trp increased the estimated frequency of sleeping behavior of pigs from the middle to the end of the starting phase, from 2:30 to 8:20 h.

A brain circuit and neuronal mechanism for decoding and adapting to change in daylength

Changes in daylight amount (photoperiod) drive pronounced alterations in physiology and behaviour1,2. Adaptive responses to seasonal photoperiods are vital to all organisms - dysregulation is associated with disease, from affective disorders3 to metabolic syndromes4. Circadian rhythm circuitry has been implicated5,6 yet little is known about the precise neural and cellular substrates that underlie phase synchronization to photoperiod change. Here we present a previously unknown brain circuit and novel system of axon branch-specific and reversible neurotransmitter deployment that together prove critical for behavioural and sleep adaptation to photoperiod change. We found that the recently defined neuron type called mrEn1-Pet17 located in the mouse brainstem Median Raphe Nucleus (MRN) segregates serotonin versus VGLUT3 (here proxy for the neurotransmitter glutamate) to different axonal branches innervating specific brain regions involved in circadian rhythm and sleep/wake timing8,9. We found that whether measured during the light or dark phase of the day this branch-specific neurotransmitter deployment in mrEn1-Pet1 neurons was indistinguishable; however, it strikingly reorganizes on photoperiod change. Specifically, axonal boutons but not cell soma show a shift in neurochemical phenotype upon change away from equinox light/dark conditions that reverses upon return to equinox. When we genetically disabled the deployment of VGLUT3 in mrEn1-Pet1 neurons, we found that sleep/wake periods and voluntary activity failed to synchronize to the new photoperiod or was significantly delayed. Combining intersectional rabies virus tracing and projection-specific neuronal silencing in vivo, we delineated a Preoptic Area-to-mrEn1Pet1 connection responsible for decoding the photoperiodic inputs, driving the neurochemical shift and promoting behavioural synchronization. Our results reveal a previously unrecognized brain circuit along with a novel form of periodic, branch-specific neurotransmitter deployment that together regulate organismal adaptation to photoperiod changes.

Withania somnifera inhibits photorefractoriness which triggers neuronal apoptosis in both pre-optic and paraventricular hypothalamic area of Coturnix coturnix japonica: involvement of oxidative stress induced p53 dependent Caspase-3 mediated low immunoreactivity of estrogen receptor alpha

Light has a very important function in the regulation of the normal physiology including the neuroendocrine system, biological rhythms, cognitive behavior, etc. The variation in photoperiod acts as a stressor due to imbalance in endogenous hormones. Estrogen and its receptors ER alpha and beta play a vital role in the control of stress response in birds. The study investigates the estrogenic effects of a well-known medicinal plant Withania somnifera (WS), mediated by estrogen receptor alpha (ERα) in the hypothalamic pre-optic area (POA) and paraventricular nuclei (PVN). Further the study elucidates its anti-oxidants and anti-apoptotic activities in the brain of Japanese quail. To validate this hypothesis, mature male quails were exposed to long day length for 3 months and then transferred to intermediate day length to become photorefractory (PR) while controls were still continued under long daylength. Supplementation of WS root extract in PR quail increases plasma estrogen and lowers corticosterone. Further, in PR quail the variation in light downregulates immunoreactivity of ERα, oxidative stress and antioxidant enzyme activities i.e. superoxide dismutase and catalase in the brain. Neuronal apoptosis was observed in the POA and PVN of PR quail as indicated by the abundant expression of Caspase-3 and p53 which reduces after the administration of WS root extract. The neuronal population also found to decrease in PR although it increased in WS administered quails. Further, the study concluded that change in photoperiod from 3 months exposure of 16L: 8D to 13.5L: 10.5D directly activates neuronal apoptosis via expression of Caspase3 and p53 expression in the brain and increases neuronal and gonadal oxidative stress while WS root extract reverses them via enhanced estrogen and its receptor ERα expression in the hypothalamic pre-optic and PVN area of Japanese quail.

Seasonal plasticity in immunocompetent cytokines (IL-2, IL-6, and TNF-α), myeloid progenitor cell (CFU-GM) proliferation, and LPS-induced oxido-inflammatory aberrations in a tropical rodent Funambulus pennanti: role of melatonin

In seasonal breeders, photoperiods regulate the levels of circulatory melatonin, a well-known immunomodulator and an antioxidant. Melatonin is known to play a complex physiological role in maintaining the immune homeostasis by affecting cytokine production in immunocompetent cells. In this study, we have quantified seasonal and temporal variations in immunocompetent cytokines-IL-2, IL-6, and TNF-α-and circulatory corticosterone along with in- vitro proliferation of bone marrow-derived granulocyte macrophage-colony forming unit (CFU-GM) progenitor cells of a tropical seasonal breeder Funambulus pennanti (northern palm squirrel). Transient variations in antioxidant status of seasonal breeders might be due to the fluctuations associated with immunity and inflammation. Further, to establish a direct immunomodulatory effect of photoperiod, we recorded the LPS-induced oxidative and inflammatory responses of squirrels by housing them in artificial photoperiodic chambers mimicking summer and winter seasons respectively. We observed a marked variation in cytokines level, melatonin, and corticosterone , and CFU-GM cell proliferation during summer and winter seasons. High Peripheral melatonin levels directly correlated with cytokine IL-2 levels, and inversely correlated with TNF-α, and circulatory corticosterone level. LPS-challenged squirrels housed in short photoperiod (10L:14D; equivalent to winter days) showed a marked reduction in the components of the inflammatory cascade, CRP, TNF-α, IL-6, NOx, NF-κB, Cox-2, and PGES, with an overall improvement in antioxidant status when compared to squirrels maintained under a long photoperiod (16L:8D; equivalent to summer days). Our results underline the impact of seasonality, photoperiod, and melatonin in maintaining an intrinsic redox-immune homeostasis which helps the animal to withstand environmental stresses.

Thyroid hormone rewires cortical circuits to coordinate body-wide metabolism and exploratory drive

Animals adapt to varying environmental conditions by modifying the function of their internal organs, including the brain. To be adaptive, alterations in behavior must be coordinated with the functional state of organs throughout the body. Here we find that thyroid hormone- a prominent regulator of metabolism in many peripheral organs- activates cell-type specific transcriptional programs in anterior regions of cortex of adult mice via direct activation of thyroid hormone receptors. These programs are enriched for axon-guidance genes in glutamatergic projection neurons, synaptic regulators across both astrocytes and neurons, and pro-myelination factors in oligodendrocytes, suggesting widespread remodeling of cortical circuits. Indeed, whole-cell electrophysiology recordings revealed that thyroid hormone induces local transcriptional programs that rewire cortical neural circuits via pre-synaptic mechanisms, resulting in increased excitatory drive with a concomitant sensitization of recruited inhibition. We find that thyroid hormone bidirectionally regulates innate exploratory behaviors and that the transcriptionally mediated circuit changes in anterior cortex causally promote exploratory decision-making. Thus, thyroid hormone acts directly on adult cerebral cortex to coordinate exploratory behaviors with whole-body metabolic state.

