Biology of mammalian photoperiodism and the critical role of the pineal gland and melatonin

Photoperiod, but not progesterone, has a strong impact upon the transcriptome of the medio-basal hypothalamus in female goats and ewes

Photoperiod is the main environmental driver of seasonal responses in organisms living at temperate and polar latitudes. Other external cues such as food and temperature, and internal cues including hormones, intervene to fine-tune phasing of physiological functions to the solar year. In mammals, the medio-basal hypothalamus (MBH) is the key integrator of these cues, which orchestrates a wide array of seasonal functions, including breeding. Here, using RNAseq and RT-qPCR, we demonstrate that molecular components of the photoperiodic response previously identified in ewes are broadly conserved in does (female goats, Capra hircus), with a common core of ∼50 genes. This core group can be defined as the "MBH seasonal trancriptome", which includes key players of the pars tuberalis-tanycytes neuroendocrine retrograde pathway that governs intra-MBH photoperiodic switches of triiodothyronine (T3) production (Tshb, Eya3, Dio2 and SlcO1c1), the two histone methyltransferases Suv39H2 and Ezh2 and the secreted protein Vmo1. Prior data in ewes revealed that T3 and estradiol (E2), both key hormones for the proper timing of seasonal breeding, differentially impact the MBH seasonal transcriptome, and identified cellular and molecular targets through which these hormones might act. In contrast, information regarding the potential impact of progesterone (P4) upon the MBH transcriptome was nonexistent. Here, we demonstrate that P4 has no discernible transcriptional impact in either does or ewes. Taken together, our data show that does and ewes possess a common core set of photoperiod-responsive genes in the MBH and conclusively demonstrate that P4 is not a key regulator of the MBH transcriptome.

The male effect associated with prostaglandins and reproductive outcomes in photo-stimulated Saanen goats during the non-breeding season

The efficiency of combining oestrous induction via a light program (16 h of light and 8 h of darkness for 60 days, ending on Day 0 - D0) with cloprostenol administration, followed by the male effect or not, was tested in acyclic Saanen goats during the non-breeding season (June/2019 to January/2020). Initially, all animals (males and females) were submitted to the described light program; 60 days after its ending (D60), the females were divided into two groups, with (G1; n = 67) or without (G2; n = 61) a male effect from D60 to D75 after the light program. At D75, both groups received two cloprostenol doses (120 μg; intramuscular) 7.5 days apart (D75 and D82.5). Artificial insemination was performed at a specific time according to the oestrous onset (approximately 68.4 ± 1.2 h between the second cloprostenol dose and IA). Ultrasound scans were performed at different intervals to evaluate follicular dynamics and confirm pregnancy. At the first cloprostenol dose (D75), the proportion of does with at least a corpus luteum (CL), which indicates resumed cyclicity, was greater in G1 than in G2 (85.2% vs. 48.8%; p < .05), although no difference was found at the second dose (p > .05). The adjusted pregnancy rates (number of pregnant goats/oestrous goats) differed between G1 and G2 (21.7% vs. 42.0%; p < .05). G1 also showed a higher frequency of functional CL (based on blood flow and morphology) compared to G2 (96.9% vs. 66.7%; p < .05) at D116. A male effect using photo-stimulated bucks after the first cloprostenol dose increased the number of does presenting CL after buck removal, and no impairment in the pregnancy rates of multiparous does was found.

Association analysis of polymorphisms in SLK, ARHGEF9, WWC2, GAB3, and FSHR genes with reproductive traits in different sheep breeds

The aim was to investigate the relationship between polymorphisms of gene mutation loci and reproductive traits in local sheep breeds (Duolang Sheep) and introduced sheep breeds (Suffolk, Hu Sheep) in Xinjiang to provide new molecular markers for the selection and breeding of high fecundity sheep. The expression pattern of typing successful genes in sheep tissues was investigated by RT-qPCR technology, providing primary data for subsequent verification of gene function. The 26 mutation loci of WWC2, ARHGEF9, SLK, GAB3, and FSHR genes were typed using KASP. Association analyses were performed using SPSS 25.0, and the typing results showed that five genes with six loci, WWC2 (g.14962207 C>T), ARHGEF9 (g.48271079 C>A), SLK (g.27107842 T>C, g.27108855 G>A), GAB3 (g.86134602 G>A), and FSHR (g.80789180 T>G) were successfully typed. The results of the association analyses showed that WWC2 (g.14962207 C>T), SLK (g.27108855 G>A), ARHGEF9 (g.48271079 C>A), and FSHR (g.80789180 T>G) caused significant or extremely significant effects on the litter size in Duolang, Suffolk and Hu Sheep populations. The expression distribution pattern of the five genes in 12 sheep reproduction-related tissues was examined by RT-qPCR. The results showed that the expression of the SLK gene in the uterus, the FSHR gene in the ovary, and the ARHGEF9 gene in hypothalamic-pituitary-gonadal axis-related tissues were significantly higher than in the tissues of other parts of the sheep. WWC2 and GAB3 genes were highly expressed both in reproductive organs and visceral tissues. In summary, the WWC2 (g.14962207 C>T), SLK (g.27108855 G>A), ARHGEF9 (g.48271079 C>A), and FSHR (g.80789180 T>G) loci can be used as potential molecular markers for detecting differences in reproductive performance in sheep. Due to variations in typing results, the SLK (g.27107842 T>C) and GAB3 (g.86134602 G>A) loci need further validation.

Thirty-seven years of MT1 and MT2 melatonin receptor localization in the brain: Past and future challenges

Identifying the target cells of a hormone is a key step in understanding its function. Once the molecular nature of the receptors for a hormone has been established, researchers can use several techniques to detect these receptors. Here I will review the different tools used over the years to localize melatonin receptors and the problems associated with each of these techniques. The radioligand 2-[125I] iodomelatonin was the first tool to allow localization of melatonin receptors on tissue sections. Once the MT1 and MT2 receptors were cloned, in situ hybridization could be used to detect the messenger RNA for these receptors. The deduced amino acid sequences for MT1 and MT2 receptors allowed the production of peptide immunogens to generate antibodies against the MT1 and MT2 receptors. Finally, transgenic reporters driven by the promoter elements of the MT1 and MT2 genes have been used to map the expression of MT1 and MT2 in the brain and the retina. Several issues have complicated the localization of melatonin receptors and the characterization of melatonin target cells over the last three decades. Melatonin receptors are expressed at low levels, leading to sensitivity issues for their detection. The second problem are specificity issues with antibodies directed against the MT1 and MT2 melatonin receptors. These receptors are G protein-coupled receptors and many antibodies directed against such receptors have been shown to present similar problems concerning their specificity. Despite these specificity problems which start to be seriously addressed by recent studies, antibodies will be important tools in the future to identify and phenotype melatonin target cells. However, we will have to be more stringent than previously when establishing their specificity. The results obtained by these antibodies will have to be confronted and be coherent with results obtained by other techniques.

Melatonin inhibits the formation of chemically induced experimental encapsulating peritoneal sclerosis through modulation of T cell differentiation by suppressing of NF-κB activation in dendritic cells

Encapsulating peritoneal sclerosis (EPS) is a severe complication of peritoneal dialysis (PD). Surgery is a therapeutic strategy for the treatment of complete intestinal obstruction. However, complete intestinal obstruction in long-term PD results in high mortality and morbidity rates after surgery. Immunopathogenesis participates in EPS formation: CD8, Th1, and Th17 cell numbers increased during the formation of EPS. The anti-inflammatory and immunomodulatory effects of melatonin may have beneficial effects on this EPS. In the present study, we determined that melatonin treatment significantly decreases the Th1 and Th17 cell populations in mice with EPS, decreases the production of IL-1β, TNF-α, IL-6, and IFN-γ, and increases the production of IL-10. The suppression of Th1 and Th17 cell differentiation by melatonin occurs through the inhibition of dendritic cell (DC) activation by affecting the initiation of the NF-κB signaling pathway in DCs. Our study suggests that melatonin has preventive potential against the formation of EPS in patients with PD.

