Regulation Of Seasonal Reproduction Research Articles

The Photoperiod-Driven Cyclical Secretion of Pineal Melatonin Regulates Seasonal Reproduction in Geese (Anser cygnoides).

The photoperiod is the predominant environmental factor that governs seasonal reproduction in animals; however, the underlying molecular regulatory mechanism has yet to be fully elucidated. Herein, Yangzhou geese (Anser cygnoides) were selected at the spring equinox (SE), summer solstice (SS), autumn equinox (AE), and winter solstice (WS), and the regulation of seasonal reproduction via the light-driven cyclical secretion of pineal melatonin was investigated. We show that there were seasonal variations in the laying rate and GSI, while the ovarian area decreased 1.5-fold from the SS to the AE. Moreover, not only did the weight and volume of the pineal gland increase with a shortened photoperiod, but the secretory activity was also enhanced. Notably, tissue distribution further revealed seasonal oscillations in melatonin receptors (Mtnrs) in the pineal gland and the hypothalamus-pituitary-gonadal (HPG) axis. The immunohistochemical staining indicated higher Mtnr levels due to the shortened photoperiod. Furthermore, the upregulation of aralkylamine N-acetyltransferase (Aanat) was observed from the SS to the AE, concurrently resulting in a downregulation of the gonadotrophin-releasing hormone (GnRH) and gonadotropins (GtHs). This trend was also evident in the secretion of hormones. These data indicate that melatonin secretion during specific seasons is indicative of alterations in the photoperiod, thereby allowing for insight into the neuroendocrine regulation of reproduction via an intrinsic molecular depiction of external photoperiodic variations.

Temporal expression of thyroid hormone regulating genes (tsh-b, tsh-r, dio2 and dio3) and their correlation with annual reproductive cycle of the Indian freshwater catfish, Heteropneustes fossilis (Bloch).

Photoperiod and temperature are well-established environmental cues for gonadal growth in seasonally reproducing organisms. The photoperiod is known to regulate seasonal reproduction via induction of thyroid hormone regulating genes in the saccus vasculosus (SV) of fishes. However, SV is absent in many seasonally breeding fishes, including Heteropneustes fossilis. H. fossilis is a long-day breeding catfish in which gonadal recrudescence begins six months earlier than spawning. The present study attempted to analyse the expression of thyroid hormone-regulating genes (tsh-b, tsh-r, dio2 and dio3) in the brain, liver and ovary. In the brain, upregulated expression of thyrotropin-beta subunit (tsh-b), deiodinase2 (dio2) and deiodinase3 (dio3) genes is concomitant with the increasing photoperiod and temperature in nature, which may appear to regulate seasonal reproduction. Both deiodinases, dio2 and dio3, were also upregulated in the liver and ovarian tissue during the gonadal growth phase. The upregulation of deiodinases may enhance the metabolism and activity of tissues, thereby facilitating their respective roles. The expression of these genes was also assessed in the brain, liver, ovary, kidney, skin, spleen and gill tissues during the spawning period. The ubiquitous expression of deiodinases may point to enhanced activity in their organ-specific role. The present study speculates that expression of tsh-b, tsh-r, dio2 and dio3 genes during the reproductive phase of H. fossilis might be involved in the regulation of seasonal reproduction.

Light receptors in the avian brain and seasonal reproduction.

Detection and transduction of photic cues by nonvisual photoreceptors, located in the deep brain, is a critical component of timing seasonal reproduction in birds. However, the precise identity of the photoreceptors responsible for detection of salient photic cues remains uncertain and debated. Here I review of the existing evidence for each of the three candidate photoreceptive opsins: Vertebrate Ancient Opsin, Melanopsin, and Neuropsin, including localization, action spectrum, and data from experimental manipulation of opsin expression. These findings are compared to an updated list of key criteria established in the literature as a litmus for classifying an opsin as the "breeding photoreceptor." Integrating evidence for each of the candidate photoreceptors with respect to these criteria reveals support for all three opsins in regulation of seasonal reproduction. Taken together these findings strongly suggest that transduction of seasonal photoperiodic information involves the activity of multiple photoreceptor types and populations functioning in concert. This review also highlights the need to shift attention from simply identifying "the breeding photoreceptor" to a more integrative approach aiming to parse the contribution of specific photoreceptor populations within the brain.