Sex and seasonal differences in neural steroid sensitivity predict territorial aggression in Siberian hamsters

Many animals display marked changes in physiology and behavior on a seasonal timescale, including non-reproductive social behaviors (e.g., aggression). Previous studies from our lab suggest that the pineal hormone melatonin acts via steroid hormones to regulate seasonal aggression in Siberian hamsters (Phodopus sungorus), a species in which both males and females display increased non-breeding aggression. The neural actions of melatonin on steroids and aggressive behavior, however, are relatively unexplored. Here, we housed male and female hamsters in long-day photoperiods (LDs, characteristic of breeding season) or short-day photoperiods (SDs, characteristic of non-breeding season) and administered timed melatonin (M) or control injections. Following 10 weeks of treatment, we quantified aggressive behavior and neural steroid sensitivity by measuring the relative mRNA expression of two steroidogenic enzymes (aromatase and 5α-reductase 3) and estrogen receptor 1 in brain regions associated with aggression or reproduction [medial preoptic area (MPOA), anterior hypothalamus (AH), arcuate nucleus (ARC), and periaqueductal gray (PAG)] via quantitative PCR. Although LD-M and SD males and females displayed increased aggression and similar changes in gene expression in the ARC, there were sex-specific effects of treatment with melatonin and SDs on gene expression in the MPOA, AH, and PAG. Furthermore, males and females exhibited different relationships between neural gene expression and aggression in response to melatonin and SDs. Collectively, these findings support a role for melatonin in regulating seasonal variation in neural steroid sensitivity and aggression and reveal how distinct neuroendocrine responses may modulate a similar behavioral phenotype in male and female hamsters.

Estrogen-responsive neural circuits governing male and female mating behavior in mice

Decades of knockout analyses have highlighted the crucial involvement of estrogen receptors and downstream genes in controlling mating behaviors. More recently, advancements in neural circuit research have unveiled a distributed subcortical network comprising estrogen-receptor or estrogen-synthesis-enzyme-expressing cells that transforms sensory inputs into sex-specific mating actions. This review provides an overview of the latest discoveries on estrogen-responsive neurons in various brain regions and the associated neural circuits that govern different aspects of male and female mating actions in mice. By contextualizing these findings within previous knockout studies of estrogen receptors, we emphasize the emerging field of "circuit genetics", where identifying mating behavior-related neural circuits may allow for a more precise evaluation of gene functions within these circuits. Such investigations will enable a deeper understanding of how hormone fluctuation, acting through estrogen receptors and downstream genes, influences the connectivity and activity of neural circuits, ultimately impacting the manifestation of innate mating actions.

Reproductive asynchrony within social groups of female eastern wild turkeys

Coordination in timing of reproduction is driven by multiple ecological and sociobiological processes for a wide array of species. Eastern wild turkeys (Meleagris gallopavo silvestris) use a male dominance polygynous mating system, where males communicate with females via elaborate courtship displays and vocalizations at display sites. Most females prefer to mate with dominant males; therefore, asynchronous breeding and nesting may occur which can disproportionately influence individual fitness within breeding groups. For female wild turkeys, there are reproductive advantages associated with earlier nesting. As such, we evaluated reproductive asynchrony within and between groups of GPS-tagged female eastern wild turkeys based on timing of nest initiation. We examined 30 social groups with an average of seven females per group (range 2-15) during 2014-2019 in west central Louisiana. We found that the estimated number of days between first nest initiation across females within groups varied between 3 and 7 days across years, although we expected 1-2 days to occur between successive nesting attempts of females within groups based on observations of captive wild turkeys in the extant literature. The number of days between successive nest attempts across females within groups was lower for successful than failed attempts, and nests with an average of 2.8 days between initiation of another nest were more likely to hatch. Our findings suggest that asynchronous reproduction may influence reproductive success in female wild turkeys.

A multi-site study of the relationship between photoperiod and ovulation rate using Natural Cycles data

Many species exhibit seasonal patterns of breeding. Although humans can shield themselves from many season-related stressors, they appear to exhibit seasonal patterns of investment in reproductive function nonetheless, with levels of sex steroid hormones being highest during the spring and summer months. The current research builds on this work, examining the relationship between day length and ovarian function in two large samples of women using data from the Natural Cycles birth control application in each Sweden and the United States. We hypothesized that longer days would predict higher ovulation rates and sexual motivation. Results revealed that increasing day length duration predicts increased ovulation rate and sexual behavior, even while controlling for other relevant factors. Results suggest that day length may contribute to observed variance in women's ovarian function and sexual desire.

Influence of Leptin on the Secretion of Growth Hormone in Ewes under Different Photoperiodic Conditions

Leptin is an adipokine with a pleiotropic impact on many physiological processes, including hypothalamic-pituitary-somatotropic (HPS) axis activity, which plays a key role in regulating mammalian metabolism. Leptin insensitivity/resistance is a pathological condition in humans, but in seasonal animals, it is a physiological adaptation. Therefore, these animals represent a promising model for studying this phenomenon. This study aimed to determine the influence of leptin on the activity of the HPS axis. Two in vivo experiments performed during short- and long-day photoperiods were conducted on 12 ewes per experiment, and the ewes were divided randomly into 2 groups. The arcuate nucleus, paraventricular nucleus, anterior pituitary (AP) tissues, and blood were collected. The concentration of growth hormone (GH) was measured in the blood, and the relative expression of GHRH, SST, GHRHR, SSTR1, SSTR2, SSTR3, SSTR5, LEPR, and GH was measured in the collected brain structures. The study showed that the photoperiod, and therefore leptin sensitivity, plays an important role in regulating HPS axis activity in the seasonal ewe. However, leptin influences the release of GH in a season-dependent manner, and its effect seems to be targeted at the posttranscriptional stages of GH secretion.

