The Two Populations of Kisspeptin Neurons Are Involved in the Ram-Induced LH Pulsatile Secretion and LH Surge in Anestrous Ewes

Hormonal dynamics reveal a stimulatory role for secretoneurin in zebrafish ovulation

Surge release of luteinizing hormone (Lh) from the pituitary is essential for fertility as it triggers ovulation. While secretoneurin (SN) is a phylogenetically conserved secretogranin-2-derived peptide that stimulates Lh, its role in ovulation has not been established. To directly compare periovulatory changes in the classical hormones to the emerging reproductive neuropeptides SNa and SNb, simultaneous mass spectrometry measurement of 9 peptides and 5 steroids was conducted in female zebrafish. Regression analysis indicated that levels of SNa1-34 in the brain peaked when type 3 gonadotropin-releasing hormone (Gnrh3) increased (R 2 = 0.71) at the time of the Lh surge, 3.5 h before ovulation. Levels of the naturally occurring derivative SNa1-14 were highest at ovulation, while SNb1-31 was invariable. The bioactivities of SNa1-34 and SNa1-14 were investigated. After injection of SNa1-34 in females that had been isolated from males, 61% (11/18) ovulated within 6 h, which was like the effects of the Lh analog human chorionic gonadotropin (72%; 13/18 females). SNa1-34 injection induces ovulation by increasing time-dependent expression of gnrh3 in the brain, a likely direct stimulation of chorionic gonadotropin alpha (cga) and luteinizing hormone b (lhb) subunit in pituitary, and via the subsequent time-dependent increase in nuclear progesterone receptor (npr) in ovaries. In contrast, SNa1-14 exhibited far fewer effects on gene expression and did not induce ovulation. Our results support the proposal that SN is a reproductive hormone.

Interactions between β-endorphin and kisspeptin neurons of the ewe arcuate nucleus are modulated by photoperiod

Opioid peptides are well-known modulators of the central control of reproduction. Among them, dynorphin coexpressed in kisspeptin (KP) neurons of the arcuate nucleus (ARC) has been thoroughly studied for its autocrine effect on KP release through κ opioid receptors. Other studies have suggested a role for β-endorphin (BEND), a peptide cleaved from the pro-opiomelanocortin precursor, on food intake and central control of reproduction. Similar to KP, BEND content in the ARC of sheep is modulated by day length and BEND modulates food intake in a dose-dependent manner. Because KP levels in the ARC vary with photoperiodic and metabolic status, a photoperiod-driven influence of BEND neurons on neighboring KP neurons is plausible. The present study aimed to investigate a possible modulatory action of BEND on KP neurons located in the ovine ARC. Using confocal microscopy, numerous KP appositions on BEND neurons were found but there was no photoperiodic variation of the number of these interactions in ovariectomized, estradiol-replaced ewes. By contrast, BEND terminals on KP neurons were twice as numerous under short days, in ewes having an activated gonadotropic axis, compared to anestrus ewes under long days. Injection of 5 μg BEND into the third ventricle of short-day ewes induced a significant and specific increase of activated KP neurons (16% vs. 9% in controls), whereas the percentage of overall activated (c-Fos positive) neurons, was similar between both groups. These data suggest a photoperiod-dependent influence of BEND on KP neurons of the ARC, which may influence gonadotropin-releasing hormone pulsatile secretion and inform KP neurons about metabolic status.

Biostimulation and pheromones in livestock: A review

This review examines aspects of the phenomenon of biostimulation in swine, goats, sheep, cattle and deer, to improve the collective knowledge and exploitation of its relevant mechanisms and effects in animal production. The long-term goal is to implement biostimulation strategies that benefit livestock reproduction and production while being both cost-effective and socially acceptable.

Frontiers in sheep reproduction - making use of natural responses to environmental challenges to manage productivity