Unraveling the Role of Thyroid Hormones in Seasonal Neuroplasticity in European Starlings (Sturnus vulgaris).

Thyroid hormones clearly play a role in the seasonal regulation of reproduction, but any role they might play in song behavior and the associated seasonal neuroplasticity in songbirds remains to be elucidated. To pursue this question, we first established seasonal patterns in the expression of thyroid hormone regulating genes in male European starlings employing in situ hybridization methods. Thyroid hormone transporter LAT1 expression in the song nucleus HVC was elevated during the photosensitive phase, pointing toward an active role of thyroid hormones during this window of possible neuroplasticity. In contrast, DIO3 expression was high in HVC during the photostimulated phase, limiting the possible effect of thyroid hormones to maintain song stability during the breeding season. Next, we studied the effect of hypothyroidism on song behavior and neuroplasticity using in vivo MRI. Both under natural conditions as with methimazole treatment, circulating thyroid hormone levels decreased during the photosensitive period, which coincided with the onset of neuroplasticity. This inverse relationship between thyroid hormones and neuroplasticity was further demonstrated by the negative correlation between plasma T3 and the microstructural changes in several song control nuclei and cerebellum. Furthermore, maintaining hypothyroidism during the photostimulated period inhibited the increase in testosterone, confirming the role of thyroid hormones in activating the hypothalamic–pituitary–gonadal (HPG) axis. The lack of high testosterone levels influenced the song behavior of hypothyroid starlings, while the lack of high plasma T4 during photostimulation affected the myelination of several tracts. Potentially, a global reduction of circulating thyroid hormones during the photosensitive period is necessary to lift the brake on neuroplasticity imposed by the photorefractory period, whereas local fine-tuning of thyroid hormone concentrations through LAT1 could activate underlying neuroplasticity mechanisms. Whereas, an increase in circulating T4 during the photostimulated period potentially influences the myelination of several white matter tracts, which stabilizes the neuroplastic changes. Given the complexity of thyroid hormone effects, this study is a steppingstone to disentangle the influence of thyroid hormones on seasonal neuroplasticity.

OPN5 Regulating Mechanism of Follicle Development Through the TSH-DIO2/DIO3 Pathway in Mountain Ducks Under Different Photoperiods.

: Photoperiod is an important environmental factor that influence seasonal reproduction behavior in bird. Birds translates photoperiodic information into neuroendocrine signals through deep brain photoreceptors (DBPs). OPN5 has been considered as candidate DBPs involving in regulation of seasonal reproduction in birds. However, little is known about the effect of OPN5 in non-seasonal breeding birds. Thus, we pondered on whether OPN5 regulating follicular development through TSH-DIO2/DIO3 system responds to different photoperiods in non-seasonal laying ducks. As an ideal non-seasonal breeding bird, a total of 120 mountain ducks were randomly divided into three groups and treated respectively to a different photoperiod: group S (8 L:16D), group C (17 L:7D), and group L (24 L:0D). The ducks were caged in a fully enclosed shelter with the same feeding conditions for each group, free water and limited feeding (150 g per duck each day). Samples were collected from each group at d 0, d 5, d 8, d 20, and d 35 (n = 8). The ducks in 24 h photoperiod had the highest laying rate and the lowest feed-to-egg ratio, while the ducks in 8 h photoperiod had the lowest laying rate and the highest feed-to-egg ratio. Long-day photoperiod for 24 h significantly increased the ovarian index and GnRH, LH, E2, and P4 levels in serum; short-day photoperiod for 8 h increased testosterone levels in serum. Compared with 8 h photoperiod, long-day photoperiod significantly or highly significantly increased the mRNA level and protein expression of OPN5 in the hypothalamus of long-day photoperiod on d 35 (p < 0.05). The gene or protein expression patterns of GnRH, TRH, TSHβ, DIO2, THRβ, VIP, and PRL were positively correlated with OPN5, whereas the gene expression patterns of GnIH and DI O 3 were negatively correlated with OPN5. The results revealed that OPN5 mediated the effect of light on follicular development through the TSH-DIO2/DIO3 pathway, the expression of OPN5 increased with light duration and improved the efficiency of the HPG axis to promote follicular development in mountain ducks.