Effects of artificial photoperiods on antigen-dependent immune responses in rainbow trout (Oncorhynchus mykiss)

In this study, we investigated the effects of the artificial photoperiods that mimic summer (16L:8D) and winter (8L:16D) solstices, equinoxes (12L:12D), and the artificial 24-h light regimen (24L:0D) on the leukocyte populations and the T helper and regulatory type responses on rainbow trout (Oncorhynchus mykiss). Using flow cytometry analysis, we found that photoperiod induces changes in head kidney leukocyte subsets. The lymphoid subset increased in the 16L:8D summer solstice regime. The analysis using antibodies against B and T cells showed the increase of CD4-1⁺ T lymphocytes and other unidentified lymphoid cells, with no changes in the B cells. To investigate the modulatory influence of the photoperiod on the fish T cell response, we quantified in the head kidney the transcript levels of genes involved in the Th1 type response (t-bet, ifn-ƴ, il-12p35, il-12p40c), Th2 type response (gata3, il-4/13a), Th17 response (ror-ƴt, il-17a/f), T regulatory response (foxp3α, il-10a, tgf-β1), and the T cell growth factor il-2. The results showed that the seasonal photoperiod alone has a limited influence on the expression of these genes, as the only difference was observed in il-14/13a and il-10a transcripts of fish kept on the 16L:8D regimen. In addition, the 24L:0D treatment used in aquaculture produces a reduction of il-14/13a and il-17a/f. We also evaluated the effect of photoperiod in the presence of an antigenic stimulus. Thus, in fish immunized with the recombinant viral protein 1 (rVP1) of infectious pancreatic necrosis virus (IPNV), the photoperiod had a striking influence on the type of adaptive immune response. Each photoperiod fosters a unique immune signature of antigenic response. A classical type 1 response is observed in fish subjected to the 16D:8L photoperiod. In contrast, fish in the 12L:12D photoperiod showed only the upregulation of il-12p40c. Furthermore, none of the cytokines were increased in fish maintained on the artificial 24L:0D regimen, and a decrease in the master transcription factors (t-bet, ror-ƴt, and foxp3α) was observed. Thus, fish on the 12L:12D and 24L:0D photoperiod appear hyporesponsive regarding the T cell response. Altogether, this study showed that photoperiods modify the magnitude and quality of the T-helper response in rainbow trout and thus impact essential mechanisms for the generation of immune memory and protection against microorganisms.

Lunar Cycle, Climate, and Onset of Parturition in Domestic Dromedary Camels: Implications of Species-Specific Metabolic Economy and Social Ecology

Given energy costs for gestating and caring for male offspring are higher than those of female newborns, external environmental conditions might be regarded as likely to affect the timing of delivery processes differentially depending on the sex of the newborn calf to be delivered. The aim of the present paper is to evaluate the association between environmental stressors such as the moon phase and weather-related factors and the onset of labor in female dromedaries. A binary logistic regression model was developed to find the most parsimonious set of variables that are most effective in predicting the probability for a gravid female dromedary to give birth to a male or a female calf, assuming that higher gestational costs and longer labor times are ascribed to the production of a male offspring. Although the differences in the quantitative distribution of spontaneous onset of labor across lunar phases and the mean climate per onset event along the whole study period were deemed nonsignificant (p > 0.05), a non-negligible prediction effect of a new moon, mean wind speed and maximum wind gust was present. At slightly brighter nights and lower mean wind speeds, a calf is more likely to be male. This microevolutionary response to the external environment may have been driven by physiological and behavioral adaptation of metabolic economy and social ecology to give birth to cooperative groups with the best possible reduction of thermoregulatory demands. Model performance indexes then highlighted the heterothermic character of camels to greatly minimize the impact of the external environment. The overall results will also enrich the general knowledge of the interplay between homeostasis and arid and semi-arid environments.

Day-night and seasonal variation of human gene expression across tissues

Circadian and circannual cycles trigger physiological changes whose reflection on human transcriptomes remains largely uncharted. We used the time and season of death of 932 individuals from GTEx to jointly investigate transcriptomic changes associated with those cycles across multiple tissues. Overall, most variation across tissues during day-night and among seasons was unique to each cycle. Although all tissues remodeled their transcriptomes, brain and gonadal tissues exhibited the highest seasonality, whereas those in the thoracic cavity showed stronger day-night regulation. Core clock genes displayed marked day-night differences across multiple tissues, which were largely conserved in baboon and mouse, but adapted to their nocturnal or diurnal habits. Seasonal variation of expression affected multiple pathways, and it was enriched among genes associated with the immune response, consistent with the seasonality of viral infections. Furthermore, they unveiled cytoarchitectural changes in brain regions. Altogether, our results provide the first combined atlas of how transcriptomes from human tissues adapt to major cycling environmental conditions. This atlas may have multiple applications; for example, drug targets with day-night or seasonal variation in gene expression may benefit from temporally adjusted doses.

Te Maramataka-An Indigenous System of Attuning with the Environment, and Its Role in Modern Health and Well-Being

The connection between the natural environment and human health is well documented in Indigenous narratives. The maramataka-a Māori system of observing the relationships between signs, rhythms, and cycles in the environment-is underpinned by generations of Indigenous knowledge, observation, and experimentation. The maramataka enabled Māori and our Pacific relatives to attune with the movements of the environment and ensure activities essential for survival and well-being were conducted at the optimal times. A recent revival of the maramataka in various communities in New Zealand is providing uniquely Indigenous ways to 'reconnect' people, and their health, with the natural environment. In a world where people have become increasingly disconnected from the natural environment, the maramataka offers an alternative to dominant perspectives of health. It also provides a mechanism to enhance the many facets of health through an understanding of the human-ecosystem relationship in a uniquely Indigenous way. This conceptual paper (i) highlights a uniquely Indigenous way of understanding the environment (the maramataka) and its connection to health, (ii) discusses the connections between the maramataka and scientific research on health and the environment, and (iii) introduces current and potential applications of the maramataka in improving health and well-being.

Photoperiod Impacts Nucleus Accumbens Dopamine Dynamics

Circadian photoperiod, or day length, changes with the seasons and influences behavior to allow animals to adapt to their environment. Photoperiod is also associated with seasonal rhythms of affective state, as evidenced by seasonality of several neuropsychiatric disorders. Interestingly, seasonality tends to be more prevalent in women for affective disorders such as major depressive disorder and bipolar disorder (BD). However, the underlying neurobiological processes contributing to sex-linked seasonality of affective behaviors are largely unknown. Mesolimbic dopamine input to the nucleus accumbens (NAc) contributes to the regulation of affective state and behaviors. Additionally, sex differences in the mesolimbic dopamine pathway are well established. Therefore, we hypothesize that photoperiod may drive differential modulation of NAc dopamine in males and females. Here, we used fast-scan cyclic voltammetry (FSCV) to explore whether photoperiod can modulate subsecond dopamine signaling dynamics in the NAc core of male and female mice raised in seasonally relevant photoperiods. We found that photoperiod modulates dopamine signaling in the NAc core, and that this effect is sex-specific to females. Both release and uptake of dopamine were enhanced in the NAc core of female mice raised in long, summer-like photoperiods, whereas we did not find photoperiodic effects on NAc core dopamine in males. These findings uncover a potential neural circuit basis for sex-linked seasonality in affective behaviors.