Multiparametric MR Evaluation of the Photoperiodic Regulation of Hypothalamic Structures in Sheep

Most organisms on earth, humans included, have developed strategies to cope with environmental day-night and seasonal cycles to survive. For most of them, their physiological and behavioral functions, including the reproductive function, are synchronized with the annual changes of day length, to ensure winter survival and subsequent reproductive success in the following spring. Sheep are sensitive to photoperiod, which also regulates natural adult neurogenesis in their hypothalamus. We postulate that the ovine model represents a good alternative to study the functional and metabolic changes occurring in response to photoperiodic changes in hypothalamic structures of the brain. Here, the impact of the photoperiod on the neurovascular coupling and the metabolism of the hypothalamic structures was investigated at 3T using BOLD fMRI, perfusion-MRI and proton magnetic resonance spectroscopy (1H-MRS). A longitudinal study involving 8 ewes was conducted during long days (LD) and short days (SD) revealing significant BOLD, rCBV and metabolic changes in hypothalamic structures of the ewe brain between LD and SD. More specifically, the transition between LD and SD revealed negative BOLD responses to hypercapnia at the beginning of SD period followed by significant increases in BOLD, rCBV, Glx and tNAA concentrations towards the end of the SD period. These observations suggest longitudinal mechanisms promoting the proliferation and differentiation of neural stem cells within the hypothalamic niche of breeding ewes. We conclude that multiparametric MRI studies including 1H-MRS could be promising non-invasive translational techniques to investigate the existence of natural adult neurogenesis in-vivo in gyrencephalic brains.

Methylene blue molecularly imprinted polymer for melatonin determination in urine and saliva samples

A highly sensitive and rapid electrochemical sensor was developed for detecting melatonin using a molecularly imprinted polymer (MIP) with methylene blue as the functional monomer and melatonin as the template. The MIP was synthesized via a simple electropolymerization process that did not require an initiating reagent. The sensor demonstrated good selectivity for melatonin against common interferences such as lactate, cytosine, cytidine, urea, ascorbic acid, creatine, creatinine, serotonin, and tryptophan. Melatonin detection was achieved at a potential of 0.60 V vs. Ag/AgCl with a sensitivity of 138.8 ± 4.7 µA µM‒1 in the linear range 0.097 - 200 µM and a limit of detection of 29 nM (3SB/m). The sensor exhibited excellent reproducibility and repeatability for both within (intra) and between (inter) electrodes (%RSD < 3% for n = 3). The sensor was applied to authentic urine and saliva samples with recoveries of 103 ± 1% and 102 ± 1%, respectively.

Melatonin Improves Turbot Oocyte Meiotic Maturation and Antioxidant Capacity, Inhibits Apoptosis-Related Genes mRNAs In Vitro

High-quality eggs are essential for the sustainability of commercial aquaculture production. Melatonin is a potent candidate for regulating the growth and maturation of oocytes. Therefore, research on the effect of melatonin on marine fish oocytes in vitro has been conducted. The present study successfully established a culture system of turbot (Scophthalmus maximus) oocytes in vitro and investigated the effect of melatonin on oocyte meiotic maturation, antioxidant capacity, and the expression of apoptosis-related genes. The cultures showed that turbot Scophthalmus maximus late-vitellogenic denuded oocytes, with diameters of 0.5-0.7 mm, had a low spontaneous maturation rate and exhibited a sensitive response to 17α, 20β-dihydroxyprogesterone (DHP) treatment in vitro. Melatonin increased by four times the rate of oocyte germinal vesicle breakdown (GVBD) in a concentration- and time-dependent manner. The mRNA of melatonin receptor 1 (mtnr1) was significantly upregulated in the oocyte and follicle after treatment with melatonin (4.3 × 10^-9 M) for 24 h in vitro, whereas melatonin receptor 2 (mtnr2) and melatonin receptor 3 (mtnr3) remained unchanged. In addition, melatonin significantly increased the activities of catalase, glutathione peroxidase, and superoxide dismutase, as well as the levels of glutathione, while decreasing the levels of malondialdehyde and reactive oxygen species (ROS) levels in turbot oocytes and follicles cultures in vitro. p53, caspase3, and bax mRNAs were significantly downregulated in oocytes and follicles, whereas bcl2 mRNAs were significantly upregulated. In conclusion, the use of turbot late-vitellogenesis oocytes (0.5-0.7 mm) is suitable for establishing a culture system in vitro. Melatonin promotes oocyte meiotic maturation and antioxidative capacity and inhibits apoptosis via the p53-bax-bcl2 and caspase-dependent pathways, which have important potential to improve the maturation and quality of oocytes.

Circulating follicle stimulating hormone levels influence body growth in pre-menarcheal girls in a latitude-dependent manner

Introduction

Age at menarche is an essential determinant of reproductive life of a woman. Latitude is an important driver of age at menarche, however the contributions of circulating follicle stimulating hormone (FSH) and socio-economic status (SES) to age at menarche in a latitude-dependent manner is not known.

Methods

This population-based cross-sectional study is a component of our major cohort of 10,050 schoolgirls aged 8-16 years from 35 schools across 10 districts. The selected districts were categorised into high and low latitudes by applying a cut-off point at latitude 31.5⁰N. We evaluated the physical parameters, SES, circulating FSH, and growth hormone (GH) levels in pre-menarche girls (N = 252) at different latitudes.

Results

Self-reported age at menarche of girls residing at different latitudes in Pakistan showed that higher latitude is associated with delayed age at menarche. Higher latitude was associated with reduced circulating FSH levels, as well as lower parameters of physical growth including body mass index (BMI), waist-hip ratio and, waist-height ratio (all p < 0.05) in the pre-menarcheal girls. However, circulating GH levels were not affected by latitude. On the other hand, lower SES was associated with reduced GH levels and lower BMI, which are considered as probably the primary determinants of physical growth.

Conclusions

Taken together, we show that higher latitude may delay the sexual maturation, while poor SES may delay the physical growth in girls.

Proper use of light environments for mitigating the effects of COVID-19 and other prospective public health emergency lockdowns on sleep quality and fatigue in adolescents

Coronavirus disease 2019 (COVID-19) remains a public health emergency of international concern, and some countries still implement strict regional lockdowns. Further, the upcoming 2023 Asian Games and World University Games will implement a closed-loop management system. Quarantine can harm mental and physical health, to which adolescents are more vulnerable compared with adults. Previous studies indicated that light can affect our psychology and physiology, and adolescents were exposed to the artificial light environment in the evening during the lockdown. Thus, this study aimed to establish and assess appropriate residential light environments to mitigate the effects of lockdowns on sleep quality and fatigue in adolescents. The participants were 66 adolescents (12.15 ± 2.45 years of age) in a closed-loop management environment, who participated in a 28-day (7-day baseline, 21-day light intervention) randomized controlled trial of a light-emitting diode (LED) light intervention. The adolescents were exposed to different correlated color temperature (CCT) LED light environments (2000 K or 8000 K) for 1 h each evening. The results for self-reported daily sleep quality indicated that the low CCT LED light environment significantly improved sleep quality (p < 0.05), and the blood test results for serum urea and hemoglobin indicated that this environment also significantly reduced fatigue (p < 0.05) and moderately increased performance, compared to the high CCT LED light environment. These findings can serve as a springboard for further research that aims to develop interventions to reduce the effects of public health emergency lockdowns on mental and physical health in adolescents, and provide a reference for participants in the upcoming Asian Games and World University Games.

Seasonal Variation of Melatonin Concentration and mRNA Expression of Melatonin-Related Genes in Developing Ovarian Follicles of Mares Kept under Natural Photoperiods in the Southern Hemisphere

This study investigated the seasonal variations in mRNA expression of FSH (Fshr), LH (Lhr) receptors, melatonin (Mt1 and Mt2) receptors, melatonin-synthetizing enzymes (Asmt and Aanat) and melatonin concentration in developing follicles from mares raised in natural photoperiods. For one year, ultrasonographic follicular aspiration procedures were performed monthly, and small (<20 mm), medium (20 to 35 mm) and large (>35 mm) follicles were recovered from five mares. One day before monthly sample collections, an exploratory ultrasonography conducted to record the number and the size of all follicles larger than 15 mm. The total number of large follicles were higher during the spring/summer (8.2 ± 1.9) than during autumn/winter (3.0 ± 0.5). Compared to autumn/winter seasons, there was an increase of Fshr and Aanat mRNA expressions in small, medium and large follicles, an increase of Lhr and Asmt mRNA expressions in medium and large follicles and an increase of Mt1 and Mt2 mRNA expressions in small and large follicles during spring/summer. The melatonin levels in follicular fluid were also higher during the spring/summer seasons. The present data show that melatonin locally upregulates the mRNA expression of Mt1 and Mt2 receptors and melatonin-forming enzymes in mare developing follicles during reproductive seasons.