This review addresses advances, directions and opportunities for research on sheep reproduction in the context of the global challenges of food security and climate change, and demand for 'clean, green and ethical' (CGE) animal management. The foundation of CGE management is an understanding of the physiological processes through which the reproductive system responds to changes in the animal's environment. These days, to the main environmental factors (photoperiod, nutrition, pheromones), we need to add stress from extreme weather events. With respect to nutrition in rams, we now have a deeper understanding of the responses of the brain centres that control gonadotrophin secretion (the kisspeptin system). At testis level, we have found that nutrition affects non-coding RNAs in Sertoli cells and germ cells, thus affecting the balance between cell proliferation and apoptosis. This proliferation-apoptosis balance is also affected during prenatal development, when undernutrition or stress in pregnant ewes seems to elicit epigenetic changes in developing gonads that could affect offspring fertility in adult life. With respect to nutrition in ewes, metabolic signals act directly on ovarian follicles, and thus change ovulation rate, but the variety of signals now includes the adipokines. An early concern was that nutritional supplements that increase ovulation rate would also increase embryo mortality but we now know that embryo survival is improved under field conditions. Finally, we had always thought that the efficiency gains from early puberty in lambs could only be achieved by accelerating fat accumulation, but we now know that faster muscle growth will achieve the same goal, offering two advantages in meat production systems. With respect to pheromones ('ram effect'), we have a deeper understanding of the brain responses (kisspeptin system) but, most importantly, a realization that the response of ewes to the ram signal involves cell division in memory centres. Many opportunities remain.

Exposure to difenoconazole induces reproductive toxicity in zebrafish by interfering with gamete maturation and reproductive behavior

Difenoconazole (DCZ) is a triazole fungicide that negatively affects aquatic organisms and humans. However, data regarding the reproductive toxicity of DCZ are insufficient. In this study, we used zebrafish (from 2 h post-fertilization [hpf] to adulthood) as a model to evaluate whether DCZ at environmentally relevant concentrations (0.1, 1.0, and 10.0 μg/L) induces reproductive toxicity. After exposure to DCZ, egg production and fertilization rates were reduced by 1.0 and 10.0 μg/L. A significant decrease in gamete frequency (late vitellogenic oocytes and spermatozoa) was observed at 10.0 μg/L. The concentrations of 17β-estradiol (E2), testosterone (T), and vitellogenin (VTG) were disrupted in females and males by 1.0 and 10.0 μg/L. Exposure to 10.0 μg/L DCZ significantly inhibited the contact time between female and male fish, which was mainly achieved by affecting male fish. The transcription of genes involved in the hypothalamus-pituitary-gonad (HPG) axis was significantly changed after treatment with DCZ. Overall, these data show that the endocrine-disrupting effect of DCZ on the zebrafish HPG axis inhibited gamete maturation and disrupted reproductive behavior, reducing fertility.

Perspective: Re-defining “Pheromone” in a Mammalian Context to Encompass Seminal Fluid

The classical view of “pheromone”—an air-borne chemical signal—is challenged by the camelids in which ovulation is triggered by ß-nerve growth factor carried in seminal plasma, effectively extending the pheromone concept to a new medium. We propose further extension of “pheromone” to include a separate class of seminal fluid molecules that acts on the female reproductive tract to enhance the prospect of pregnancy. These molecules include transforming growth factor-ß, 19-OH prostaglandins, various ligands of Toll-like receptor-4 (TLR4), and cyclic ADP ribose hydrolase (CD38). They modulate the immune response to “foreign” male-derived histocompatibility antigens on both sperm and the conceptus, determine pre-implantation embryo development, and then promote implantation by increasing uterine receptivity to the embryo. The relative abundance of these immunological molecules in seminal plasma determines the strength and quality of the immune tolerance that is generated in the female. This phenomenon has profound implications in reproductive biology because it provides a pathway, independent of the fertilizing sperm, by which paternal factors can influence the likelihood of reproductive success, as well as the phenotype and health status of offspring. Moreover, the female actively participates in this exchange—information in seminal fluid is subject to “cryptic female choice,” a process by which females interrogate the reproductive fitness of prospective mates and invest reproductive resources accordingly. These processes participate in driving the evolution of male accessory glands, ensuring optimal female reproductive investment and maximal progeny fitness. An expanded pheromone concept will avoid a constraint in our understanding of mammalian reproductive biology.

Estrus Synchronization in the Sheep and Goat

Estrus synchronization and manipulation are a tool that has been used by producers to provide uniform lamb and kid meat production and dairy sheep and goat milk production, to concentrate work and labor cost, and to plan for the lambing and kidding time. Breeders can also use estrus synchronization to stimulate ewes and does to exhibit estrus and ovulate outside of the breeding season, although both the ovulation rate and pregnancy rate may be decreased. To increase the ovulation rate outside of the breeding season, a variety of estrus synchronization methods have been used.