Light conditions during Atlantic salmon embryogenesis affect key neuropeptides in the melanocortin system during transition from endogenous to exogenous feeding

During the first feeding period, fish will adapt to exogenous feeding as their endogenous source of nutrients is depleted. This requires the development of a functional physiological system to control active search for food, appetite, and food intake. The Atlantic salmon (Salmo salar) melanocortin system, a key player in appetite control, includes neuronal circuits expressing neuropeptide y (npya), agouti-related peptide (agrp1), cocaine- and amphetamine-regulated transcript (cart), and proopiomelanocortin (pomca). Little is known about the ontogeny and function of the melanocortin system during early developmental stages. Atlantic salmon [0-730 day degrees (dd)] were reared under three different light conditions (DD, continuous darkness; LD, 14:10 Light: Dark; LL, continuous light) before the light was switched to LD and the fish fed twice a day. We examined the effects of different light conditions (DD _LD , LD _LD , and LL _LD ) on salmon growth, yolk utilization, and periprandial responses of the neuropeptides npya1, npya2, agrp1, cart2a, cart2b, cart4, pomca1, and pomca2. Fish were collected 1 week (alevins, 830 dd, still containing yolk sac) and 3 weeks (fry, 991 dd, yolk sac fully consumed) into the first feeding period and sampled before (-1 h) and after (0.5, 1.5, 3, and 6 h) the first meal of the day. Atlantic salmon reared under DD _LD , LD _LD , and LL _LD had similar standard lengths and myotome heights at the onset of first feeding. However, salmon kept under a constant light condition during endogenous feeding (DD _LD and LL _LD ) had less yolk at first feeding. At 830 dd none of the neuropeptides analyzed displayed a periprandial response. But 2 weeks later, and with no yolk remaining, significant periprandial changes were observed for npya1, pomca1, and pomca2, but only in the LD _LD fish. This suggests that these key neuropeptides serve an important role in controlling feeding once Atlantic salmon need to rely entirely on active search and ingestion of exogenous food. Moreover, light conditions during early development did not affect the size of salmon at first feeding but did affect the mRNA levels of npya1, pomca1, and pomca2 in the brain indicating that mimicking natural light conditions (LD _LD ) better stimulates appetite control.

Winter madness: Melatonin as a neuroendocrine regulator of seasonal aggression

Individuals of virtually all vertebrate species are exposed to annual fluctuations in the deterioration and renewal of their environments. As such, organisms have evolved to restrict energetically expensive processes and activities to a specific time of the year. Thus, the precise timing of physiology and behavior is critical for individual reproductive success and subsequent fitness. Although the majority of research on seasonality has focused on seasonal reproduction, pronounced fluctuations in other non-reproductive social behaviors, including agonistic behaviors (e.g., aggression), also occur. To date, most studies that have investigated the neuroendocrine mechanisms underlying seasonal aggression have focused on the role of photoperiod (i.e., day length); prior findings have demonstrated that some seasonally breeding species housed in short "winter-like" photoperiods display increased aggression compared with those housed in long "summer-like" photoperiods, despite inhibited reproduction and low gonadal steroid levels. While fewer studies have examined how the hormonal correlates of environmental cues regulate seasonal aggression, our previous work suggests that the pineal hormone melatonin acts to increase non-breeding aggression in Siberian hamsters (Phodopus sungorus) by altering steroid hormone secretion. This review addresses the physiological and cellular mechanisms underlying seasonal plasticity in aggressive and non-aggressive social behaviors, including a key role for melatonin in facilitating a "neuroendocrine switch" to alternative physiological mechanisms of aggression across the annual cycle. Collectively, these studies highlight novel and important mechanisms by which melatonin regulates aggressive behavior in vertebrates and provide a more comprehensive understanding of the neuroendocrine bases of seasonal social behaviors broadly.

The maturation of exploratory behavior in adolescent Mus spicilegus on two photoperiods

Dispersal from the natal site or familial group is a core milestone of adolescent development in many species. A wild species of mouse, Mus spicilegus, presents an exciting model in which to study adolescent development and dispersal because it shows different life history trajectory depending on season of birth. M. spicilegus born in spring and summer on long days (LD) disperse in the first 3 months of life, while M. spicilegus born on shorter autumnal days (SD) delay dispersal through the wintertime. We were interested in using these mice in a laboratory context to compare age-matched mice with differential motivation to disperse. To first test if we could find a proxy for dispersal related behavior in the laboratory environment, we measured open field and novel object investigation across development in M. spicilegus raised on a LD 12 h:12 h light:dark cycle. We found that between the first and second month of life, distance traveled and time in center of the open field increased significantly with age in M. spicilegus. Robust novel object investigation was observed in all age groups and decreased between the 2nd and 3rd month of life in LD males. Compared to male C57BL/6 mice, male M. spicilegus traveled significantly longer distances in the open field but spent less time in the center of the field. However, when a novel object was placed in the center of the open field, Male M. spicilegus, were significantly more willing to contact and mount it. To test if autumnal photoperiod affects exploratory behavior in M. spicilegus in a laboratory environment, we reared a cohort of M. spicilegus on a SD 10 h:14 h photoperiod and tested their exploratory behavior at P60-70. At this timepoint, we found SD rearing had no effect on open field metrics, but led to reduced novel object investigation. We also observed that in P60-70 males, SD reared M. spicilegus weighed less than LD reared M. spicilegus. These observations establish that SD photoperiod can delay weight gain and blunt some, but not all forms of exploratory behavior in adolescent M. spicilegus.

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.

Seasonal variation in gonadal hormones, spatial cognition, and hippocampal attributes: More questions than answers

A large body of research has been dedicated to understanding the factors that modulate spatial cognition and attributes of the hippocampus, a highly plastic brain region that underlies spatial processing abilities. Variation in gonadal hormones impacts spatial memory and hippocampal attributes in vertebrates, although the direction of the effect has not been entirely consistent. To add complexity, individuals in the field must optimize fitness by coordinating activities with the appropriate environmental cues, and many of these behaviors are correlated tightly with seasonal variation in gonadal hormone release. As such, it remains unclear if the relationship among systemic gonadal hormones, spatial cognition, and the hippocampus also exhibits seasonal variation. This review presents an overview of the relationship among gonadal hormones, the hippocampus, and spatial cognition, and how the seasonal release of gonadal hormones correlates with seasonal variation in spatial cognition and hippocampal attributes. Additionally, this review presents other neuroendocrine mechanisms that may be involved in modulating the relationship among seasonality, gonadal hormone release, and the hippocampus and spatial cognition, including seasonal rhythms of steroid hormone binding globulins, neurosteroids, sex steroid hormone receptor expression, and hormone interactions. Here, endocrinology, ecology, and behavioral neuroscience are brought together to present an overview of the research demonstrating the mechanistic effects of systemic gonadal hormones on spatial cognition and the hippocampus, while, at a functional level, superimposing seasonal effects to examine ecologically-relevant circannual changes in gonadal hormones and spatial behaviors.