Melatonin as a Potential Approach to Anxiety Treatment

Anxiety disorders are the most common mental diseases. Anxiety and the associated physical symptoms may disturb social and occupational life and increase the risk of somatic diseases. The pathophysiology of anxiety development is complex and involves alterations in stress hormone production, neurosignaling pathways or free radical production. The various manifestations of anxiety, its complex pathophysiological background and the side effects of available treatments underlie the quest for constantly seeking therapies for these conditions. Melatonin, an indolamine produced in the pineal gland and released into the blood on a nightly basis, has been demonstrated to exert anxiolytic action in animal experiments and different clinical conditions. This hormone influences a number of physiological actions either via specific melatonin receptors or by receptor-independent pleiotropic effects. The underlying pathomechanism of melatonin's benefit in anxiety may reside in its sympatholytic action, interaction with the renin-angiotensin and glucocorticoid systems, modulation of interneuronal signaling and its extraordinary antioxidant and radical scavenging nature. Of importance, the concentration of this indolamine is significantly higher in cerebrospinal fluid than in the blood. Thus, ensuring sufficient melatonin production by reducing light pollution, which suppresses melatonin levels, may represent an endogenous neuroprotective and anxiolytic treatment. Since melatonin is freely available, economically undemanding and has limited side effects, it may be considered an additional or alternative treatment for various conditions associated with anxiety.

Imaging and spectroscopic methods to investigate adult neurogenesis in vivo: New models and new avenues

Adult neurogenesis (AN) can be defined as the birth and development of new neurons in adulthood. Until the 1990s, AN was deemed not to happen after birth. Gradually, several groups demonstrated that specific zones of the brain of various species had a neurogenic potential. AN could be the key to treating a large range of neurodegenerative, neuropsychiatric, and metabolic diseases, with a better understanding of the mechanisms allowing for regeneration of new neurons. Despite this promising prospect, the existence of AN has not been validated in vivo in humans and therefore remains controversial. Moreover, the weight of AN-induced plasticity against other mechanisms of brain plasticity is not known, adding to the controversy. In this review, we would like to show that recent technical advances in brain MR imaging methods combined with improved models can resolve the debate.

Melatonin alleviates the immune response and improves salivary gland function in primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is an autoimmune disease that primarily affects exocrine glands and is characterized by sicca syndrome and systemic manifestation. Mounting evidence indicates that circadian clocks are involved in the onset and progression of autoimmune diseases, including rheumatic arthritis, multiple sclerosis, and systemic lupus erythematosus. However, few studies have reported the expression of clock genes in pSS. There is no ideal therapeuticmethod for pSS, the management of pSS is mainly palliative, aims to alleviate sicca symptoms. Melatonin is a neuroendocrine hormone mainly secreted by the pineal gland that plays an important role in the maintenance of the circadian rhythm and immunomodulation. Hence, this study aimed to analyse the circadian expression profile of clock genes in pSS, and further evaluate the therapeutic potential of melatonin in pSS. We discovered a distinct clock gene expression profile in an animal model and in patients with pSS. More importantly, melatonin administration regulated clock gene expression, improved the hypofunction of the salivary glands, and inhibited inflammatory development in animal model of pSS. Our study suggested that the pathogenesis of pSS might correlate with abnormal expression of circadian genes, and that melatonin might be a potential candidate for prevention and treatment of pSS.

GnRH and the photoperiodic control of seasonal reproduction: Delegating the task to kisspeptin and RFRP-3

Synchronization of mammalian breeding activity to the annual change of photoperiod and environmental conditions is of the utmost importance for individual survival and species perpetuation. Subsequent to the early 1960s, when the central role of melatonin in this adaptive process was demonstrated, our comprehension of the mechanisms through which light regulates gonadal activity has increased considerably. The current model for the photoperiodic neuroendocrine system points to pivotal roles for the melatonin-sensitive pars tuberalis (PT) and its seasonally-regulated production of thyroid-stimulating hormone (TSH), as well as for TSH-sensitive hypothalamic tanycytes, radial glia-like cells located in the basal part of the third ventricle. Tanycytes respond to TSH through increased expression of thyroid hormone (TH) deiodinase 2 (Dio2), which leads to heightened production of intrahypothalamic triiodothyronine (T3) during longer days of spring and summer. There is strong evidence that this local, long-day driven, increase in T3 links melatonin input at the PT to gonadotropin-releasing hormone (GnRH) output, to align breeding with the seasons. The mechanism(s) through which T3 impinges upon GnRH remain(s) unclear. However, two distinct neuronal populations of the medio-basal hypothalamus, which express the (Arg)(Phe)-amide peptides kisspeptin and RFamide-related peptide-3, appear to be well-positioned to relay this seasonal T3 message towards GnRH neurons. Here, we summarize our current understanding of the cellular, molecular and neuroendocrine players, which keep track of photoperiod and ultimately govern GnRH output and seasonal breeding.

Testicular Ultrasound Analysis as a Predictive Tool of Ram Sperm Quality

Simple Summary

In animal production, the prediction of male fertility is vital for the success of specific techniques such as artificial insemination. Thus, testicular ultrasound, a non-invasive diagnostic procedure, could be a useful tool. Moreover, recent ultrasound-video analysis and software developments allow the visualization of tissue at the microscopic level. The objective of this work was to establish a possible correlation between testicular ultrasonography and semen quality in rams. For this purpose, the testicles of nine rams were evaluated and the semen was analyzed for one year. The results revealed that the number of white and grey pixels correlated with sperm parameters indicating poor seminal quality. On the other hand, the increase in the seminiferous-tubule density or the lumen area of these tubules was related to a rise in seminal quality. Therefore, ultrasound-video analysis could be a good tool for evaluating the fertility of rams, either for artificial insemination or on the farm.

Abstract

Testicular ultrasound is a non-invasive technique that could be very useful for predicting ram seminal quality. Recent software developments allow macroscopic and microscopic evaluation of testicular parenchyma. Thus, the aim of this study was to evaluate the testicular echotexture using ultrasound-video analysis and investigate its possible correlation with semen quality. Nine rams were evaluated for one year using a portable ultrasound scanner and the echotexture was analyzed with ECOTEXT^® software. The number of black (Ec1), white (Ec2), and grey pixels (Ec3), tubular density (TD), lumen area (LA), and lumen diameter (LD) were analyzed. Semen was collected by an artificial vagina the same day and the sperm concentration, morphology, motility, viability, phosphatidylserine (PS) translocation, reactive-oxygen-species (ROS) levels, DNA damage and capacitation state were evaluated. Ec2 and Ec3 correlated positively with “bad quality” sperm parameters (the percentage of spermatozoa with high ROS levels, with PS translocation and proximal cytoplasmic droplets), and negatively with motility. In contrast, TD and LA showed a positive correlation with “good quality” parameters (motility or normal morphology) and a negative correlation with spermatozoa with high ROS levels, with DNA fragmentation, and proximal or distal cytoplasmic droplets. Thus, echotexture analysis by ultrasound-video analysis could be a valuable tool for assessing ram fertility.

The Effect of Photoperiodic Conditions on GnRH/LH Secretion in Ewes

Simple Summary

During the course of evolution, animals have evolved biological rhythms that are associated with changes in the lighting and temperature of their environment. Females in most breeds of sheep are seasonal breeders, with ovulatory cycles occurring in the autumn and winter and anovulation in the spring and summer. Secretion of gonadotropin releasing hormone and luteinizing hormone, the main hormones regulating reproduction in females, displays a circadian pattern; however, data concerning the day/night differences in their secretion in ewes are incomplete. The aim of the undertaken study was to determine the day/night differences in the secretion of gonadotropin releasing hormone and luteinizing hormone in follicular phase and anestrous ewes. It was demonstrated that secretion of investigated hormones is subject to diurnal and seasonal changes. The observed reduction in luteinizing hormone release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase. It could be concluded that the nocturnal suppression of luteinizing hormone secretion in follicular phase ewes may be a mechanism moving this hormone surge to the early morning.

