Kisspeptin as a master player in the central control of reproduction in mammals: an overview of kisspeptin research in domestic animals

Regulatory Involvement of Kisspeptin in Energy Balance and Reproduction

The hypothalamic-pituitary-gonadal axis, which regulates steroidogenesis and germ cell formation, closely regulates the reproduction process. Nonetheless, other chemical mediators, such as kisspeptin, influence this axis. Kisspeptin is a hypothalamic neuropeptide that modulates the function of this axis and also plays a central role in energy balance. The present study reviews the impact and associated mechanisms of kisspeptin on male and female reproduction based on available evidence in the literature. Kisspeptin and its neurons exert anorexigenic activity, thus maintaining adequate energy balance for optimal reproductive function. Also, they stimulate the release of GnRH, resulting in the optimal performance of gonadal physiological processes viz. production of steroid sex hormones and germ cells. However, studies linking kisspeptin to reproduction are yet scanty. Hence, studies exploring the upstream and downstream signaling pathways activated by kisspeptin concerning reproduction in an attempt to better understand the associated mechanisms of the regulatory activities of kisspeptin on reproduction are recommended. In addition, potential factors that may modulate kisspeptin activities may be useful in the management of infertility and perhaps, in the development of contraceptives for those who do not intend to achieve conception.

Understanding the role of temperature in seasonal timing: Effects on behavioural, physiological and molecular phenotypes

Organisms adapt to daily and seasonal environmental changes to maximise their metabolic and reproductive fitness. For seasonally breeding animals, photoperiod is considered the most robust cue to drive these changes. It, however, does not explain the interannual variations in different seasonal phenotypes. Several studies have repeatedly shown the influence of ambient temperature on the timing of different seasonal physiologies including the timing of migration, reproduction and its associated behaviours, etc. In the present review, we have discussed the effects of changes in ambient temperature on different seasonal events in endotherms with a focus on migratory birds as they have evolved to draw benefits from distinct but largely predictable seasonal patterns of natural resources. We have further discussed the physiological and molecular mechanisms by which temperature affects seasonal timings. The primary brain area involved in detecting temperature changes is the hypothalamic preoptic area. This area receives thermal inputs via sensory neurons in the peripheral ganglia that measure changes in thermoregulatory tissues such as the skin and spinal cord. For the input signals, several thermal sensory TRP (transient receptor potential ion channels) channels have been identified across different classes of vertebrates. These channels are activated at specific thermal ranges. Once perceived, this information should activate an effector function. However, the link between temperature sensation and the effector pathways is not properly understood yet. Here, we have summarised the available information that may help us understand how temperature information is translated into seasonal timing.

Pathogenesis of the crosstalk between reproductive function and stress in animals-part 1: Hypothalamo-pituitary-adrenal axis, sympatho-adrenomedullary system and kisspeptin

Stress is defined as a disruption of the body homeostasis in response to modest as well as perceived challenge. Two main physiological routes, the hypothalamic-pituitary-adrenal system (HPA) and the sympatho-adrenomedullary system (SAM), aim to maintain or restore homeostasis by mutual interaction. SAM is quickly-reacting as it primarily works through the nervous system-the sympathetic nervous system. In response to stress, signals are sent to activate the adrenal medulla which releases catecholamines (primarily adrenaline and norepinephrine). The catecholamines have a momentary effect on the body's organs that are prepared for a fight situation. At the same time, the stressor activates the HPA axis by signals from the brain causing secretion of the pituitary hormone adrenocorticotropic hormone (ACTH). ACTH acts on the adrenal cortex, which secretes glucocorticoids, including cortisol. Since HPA primarily works through hormones, the system is slightly slower than SAM and gives rise to a metabolic effect. While short-term stress response is an adaptive and beneficial process, chronic or excessive stress can lead to a range of negative health outcomes including reproductive disorders and infertility. Several mechanisms have been proposed to explain the link between stress and reproduction. This includes in particular kisspeptin, which is closely related to reproduction, as it is a powerful stimulator of the Hypothalamic-pituitary-gonadal (HPG) system. The present review, through current knowledge in various male and female species, deals with the role of the SAM and the HPA, including the major action of kisspeptin and glucocorticoids that trigger the consequences of psychological or physiological stress on reproductive function.

Functional evaluation of a novel kisspeptin analogue on the reproduction of female goldfish

Kisspeptin (kp) is a key regulator of reproduction, which stimulates sexual maturation and gametogenesis in mammals, amphibians, and teleosts. In the present study, to enhance the biological activity of kp10, a novel analog (referred to as M-kp10) was designed based on the endogenous goldfish variant, in which phenylalanine 6 was substituted by tryptophan and the N-terminus was acetylated. Compared with the native kp-10 and salmon gonadotropin-releasing hormone (GnRH3), the effect of M-kp10 on sexual hormones and reproductive indices as well as the expression of kiss1, cyp19a1, and kiss1ra genes in goldfish (Carassius auratus) was investigated. In practice, peptides were synthesized based on the standard Fmoc-solid-phase peptide synthesis and purified by employing RP-HPLC, followed by approving their structure using ESI-MS. The results showed that M-kp10 increased significantly 17,20β-DHP, LH, FSH and E2 as well as fecundity, hatching and fertilization percentages than the other peptides. Histological studies revealed that M-kp10 led to the faster growth of ovarian follicles compared to the kp-10 and GnRH3. The genes of cyp19a1, kiss1ra, and kiss1 were remarkably more expressed after treatment with M-kp10. In conclusion, the results indicated the superiority of M-kp10 over kp-10 in inducing sexual maturation and accelerating the percentage of fecundity, suggesting that M-kp10 could be a promising candidate for application in the artificial breeding of fish.