Effects of light pollution on photoperiod-driven seasonality

Changes to photoperiod (day length) occur in anticipation of seasonal environmental changes, altering physiology and behavior to maximize fitness. In order for photoperiod to be useful as a predictive factor of temperature or food availability, day and night must be distinct. The increasing prevalence of exposure to artificial light at night (ALAN) in both field and laboratory settings disrupts photoperiodic time measurement and may block development of appropriate seasonal adaptations. Here, we review the effects of ALAN as a disruptor of photoperiodic time measurement and season-specific adaptations, including reproduction, metabolism, immune function, and thermoregulation.

The Epigenetics of Psychosis: A Structured Review with Representative Loci

The evidence for an environmental component in chronic psychotic disorders is strong and research on the epigenetic manifestations of these environmental impacts has commenced in earnest. In reviewing this research, the focus is on three genes as models for differential methylation, MCHR1, AKT1 and TDO2, each of which have been investigated for genetic association with psychotic disorders. Environmental factors associated with psychotic disorders, and which interact with these model genes, are explored in depth. The location of transcription factor motifs relative to key methylation sites is evaluated for predicted gene expression results, and for other sites, evidence is presented for methylation directing alternative splicing. Experimental results from key studies show differential methylation: for MCHR1, in psychosis cases versus controls; for AKT1, as a pre-existing methylation pattern influencing brain activation following acute administration of a psychosis-eliciting environmental stimulus; and for TDO2, in a pattern associated with a developmental factor of risk for psychosis, in all cases the predicted expression impact being highly dependent on location. Methylation induced by smoking, a confounding variable, exhibits an intriguing pattern for all three genes. Finally, how differential methylation meshes with Darwinian principles is examined, in particular as it relates to the “flexible stem” theory of evolution.

Adrenal MT1 melatonin receptor expression is linked with seasonal variation in social behavior in male Siberian hamsters

Many animals exhibit pronounced changes in physiology and behavior on a seasonal basis, and these adaptations have evolved to promote survival and reproductive success. While the neuroendocrine pathways mediating seasonal reproduction are well-studied, far less is known about the mechanisms underlying seasonal changes in social behavior, particularly outside of the context of the breeding season. Our previous work suggests that seasonal changes in melatonin secretion are important in regulating aggression in Siberian hamsters (Phodopus sungorus); it is unclear, however, how melatonin acts via its receptors to modulate seasonal variation in social behavior. In this study, we infused a MT₁ melatonin receptor-expressing (MT₁) or control (CON) lentivirus into the adrenal glands of male Siberian hamsters. We then housed hamsters in long-day (LD) or short-day (SD) photoperiods, administered timed melatonin or control injections, and quantified aggressive and non-aggressive social behaviors (e.g., investigation, self-grooming) following 10 weeks of treatment. LD hamsters infused with the MT₁ lentivirus had significantly higher adrenal mt1 expression than LD CON hamsters, as determined via quantitative PCR. While melatonin administration was necessary to induce SD-like reductions in body and relative reproductive mass, only LD hamsters infused with the MT₁ lentivirus displayed SD-like changes in social behavior, including increased aggression and decreased investigation and grooming. In addition, SD CON and LD hamsters infused with the MT₁ lentivirus exhibited similar relationships between adrenal mt1 expression and aggressive behavior. Together, our findings suggest a role for adrenal MT₁ receptor signaling in regulating behavior, but not energetics or reproduction in seasonally breeding species.

Day-night and seasonal variation of human gene expression across tissues

Circadian and circannual cycles trigger physiological changes whose reflection on human transcriptomes remains largely uncharted. We used the time and season of death of 932 individuals from GTEx to jointly investigate transcriptomic changes associated with those cycles across multiple tissues. Overall, most variation across tissues during day-night and among seasons was unique to each cycle. Although all tissues remodeled their transcriptomes, brain and gonadal tissues exhibited the highest seasonality, whereas those in the thoracic cavity showed stronger day-night regulation. Core clock genes displayed marked day-night differences across multiple tissues, which were largely conserved in baboon and mouse, but adapted to their nocturnal or diurnal habits. Seasonal variation of expression affected multiple pathways and it was enriched among genes associated with the immune response, consistent with the seasonality of viral infections. Furthermore, they unveiled cytoarchitectural changes in brain regions. Altogether, our results provide the first combined atlas of how transcriptomes from human tissues adapt to major cycling environmental conditions.

Chronic Sleep Restriction While Minimizing Circadian Disruption Does Not Adversely Affect Glucose Tolerance

Insufficient sleep, which has been shown to adversely affect metabolism, is generally associated with prolonged exposure to artificial light at night, a known circadian disruptor. There is growing evidence suggesting that circadian disruption adversely affects metabolism, yet few studies have attempted to evaluate the adverse metabolic effects of insufficient sleep while controlling for circadian disruption. We assessed postprandial glucose and insulin responses to a standard breakfast meal in healthy adults (n = 9) who underwent 3 weeks of chronic sleep restriction (CSR) in a 37-day inpatient study while minimizing circadian disruption by maintaining the same duration of light exposure each study day. We compared these results to findings from an earlier inpatient study which used a forced desynchrony (FD) protocol to assess the influence of 3 weeks of CSR combined with recurrent circadian disruption (RCD) on glycemic control in healthy adults (n = 21). CSR combined with RCD resulted in significantly elevated postprandial plasma glucose levels (p < 0.0001), while CSR with minimized circadian disruption had no adverse glycemic effects after 3 weeks of exposure (EXP). These results suggest that one mechanism by which sleep restriction impacts metabolism may be via concurrent circadian disruption.

New Insights Into Blue Light Phototherapy in Experimental Trypanosoma cruzi Infection

The search for an effective etiologic treatment to eliminate Trypanosoma cruzi, the causative agent of Chagas disease, has continued for decades and yielded controversial results. In the 1970s, nifurtimox and benznidazole were introduced for clinical assessment, but factors such as parasite resistance, high cellular toxicity, and efficacy in acute and chronic phases of the infection have been debated even today. This study proposes an innovative strategy to support the controlling of the T. cruzi using blue light phototherapy or blue light-emitting diode (LED) intervention. In in vitro assays, axenic cultures of Y and CL strains of T. cruzi were exposed to 460 nm and 40 µW/cm² of blue light for 5 days (6 h/day), and parasite replication was evaluated daily. For in vivo experiments, C57BL6 mice were infected with the Y strain of T. cruzi and exposed to 460 nm and 7 µW/cm² of blue light for 9 days (12 h/day). Parasite count in the blood and cardiac tissue was determined, and plasma interleukin (IL-6), tumoral necrosis factor (TNF), chemokine ligand 2 (CCL2), and IL-10 levels and the morphometry of the cardiac tissue were evaluated. Blue light induced a 50% reduction in T. cruzi (epimastigote forms) replication in vitro after 5 days of exposure. This blue light-mediated parasite control was also observed by the T. cruzi reduction in the blood (trypomastigote forms) and in the cardiac tissue (parasite DNA and amastigote nests) of infected mice. Phototherapy reduced plasma IL-6, TNF and IL-10, but not CCL2, levels in infected animals. This non-chemical therapy reduced the volume density of the heart stroma in the cardiac connective tissue but did not ameliorate the mouse myocarditis, maintaining a predominance of pericellular and perivascular mononuclear inflammatory infiltration with an increase in polymorphonuclear cells. Together, these data highlight, for the first time, the use of blue light therapy to control circulating and tissue forms of T. cruzi. Further investigation would demonstrate the application of this promising and potential complementary strategy for the treatment of Chagas disease.