Abstract

Secretion of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH) displays a circadian pattern. Data concerning differences in daily GnRH/LH secretion during different seasons in sheep are fragmentary. The aim of the study was to determine day/night differences in GnRH/LH secretion in the follicular phase and in the anestrous ewes. The studies were performed on Blackhead ewes (n = 24). Ewes from each season were divided into two groups of six animals (day and night group). The animals were euthanized 5 h after sunset or 5 h after sunrise and blood was taken to determine LH and melatonin concentrations. In the hypothalamus, the expression of GnRH and gonadotropin releasing hormone receptor (GnRHR) was determined. In the anterior pituitary, the expression of mRNA encoding subunit β of LH (LHβ) and GnRHR was assayed. Our study showed that GnRH/LH secretion is subject to diurnal and seasonal changes. The observed reduction in LH release, a few hours after the sunset, seems to be universal for both the anestrus and follicular phase, when the processes occurring at the hypothalamus are more equivocal. It could be concluded that the nocturnal suppression of LH secretion in follicular phase ewes may be a mechanism moving the LH surge to the early morning.

Melatonin Promotes Antler Growth by Accelerating MT1-Mediated Mesenchymal Cell Differentiation and Inhibiting VEGF-Induced Degeneration of Chondrocytes

The sika deer is one type of seasonal breeding animal, and the growth of its antler is affected by light signals. Melatonin (MLT) is a neuroendocrine hormone synthesized by the pineal gland and plays an important role in controlling the circadian rhythm. Although the MLT/MT1 (melatonin 1A receptor) signal has been identified during antler development, its physiological function remains almost unknown. The role of MLT on antler growth in vivo and in vitro is discussed in this paper. In vivo, MLT implantation was found to significantly increase the weight of antlers. The relative growth rate of antlers showed a remarkable increased trend as well. In vitro, the experiment showed MLT accelerated antler mesenchymal cell differentiation. Further, results revealed that MLT regulated the expression of Collage type II (Col2a) through the MT1 binding mediated transcription of Yes-associated protein 1 (YAP1) in antler mesenchymal cells. In addition, treatment with vascular endothelial growth factor (VEGF) promoted chondrocytes degeneration by downregulating the expression of Col2a and Sox9 (SRY-Box Transcription Factor 9). MLT effectively inhibited VEGF-induced degeneration of antler chondrocytes by inhibiting the Signal transducers and activators of transcription 5/Interleukin-6 (STAT5/IL-6) pathway and activating the AKT/CREB (Cyclin AMP response-element binding protein) pathway dependent on Sox9 expression. Together, our results indicate that MLT plays a vital role in the development of antler cartilage.

The Crosstalk between Melatonin and Sex Steroid Hormones

Melatonin, an indolamine mainly released from the pineal gland, is associated with many biological functions, namely, the modulation of circadian and seasonal rhythms, sleep inducer, regulator of energy metabolism, antioxidant, and anticarcinogenic. Although several pieces of evidence also recognize the influence of melatonin in the reproductive physiology, the crosstalk between melatonin and sex hormones is not clear. Here, we review the effects of sex differences in the circulating levels of melatonin and update the current knowledge on the link between sex hormones and melatonin. Furthermore, we explore the effects of melatonin on gonadal steroidogenesis and hormonal control in females. The literature review shows that despite the strong evidence that sex differences impact on the circadian profiles of melatonin, reports are still considerably ambiguous, and these differences may arise from several factors, like the use of contraceptive pills, hormonal status, and sleep deprivation. Furthermore, there has been an inconclusive debate about the characteristics of the reciprocal relationship between melatonin and reproductive hormones. In this regard, there is evidence for the role of melatonin in gonadal steroidogenesis brought about by research that shows that melatonin affects multiple transduction pathways that modulate Sertoli cell physiology and consequently spermatogenesis, and also estrogen and progesterone production. From the outcome of our research, it is possible to conclude that understanding the correlation between melatonin and reproductive hormones is crucial for the correction of several complications occurring during pregnancy, like preeclampsia, and for the control of climacteric symptoms.

Expression of arylalkylamine n-acetyltransferase (AANAT) and acetylserotonin o-methyltransferase (ASMT) in the corpus luteum of pregnant sows and synthesis of melatonin in luteal cells

In vertebrates, melatonin is mainly synthesized from serotonin in the pineal gland. Many reports have documented that melatonin is also synthesized in the extra-pineal tissues, but the synthesis of melatonin in the corpus luteum (CL) of pregnant sows has never been studied. The objectives of this study were to evaluate the expression of melatonin-synthesizing enzymes, arylalkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT), in the CL of sows during pregnancy and to investigate the synthesis of melatonin in luteal cells. Results showed that AANAT and ASMT were both expressed in the CL of sows during pregnancy, higher levels were observed in the early- and mid-stage CL, and the lowest abundance was found in the regressing CL (later-stage). The immunostaining for AANAT and ASMT was predominantly localized in the large luteal cells of porcine CL during pregnancy. Furthermore, melatonin was synthesized in luteal cells from serotonin in a dose- and time-dependent manner. And the expressions of AANAT and ASMT were upregulated by serotonin in luteal cells. In addition, progesterone (P4) secretion and cell viability were promoted in luteal cells treated with serotonin, and the stimulatory effects were blocked by luzindole (a non-selective MT1 and MT2 antagonist). Finally, the expressions of MT1 and MT2 were augmented by serotonin in luteal cells. In conclusion, this study demonstrates for the first time the developmental expression of AANAT and ASMT in the CL and a local synthesis of melatonin in luteal cells of pregnant sows, and suggests a paracrine and/or autocrine role for melatonin in luteal function.

Effect of Exogenous Melatonin on the Development of Mice Ovarian Follicles and Follicular Angiogenesis

In mammalian, the periodic growth and development of ovarian follicles constitutes the physiological basis of female estrus and ovulation. Concomitantly, follicular angiogenesis exerts a pivotal role in the growth of ovarian follicles. Melatonin (N-acetyl-5-methoxytryptamine, Mel), exists in follicle fluid, was suggested to affect the development of follicles and angiogenesis. This research was conducted to investigate the effects and mechanisms of Mel on the development of ovarian follicles and its angiogenesis. In total, 40 ICR mice at age of 3 weeks were allocated into four groups at liberty: control, Mel, FSH and FSH + Mel for a 12-day trial. Ovaries were collected at 8:00 a.m. on Day 13 for detecting the development of ovarian follicles and angiogenesis. Results indicated that Mel promoted the development of ovarian follicles of 50–250 μm (secondary follicles) and periphery angiogenesis, while FSH remarkably increased the number of antral follicles and periphery angiogenesis. Mechanically, Mel and FSH may regulate the expression of VEGF and antioxidant enzymes in different follicular stages. In conclusion, Mel primarily acted on the secondary follicles, while FSH mainly promoted the development of antral follicles. They both conduced to related periphery angiogenesis by increasing the expression of VEGF. These findings may provide new targets for the regulating of follicular development.

RFamide peptides, the novel regulators of mammalian HPG axis: A review

The RFamide-related peptides (RFRPs) are the group of neuropeptides synthesized predominantly from the hypothalamus that negatively affects the hypothalamo-hypophyseal-gonadal (hypothalamic–pituitary–gonadal [HPG]) axis. These peptides are first identified in quail brains and emerged as the mammalian orthologs of avian gonadotropin inhibitory hormones. The RFRP-3 neurons in the hypothalamus are present in several mammalian species. The action of RFRP-3 is mediated through a G-protein-coupled receptor called OT7T022. The predominant role of RFRP-3 is the inhibition of HPG axis with several other effects such as the regulation of metabolic activity, stress regulation, controlling of non-sexual motivated behavior, and sexual photoperiodicity in concert with other neuropeptides such as kisspeptin, neuropeptide-Y (NPY), pro-opiomelanocortin, orexin, and melanin. RFamide peptides synthesized in the granulosa cells, interstitial cells, and seminiferous tubule regulate steroidogenesis and gametogenesis in the gonads. The present review is intended to provide the recent findings that explore the role of RFRP-3 in regulating HPG axis and its potential applications in the synchronization of reproduction and its therapeutic interventions to prevent stress-induced amenorrhea.