Estradiol and progesterone-induced lordosis behavior is modulated by both the Kisspeptin receptor and melanin-concentrating hormone in estradiol benzoate-primed rats

Intracerebroventricular (ICV) administration of estradiol benzoate (E₂B) and progesterone (P) induces intense lordosis behavior in ovariectomized rats primed peripherally with E₂B. The present study tested the hypothesis that the Kisspeptin (Kiss) and melanin-concentrating hormone (MCH) pathways regulate female sexual behavior induced by these steroid hormones. In Experiment 1, we tested the relevance of the Kiss pathway by ICV infusion of its inhibitor, kiss-234, before administration of E₂B or P in estrogen-primed rats. Lordosis induced by E₂B alone or with the addition of P was reduced significantly at 30, 120, and 240 min. In Experiment 2, ICV infusion of MCH 30 min before E₂B or P significantly reduced lordosis in rats primed with E₂B alone. These data support the hypothesis that the Kiss and MCH pathways, which can release or modulate gonadotropin-releasing hormone (GnRH), are involved in E₂B- and P-induced lordosis.

The Kisspeptin analogue C6 induces ovulation in jennies

Kisspeptins (KPs) are the most potent stimulating neurotransmitters of GnRH release, and consequently KP administration triggers LH and/or FSH release. In small ruminants, KP or its analogs induced an LH surge followed by ovulation in both cyclic and acyclic animals, while in the mare KP only increased LH plasma levels but failed to induce ovulation. This study in jennies compares the endocrinological effects, ovulatory and pregnancy rates of the KP analog C6 and the GnRH analog buserelin acetate. The ovarian activity of nine Amiata jennies was monitored daily by transrectal ultrasound for three complete estrous cycles. Jennies in estrus were assigned, to one of three treatment groups: 50 nmol of the KP analog C6 (injected twice, 24 h apart, C6 group); 0.4 mg buserelin acetate (injected once, Bu group); and 2 mL of saline (injected once, CTRL group). Blood samples were collected at Day-1 (-24 h) Day0 (h0, before treatment), h2, h4, h6, h8, h10, h24 (before second treatment with C6), h26, h28, h30, h32, h34, h48 and every 24 h until ovulation. Jennies were inseminated once at h24 with fresh extended semen from a donkey stallion. Pregnancy diagnoses were performed 14 days after ovulation. On days 5, 10, and 14 after ovulation, for every CL the cross-sectional area (CSA) and the vascularized area (VA) were recorded by color doppler ultrasound and measured. Significantly higher plasma LH levels were found after induction between the Bu and CTRL groups at h6 and h8 (P < 0.05), while tendentially higher differences were found between the Bu/C6 groups and CTRL at h10. Five/9, 4/9, and 2/9 jennies ovulated between 24 and 48 h after induction from the Bu, C6, and CTRL groups respectively, (P > 0.05). Correlations between corpora lutea CSA and VA with serum progesterone concentration were r = 0.31, P = 0.01, r = 0.38, P = 0.01, respectively. Pregnancy rates after artificial insemination did not differ among groups (CTRL: 6/9, 66.7%; C6: 7/9, 77.8%; Bu: 6/9, 66.7%; P > 0.05). Ovulation rates after C6 treatment were comparable to that of Bu, although not different from the CTRL. Pregnancy rates were comparable to the literature in terms of fresh extended donkey semen in every group. This study suggests that stimulation of the Kp system in jennies, in contrast to findings observed in mares, induces ovulation. Further studies using higher doses and/or more animals are needed to better characterize the efficacy of C6 in jennies.

Neuroendocrine control of gonadotropin-releasing hormone: Pulsatile and surge modes of secretion

The concept that different systems control episodic and surge secretion of gonadotropin-releasing hormone (GnRH) was well established by the time that GnRH was identified and formed the framework for studies of the physiological roles of GnRH, and later kisspeptin. Here, we focus on recent studies identifying the neural mechanisms underlying these two modes of secretion, with an emphasis on their core components. There is now compelling data that kisspeptin neurons in the arcuate nucleus that also contain neurokinin B (NKB) and dynorphin (i.e., KNDy cells) and their projections to GnRH dendrons constitute the GnRH pulse generator in mice and rats. There is also strong evidence for a similar role for KNDy neurons in sheep and goats, and weaker data in monkeys and humans. However, whether KNDy neurons act on GnRH dendrons and/or GnRH soma and dendrites that are found in the mediobasal hypothalamus (MBH) of these species remains unclear. The core components of the GnRH/luteinising hormone surge consist of an endocrine signal that initiates the process and a neural trigger that drives GnRH secretion during the surge. In all spontaneous ovulators, the core endocrine signal is a rise in estradiol secretion from the maturing follicle(s), with the site of estrogen positive feedback being the rostral periventricular kisspeptin neurons in rodents and neurons in the MBH of sheep and primates. There is considerable species variations in the neural trigger, with three major classes. First, in reflex ovulators, this trigger is initiated by coitus and carried to the hypothalamus by neural or vascular pathways. Second, in rodents, there is a time of day signal that originates in the suprachiasmatic nucleus and activates rostral periventricular kisspeptin neurons and GnRH soma and dendrites. Finally, in sheep nitric oxide-producing neurons in the ventromedial nucleus, KNDy neurons and rostral kisspeptin neurons all appear to participate in driving GnRH release during the surge.