Regulation of uterine function during estrous cycle, anestrus phase and pregnancy by steroids in red deer (Cervus elaphus L.)

Steroid synthesis and production in ruminant uterus is not obvious, especially in seasonally reproduced. We compared steroid production by investigating enzymes involved in red deer uterine steroid metabolism in reproductive seasons. Blood and uteri (endometrium and myometrium) were collected post mortem from hinds on 4th day (N = 8), 13th day of the cycle (N = 8), anestrus (N = 8) and pregnancy (N = 8). The expression of cytochrome P450 aromatase (P450), 3 -beta-hydroxysteroid dehydrogenase (3β-HSD), 17 -beta-hydroxysteroid dehydrogenase (17β-HSD), aldo-keto reductase family 1 C1 (AKR1C1), estrogen receptor alpha (ERα), and progesterone receptors (PRs), were analyzed using real-time-PCR and Western Blotting. Plasma samples were assayed for 17-beta-estradiol (E2), progesterone (P4), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T4) concentrations by EIA. Hinds at the beginning of the estrous cycle, mainly in endometrium, were characterized by a high mRNA expression of 3β-HSD, AKR1C1, PRs and ERα, contrary to the expression in myometrium during pregnancy (P < 0.05). For P4, E2, and FSH, concentration was the highest during the 13th day of the estrous cycle (P < 0.05). Uterine steroid production and output in hinds as a representative seasonally reproduced ruminant occurred mainly during the estrous cycle and sustained in anestrus.

Litopenaeus vannamei BMAL1 Is a Critical Mediator Regulating the Expression of Glucose Transporters and Can Be Suppressed by Constant Darkness

Simple Summary

Growing evidence has indicated that glucose absorption exhibits profound circadian rhythmicity, mediated entirely by glucose transporters. We observed that the daily profile of BMAL1, GLUT1 and SGLT1 expression was also synchronized in the intestine and the hepatopancreas of Litopenaeus vannamei. Our result identified for the first time that BMAL1 is a critical mediator regulating the expression of glucose transporters, which could be suppressed by constant darkness in L. vannamei.

Abstract

Aryl hydrocarbon receptor nuclear translocator-like protein 1 (BMAL1) is a core circadian transcription factor that controls the 24-h cycle of physiological processes. In shrimp, the role of BMAL1 in the regulating glucose metabolism remains unclear. Firstly, we observed that the daily profile of BMAL1, GLUT1 and SGLT1 expression were synchronized in the intestine and the hepatopancreas of Litopenaeus vannamei. Then we examined the effects of BMAL1 on the gene expression of glucose transporter type 1 (SGLT1) and sodium-glucose cotransporter 1 (GLUT1) in vivo and in vitro. BMAL1 in L. vannamei shares 70.91–96.35% of sequence identities with other shrimp species and possesses the conserved helix-loop-helix domain and polyadenylation site domain. The in vitro dual-luciferase reporter assay and in vivo RNA interference experiment demonstrated that BMAL1 exerted a positive regulation effect on the expression of glucose transporters in L. vannamei. Moreover, we conducted an eight-week treatment to investigate whether light/dark cycle change would influence growth performance, and gene expression of BMAL1, GLUT1 and SGLT1 in L. vannamei. Our result showed that compared with natural light treatment, constant darkness (24-h darkness) significantly decreased (p < 0.05) serum glucose concentration, and suppressed (p < 0.05) the gene expression of BMAL1, GLUT1 and SGLT1 in the hepatopancreas and the intestine. Growth performance and survival rate were also decreased (p < 0.05) by constant darkness treatment. Our result identified BMAL1 as a critical mediator regulating the expression of glucose transporters, which could be suppressed by constant darkness in L. vannamei. It would be quite interesting to explore the mechanism of dark/light cycles on glucose transport and metabolism in L. vannamei, which might provide a feeding strategy for improving carbohydrate utilization in the future.

Physiological impacts of temperature variability and climate warming in hellbenders (Cryptobranchus alleganiensis)

Cold-adapted hellbender salamanders that inhabit cool mountain streams are expected to fare poorly under warmer projected climate scenarios. This study investigated the physiological consequences of long-term, naturalistic temperature variation on juvenile hellbenders under simulated current and warmer (+1.6 C) climates vs. controlled steady temperatures. Mean temperature and temperature variability were both important predictors of growth as indicated by monthly body mass change (%), stress as indicated by neutrophil:lymphocyte (N:L) ratio and bacteria-killing ability of blood. Cold exposure in hellbenders was associated with weight loss, increased N:L ratios and reduced Escherichia coli killing ability of blood, and these effects were less pronounced under a warmer climate scenario. These observations suggest that cold periods may be more stressful for hellbenders than previously understood. Growth rates peaked in late spring and late fall around 14-17°C. Hellbenders experiencing warmer simulated climates retained body condition better in winter, but this was counter-balanced by a prolonged lack of growth in the 3-month summer period leading up to the fall breeding season where warmer simulated conditions resulted in an average loss of -0.6% body mass/month, compared to a gain +1.5% body mass/month under current climate scenario. Hellbenders can physiologically tolerate projected warmer temperatures and temperature fluctuations, but warmer summers may cause animals to enter the fall breeding season with a caloric deficit that may have population-level consequences.

Migratory state and patterns of steroid hormone regulation in the pectoralis muscle of a nomadic migrant, the pine siskin (Spinus pinus)