Transcriptomic Changes of Photoperiodic Response in the Hypothalamus Were Identified in Ovariectomized and Estradiol-Treated Sheep.

Accurate timing of seasonal changes is an essential ability for an animal’s survival, and the change in the photoperiod is the key factor affecting reproductive seasonality in mammals. Emerging evidence has suggested that multiple hypothalamic genes participate in the photoperiod-induced regulation of reproductive activities in sheep, but the mechanism is still unclear. In this study, we initially examined the plasma level of two major reproductive hormones, namely, follicle-stimulating hormone (FSH) and prolactin (PRL), under different photoperiods in ovariectomized and estradiol-treated (OVX + E2) sheep using radioimmunoassay (RIA). Of the two hormones, the concentration of PRL significantly increased with the extension of the photoperiod, while FSH showed the opposite trend. Subsequently, an examination of the transcriptomic variation between the short photoperiod (SP) and long photoperiod (LP) was conducted. Differential expression analyses and functional annotation showed that several key genes in the insulin secretion (VAMP2, PRKACB, PRKCG, and PLCB1), GnRH (MAPK13, CGA, CDC42, ATF4, and LHB) pathways, and circadian entrainment (KCNJ5, PER1, GNB2, MTNR1A, and RASD1), as well as numerous lncRNAs, including XR_173257.3, XR_173415.3, XR_001435315.1, XR_001024596.2, and XR_001023464.2, were shown potentially vital for the hypothalamic photoperiodic response. Four of the differentially expressed mRNAs and lncRNAs were validated by qPCR. The constructed mRNA–mRNA interaction networks further revealed that transcripts potentially participated in hypothalamic thyroid hormone synthesis, endocrine resistance, and neuroactive ligand–receptor interactions. The interactome analysis of lncRNAs and their targets implied that XR_173257.3 and its target arylalkylamine N-acetyltransferase (AANAT) and XR_173415.3 and its target TH might participate in the regulation of seasonal reproduction. Together, the changes in reproductive hormones and transcriptome will help to determine the important photoperiod-induced lncRNAs and mRNAs and provide a valuable resource for further research on reproductive seasonality in sheep.

Functional differences between TSHR alleles associate with variation in spawning season in Atlantic herring

The underlying molecular mechanisms that determine long day versus short day breeders remain unknown in any organism. Atlantic herring provides a unique opportunity to examine the molecular mechanisms involved in reproduction timing, because both spring and autumn spawners exist within the same species. Although our previous whole genome comparisons revealed a strong association of TSHR alleles with spawning seasons, the functional consequences of these variants remain unknown. Here we examined the functional significance of six candidate TSHR mutations strongly associated with herring reproductive seasonality. We show that the L471M missense mutation in the spring-allele causes enhanced cAMP signaling. The best candidate non-coding mutation is a 5.2 kb retrotransposon insertion upstream of the TSHR transcription start site, near an open chromatin region, which is likely to affect TSHR expression. The insertion occurred prior to the split between Pacific and Atlantic herring and was lost in the autumn-allele. Our study shows that strongly associated coding and non-coding variants at the TSHR locus may both contribute to the regulation of seasonal reproduction in herring.

Regulatory effects of prolactin on breeding and migratory behaviours in birds

Prolactin is an adenohypophyseal hormone of vertebrates produced by the neuroendocrine signaling of the hypothalamus. It plays important role in different vertebrate species and referred to as “The Parental Hormone” or “The Hormone of Maternity”. In birds the role of Prolactin is limited as the parental hormone but the behavioral functions like the regulation of season-al reproduction, combating stress of predators, nest building abilities and regulations of migratory cycle are diversified. The classical role of Prolactin in different birds’ species like pigeons and doves is secretion of crop sac “milk” after hatching of eggs and regulation of migration in different type of mi-grants. Reports have suggested that acute and chronic stressors and ener-getic constraints depress prolactin levels disrupting the parental effort in nest building, mate selection, incubation and crop milk production. Although prolactin is diverse in its function but acts through the same receptors throughout the vertebrate series. However, this review establishes that pro-lactin plays an intense role in regulating breeding behaviours and migration in birds along with the interactions of other hormones. Prolactin helps the birds to carry out wide range of behaviour and become evolutionarily suc-cessful.