Cellular and molecular mechanisms regulating the KNDy neuronal activities to generate and modulate GnRH pulse in mammals

Accumulating findings during the past decades have demonstrated that the hypothalamic arcuate kisspeptin neurons are supposed to be responsible for pulsatile release of gonadotropin-releasing hormone (GnRH) to regulate gametogenesis and steroidogenesis in mammals. The arcuate kisspeptin neurons express neurokinin B (NKB) and dynorphin A (Dyn), thus, the neurons are also referred to as KNDy neurons. In the present article, we mainly focus on the cellular and molecular mechanisms underlying GnRH pulse generation, that is focused on the action of NKB and Dyn and an interaction between KNDy neurons and astrocytes to control GnRH pulse generation. Then, we also discuss the factors that modulate the activity of KNDy neurons and consequent pulsatile GnRH/LH release in mammals.

Kisspeptin and the "Special Relationship" Between Reproduction and Metabolism: A Computational Approach

BACKGROUND

Kisspeptin is one of the most potent stimulators of GnRH secretion and consequent gonadotropin release from the anterior pituitary. Kisspeptin is considered critical in regulating reproductive function in relation to metabolic cues. Reproductive function is gated by the energy reserves of the individual. Conditions of energy insufficiency, such as Anorexia Nervosa, often disturb reproductive function and fertility.

OBJECTIVE

The aim of this research was to investigate similar or comparable hormonal patterns in kisspeptin mechanics using computational methodology tools.

METHODS

Twenty-two females with typical or atypical anorexia nervosa and fifteen control females, were recruited from the Center for Adolescent Medicine of the University of Athens. Serum levels of Prolactin (PRL), 17-Hydroxy-Progesterone (17OHPR), Free Triiodothyronine (FT3), Triiodothyronine (T3), Free Thyroxine (FT4), Thyroid Stimulating Hormone (TSH), Luteinizing Hormone (LH), Follicle Stimulating Hormone (FSH) and Estradiol (E2) were measured in patients and controls. Data were modelled computationally in order to find similar or comparable patterns between control and anorexic participants, with respect to kisspeptin.

RESULTS

Kisspeptin manifested symmetrical regression plots between controls and anorexics with respect to 17OHPR, LH and FSH, as well as a threshold pattern among controls, typical and atypical anorexics.

CONCLUSION

Kisspeptin seems to participate in the anorexic hormonal milieu through threshold or symmetrical mechanisms.

Whole-Genome Sequencing and Characterization of Buffalo Genetic Resources: Recent Advances and Future Challenges

The buffalo was domesticated around 3000-6000 years ago and has substantial economic significance as a meat, dairy, and draught animal. The buffalo has remained underutilized in terms of the development of a well-annotated and assembled reference genome de novo. It is mandatory to explore the genetic architecture of a species to understand the biology that helps to manage its genetic variability, which is ultimately used for selective breeding and genomic selection. Morphological and molecular data have revealed that the swamp buffalo population has strong geographical genomic diversity with low gene flow but strong phenotypic consistency, while the river buffalo population has higher phenotypic diversity with a weak phylogeographic structure. The availability of recent high-quality reference genome and genotyping marker panels has invigorated many genome-based studies on evolutionary history, genetic diversity, functional elements, and performance traits. The increasing molecular knowledge syndicate with selective breeding should pave the way for genetic improvement in the climatic resilience, disease resistance, and production performance of water buffalo populations globally.

Peripheral action of kisspeptin at reproductive tissues-role in ovarian function and embryo implantation and relevance to assisted reproductive technology in livestock: a review

Kisspeptin (KISS1) is encoded by the KISS1 gene and was initially found to be a repressor of metastasis. Natural mutations in the KISS1 receptor gene (KISS1R) were subsequently shown to be associated with idiopathic hypothalamic hypogonadism and impaired puberty. This led to interest in the role of KISS1 in reproduction. It was established that KISS1 had a fundamental role in the control of gonadotropin releasing hormone (GnRH) secretion. KISS1 neurons have receptors for leptin and estrogen receptor α (ERα), which places KISS1 at the gateway of metabolic (leptin) and gonadal (ERα) regulation of GnRH secretion. More recently, KISS1 has been shown to act at peripheral reproductive tissues. KISS1 and KISS1R genes are expressed in follicles (granulosa, theca, oocyte), trophoblast, and uterus. KISS1 and KISS1R proteins are found in the same tissues. KISS1 appears to have autocrine and paracrine actions in follicle and oocyte maturation, trophoblast development, and implantation and placentation. In some studies, KISS1 was beneficial to in vitro oocyte maturation and blastocyst development. The next phase of KISS1 research will explore potential benefits on embryo survival and pregnancy. This will likely involve longer-term KISS1 treatments during proestrus, early embryo development, trophoblast attachment, and implantation and pregnancy. A deeper understanding of the direct action of KISS1 at reproductive tissues could help to achieve the next step change in embryo survival and improvement in the efficiency of assisted reproductive technology.