Prolonging photoperiod promotes testosterone synthesis of Leydig cells by directly targeting local melatonin system in rooster testes

The study investigated the effects of prolonging photoperiod on the synthesis of testosterone and melatonin in roosters, and the effect of melatonin on testosterone synthesis in rooster Leydig cells as well as its molecular mechanisms. We randomly divided one hundred and twenty 20-week-old roosters into three groups and provided 6, 12.5 and 16 h light, respectively. The results showed that prolonging photoperiod promoted testosterone synthesis, decreased melatonin production, and inhibited the expression of melatonin membrane receptors MEL1A, MEL1B, MEL1C, and aralkylamine n-acetyltransferase (AANAT) in rooster testes. Subsequently, rooster Leydig cells were isolated and treated with 0, 0.1, 1, 10, and 100 ng/mL melatonin for 36 h. The results suggested that melatonin inhibited testosterone synthesis in rooster Leydig cells, and silencing MEL1A and MEL1B relieved the inhibition of melatonin on testosterone synthesis. Additionally, melatonin reduced the intracellular cyclic adenosine monophosphate (cAMP) level and the phosphorylation level of cAMP-response element binding protein (CREB), and CREB overexpression alleviated the inhibition of melatonin on testosterone synthesis. Furthermore, pretreatment with cAMP activator forskolin or protein kinase A (PKA) activator 8-bromo-cAMP blocked the inhibition of melatonin on CREB phosphorylation and testosterone synthesis. These results indicated that prolonging photoperiod promoted testosterone synthesis associated with the decrease in melatonin production and membrane receptors and biosynthetic enzyme of melatonin in rooster testes, and melatonin inhibited testosterone synthesis of rooster Leydig cells by inhibiting the cAMP/PKA/CREB pathway via MEL1A and MEL1B. This may be evidence that prolonging photoperiod could promote testosterone synthesis through the inhibition of the local melatonin pathway in rooster testes.

Role of kisspeptin on cell proliferation and steroidogenesis in luteal cells in vitro and in vivo

BACKGROUND

Kisspeptin (KISS1) and kisspeptin receptor (KISS1R) are essential gatekeepers of the reproductive system. The functions of KISS1 and KISS1R in corpus luteal cells remain ambiguous. The objective was to observe normal physiologic functions of corpus luteal cells in vivo and clarify the functions of KISS1 in vitro.

METHODS

We conducted an in vivo observation of cellular patterns as well as the levels of steroidogenic enzymes and KISS1/KISS1R in corpus luteal cells obtained from female crossbred Taiwan native goats in the estrous cycle; the observation was performed using hematoxylin and eosin and immunohistochemistry staining. Subsequently, we used kisspeptin-10 (Kp-10) to stimulate temperature sensitive-caprine luteal cell line (ts-CLC-D) cells to investigate the progesterone (P4) levels, steroidogenic messenger RNA (mRNA)/protein levels, cell survival rate, intracellular Ca2+ concentration, and cell proliferation-related mRNA/protein levels in the mitogen-activated protein kinase pathway in vitro by applying immunofluorescence staining, Western blotting, 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide assay, and real-time polymerase chain reaction.

RESULTS

We observed the presence of proteins and mRNAs for STAR, CYP11A1, HSD3B, KISS1, and KISS1R in the corpus luteal cells from goats in vivo. In vitro, the addition of Kp-10 reduced the P4 levels (p < 0.01) and increased cell proliferation (p < 0.05) of the ts-CLC-D cells. Furthermore, we found that the levels of proteins and mRNA for STAR, CYP11A1, and HSD3B decreased significantly when Kp-10 was added (p < 0.05). However, adding Kp-10 did not affect the mRNA levels for PLCG2, DAG1, PRKCA, KRAS, RAF1, MAP2K1, MAP2K2, MAPK3, MAPK1, and MAPK14.

CONCLUSION

We determined that KISS1 could affect the P4 levels, steroidogenesis, and cell proliferation in luteal cells. However, further research is required to clarify how KISS1 regulates proliferation and steroid production in luteal cells.

Thyroid hormone and hypothalamic stem cells in seasonal functions

Seasonal rhythms are a pervasive feature of most living organisms, which underlie yearly timeliness in breeding, migration, hibernation or weight gain and loss. To achieve this, organisms have developed inner timing devices (circannual clocks) that endow them with the ability to predict then anticipate changes to come, usually using daylength as the proximate cue. In Vertebrates, daylength interpretation involves photoperiodic control of TSH production by the pars tuberalis (PT) of the pituitary, which governs a seasonal switch in thyroid hormone (TH) availability in the neighboring hypothalamus. Tanycytes, specialized glial cells lining the third ventricle (3V), are responsible for this TH output through the opposite, PT-TSH-driven, seasonal control of deiodinases 2/3 (Dio 2/3). Tanycytes comprise a photoperiod-sensitive stem cell niche and TH is known to play major roles in cell proliferation and differentiation, which suggests that seasonal control of tanycyte proliferation may be involved in the photoperiodic synchronization of seasonal rhythms. Here we review our current knowledge of the molecular and neuroendocrine pathway linking photoperiodic information to seasonal changes in physiological functions and discuss the potential implication of tanycytes, TH and cell proliferation in seasonal timing.

Daily and seasonal rhythmic secretary pattern of endocrinological profiles in mithun bull

Mithun (Bos frontalis) is a unique domestic free-range bovine species available in North Eastern hilly (NEH) regions of India and is reared for its protein rich meat. Mithun suffers severe non-cyclical population fluctuations; however, it is not yet declared as endangered species. Mithun follows some sort of seasonality based on the calving trend and semen production, although it is a perennial breeder. However, there is need to study the rhythmic changes of endocrine profiles to understand the hormone flow pattern in mithun to select the suitable time for blood collection to assess the exact endocrine profiles and to select the suitable time for natural breeding or semen collection by artificial methods for further research, conservation and propagation of its germplasm. Therefore, the present study was designed to evaluate the reproductive as well as metabolic endocrinological profiles in 24:00 h in intact adult mithun bulls during different seasons (winter, spring, summer and autumn) to know the rhythmic changes and flow pattern of the endocrinological profiles to improve its reproductive efficiency. Experimental mithun bulls (n = 6; age: 5-6 years; body condition score: 5-6 out of 10, classified as good) were selected for the study. Endocrinological profiles, follicle stimulating hormone (FSH), luteinizing hormone/interstitial cell stimulating hormone (LH/ICSH), testosterone, cortisol, thyroxine (T4), insulin like growth factor-1 (IGF-1), prolactin and melatonin (MT) were estimated at 04:00 h interval for one whole day in four seasons. The analysis was completed in two different ways as different times of collection (08:00, 12:00, 16:00, 20:00, 24:00 and 04:00 h) and day (08:00 to 16:00 h) & night time (20:00 to 04:00 h) collections. Repeated measures ANOVA analysis revealed that the bulls in winter and spring had significantly (p < 0.05) higher FSH, LH, testosterone, T4, IGF-1 and MT than those in summer whereas the bulls in summer had significantly higher cortisol and prolactin than those in winter and spring seasons. Similarly FSH, LH, testosterone, T4, IGF-1 and MT were significantly (p < 0.05) higher in night than in day time collections whereas cortisol and prolactin were significantly (p < 0.05) higher in day than in night time collections in different seasons. Correlation analysis revealed that FSH, LH, testosterone, T4, IGF-1 and MT had significant (p < 0.05) positive correlation with each other whereas these had significant (p < 0.05) negative correlation with cortisol and prolactin. The study concludes that season and time of blood collection had significant effect on the endocrinological profiles in mithun bulls. Estimation of FSH, LH, testosterone, T4, IGF-1 and MT during night time and cortisol and prolactin during day time was more appropriate to get correct value of the endocrinological profiles. Spring and winter have significantly greater beneficial effects than summer on reproduction and artificial breeding programs in mithun species in the semi-intensive management in the present location.

Melatonin for the prevention of fetal injury associated with intrauterine inflammation

Intrauterine inflammation is shown to be associated with preterm birth, fetal inflammatory response syndrome, and other pregnancy-related comorbidities such as central nervous system diseases including cerebral palsy and periventricular leukomalacia, pulmonary diseases such as bronchopulmonary dysplasia and respiratory distress syndrome, and necrotizing enterocolitis, to name a few. Many animal studies on intrauterine inflammation demonstrate that ascending infection of reproductive organs or the production of proinflammatory cytokines by some stimuli in utero results in such manifestations. Melatonin, known for its primary function in maintaining circadian rhythm, is now recognized as one of the most potent antioxidant and anti-inflammatory drugs. In some studies, melatonin injection in pregnant animals with intrauterine inflammation significantly reduced the number of preterm births, the severity of structural disintegration of the fetal lungs observed in bronchopulmonary dysplasia, and perinatal brain injuries with improvement in neuromotor function. These implicated benefits of melatonin in pregnant women with intrauterine inflammation seem promising in many research studies, strongly supporting the hypothesis that melatonin has antioxidative and anti-inflammatory properties that can potentially be taken by pregnant women who are at risk of having intrauterine inflammation. In this review, the potential of melatonin for improving outcomes of the pregnancies with intrauterine inflammation will be discussed.