Expression characteristics of pineal miRNAs at ovine different reproductive stages and the identification of miRNAs targeting the AANAT gene

BackgroundMany recent studies have shown that miRNAs play important roles in the regulation of animal reproduction, including seasonal reproduction. The pineal gland is a crucial hub in the regulation of seasonal reproduction. However, little is known about the expression characteristics of pineal miRNAs in different reproductive seasons (anestrus and breeding season). Therefore, the expression profiles and regulatory roles of ovine pineal miRNAs were investigated during different reproductive stages using Solexa sequencing technology and dual luciferase reporter assays.ResultsA total of 427 miRNAs were identified in the sheep pineal gland. Significant differences in miRNA expression were demonstrated between anestrus and the breeding season in terms of the frequency distributions of miRNA lengths, number of expressed miRNAs, and specifically and highly expressed miRNAs in each reproductive stage. KEGG analysis of the differentially expressed (DE) miRNAs between anestrus and the breeding season indicated that they are significantly enriched in pathways related to protein synthesis, secretion and uptake. Furthermore, transcriptome analysis revealed that many target genes of DE miRNAs in the ribosome pathway showed relatively low expression in the breeding season. On the other hand, analyses combining miRNA-gene expression data with target relationship validation in vitro implied that miR-89 may participate in the negative regulation of aralkylamine N-acetyltransferase (AANAT) mRNA expression by targeting its 3’UTR at a unique binding site.ConclusionsOur results provide new insights into the expression characteristics of sheep pineal miRNAs at different reproductive stages and into the negative regulatory effects of pineal miRNAs on AANAT mRNA expression.

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

&lt;b&gt;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. &lt;/b&gt;

Molecular cloning, characterization and functional analysis of two neuropeptide F genes from the oriental river prawn (Macrobrachium nipponense)

In invertebrates, neuropeptide F (NPF) has many regulatory functions, similar to NPY, its homologous peptide. In this study, two neuropeptide F genes were identified in Macrobrachium nipponense: Mn-NPF1 and Mn-NPF2. Mn-NPF2 shared the same amino acid sequence with Mn-NPF1, except for a 37 amino acid insert in the middle of the NPF region. The quantitative-PCR (qPCR) results indicated that Mn-NPF1 expression was positively correlated with ovarian maturation, whereas Mn-NPF2 had opposing expression patterns. Both Mn-NPFs were poorly expressed at early embryonic stages, but enhanced expression levels were observed up to day 10 after hatching, when the gonads began to differentiate. Ovary in situ hybridization (ISH) analyses showed that both Mn-NPFs were present at all stages, but were differentially localized to distinct compartments. Temperature gradient studies showed that both Mn-NPFs were implicated in the seasonal regulation of reproduction. A double-stranded (ds) RNA-Mn-NPF2 injection led to a significant 38.5% increase in the vitellogenin (VG) transcript (P < 0.05). These results demonstrated that Mn-NPF2 plays an important role in inhibiting ovarian maturation.

Light and Hormones in Seasonal Regulation of Reproduction and Mood.

Organisms that inhabit the temperate zone exhibit various seasonal adaptive behaviors, including reproduction, hibernation, molting, and migration. Day length, known as photoperiod, is the most noise-free and widely used environmental cue that enables animals to anticipate the oncoming seasons and adapt their physiologies accordingly. Although less clear, some human traits also exhibit seasonality, such as birthrate, mood, cognitive brain responses, and various diseases. However, the molecular basis for human seasonality is poorly understood. Herein, we first review the underlying mechanisms of seasonal adaptive strategies of animals, including seasonal reproduction and stress responses during the breeding season. We then briefly summarize our recent discovery of signaling pathways involved in the winter depression–like phenotype in medaka fish. We believe that exploring the regulation of seasonal traits in animal models will provide insight into human seasonality and aid in the understanding of human diseases such as seasonal affective disorder (SAD).