Estrogen increases KISS1 expression in newly generated immortalized KISS1-expressing cell line derived from goat preoptic area

Kisspeptin neurons located in the hypothalamic preoptic area (POA) are suggested to be responsible for the induction of the gonadotropin-releasing hormone (GnRH) surge and the following luteinizing hormone (LH) surge to regulate female mammals’ ovulation. Accumulating evidence demonstrates that the preovulatory level of estrogen activates the POA kisspeptin neurons (estrogen positive feedback), which in turn induces a GnRH/LH surge. This study aimed to derive a cell line from goat POA kisspeptin neurons as an in vitro model to analyze the estrogen positive feedback mechanism in ruminants. Neuron-derived cell clones obtained by the immortalization of POA tissue from a female Shiba goat fetus were analyzed for the expression of kisspeptin (KISS1) and estrogen receptor α (ESR1) genes using quantitative real-time reverse transcription-polymerase chain reaction and three cell clones were selected as POA kisspeptin neuron cell line candidates. One cell line (GP64) out of the three clones showed significant increase in the KISS1 level by incubation with estradiol for 24 h, indicating that the GP64 cells mimic endogenous goat POA kisspeptin neurons. The GP64 cells showed immunoreactivities for kisspeptin and estrogen receptor α and retained a stable growth rate throughout three passages. Further, intracellular calcium levels in the GP64 cells were increased by the KCl challenge, indicating their neurosecretory ability. In conclusion, we generated a new KISS1-expressing cell line derived from goat POA. The current GP64 cell line could be a useful model to elucidate the estrogen positive feedback mechanism responsible for the GnRH/LH surge generation in ruminants.

The kisspeptin system in domestic animals: what we know and what we still need to understand of its role in reproduction

The discovery of the kisspeptin (Kp) system stirred a burst of research in the field of reproductive neuroendocrinology. In the last 15 yr, the organization and activity of the system, including its neuroanatomical structure, its major physiological functions, and its main pharmacological properties, were outlined. To this endeavor, the use of genetic tools to delete and to restore Kp system functionality in a specific tissue was essential. At present, there is no question as to the key role of the Kp system in mammalian reproduction. However, easily applicable genetic manipulations are unavailable for domestic animals. Hence, many essential details on the physiological mechanisms underlying its action on domestic animals require further investigation. The potentially different effects of the various Kp isoforms, the precise anatomical localization of the Kp receptor, and the respective role played by the 2 main populations of Kp cells in different species are only few of the questions that remain unanswered and that will be illustrated in this review. Furthermore, the application of synthetic pharmacologic tools to manipulate the Kp system is still in its infancy but has produced some interesting results, suggesting the possibility of developing new methods to manage reproduction in domestic animals. In spite of a decade and a half of intense research effort, much work is still required to achieve a comprehensive understanding of the influence of the Kp system on reproduction. Furthermore, Kp system ramifications in other physiological functions are emerging and open new research perspectives.

Association of bovine KISS1 single nucleotide polymorphisms with reproductive traits in Indian Cattle

Kisspeptins, a family of neuropeptide encoded by the Kiss1 gene, have emerged as crucial regulator of fertility and reproduction by regulating the hypothalamic-pituitary-gonadal axis. The present study was aimed to identify and associate SNPs in the KISS1 gene with reproductive traits in cattle of Indian origin. DNA samples collected from 300 individual cows of three Indian dairy breeds (Gir, Kankrej and Frieswal) of cattle were used in the study. The SNPs of KISS1 gene were identified with PCR-RFLP and sequence analysis using two sets of primer pairs. A total of 5 SNPs were identified in the targeted region of which, two were selected for screening the population and association studies. The analysis revealed that genotypes of rs442633552G>A and rs42022871C>T had a significant association with dry period. The SNP rs42022871C>T also established significant role in milk production traits, and selection of TT-genotyped animals will improve the reproduction and production potential of the animals.

Patterns of preoptic-hypothalamic neuronal activation and LH secretion in female sheep following the introduction and withdrawal of novel males

The neuroendocrine response of female sheep to a novel male involves neural activation in the hypothalamus. However, if males are removed, the gonadotrophic signal declines, so the neural activity is likely to change. We examined Fos-immunoreactive (IR) cells in hypothalamic tissues from seasonally anovulatory female sheep exposed to males for 2 or 6h, or for 2h followed by 4h isolation from males. Control females were killed in the absence of male exposure. Male introduction increased LH secretion in all females; male removal was associated with a reduction only in mean and basal LH concentrations. Females exposed to males for 2h had more Fos-IR cells in the arcuate nucleus (ARC), ventromedial nucleus of the hypothalamus (VMH) and organum vasculosum of the lamina terminalis (OVLT) than control females. Fos-IR cells in the preoptic area (POA) were only greater than in control females after 6h exposure to a male. Removal of males decreased the number of Fos-IR cells in the ARC, VMH and OVLT, but not in the POA. Thus, hypothalamic neural activation and LH secretion in female sheep are stimulated by males and decline after male removal. However, activation in the POA persists after removal and may explain the incomplete decline in the LH response.