Melatonin enhances antioxidant defenses but could not ameliorate the reproductive disorders in induced hyperthyroidism model in male rats

The present study was carried out to clarify the effect of different doses of melatonin on some reproductive hormones, serum total antioxidant, histopathological examination, lipid peroxidation, and antioxidant parameters in liver, kidney, heart, and testis tissues in induced-hyperthyroidism (HT) male rat model. A total of 75 mature male Wistar rats were equally allocated into five groups; control groups were daily I/P injected with distilled water containing 4 M ammonium hydroxide in methanol and 1% absolute ethanol; on hyperthyroidism model group, rats received daily I/P injection of L-thyroxine (0.2 mg/kg body weight). In melatonin-treated groups, rats were injected with the same dose of L-thyroxine followed by I/P injection of melatonin (1, 5, or 10 mg/kg, respectively) for 21 days. The hyperthyroidism group showed significant increase in serum thyroxine (T4), triiodothyronine (T3), and testosterone levels and a significant decrease in the levels of thyroid stimulating hormone (TSH), follicle stimulating hormone (FSH), luteinizing hormone (LH), and serum total antioxidants capacity, with a significant decrease in superoxide dismutase (SOD) activity and glutathione reductase (GSH) content with a significant increase in malondialdehyde (MDA) concentration in all examined tissues. While, melatonin co-treatment to HT groups partially counteracted the effect of hyperthyroidism by decreasing serum T4 and T3 levels and increasing serum TSH. In addition, melatonin could decrease serum levels of FSH, LH, and testosterone, as well as it could increase serum total antioxidants capacity, SOD activity, and GSH content and decreased MDA concentration in all examined tissues. Additionally, melatonin could amend the histopathological alterations in the examined tissues of hyperthyroid rats but not the testicular tissue. It is concluded that melatonin has a protective role against the hyperthyroidism-induced oxidative damage but cannot ameliorate the reproductive disorders in male rat model.

The LEPR Gene Is Associated with Reproductive Seasonality Traits in Rasa Aragonesa Sheep

The aim of this study was to characterize and identify causative polymorphisms in the leptin receptor (LEPR) gene responsible for the seasonal variation of reproductive traits in sheep. Three reproductive seasonality traits were studied: the total days of anoestrous (TDA), the progesterone cycling months (P4CM) and the oestrous cycling months (OCM). In total, 18 SNPs were detected in 33 ewes with extreme values for TDA and OCM. Six SNPs were non-synonymous substitutions and two of them were predicted in silico as deleterious: rs596133197 and rs403578195. These polymorphisms were then validated in 239 ewes. The SNP rs403578195, located in exon 8 and leading to a change of alanine to glycine (Ala284Gly) in the extracellular domain of the protein, was associated with the OCM trait, being the G allele associated with a decrease of 12 percent of the OCM trait. Haplotype analyses also suggested the involvement of other non-synonymous SNP located in exon 20 (rs405459906). This SNP also produces an amino acid change (Lys1069Glu) in the intracellular domain of the protein and segregates independently of rs403578195. These results confirm for the first time the role of the LEPR gene in sheep reproductive seasonality.

Role of Melatonin in Plant Tolerance to Soil Stressors: Salinity, pH and Heavy Metals

Melatonin (MT) is a pleiotropic molecule with diverse and numerous actions both in plants and animals. In plants, MT acts as an excellent promotor of tolerance against abiotic stress situations such as drought, cold, heat, salinity, and chemical pollutants. In all these situations, MT has a stimulating effect on plants, fomenting many changes in biochemical processes and stress-related gene expression. Melatonin plays vital roles as an antioxidant and can work as a free radical scavenger to protect plants from oxidative stress by stabilization cell redox status; however, MT can alleviate the toxic oxygen and nitrogen species. Beyond this, MT stimulates the antioxidant enzymes and augments antioxidants, as well as activates the ascorbate–glutathione (AsA–GSH) cycle to scavenge excess reactive oxygen species (ROS). In this review, we examine the recent data on the capacity of MT to alleviate the effects of common abiotic soil stressors, such as salinity, alkalinity, acidity, and the presence of heavy metals, reinforcing the general metabolism of plants and counteracting harmful agents. An exhaustive analysis of the latest advances in this regard is presented, and possible future applications of MT are discussed.

Circadian disruption, melatonin rhythm perturbations and their contributions to chaotic physiology

The aim of this report is to summarize the data documenting the vital nature of well-regulated cellular and organismal circadian rhythms, which are also reflected in a stable melatonin cycle, in supporting optimal health. Cellular fluctuations in physiology exist in most cells of multicellular organisms with their stability relying on the prevailing light:dark cycle, since it regulates, via specialized intrinsically-photoreceptive retinal ganglion cells (ipRGC) and the retinohypothalamic tract, the master circadian oscillator, i.e., the suprachiasmatic nuclei (SCN). The output message of the SCN, as determined by the light:dark cycle, is transferred to peripheral oscillators, so-called slave cellular oscillators, directly via the autonomic nervous system with its limited distribution. and indirectly via the pineal-derived circulating melatonin rhythm, which contacts every cell. Via its regulatory effects on the neuroendocrine system, particularly the hypothalamo-pituitary-adrenal axis, the SCN also has a major influence on the adrenal glucocorticoid rhythm which impacts neurological diseases and psychological behaviors. Moreover, the SCN regulates the circadian production and secretion of melatonin. When the central circadian oscillator is disturbed, such as by light at night, it passes misinformation to all organs in the body. When this occurs the physiology of cells becomes altered and normal cellular functions are compromised. This physiological upheaval is a precursor to pathologies. The deterioration of the SCN/pineal network is often a normal consequence of aging and its related diseases, but in today's societies where manufactured light is becoming progressively more common worldwide, the associated pathologies may also be occurring at an earlier age.

Melatonin and Mesenchymal Stem Cells as a Key for Functional Integrity for Liver Cancer Treatment

Hepatocellular carcinoma (HCC) is the most common hepatobiliary malignancy with limited therapeutic options. On the other hand, melatonin is an indoleamine that modulates a variety of potential therapeutic effects. In addition to its important role in the regulation of sleep–wake rhythms, several previous studies linked the biologic effects of melatonin to various substantial endocrine, neural, immune and antioxidant functions, among others. Furthermore, the effects of melatonin could be influenced through receptor dependent and receptor independent manner. Among the other numerous physiological and therapeutic effects of melatonin, controlling the survival and differentiation of mesenchymal stem cells (MSCs) has been recently discussed. Given its controversial interaction, several previous reports revealed the therapeutic potential of MSCs in controlling the hepatocellular carcinoma (HCC). Taken together, the intention of the present review is to highlight the effects of melatonin and mesenchymal stem cells as a key for functional integrity for liver cancer treatment. We hope to provide solid piece of information that may be helpful in designing novel drug targets to control HCC.

Melatonin membrane receptors MT1 and MT2 are expressed in ram spermatozoa from non-seasonal breeds

In mammals, many melatonin biological functions are mediated through its interaction with the membrane receptors MT₁ and MT₂. We have previously reported their presence in ram spermatozoa from males located in temperate climates, but there is no information on their presence in spermatozoa from rams in areas with an equatorial photoperiod (12L:12D). Thus, we have investigated the existence and cellular distribution of melatonin receptors in spermatozoa from three sheep breeds in Colombia (Colombian Creole, Hampshire, and Romney Marsh) during dry and rainy seasons, using indirect immunofluorescence and western blot. Our results indicated the presence of melatonin receptors in spermatozoa from these rams, and that their distribution differs from that previously found in spermatozoa from rams in temperate climates. Moreover, two new immunotypes of MT₂ were identified: type N, with staining only in the neck, and type E with a band of immunofluorescence in the upper part of the post-acrosome and the apical edge. Likewise, differences between breeds and climate seasons were detected for both receptors. However, densitometry analysis of western blot bands only revealed differences between seasons in the Creole rams for MT₁ and the Romney Marsh rams for MT₂, whereas differences between breeds were only detected for MT₂. It could be inferred that melatonin receptors in rams subjected to an equatorial photoperiod might be more closely related to sperm quality than seasonal control. Therefore, the presence of these receptors suggests that melatonin could be a useful tool to increase the fertility of rams located in tropical or equatorial climates.