The endocrine system is known to mediate responses to environmental change and transitions between different life stages (e.g., a non-breeding to a breeding life stage). Previous works from the field of environmental endocrinology have primarily focused on changes in circulating hormones, but a comprehensive understanding of endocrine signaling pathways requires studying changes in additional endocrine components (e.g., receptor densities) in a diversity of contexts and life stages. Migratory birds, for instance, can exhibit dramatic changes in their physiology and behavior, and both sex steroids as well as glucocorticoids are proposed mediators of the transition into a migratory state. However, the role of changes in endocrine signaling components within integral target tissues, such as flight muscles, in modulating the transition into a migratory state remains poorly understood. Here, we examined changes in gene expression levels of and correlational patterns (i.e., integration) between 8 endocrine signaling components associated with either glucocorticoids or sex steroid signaling in the pectoralis muscles of a nomadic migratory bird, the pine siskin (Spinus pinus). The pectoralis muscle is essential to migratory flight and undergoes conspicuous changes in preparation for migration, including hypertrophy. We focus on endocrine receptors and enzymes (e.g., 5α-reductase) that modulate the signaling capacity of circulating hormones within target tissues and may influence either catabolic or anabolic functioning within the pectoralis. Endocrine signaling components were compared between captive birds sampled prior to the expression of vernal migratory preparation and during the expression of a vernal migratory state. While birds exhibited differences in the size and color of the flight muscle and behavioral shifts indicative of a migratory state (i.e., zugunruhe), none of the measured endocrine components differed before and after the transition into the migratory state. Patterns of integration amongst all genes did, however, differ between the two life stages, suggesting the contrasting demands of different life stages may shape entire endocrine signaling networks within target tissues rather than individual components. Our work aligns with previous endocrine studies on pine siskins and, viewed together, suggest additional studies are needed to understand the endocrine system's role in mediating the development and progression of the vernal migratory state in this species. Further, the patterns observed in pine siskins, a nomadic migrant, differ from previous studies on obligate migrants and suggest that different mechanisms or interactions between endocrine signaling components may mediate the migratory transition in nomadic migrants.

The paraventricular thalamus serves as a nexus in the regulation of stress and immunity

Many temperate zone animals exhibit seasonal rhythms in physiology and behavior, including seasonal cycles of reproduction, energetics, stress responsiveness, and immune function, among many others. These rhythms are driven by seasonal changes in the duration of pineal melatonin secretion. The neural melatonin target tissues that mediate several of these rhythms have been identified, though the target(s) mediating melatonin's regulation of glucocorticoid secretion, immune cell numbers, and bacterial killing capacity remain unspecified. The present results indicate that one melatonin target tissue, the paraventricular nucleus of the thalamus (PVT), is necessary for the expression of these seasonal rhythms. Thus, while radiofrequency ablations of the PVT failed to alter testicular and body mass response to short photoperiod exposure, they did block the effect of short day lengths on cortisol secretion and bacterial killing efficacy. These results are consistent with the independent regulation by separate neural circuits of several physiological traits that vary seasonally in mammals.

The probiotic Lactobacillus rhamnosus mimics the dark-driven regulation of appetite markers and melatonin receptors' expression in zebrafish (Danio rerio) larvae: Understanding the role of the gut microbiome

The use of probiotics has been recently considered a novel therapeutic strategy to prevent pathologies such as obesity; however, the specific mechanisms of action by which probiotics exert their beneficial effects on metabolic health remain unclear. The aim of the present study was to investigate the short-term effects of a probiotic Lactobacillus rhamnosus supplementation (PROB) on appetite regulation, growth-related markers, and microbiota diversity in zebrafish (Danio rerio) larvae, compared to a group subjected to a constant darkness photoperiod (DARK), as well as to evaluate the effects of both treatments on melatonin receptors' expression. After a 24 h treatment, both PROB and DARK conditions caused a significant increase in leptin a expression. Moreover, mRNA abundances of leptin b and proopiomelanocortin a were elevated in the PROB group, and DARK showed a similar tendency, supporting a negative regulation of appetite markers by the treatments. Moreover, both PROB and DARK also enhanced the abundances of melatonin receptors transcript (melatonin receptor 1 ba and bb) and protein (melatonin receptor 1) suggesting a potential involvement of melatonin in mediating these effects. Nevertheless, treatments did not exhibit a significant effect on the expression of most of the growth hormone/insulin-like growth factor axis genes evaluated. Finally, only the DARK condition significantly modulated gut microbiota diversity at such short time, altogether highlighting the rapid effects of this probiotic on modulating appetite regulatory and melatonin receptors' expression, without a concomitant variation of gut microbiota.

Sickness behaviors across vertebrate taxa: proximate and ultimate mechanisms

There is nothing like a pandemic to get the world thinking about how infectious diseases affect individual behavior. In this respect, sick animals can behave in ways that are dramatically different from healthy animals: altered social interactions and changes to patterns of eating and drinking are all hallmarks of sickness. As a result, behavioral changes associated with inflammatory responses (i.e. sickness behaviors) have important implications for disease spread by affecting contacts with others and with common resources, including water and/or sleeping sites. In this Review, we summarize the behavioral modifications, including changes to thermoregulatory behaviors, known to occur in vertebrates during infection, with an emphasis on non-mammalian taxa, which have historically received less attention. We then outline and discuss our current understanding of the changes in physiology associated with the production of these behaviors and highlight areas where more research is needed, including an exploration of individual and sex differences in the acute phase response and a greater understanding of the ecophysiological implications of sickness behaviors for disease at the population level.

Melatonin-dependent changes in neurosteroids are associated with increased aggression in a seasonally breeding rodent

Aggression is a complex social behaviour that allows individuals to compete for access to limited resources (eg, mates, food and territories). Excessive or inappropriate aggression, however, has become problematic in modern societies, and current treatments are largely ineffective. Although previous work in mammals suggests that aggressive behaviour varies seasonally, seasonality is largely overlooked when developing clinical treatments for inappropriate aggression. Here, we investigated how the hormone melatonin regulates seasonal changes in neurosteroid levels and aggressive behaviour in Siberian hamsters, a rodent model of seasonal aggression. Specifically, we housed males in long-day (LD) or short-day (SD) photoperiods, administered timed s.c. melatonin injections (which mimic a SD-like signal) or control injections, and measured aggression using a resident-intruder paradigm after 9 weeks of treatment. Moreover, we quantified five steroid hormones in circulation and in brain regions associated with aggressive behaviour (lateral septum, anterior hypothalamus, medial amygdala and periaqueductal gray) using liquid chromatography-tandem mass spectrometry. SD hamsters and LD hamsters administered timed melatonin injections (LD-M) displayed increased aggression and exhibited region-specific decreases in neural dehydroepiandrosterone, testosterone and oestradiol, but showed no changes in progesterone or cortisol. Male hamsters also showed distinct associations between neurosteroids and aggressive behaviour, in which neural progesterone and dehydroepiandrosterone were positively correlated with aggression in all treatment groups, whereas neural testosterone, oestradiol and cortisol were negatively correlated with aggression only in LD-M and SD hamsters. Collectively, these results provide insight into a novel neuroendocrine mechanism of mammalian aggression, in which melatonin reduces neurosteroid levels and elevates aggressive behaviour.

Canid Reproductive Biology: Norm and Unique Aspects in Strategies and Mechanisms

The reproductive physiology of canids is unique compared to other mammalian species. Specifically, the reproductive cycle of female canids is characterized by extended periods of proestrus and estrus followed by obligatory diestrus and protracted ovarian inactivity (anestrus). Although canid reproduction follows this general pattern, studies have shown variations in reproductive biology among species and geographic regions. Understanding of these differences is critical to the development of assisted reproductive technologies including estrus induction, gamete rescue, and embryo production techniques for canid conservation efforts. This review summarizes current knowledge of canid reproduction, including estrus cyclicity, seasonality, and seminal traits, with the emphasis on species diversity. The application of reproductive technologies in wild canid conservation will also be discussed.