Expression of Kisspeptin and its receptor in the hypothalamus of cyclic and acyclic buffalo (Bubalus bubalis)

Kisspeptin (Kiss1), neurokinin-B (NKB) and dynorphin (Dyn) neurons regulate the surge and pulsatile centres of gonadotropin releasing hormone (GnRH) in the hypothalamus and are modulated by the ovarian steroids. Accordingly, we studied the temporospatial expression of Kiss1, its receptor and other genes that regulate GnRH in the preoptic area (POA) and arcuate (ARC) regions of hypothalamus at different phases of bubaline estrous cycle. Brain of buffalo (n = 32) was collected immediately after exsanguination and categorized into early luteal (EL), mid luteal (ML), follicular (FL) stages and acyclic (n = 8/group). Total RNA was extracted from the POA and ARC of each stage and real time PCR amplification of Kiss1, Kiss1r, NKB, NKB receptor (NKBR), Dyn, Dyn receptor (OPRK1), GnRH1, ERα, PR, LEPR and GHSR was done using GAPDH as endogenous control and acyclic stage as calibrator group. Further, immunolocalization of Kiss1 and Kiss1r was done on the hypothalamus. In the POA, significant up-regulation of Kiss1 and NKB with a concomitant down-regulation of Dyn transcripts was recorded at FL stage. There was, however, down-regulation of Kiss1 and Kiss1r during the EL perhaps due to the loss of estradiol as a consequence of ovulation. On the other hand, in the ARC, there was a significant up-regulation of Kiss1 and Dyn at FL and ML, while NKB transcript was consistently down-regulated at any stage of estrous cycle. In the POA, expression of ERα was not modulated; however, PR was down-regulated in the EL. In the ARC, the ERα expression was significantly up-regulated in the EL, whereas, PR was moderately expressed irrespective of the stage of estrous cycle. The immunolocalization study revealed the presence of Kiss1 and Kiss1r in the POA and ARC in the cyclic buffalo with relative abundance at FL. The transcriptional profile of the genes suggests that there is estrous cycle stage specific expression of Kiss1, Kiss1r and other GnRH regulating genes in the POA and ARC regions of hypothalamus in the buffalo. Up-regulation of Kiss1r in the POA during ML and ARC during EL indicates the involvement of kisspeptinergic system in the regulation of low LH pulse frequencies during the early and mid luteal phases in the cyclic buffalo.

Kisspeptin and the regulation of the reproductive axis in domestic animals

The control of reproductive processes involves the integration of a number of factors from the internal and external environment, with the final output signal of these processes being the pulsatile secretion of gonadotrophin releasing hormone (GnRH) from the hypothalamus. These factors include the feedback actions of sex steroids, feed intake and nutritional status, season/photoperiod, pheromones, age and stress. Understanding these factors and how they influence GnRH secretion and hence reproduction is important for the management of farm animals. There is evidence that the RF-amide neuropeptide, kisspeptin, may be involved in relaying the effects of these factors to the GnRH neurons. This paper will review the evidence from the common domestic animals (sheep, goats, cattle, horses and pigs), that kisspeptin neurons are i) regulated by the factors listed above, ii) contact GnRH neurons, and iii) involved in the regulation of GnRH/gonadotrophin secretion.

Kisspeptin Modulates Luteinizing Hormone Release and Ovarian Follicular Dynamics in Pre-pubertal and Adult Murrah Buffaloes

Kisspeptin is a neuropeptide that governs the reproductive axis upstream to GnRH. We wanted to study whether kisspeptin modulates plasma LH and FSH levels and ovarian follicular dynamics in buffaloes and whether kisspeptin can be used for fixed time artificial insemination (FTAI). We carried out these studies in comparison with buserelin, a potent GnRH agonist. Kisspeptin dose-dependently increased plasma LH levels. However, the kisspeptin-induced increase in LH was short-lived as the peak reached in 15–30 min returned to basal values by 1–2 h. The kisspeptin-induced increase in LH level was less compared to buserelin-induced increase in LH level which sustained over time. Kisspeptin did not enhance FSH release while buserelin resulted in a gradual increase over time. LH response to repeated injections of kisspeptin was greater than that induced by buserelin. While buserelin induced an increase in the number of follicles, kisspeptin induced an increase in the growth rate of the follicle. In adult cycling animals, while both the drugs increased plasma LH levels, the increase was greater in buserelin group compared to kisspeptin group. In contrast to the findings in pre-pubertal animals, kisspeptin induced an increase in both the number as well as the size of follicles compared to buserelin. Our studies on oestrus synchronization, using either kisspeptin-PGF_2α-kisspeptin protocol or buserelin-PGF_2α-buserelin Ovsynch protocol on day 0, 7, and 9, respectively, revealed that kisspeptin increased the number of follicles at wave emergence and the diameter of dominant follicle after 2nd dose of drug, the oestrus response rate and duration of oestrus, compared to buserelin. However, conception rate was not significantly different among the groups. From our studies, it appears that Kp and Buserelin differentially modulate follicular dynamics depending on the reproductive age of the animals.However, studies in a larger herd are required to confirm whether kisspeptin can be used for oestrous synchronization in buffaloes.