Roles of melatonin in the teleost ovary: A review of the current status

Melatonin, the neurohormone mainly synthesized in and secreted from the pineal gland of vertebrates following a circadian rhythm, is an important factor regulating various physiological processes, including reproduction. Recent data indicate that melatonin is also synthesized in the ovary and that it acts directly at the level of the ovary to modulate ovarian physiology. In some teleosts, melatonin is reported to affect ovarian steroidogenesis. The direct action of melatonin on the ovary could be a possible factor promoting oocyte maturation in teleosts. A role for melatonin in follicle rupture during ovulation in the teleost medaka has recently emerged. In addition, melatonin is suggested to affect oocyte maturation by its antioxidant activity. However, the molecular mechanisms underlying these direct effects of melatonin are largely unknown.

Is it time to reconsider the relative weight of sociosexual relationships compared with photoperiod in the control of reproduction of small ruminant females?

In goats and sheep from the temperate and subtropical latitudes, the breeding season lasts from early autumn to late winter, whereas the anestrous season lasts from late winter to late summer. In prepubertal or postpartum females, the duration of the quiescent period depends mainly on the season of parturition and of nursing duration. In both situations, the ovulatory activity starts only during the breeding season. Photoperiod has been generally considered as a major regulator of all these periods of reproductive activity/inactivity in female sheep and goats (ie puberty, seasonal anestrus, postpartum anestrus). In particular, regarding seasonal anestrus, the sociosexual interactions between males and females have been considered to have only a modulatory role, limited to few weeks preceding the onset or after the offset of the breeding season. Nonetheless, we recently showed that the use of sexually active males plays a crucial role to trigger ovulatory and estrous activities during the anestrous season and also in prepubertal and postpartum females. In fact, in females exposed to sexually active males, puberty is strikingly advanced in comparison with females exposed to sexually inactive castrated males or to isolated females (6 mo vs 7.5 mo). Most females (>85%) exposed during the anestrous season to sexually active males ovulated, whereas a low proportion of them ovulated when in contact with sexually inactive males (<10%). Interestingly, the presence of these sexually active males allows females to ovulate all the year round and prevents the seasonal decrease of LH plasma concentrations in ovariectomized females treated with an estradiol implant. Finally, the presence of sexually active males triggers ovulation in postpartum anestrous females nursing their offspring. All these findings show that sexually active males can play an important role to reduce anestrous periods. We need, therefore, to reconsider the relative weight of sociosexual relationships, compared with photoperiod, in the management of reproduction of goat does and ewes.

Arcuate nucleus kisspeptin response to increased nutrition in rams

Rams respond to acute nutritional supplementation by increasing the frequency of gonadotrophin-releasing hormone (GnRH) pulses. Kisspeptin neurons may mediate the effect of environmental cues on GnRH secretion, so we tested whether the ram response to nutrition involves activation of kisspeptin neurons in the arcuate nucleus (ARC), namely kisspeptin, neurokin B, dynorphin (KNDy) neurons. Rams were given extra lupin grain with their normal ration. Blood was sampled before feeding, and continued until animals were killed for collection of brain tissue at 2 or 11h after supplementation. In supplemented rams, LH pulse frequency increased after feeding, whereas control animals showed no change. Within the caudal ARC, there were more kisspeptin neurons in supplemented rams than in controls and a higher proportion of kisspeptin cells coexpressed Fos, regardless of the time the rams were killed. There were more Fos cells in the mid-ARC and mid-dorsomedial hypothalamus of the supplemented compared with control rams. No effect of nutrition was found on kisspeptin expression in the rostral or mid-ARC, or on GnRH expression in the preoptic area. Kisspeptin neurons in the caudal ARC appear to mediate the increase in GnRH and LH production due to acute nutritional supplementation, supporting the hypothesised role of the KNDy neurons as the pulse generator for GnRH.

Targeted mutation of secretogranin-2 disrupts sexual behavior and reproduction in zebrafish