Reproductive performance in three Slovenian sheep breeds with different alleles for the MTNR1A gene

The aim of the research was to describe the polymorphisms of the MTNR1A gene in three Slovenian sheep breeds, and determine whether these polymorphisms affect reproductive performance. A total of 100 Bovška, 110 Istrian Pramenka, and 108 Jezersko-Solčavska ewes, were used. The rams were placed with the ewes on 10 October (Bovška), and 20 September (Istrian Pramenka). At each farm, the lambing date and number of newborn lambs were recorded to evaluate the fertility rate, number of days from ram placement with ewes to lambing (DRIL), and litter size. The Jezersko-Solčavska rams were maintained with the ewes of the flock throughout the year and data related to lambing during the entire year were recorded. The DNA sequences indicated there were eight nucleotide variations and that in the position g.17355358 was always associated with that in the position g.17355452. For the Bovška breed, there was an association between the G/G genotype in the position g.17355452, and relatively greater fertility (P < 0.05) and a shorter DIRL (P < 0.05). For the Istrian Pramenka breed, the T/T genotype in the position g.17355458 was positively associated with a greater fertility (P < 0.05) and shorter DRIL (P < 0.05). For the Jezersko-Solčavska breed, ewes with the G/G genotype in the position g.17355452 lambed more when there was a decreasing photoperiod whereas the ewes with the A/A genotype lambed more (P < 0.05) during the period when there were increasing photoperiods. The different polymorphisms studied were associated with reproductive performance in the three Slovenian breeds.

Reproduction in female wild cattle: Influence of seasonality on ARTs

Wild cattle species, often considered less alluring than certain conservation-dependent species, have not attracted the same level of interest as the charismatic megafauna from the general public, private or corporate donors, and other funding agencies. Currently, most wild cattle populations are vulnerable or threatened with extinction. The implementation of reproductive technologies to maintain genetically healthy cattle populations in situ and ex situ has been considered for more than 30 years. Protocols developed for domestic cattle breeds have been used with some success in various wild cattle species. However, inherent differences in the natural life history of these species makes extrapolation of domestic cattle protocols difficult, and in some cases, minimally effective. Reproductive seasonality, driven by either photoperiod or nutritional resource availability, has significant influence on the success of assisted reproductive technologies (ARTs). This review focuses on the physiological processes that differ in breeding (ovulatory) and non-breeding (anovulatory) seasons in female cattle, and the potential methods used to overcome these challenges. Techniques to be discussed within the context of seasonality include: estrus synchronization and ovulation induction, ovarian superstimulation, artificial insemination (AI), multiple ovulation embryo transfer (MOET), and ovum pick-up (OPU) with in vitro fertilization (IVF) and embryo transfer (ET).

Effects of feeding melatonin during proestrus and early gestation to gilts and parity 1 sows to minimize effects of seasonal infertility1

This study tested whether supplemental melatonin given to mimic the extended nighttime melatonin pattern observed in the higher fertility winter season could minimize infertility during summer and fall in swine. Exogenous melatonin was fed during periods coinciding with follicle selection, corpus luteum formation, pregnancy recognition, and early embryo survival. Experiments were conducted at a commercial farm in 12 sequential replicates. In Exp. 1a, mature gilts (n = 420) that had expressed a second estrus were assigned by weight to receive once daily oral Melatonin (MEL, 3 mg) or Control (CON, placebo) at 1400 h for 3 wk starting before insemination at third estrus. In Exp. 1b, parity 1 sows (n = 470) were randomly assigned by lactation length to receive MEL or CON for 3 wk, starting 2 d before weaning. Follicles, estrus, pregnancy, and farrowing data were analyzed for the main effects of treatment, season (4-wk periods), and their interaction. Environmental measures were also analyzed for reproductive responses. In Exp. 1a, there was no effect (P > 0.10) of MEL on age at third estrus (203 d), follicle size after 7 d of treatment (5.0 mm), estrous cycle length (22.6 d), return to service (9.2%), farrowing rate (FR, 80.0%), or total born pigs (TB, 13.6). However, there was an effect of season (P = 0.03) on number of follicles and on gilts expressing estrus within 23 d of the previous estrus (P < 0.005). In Exp. 1b, there was no effect of MEL (P > 0.10) on follicle measures, wean to estrous interval, FR (84.0%), or TB (13.0). But MEL (73.5%) reduced (P = 0.03) estrous expression within 7 d of weaning compared with CON (82.0%) and season (P = 0.001) decreased FR by ~14.0% during mid summer. Also, gilts and parity 1 sows exposed to low light intensity (<45 lx) during breeding had reduced conception (-8%) and farrowing (-15%) rates, compared with higher light intensity. Similarly, high temperatures (>25 °C) during breeding also reduced gilt conception rates by 7%. Although there was clear evidence of seasonal fertility failures in gilts and sows, MEL treatment did not improve fertility in gilts and reduced estrus in parity 1 sows. It is possible that differences in lighting and thermal environments before breeding could explain the differential response to MEL in sows and gilts.

Melatonin protects mouse oocytes from DNA damage by enhancing nonhomologous end-joining repair

Mammalian oocytes remain arrested at the first prophase of meiosis in ovarian follicles for an extended period. During this protracted arrest, oocytes are remarkably susceptible to the accumulation of DNA damage. Melatonin (N-acetyl-5-methoxytryptamine), a hormone secreted by the pineal gland, has diverse effects on various physiological processes. However, the effect of melatonin on DNA damage response in mammalian oocytes has not been explored. Here, we showed that melatonin protected mouse oocytes from DNA damage induced by double-strand breaks (DSBs) during prophase arrest and subsequently improved oocyte quality. We found that DNA damage during prophase arrest impaired subsequent meiotic maturation and deteriorated oocyte quality, increasing chromosome fragmentation, spindle abnormality, mitochondrial aggregation, and oxidative stress. However, melatonin treatment during DNA damage accumulation at prophase improved meiotic maturation and relieved the quality decline of oocytes. In addition, melatonin inhibited the accumulation of DNA damage during prophase arrest by reducing the γ-H2AX levels. Although activated ATM levels were decreased by melatonin treatment, the effect of melatonin on DNA damage response was not a direct consequence of ATM inhibition. Instead, melatonin enhanced DNA repair via nonhomologous end-joining (NHEJ) pathway. Interestingly, these actions of melatonin on DNA damage response are receptor-independent in mouse oocytes. Therefore, our results demonstrated that melatonin protects oocytes from DNA damage during prophase arrest by enhancing DNA repair via NHEJ and subsequently prevents the deterioration of oocyte quality during meiotic maturation.

Effect of environmental factors and changes in the body condition score on the onset of the breeding season in mares

Several methods have been proposed to advance the onset of the breeding season in horses. Most of them are based on the exposure to an artificial lighting period combined with hormonal treatments. Mares exposed to an artificial photoperiod are most often housed indoors where the ambient temperature is often higher than the outside temperature. Mares held in barns are also exposed to different daylight intensities than horses kept outside, depending on the architecture. In the current study, we evaluated the impact of ambient temperature, daylight intensity and changes in body condition score (BCS) on the timing of first ovulation after winter anestrus in mares exposed to an artificial photoperiod. Mares (n = 211) were housed in barns with different ambient temperature and daylight exposure but with the same artificial photoperiod exposure (except for a natural photoperiod control group). Artificial photoperiod as well as an increase in BCS over the winter significantly advanced the first spring ovulation. The BCS at the start and end of the anestrus period did not have an effect on the interval to first ovulation and neither did the modest increase in ambient temperature in the barn. However, a higher light intensity during the daytime significantly advanced the first spring ovulation. The results of this study suggest that exposure to more sunlight advances the onset of the breeding season. This effect is likely mediated through the biological effect of short wavelength blue light and its impact on melatonin suppression and biological rhythms. We suggest that greater/direct exposure to the blue light component of daylight improves the response to the artificial photoperiod. The results of the present study can further assist to optimize the conditions that lead to an efficient spring transition of breeding mares.