Mapping of KNDy neurons and immunohistochemical analysis of the interaction between KNDy and substance P neural systems in goat

A population of neurons in the arcuate nucleus (ARC) coexpresses kisspeptin, neurokinin B (NKB), and dynorphin, and therefore they are referred to as KNDy neurons. It has been suggested that KNDy neurons participate in several brain functions, including the control of reproduction. The present study aimed to advance our understanding of the anatomy of the KNDy neural system. We first produced an antiserum against goat kisspeptin. After confirming its specificity, the antiserum was used to histochemically detect kisspeptin-positive signals. Using the colocalization of kisspeptin and NKB immunoreactivity as a marker for KNDy neurons, we mapped distributions of their cell somata and fibers in the whole brain (except the cerebellum) of ovariectomized (OVX) goats. KNDy neuronal somata were distributed throughout the ARC, and were particularly abundant in its caudal aspect. KNDy neuronal fibers projected into several areas within the septo-preoptic-hypothalamic continuum, such as the ARC, median eminence, medial preoptic nucleus, and bed nucleus of the stria terminalis. Kisspeptin immunoreactivity was not found outside of the continuum. We then addressed to the hypothesis that substance P (SP) is also involved in the KNDy neural system. Double-labeling immunohistochemistry for kisspeptin and SP revealed that KNDy neurons did not coexpress SP, but nearly all of the KNDy neuronal somata were surrounded by fibers containing SP in the OVX goats. The present results demonstrate anatomical evidence for a robust association between the KNDy and SP neural systems.

Towards new strategies to manage livestock reproduction using kisspeptin analogs

The discovery of the hypothalamic neuropeptide kisspeptin and its receptor (KISS1R) have dramatically improved our knowledge about the central mechanisms controlling reproduction. Kisspeptin neurons could be considered the hub where internal and external information controlling reproduction converge. The information is here elaborated and the command dispatched to GnRH neurons, the final output of the brain system controlling reproduction. Several studies have shown that in mammals administration of kisspeptin could finely modulate many aspects of reproduction from puberty to ovulation. For example in ewes kisspeptin infusion triggered ovulation during the non-breeding season and in prepubertal rat repeated injections advanced puberty onset. However, especially in livestock, the suboptimal pharmacological properties of endogenous kisspeptin, notably it short half-life and consequently its poor pharmacodynamics, fetters its use to experimental setting. To overcome this issue synthetic KISS1R agonists, mainly based on kisspeptin backbone, were created. Their more favorable pharmacological profile, longer half-life and duration of action, allowed to perform promising initial experiments for controlling ovulation and puberty. Additional experiments and further refinement of analogs would still be necessary to exploit fully the potential of targeting the kisspeptin system. Nevertheless, it is already clear that this new strategy may represent a breakthrough in the field of reproduction control.

An administration of TAK-683 at a minimally effective dose for luteinizing hormone stimulation under the absence of the ovary induces luteinizing hormone surge in ovary-intact goats

The present study aimed to evaluate hormonal responses and their association with the TAK-683 blood concentrations in goats administered TAK-683 at a low dose, which had been previously determined as the minimally effective dose for luteinizing hormone (LH) stimulation in ovariectomized goats. In Experiment 1, 5 µg of TAK-683 treatment had no significant stimulatory effect on LH secretion in ovariectomized Shiba goats (n = 4). In Experiment 2, cycling goats received the treatment of prostaglandin F_2α and progesterone-releasing controlled internal drug releasing (CIDR) to induce the follicular phase, then they were treated with 5 µg of TAK-683 (hour 0) intravenously (n = 4, IV) or subcutaneously (n = 3, SC) or with vehicle intravenously (n = 4, control) at 12 h after CIDR removal. Blood samples were collected at 10-min (–2–6 h), 2-h (6–24 h), or 6-h (24–48 h) intervals. Ovarian ultrasonographic images were assessed daily to confirm ovulation after the treatment. A surge-like release of LH was immediately observed after injection in all animals in the IV (peak time: 4.2 ± 0.6 h, peak concentration: 73.3 ± 27.5 ng/ml) and SC (peak time: 4.6 ± 0.4 h, peak concentration: 62.6 ± 23.2 ng/ml) groups, but not in the control group. Ovulation was detected within 3 days after TAK-683 injection in all animals in the IV and SC groups, and the interval period from TAK-683 administration to ovulation in the IV group was significantly (P < 0.05) shorter than that of the control group. No significant changes were observed between the IV and SC groups in terms of luteal diameter and blood progesterone levels after ovulation. The present findings suggest that the involvement of one or more ovarian factor(s) is indispensable for a TAK-683-induced LH surge leading to ovulation in goats.