Control of seasonal reproduction in sheep and goats by light and hormones

Seasonal variations of reproductive ability have been demonstrated in male and female sheep and goats. For the female, there is a distinct breeding season. Whilst there are large breed differences in the duration of the sexual season, oestrous cycles generally start when daylength is decreasing and end when daylength is increasing. In some breeds, ovulation without oestrus occurs during the non-breeding season. Although males are able to mate all the year round, seasonal variations occur in the weight of the testis and seminal vesicles and in the fructose concentration of the seminal vesicles. Sexual behaviour and semen characteristics also show seasonal variations. These seasonal variations in males and females are related to hormonal levels. FSH and LH concentrations in the pituitary are reduced to 50% during the non-breeding season. In the peripheral blood, LH concentrations vary throughout the year whilst prolactin concentrations follow the pattern of daylength. Steroid hormones and their feedback actions at the hypothalamo-pituitary axis play a role in the regulation of seasonal reproduction. Three different ways are proposed to overcome these seasonal variations. (1) Males can be introduced into a flock of females before the onset of the breeding season. This leads to induction of ovulation and oestrus, although the first ovulation is frequently followed by a short luteal phase. Teasing does not necessitate contact or sight and is only effective after a period of isolation of the females from the males. (2) Oestrus and ovulation may be induced during the anoestrous period by hormonal treatments. Inducers of LH release have to be associated with a progestagen treatment; PMSG is still the most efficient inducer of LH release. Artificial insemination is useful in this context to avoid subfertility due to seasonal variations of the male. (3) The period of reproduction may be controlled by artificial light regimens. There is a photoinducible period in the circadian cycle of the ewe and it may soon be practical to breed out of season by timed exposure of ewes to short periods of light during the normal hours of darkness.

Transcriptomic profiling reveals molecular regulation of seasonal reproduction in Tibetan highland fish, Gymnocypris przewalskii

BackgroundThe Tibetan highland fish, Gymnocypris przewalskii, migrates from Lake Qinghai to its spawning grounds every summer. This seasonal reproduction is critically regulated by intrinsic and extrinsic signals. However, the molecular mechanisms that process environmental oscillations to initiate the seasonal mating are largely unknown.ResultsA transcriptomic analysis was conducted on the brain and gonad of male and female G. przewalskii in reproductive and nonreproductive seasons. We obtained 2034, 760, 1158 and 17,856 differentially expressed genes between the reproductively active and dormant female brain, male brain, ovary and testis. Among these genes, DIO2 was upregulated in the reproductively active brain and gonad of both males and females. Neuroactive ligand-receptor genes were activated in male and female brain. Functional enrichment analysis suggested that retinol metabolism was uniquely stimulated in reproductively active males. Genes involved in GnRH signaling and sex hormone synthesis exhibited higher expression levels in brain and gonad during the reproductive season. A co-expression network classified all the genes into 9 modules. The network pinpointed CDC42 as the hub gene that connected the pathways in responsible for modulating reproduction in G. przewalskii. Meanwhile, the sex pheromone receptor gene prostaglandin receptor was identified to link to multiple endocrine receptors, such as GnRHR2 in the network.ConclusionsThe current study profiled transcriptomic variations between reproductively active and dormant fish, highlighting the potential regulatory mechanisms of seasonal reproduction in G. przewalskii. Our data suggested that the seasonal regulation of reproduction in G. przewalskii was controlled by the external stimulation of photoperiodic variations. The activated transcription of neuroendocrine and sex hormone synthesis genes contributed to seasonal reproduction regulation in G. przewalskii, which was presumably influenced by the increased day-length during the breeding season.