Higher melatonin in the follicle fluid and MT2 expression in the granulosa cells contribute to the OHSS occurrence

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) is a common and severe complication for patients undergoing IVF/ICSI-ET. Melatonin widely participates in the regulation of female reproductive endocrine activity. However, whether melatonin participates in the progression of OHSS is largely unknown. This study aims to identify the predictive value of follicular fluid (FF) melatonin for OHSS establishment and the underlying mechanism.

METHODS

All participants of this case-control study were enrolled at the Reproductive Medicine Center located in the First Affiliated Hospital of Zhengzhou University in China from January to October in 2017. Quantitative real-time PCR and western blot were used to examine the mRNA and protein levels. Primary granulosa cells were extracted and cultured for in vitro studies. Melatonin concentration was measured by ELISA. Logistic analysis and receiver-operating characteristic (ROC) curves were used to evaluate the predicting value of melatonin on OHSS occurrence.

MAIN OUTCOME MEASURES

The expression level of melatonin receptor 2 (MT2), P450 aromatase cytochrome (aromatase), vascular endothelial growth factor (VEGF), and inducible nitric oxide synthase (iNOS) mRNA in human primary granulosa cells. The concentration of melatonin in FF. The predicting value of melatonin on OHSS and the cut-off value of the prediction.

RESULTS

FF melatonin concentrations were significantly higher in patients with OHSS compared to non-OHSS group (35.94 ± 10.18 ng/mL vs 23.93 ± 10.94 ng/mL, p<0.001). The expression of MT2 mRNA (p = 0.0459) and protein in granulosa cells was also significantly higher in the OHSS group. When using a cut-off level of 27.52 ng/ml, the sensitivity and specificity of FF melatonin to predict OHSS was 84.6 and 74.0%, respectively (p < 0.0001). We also found that melatonin could up-regulates aromatase mRNA, VEGF mRNA expression and down-regulates iNOS mRNA expression in the granulosa cells.

CONCLUSION

OHSS patients have higher melatonin in the FF as well as higher MT2 expression in the granulosa cells. The melatonin in FF might be used as an effective predictor for the occurrence of OHSS.

Circadian and Circannual Regulation in the Horse: Internal Timing in an Elite Athlete

Biological rhythms evolved to provide temporal coordination across all tissues and organs and allow synchronization of physiology with predictable environmental cycles. Most important of these are circadian and circannual rhythms, primarily regulated via photoperiod signals from the retina. Understanding the nature of physiological rhythms in horses is crucially important for equine management. Predominantly, they have been removed from exposure to their natural environmental stimuli; the seasonally changing photoperiod, continuous foraging and feeding activity, social herd interactions, and the continuous low-intensity exercise of a grassland dweller. These have been replaced in many cases with confined indoor housing, regimental feeding and exercise times, social isolation, and exposure to lighting that is often erratic and does not come close to mimicking the spectral composition of sunlight. Man has further altered seasonal timing cues through the use of artificial lighting programs that impact reproductive behavior, breeding efficiency, and the development of youngstock. Understanding how these new environmental cues (some stronger and some weaker) impact the internal physiology of the horse in the context of the natural endogenous rhythms that evolved over millennia is key to helping to improve equine health, welfare, and performance, now and into the future. This review provides an overview of the field, highlights the recent discoveries related to biological timing in horses, and discusses the implications that these findings may have for the production and management of the elite equine athlete.

Intrafollicular melatonin concentration is elevated in patients with ovarian hyperstimulation syndrome (OHSS) and can serve as an important predictor of OHSS

PURPOSE

Melatonin is an important factor in regulating numerous processes in human female reproduction. The aim of the present study was to compare melatonin levels in the follicular fluid (FF) of ovarian hyperstimulation syndrome (OHSS) women with those of non-OHSS women undergoing in vitro fertilization (IVF)-embryo transfer and to evaluate the relationship between FF melatonin levels and IVF outcomes in these women.

METHODS

We determined FF melatonin levels in 20 OHSS women and 23 non-OHSS women on oocyte retrieval day.

RESULTS

OHSS patients had significantly higher melatonin levels as compared to the non-OHSS women (P < 0.001). In addition, melatonin levels of the patients were significantly positively correlated with antral follicle count (AFC), serum anti-Müllerian hormone (AMH) levels, serum estradiol (E₂) levels on human chorionic gonadotropin (HCG) administration day, number of retrieved oocytes, total fertilized oocytes, normally fertilized oocytes, cleaved zygotes, top quality embryos on day 3, blastocysts obtained and embryos suitable for transplantation (day 3 embryos + day 5/6 blastocysts) (P < 0.05). While, the intrafollicular melatonin levels were significantly negatively correlated with age, basal serum follicle-stimulating hormone (FSH) levels, serum FSH levels on HCG administration day (P < 0.01). Since younger women with more AFC, higher AMH levels, higher serum E₂ levels and larger number of retrieved oocytes are much easier to encounter OHSS, while FF melatonin levels are significantly correlated with these five indices in our study, we propose that intrafollicular melatonin concentration can also be an important predictor of OHSS.

CONCLUSIONS

This is the first demonstration that FF melatonin levels were significantly higher in OHSS patients than in non-OHSS group and FF melatonin levels may serve as an important predictor of OHSS.

Genotype of MTNR1A gene regulates the conception rate following melatonin treatment in water buffalo

Buffaloes have tendency to show seasonal reproduction and remain in anestrus due to limited ovarian activity during summer. The seasonal reproductive behavior is ascribed the effect of melatonin related to photoperiod. Treating animals with melatonin could be a possible strategy to overcome the problem. The role of MTNR1A gene has not been fully explained in the buffalo. Therefore, we conducted a study on 114 buffalo heifers to detect the polymorphic site in MTNR1A gene and further treated them with melatonin implants to investigate the role of most frequent genotype following melatonin treatment on pregnancy. The present investigation is the first to investigate the association between melatonin treated different MTNR1A genotype buffalo and pregnancy. We confirmed SNP at position 72 in 812 bp fragment exon II of MTNR1A gene. RFLP of PCR products with Hpa I enzyme resulted in three genotypes: TT (812bp), CT (812, 743, 69bp) and CC (743, 69bp). Next, buffaloes of each genotype (TT, CC, CT; n = 28 for each) were treated with melatonin implants to compare the conception rate with their corresponding untreated control (n = 10 for each genotype). Melatonin concentrations were higher (P < 0.05) for the treatment groups of all genotypes compared to their respective untreated control from day 1-28. The pregnancy rate was significantly associated with the MTNR1A genotype. The conception rate was higher (P < 0.05) for TT genotype than for the other genotypes of buffaloes treated with melatonin. Furthermore, buffaloes of TT genotype treated with melatonin started exhibiting estrus activity soon from second week of melatonin treatment (14.1 ± 2.1; range: 10-17 days) and were found to be 7.8 times more likely to become pregnant compared to other genotypes following melatonin treatment. In conclusion, TT genotype of MTNR1A gene is more sensitive to melatonin treatment that favours pregnancy in buffaloes during summer.

Could long-term administration of melatonin to prepubertal children affect timing of puberty? A clinician's perspective

Exogenous melatonin can be used to treat sleep disturbance in adults, children, and adolescents. While its short-term use is considered safe, there are some concerns that long-term use might delay children's sexual maturation, possibly by disrupting the decline in nocturnal melatonin levels that occur at the onset of puberty. This narrative review aimed to summarize some of the current knowledge about the potential effects of exogenous melatonin on puberty. We found no clinical studies that experimentally tested the effects of melatonin on pubertal timing in children, but we reviewed the small number of observational studies. We also drew on animal data to try to answer our question. The photoperiod and melatonin-mediated seasonal transitions in sexual activity and breeding in some mammals across the seasons have been used as a model of sexual development in mammals, including humans. The switch from non-sexual activity (in the non-breeding period) to sexual activity (in the breeding period) has been likened to the onset of puberty as there are similarities between the two. We conclude that to investigate an association between melatonin and pubertal timing, it will be important to conduct long-term randomized controlled trials of latency age children and also examine the cellular and systems-level interactions between melatonin and kisspeptin, a recently identified neuropeptide with a locus of action at the gonadotropin releasing hormone neurons that is important in contributing to the timing of puberty onset.