Immunohistochemical characterization of the arcuate kisspeptin/neurokinin B/dynorphin (KNDy) and preoptic kisspeptin neuronal populations in the hypothalamus during the estrous cycle in heifers

Elucidating the physiological mechanisms that control reproduction is an obvious strategy for improving the fertility of cattle and developing new agents to control reproductive functions. The present study aimed to identify kisspeptin neurons in the bovine hypothalamus, clarifying that a central mechanism is also present in the cattle brain, as kisspeptin is known to play an important role in the stimulation of gonadotropin-releasing hormone (GnRH)/gonadotropin secretion in other mammals. To characterize kisspeptin neurons in the bovine hypothalamus, the co-localizations of kisspeptin and neurokinin B (NKB) or kisspeptin and dynorphin A (Dyn) were examined. Hypothalamic tissue was collected from Japanese Black or Japanese Black × Holstein crossbred cows during the follicular and luteal phases. Brain sections, including the arcuate nucleus (ARC) and the preoptic area (POA), were dual immunostained with kisspeptin and either NKB or Dyn. In the ARC, both NKB and Dyn were co-localized in kisspeptin neurons during both the follicular and luteal phases, demonstrating the presence of kisspeptin/NKB/Dyn-containing neurons, referred to as KNDy neurons, in cows. In the POA, no co-localization of kisspeptin with either NKB or Dyn was detected. Kisspeptin expression in the follicular phase was higher than that in the luteal phase, suggesting that kisspeptin expression in the POA is positively controlled by estrogen in cows. The kisspeptin neuronal populations in the ARC and POA likely play important roles in regulating the GnRH pulse and surge, respectively, in cows.

Oestrogenic action of neonatal tamoxifen on the hypothalamus and reproductive system in female mice

Tamoxifen, a selective oestrogen receptor modulator, is widely used for both the treatment and prevention of breast cancer in women; however, it is known to have adverse effects in the female reproductive system. Growing evidence suggests that oestrogen-sensitive neuron populations of the anteroventral periventricular (AVPV) nucleus and arcuate (ARC) nucleus, especially kisspeptin neurons, play a pivotal role in the timing of puberty onset and reproductive function. The aim of the present study was to evaluate whether neonatal exposure to tamoxifen affects oestrogenic actions in the brain and reproductive function in mice. On 1 to 5 postnatal days, female pups were injected subcutaneously with sesame oil (sham), oestradiol benzoate (EB; 20 µg kg-1), tamoxifen (0.4 mg kg-1) or EB+tamoxifen. Control mice received no treatment. Mice in the EB, tamoxifen and tamoxifen+EB groups exhibited advanced vaginal opening, disrupted oestrous cycles and a decreased follicular pool. Conversely, in these groups, there was a reduction in kisspeptin (Kiss1) mRNA expression, the neuronal density of AVPV and ARC nuclei and LH and oestradiol concentrations in the serum. The results of the present study confirm oestrogenic actions of tamoxifen in the brain and reproductive system. In addition, we show, for the first time, that tamoxifen has oestrogenic effects on the oestrogen-sensitive hypothalamic AVPV and ARC nuclei controlling the reproductive axis in female mice.

Expression of regulatory neuropeptides in the hypothalamus of red deer (Cervus elaphus) reveals anomalous relationships in the seasonal control of appetite and reproduction

Red deer are seasonal with respect to reproduction and food intake, so we tested the hypothesis that their brains would show seasonal changes in numbers of cells containing hypothalamic neuropeptides that regulate these functions. We examined the brains of male and female deer in non-breeding and breeding seasons to quantify the production of kisspeptin, gonadotropin inhibitory hormone (GnIH), neuropeptide Y (NPY) and γ-melanocyte stimulating hormone (γ-MSH - an index of pro-opiomelanocortin production), using immunohistochemistry. These neuropeptides are likely to be involved in the regulation of reproductive function and appetite. During the annual breeding season there were more cells producing kisspeptin in the arcuate nucleus of the hypothalamus than during the non-breeding season in males and females whereas there was no seasonal difference in the expression of GnIH. There were more cells producing the appetite stimulating peptide, NPY, in the arcuate/median eminence regions of the hypothalamus of females during the non-breeding season whereas the levels of an appetite suppressing peptide, γ-MSH, were highest in the breeding season. Male deer brains exhibited the converse, with NPY cell numbers highest in the breeding season and γ-MSH levels highest in the non-breeding season. These results support a role for kisspeptin as an important stimulatory regulator of seasonal breeding in deer, as in other species, but suggest a lack of involvement of GnIH in the seasonality of reproduction in deer. In the case of appetite regulation, the pattern exhibited by females for NPY and γ-MSH was as expected for the breeding and non-breeding seasons, based on previous studies of these peptides in sheep and the seasonal cycle of appetite reported for various species of deer. An inverse result in male deer most probably reflects the response of appetite regulating cells to negative energy balance during the mating season. Differences between the sexes in the seasonal changes in appetite regulating peptide cells of the hypothalamus present an interesting model for future studies.