Historical Perspective and Evaluation of the Mechanisms by which Melatonin Mediates Seasonal Reproduction in Mammals

The discovery of melatonin and its photoperiod-regulated circadian rhythm were important milestones in defining the events associated with the regulation of seasonal reproduction in both short-day and long-day breeding mammals. By means of the seasonal changes in the duration of the nocturnal melatonin rise, which provides both clock and calendar information, animals adjust their reproductive state to the appropriate time of year. Thus, melatonin dictates the proper season for mating which ensures the optimal time for delivery of offspring. The photoperiodic information is transduced into a chemical messenger, melatonin, in the pineal gland. The initial studies related to the importance of day length and the melatonin message in impelling seasonal reproduction involved the use of photoperiod-sensitive rodents, especially several long-day breeding hamster species. Since then, a large group of interested reproductive biologists have extended these findings to numerous other mammals including short-day breeding ungulates. Moreover, critical information related to the molecular processes at the level of the pars tuberalis of the anterior pituitary and the mediobasal hypothalamus has been provided. In this scheme, the pars tuberalis, until recently an almost ignored portion of the adenohypophysis, has been identified as a critical intermediate between the melatonin signal and the functional state of the reproductive organs. It is somewhat ironic that two organs, the pineal gland and the pars tuberalis, which suffered with the image of vestigiality for so long have now been identified as unequivocally essential for this most basic and important function, i.e., regulating seasonal reproduction.

Density‐dependent reproduction and pollen limitation in an invasive milkweed, Calotropis procera (Ait.) R. Br. (Apocynaceae)

AbstractCalotropis procera (Ait.) R.Br. (Apocynaceae), an invasive woody milkweed, has expanded its range in northern Australia affecting rangeland and pastoral productivity. While self‐compatibility should enhance the species range expansion, spread of C. procera is limited by the availability of larger wasp and bee species that are able to vector its solid pollinia. Pollination efficiency is thus likely dependent on both pollinator abundance and plant density. Calotropis procera flowers year round in Australia but fruiting is limited to the warm months of the year when pollinators are most abundant, indicating that seasonal regulation of reproduction may be due to pollinator limitation. We examine the propositions that C. procera reproduction is regulated by the interaction between plant population density and pollinator pressure and that low pollinator pressure causes low per capita plant fecundity. All pollinators belonged to Order Hymenoptera and pollinator composition was similar at six of the seven sites. Fruit production per plant (fecundity) was lower above and below intermediate densities (350–550 plants ha−1) of flowering plants with evidence of a weak Allee effect at lower plant density. Pollinator visitation rates per plant were low at high and low plant densities, and greatest at intermediate densities, while pollen supplementation experiments showed that C. procera is pollen limited (Pollen Limitation Indexfruit = 0.9) even at intermediate densities. Pollen limitation caused by low pollinator pressure at low plant densities and pollinator satiation at high plant densities may account for these fruit production trends. Management should be conducted in the colder months when pollinator pressure is low and plants are not reproducing. In addition, where stand eradication cannot be achieved in one attempt, management should reduce flowering plants to below intermediate densities where the fecundity per plant is low.

Effect of Photoperiod Extension on the Testicular Sonographic Appearance and Sexual Behavior of Captive Yangtze Finless porpoise (Neophocaena asiaeorientalis asiaeorientalis).

Xueying Yu, Yujiang Hao, Brian CW Kot, and Ding Wang (2016) Photoperiod plays an important role in the seasonal regulation of reproduction in mammals. In the present study, we examined the effect of an extended photoperiod (light/dark: 14 h/10 h) during the usual sexually inactive phase (Jan-Mar) on testicular sonographic appearance and sexual behaviors of two captive Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis, YFP). During the extended photoperiod treatment, the parenchyma pixel intensity, cross- sectional area of testicular sonographic images, as well as the frequency of sexual behaviors of the two male porpoises increased significantly compared to the control treatment. Parenchyma pixel intensity, the cross- sectional area of testicular sonographic images and the frequency of sexual behaviors of the two captive males all increased in response to extended photoperiod. These results may suggest that photoperiod is a potent factor regulating the reproductive seasonality in YFPs.

Sex differences in the photoperiodic regulation of RF-Amide related peptide (RFRP) and its receptor GPR147 in the syrian hamster.