Environment-induced changes in reproductive strategies and their transgenerational effects in the three-spined stickleback

An organism may increase its fitness by changing its reproductive strategies in response to environmental cues, but the possible consequences of those changes for the next generation have rarely been explored. By using an experiment on the three-spined stickleback (Gasterosteus aculeatus), we studied how changes in the onset of breeding photoperiod (early versus late) affect reproductive strategies of males and females, and life histories of their offspring. We also explored whether telomeres are involved in the within- and transgenerational effects. In response to the late onset of breeding photoperiod, females reduced their investment in the early clutches, but males increased their investment in sexual signals. Costs of increased reproductive investment in terms of telomere loss were evident only in the late females. The environmentally induced changes in reproductive strategies affected offspring growth and survival. Most notably, offspring growth rate was the fastest when both parents experienced a delayed (i.e., late) breeding photoperiod, and survival rate was the highest when both parents experienced an advanced (i.e., early) breeding photoperiod. There was no evidence of transgenerational effects on offspring telomere length despite positive parents-offspring relationships in this trait. Our results highlight that environmental changes may impact more than one generation by altering reproductive strategies of seasonal breeders with consequences for offspring viability.

The role of photoperiod and melatonin in the control of seasonal reproduction in mammals

<b>Melatonin secreted by pineal cells is a hormone whose biosynthesis is coordinated by neurons of the master clock located in the hypothalamic suprachiasmatic nuclei (SCN), characterized by the generation of a 24-hour rhythm. In many species of mammals, fluctuations in melatonin secretion affect reproductive functions, e.g. by regulating the frequency and amount of pulsatile secretion of hypothalamic and gonadotropic hormones. Seasonal breeding is a common adaptive strategy among mammals, allowing them to reproduce during the periods of the year that are most favourable for the later survival and growth of the offspring. This type of reproduction is characteristic of sheep, with winter reproductive activity, and hamsters, with summer reproductive activity. In these animals, melatonin synthesis is largely regulated by the photoperiod, which indirectly influences the period of reproductive activity or passivity. The aim of this study was to gather available knowledge on melatonin as a key element controlling seasonal reproduction. The paper presents the general shape of the circadian rhythm and the neuroendocrine mechanism regulating animal reproduction depending on the variable photoperiod. The collected results suggest that melatonin, kisspeptins, gonadotropin-releasing hormone (GnRH), sex hormones and thyroid hormones participate in the regulation of seasonal reproduction in mammals. </b>

Reproductive events and respective faecal androgen metabolite concentrations in captive male roan antelope (Hippotragus equinus)

Understanding the reproductive biology of the roan antelope (Hippotragus equinus) (É. Geoffroy Saint-Hilaire, 1803) is crucial to optimise breeding success in captive breeding programmes of this threatened species. In this study, the pattern of faecal androgen metabolite (fAM) production related to reproductive events (calving or birthing, mating, gestation, and lactation), sexual behaviours as well as environmental cues were studied in captive adult male roan antelope. Faecal sample collection and behavioural observations were carried out from August 2017 to July 2018 for three reproductive males participating in a conservation breeding programme at the Lapalala Wilderness Nature Reserve in South Africa. As a prerequisite, the enzyme immunoassay used in this study was biologically validated for the species by demonstrating a significant difference between fAM concentrations in non-breeding adults, breeding adults and juvenile males. Results revealed that in adults males, the overall mean fAM levels were 73% higher during the breeding period compared to the non-breeding periods, and 85% higher when exclusively compared to the lactation/gestation periods, but only 5.3% higher when compared to the birthing period. Simultaneously, fAM concentrations were lower during the wet season compared to the dry season, increasing with a reduction in photoperiod. With the exception of courtship, frequencies of sexual behaviours monitored changed in accordance with individual mean fAM concentrations in male roan antelope, the findings suggest that androgen production varies with the occurrence of mating activity and may be influenced by photoperiod but not with rainfall.

Constant light exposure causes oocyte meiotic defects and quality deterioration in mice

Artificial light at night (ALAN) exposes us to prolonged illumination, that adversely affects female reproduction. However, it remains to be clarified how prolonged light exposure affects oocyte meiotic maturation and quality. To this end, we exposed female mice to a constant light (CL) of 250 lux for different durations. Our findings showed that CL exposure for 7 weeks reduced the oocyte maturation rate. Meanwhile, CL exposure caused greater abnormalities in spindle assembly and chromosome alignment and a higher rate of oocyte aneuploidy than the regular light dark cycle. CL exposure also induced oxidative stress and caused mitochondrial dysfunction, which resulted in oocyte apoptosis and autophagy. Notably, our results showed that CL exposure reduced the levels of α-tubulin acetylation, DNA methylation at 5 mC, RNA methylation at m⁶A and histone methylation at H3K4me2 but increased the levels of histone methylation at H3K27me2 in oocytes. In summary, our findings demonstrate that constant bright light exposure causes oocyte meiotic defects and reduces cytoplasmic quality. These results extend the current understanding of ALAN-mediated defects in female reproduction.

A novel role for the pineal gland: Regulating seasonal shifts in the gut microbiota of Siberian hamsters

The gut microbiota plays a significant role in a variety of host behavioral and physiological processes. The mechanisms by which the gut microbiota and the host communicate are not fully resolved but include both humoral and direct neural signals. The composition of the microbiota is affected by internal (host) factors and external (environmental) factors. One such signal is photoperiod, which is represented endogenously by nocturnal pineal melatonin (MEL) secretion. Removal of the MEL signal via pinealectomy abolishes many seasonal responses to photoperiod. In Siberian hamsters (Phodopus sungorus), MEL drives robust seasonal shifts in physiology and behavior, such as immunity, stress, body mass, and aggression. While the profile of the gut microbiota also changes by season, it is unclear whether these changes are driven by pineal signals. We hypothesized that the pineal gland mediates seasonal alterations in the composition of the gut microbiota. To test this, we placed pinealectomized and intact hamsters into long or short photoperiods for 8 weeks, collected weekly fecal samples, and measured weekly food intake, testis volume, and body mass. We determined microbiota composition using 16S rRNA sequencing (Illumina MiSeq). We found significant effects of treatment and time on the abundances of numerous bacterial genera. We also found significant associations between individual OTU abundances and body mass, testis mass, and food intake, respectively. Finally, results indicate a relationship between overall community structure, and body and testis masses. These results firmly establish a role for the pineal gland in mediating seasonal alterations in the gut microbiota. Further, these results identify a novel neuroendocrine pathway by which a host regulates seasonal shifts in gut community composition, and indicates a relationship between seasonal changes in the gut microbiota and seasonal physiological adjustments.