The luteinizing hormone surge is essential for fertility as it triggers ovulation in females and sperm release in males. We previously reported that secretoneurin-a, a neuropeptide derived from the processing of secretogranin-2a (Scg2a), stimulates luteinizing hormone release, suggesting a role in reproduction. Here we provide evidence that mutation of the scg2a and scg2b genes using TALENs in zebrafish reduces sexual behavior, ovulation, oviposition, and fertility. Large-scale spawning within-line crossings (n = 82 to 101) were conducted. Wild-type (WT) males paired with WT females successfully spawned in 62% of the breeding trials. Spawning success was reduced to 37% (P = 0.006), 44% (P = 0.0169), and 6% (P < 0.0001) for scg2a ^-/- , scg2b ^-/- , and scg2a ^-/- ;scg2b ^-/- mutants, respectively. Comprehensive video analysis indicates that scg2a ^-/- ;scg2b ^-/- mutation reduces all male courtship behaviors. Spawning success was 47% in saline-injected WT controls compared to 11% in saline-injected scg2a ^-/- ;scg2b ^-/- double mutants. For these mutants, spawning success increased 3-fold following a single intraperitoneal (i.p.) injection of synthetic secretoneurin-a (P = 0.0403) and increased 3.5-fold with injection of human chorionic gonadotropin (hCG). Embryonic survival at 24 h remained on average lower in scg2a ^-/- ;scg2b ^-/- fish compared to WT injected with secretoneurin-a (P < 0.001). Significant reductions in the expression of gonadotropin-releasing hormone 3 in the hypothalamus, and luteinizing hormone beta and glycoprotein alpha subunits in the pituitary provide evidence for disrupted hypothalamo-pituitary function in scg2a and scg2b mutant fish. Our results indicate that secretogranin-2 is required for optimal reproductive function and support the hypothesis that secretoneurin is a reproductive hormone.

Optogenetic stimulation of kisspeptin neurones within the posterodorsal medial amygdala increases luteinising hormone pulse frequency in female mice

Kisspeptin within the arcuate nucleus of the hypothalamus is a critical neuropeptide in the regulation of reproduction. Together with neurokinin B and dynorphin A, arcuate kisspeptin provides the oscillatory activity that drives the pulsatile secretion of gonadotrophin-releasing hormone (GnRH), and therefore luteinising hormone (LH) pulses, and is considered to be a central component of the GnRH pulse generator. It is well established that the amygdala also exerts an influence over gonadotrophic hormone secretion and reproductive physiology. The discovery of kisspeptin and its receptor within the posterodorsal medial amygdala (MePD) and our recent finding showing that intra-MePD administration of kisspeptin or a kisspeptin receptor antagonist results in increased LH secretion and decreased LH pulse frequency, respectively, suggests an important role for amygdala kisspeptin signalling in the regulation of the GnRH pulse generator. To further investigate the function of amygdala kisspeptin, the present study used an optogenetic approach to selectively stimulate MePD kisspeptin neurones and examine the effect on pulsatile LH secretion. MePD kisspeptin neurones in conscious Kiss1-Cre mice were virally infected to express the channelrhodopsin 2 protein and selectively stimulated by light via a chronically implanted fibre optic cannula. Continuous stimulation using 5 Hz resulted in an increased LH pulse frequency, which was not observed at the lower stimulation frequencies of 0.5 and 2 Hz. In wild-type animals, continuous stimulation at 5 Hz did not affect LH pulse frequency. These results demonstrate that selective activation of MePD Kiss1 neurones can modulate hypothalamic GnRH pulse generator frequency.

Facing the Challenges of Neuropeptide Gene Knockouts: Why Do They Not Inhibit Reproduction in Adult Teleost Fish?

Genetic manipulation of teleost endocrine systems started with transgenic overexpression of pituitary growth hormone. Such strategies enhance growth and reduce fertility, but the fish still breed. Genome editing using transcription activator-like effector nuclease in zebrafish and medaka has established the role of follicle stimulating hormone for gonadal development and luteinizing hormone for ovulation. Attempts to genetically manipulate the hypophysiotropic neuropeptidergic systems have been less successful. Overexpression of a gonadotropin-releasing hormone (gnrh) antisense in common carp delays puberty but does not block reproduction. Knockout of Gnrh in zebrafish does not impact either sex, while in medaka this blocks ovulation in females without affecting males. Spawning success is not reduced by knockout of the kisspeptins and receptors, agouti-related protein, agouti signaling peptide or spexin. Hypotheses for the lack of effect of these genome edits are presented. Over evolutionary time, teleosts have lost the median eminence typical of mammals. There is consequently direct innervation of gonadotrophs, with the possibility of independent regulation by >20 neurohormones. Removal of a few may have minimal impact. Neuropeptide knockout could leave co-expressed stimulators of gonadotropins functionally intact. Genetic compensation in response to loss of protein function may maintain sufficient reproduction. The species differences in hypothalamo-hypophysial anatomy could be an example of compensation over the evolutionary timescale as teleosts diversified and adapted to new ecological niches. The key neuropeptidergic systems controlling teleost reproduction remain to be uncovered. Classical neurotransmitters are also regulators of luteinizing hormone release, but have yet to be targeted by genome editing. Their essentiality for reproduction should also be explored.