RF-(Arg-Phe) related peptides (RFRP-1 and -3) are considered to play a role in the seasonal regulation of reproduction; however, the effect of the peptides depends on species and gender. This study aimed at comparing the RFRP system in male and female Syrian hamsters over long and short photoperiods to investigate the neuroanatomical basis of these differential effects. The neuroanatomical distribution of RFRP neurons and fibers, revealed using an antiserum recognizing RFRP-1 and -3, as well as GPR147 mRNA, are similar in male and female Syrian hamsters. RFRP neurons are mainly found in the medial hypothalamus, whereas RFRP projections and GPR147 mRNA are observed in the preoptic area, anteroventral-periventricular nucleus, suprachiasmatic nucleus, paraventricular nucleus, bed nucleus of the stria terminalis, ventromedial hypothalamus, habenular nucleus, and arcuate nucleus. The number of RFRP neurons is higher in females than in males, and in both sexes, the number of RFRP neurons is reduced in short photoperiods. GPR147 mRNA levels are higher in females than in males and are downregulated in short photoperiods, particularly in females. Interestingly, the number of RFRP-positive fibers in the anteroventral-periventricular nucleus is higher only in females adjusted to a short photoperiod. Our results suggest that the RFRP system, which is strongly regulated by photoperiod in both male and female Syrian hamsters, is particularly important in females, with a distinct role in the anteroventral-periventricular nucleus, possibly in the regulation of the preovulatory luteinizing hormone surge via kisspeptin neurons.

Molecular, cellular, morphological, physiological and behavioral aspects of gonadotropin-inhibitory hormone

Gonadotropin-inhibitory hormone (GnIH) is a hypothalamic neuropeptide that was isolated from the brains of Japanese quail in 2000, which inhibited luteinizing hormone release from the anterior pituitary gland. Here, we summarize the following fifteen years of researches that investigated on the mechanism of GnIH actions at molecular, cellular, morphological, physiological, and behavioral levels. The unique molecular structure of GnIH peptide is in its LPXRFamide (X=L or Q) motif at its C-terminal. The primary receptor for GnIH is GPR147. The cell signaling pathway triggered by GnIH is initiated by inhibiting adenylate cyclase and decreasing cAMP production in the target cell. GnIH neurons regulate not only gonadotropin synthesis and release in the pituitary, but also regulate various neurons in the brain, such as GnRH1, GnRH2, dopamine, POMC, NPY, orexin, MCH, CRH, oxytocin, and kisspeptin neurons. GnIH and GPR147 are also expressed in gonads and they may regulate steroidogenesis and germ cell maturation in an autocrine/paracrine manner. GnIH regulates reproductive development and activity. In female mammals, GnIH may regulate estrous or menstrual cycle. GnIH is also involved in the regulation of seasonal reproduction, but GnIH may finely tune reproductive activities in the breeding seasons. It is involved in stress responses not only in the brain but also in gonads. GnIH may inhibit male socio-sexual behavior by stimulating the activity of cytochrome P450 aromatase in the brain and stimulates feeding behavior by modulating the activities of hypothalamic and central amygdala neurons.

Comparative analysis reveals the underlying mechanism of vertebrate seasonal reproduction

Animals utilize photoperiodic changes as a calendar to regulate seasonal reproduction. Birds have highly sophisticated photoperiodic mechanisms and functional genomics analysis in quail uncovered the signal transduction pathway regulating avian seasonal reproduction. Birds detect light with deep brain photoreceptors. Long day (LD) stimulus induces secretion of thyroid-stimulating hormone (TSH) from the pars tuberalis (PT) of the pituitary gland. PT-derived TSH locally activates thyroid hormone (TH) in the hypothalamus, which induces gonadotropin-releasing hormone (GnRH) and hence gonadotropin secretion. However, during winter, low temperatures increase serum TH for adaptive thermogenesis, which accelerates germ cell apoptosis by activating the genes involved in metamorphosis. Therefore, TH has a dual role in the regulation of seasonal reproduction. Studies using TSH receptor knockout mice confirmed the involvement of PT-derived TSH in mammalian seasonal reproduction. In addition, studies in mice revealed that the tissue-specific glycosylation of TSH diversifies its function in the circulation to avoid crosstalk. In contrast to birds and mammals, one of the molecular machineries necessary for the seasonal reproduction of fish are localized in the saccus vasculosus from the photoreceptor to the neuroendocrine output. Thus, comparative analysis is a powerful tool to uncover the universality and diversity of fundamental properties in various organisms.