Cardiometabolic and reproductive benefits of early dietary energy restriction and voluntary exercise in an obese PCOS-prone rodent model

Polycystic ovary syndrome (PCOS) is one of the most common endocrine-metabolic disorders in women of reproductive age characterized by ovulatory dysfunction, hyperandrogenism and cardiometabolic risk. The overweight-obese PCOS phenotype appears to have exacerbated reproductive dysfunction and cardiometabolic risk. In overweight-obese adult women with PCOS, exercise and energy restricted diets have shown limited and inconsistent effects on both cardiometabolic indices and reproductive outcomes. We hypothesized that an early lifestyle intervention involving exercise and dietary energy restriction to prevent or reduce the propensity for adiposity would modulate reproductive indices and cardiometabolic risk in an obese PCOS-prone rodent model. Weanling obese PCOS-prone and Lean-Control JCR:LA-cp rodents were given a chow diet ad libitum or an energy-restricted diet combined with or without voluntary exercise (4  h/day) for 8 weeks. Dietary energy restriction and exercise lowered total body weight gain and body fat mass by 30% compared to free-fed sedentary or exercising obese PCOS-prone animals (P<0.01). Energy restriction induced an increase in exercise intensity compared to free-feeding plus exercise conditions. Energy restriction and exercise decreased fasting plasma triglycerides and apoB48 concentrations in obese PCOS-prone animals compared to free-fed and exercise or sedentary groups. The energy restriction and exercise combination in obese PCOS-prone animals significantly increased plasma sex-hormone binding globulin, hypothalamic cocaine-and amphetamine-regulated transcript (CART) and Kisspeptin mRNA expression to levels of the Lean-Control group, and this was further associated with improvements in estrous cyclicity. The combination of exercise and dietary energy restriction when initiated in early life exerts beneficial effects on cardiometabolic and reproductive indices in an obese PCOS-prone rodent model, and this may be associated with normalization of the hypothalamic neuropeptides, Kisspeptin and CART.

A review of recent developments in buffalo reproduction - a review

The buffalo is an important livestock resource in several countries of South Asia and the Mediterranean regions. However, reproductive efficiency is compromised due to known problems of biological and management origins, such as lack of animal selection and poor nutrition. Under optimal conditions puberty is attained at 15 to 18 months in river buffalo, 21 to 24 months in swamp buffalo and is influenced by genotype, nutrition, management and climate. However, under field conditions these values deteriorate up to a significant extant. To improve reproductive efficiency, several protocols of oestrus and ovulation synchronization have been adopted from their use in commercial cattle production. These protocols yield encouraging pregnancy rates of (30% to 50%), which are comparable to those achieved in buffaloes bred at natural oestrus. The use of sexed semen in buffalo heifers also showed promising pregnancy rates (50%) when compared with conventional non-sexed semen. Assisted reproductive technologies have been transferred and adapted to buffalo but the efficiency of these technologies are low. However, these latest technologies offer the opportunity to accelerate the genetic gain in the buffalo industry after improving the technology and reducing its cost. Most buffaloes are kept under the small holder farming system in developing countries. Hence, future research should focus on simple, adoptable and impact- oriented approaches which identify the factors determining low fertility and oestrus behaviour in this species. Furthermore, role of kisspeptin needs to be explored in buffalo.

Effects of senktide, a neurokinin 3 receptor agonist, on luteinizing hormone secretion and follicular development in anestrous Shiba goats: a pilot study

Background

Recent studies suggest that neurokinin B and its receptor, neurokinin 3 receptor, have an essential role in the regulation of gonadotropin-releasing hormone and luteinizing hormone (LH) release in several mammalian species. As the first trial, this pilot study reports the effect of intravenous treatment with senktide, a selective agonist of neurokinin 3 receptor, on LH secretion, follicular development in female goats that were clinically diagnosed with anestrus.

Findings

Anestrous goats were intravenously administered 200 nmol senktide at 4-h intervals for 24 h. Most of them examined (5/6 cases) showed a pulsatile increase in LH secretion after each injection of senktide, whereas the remaining one case showed a surge-like increase of LH secretion. Ovulation was confirmed in 5/6 cases at the range of 48–96 h after the beginning of treatment.

Conclusions

This pilot study demonstrated that intravenous treatment with senktide has therapeutic action in goats with anestrus by inducing LH release, which could promote follicular development and ovulation.

Effects of intravenous administration of neurokinin receptor subtype-selective agonists on gonadotropin-releasing hormone pulse generator activity and luteinizing hormone secretion in goats

Recent evidence suggests that neurokinin B (NKB), a member of the neurokinin (tachykinin) peptide family, plays a pivotal role in gonadotropin-releasing hormone (GnRH) pulse generation. Three types of neurokinin receptors (NKRs), NK1R, NK2R and NK3R, are found in the brain. Although NKB preferentially binds to NK3R, other NKRs are possibly also involved in NKB action. The present study examined the effects of intravenous administration of the NKR subtype-selective agonists GR73632 (NK1R), GR64349 (NK2R), and senktide (NK3R) on GnRH pulse generator activity and luteinizing hormone (LH) secretion. Multiple-unit activity (MUA) was monitored in ovariectomized goats (n = 5) implanted with recording electrodes. Characteristic increases in MUA (MUA volleys) were considered GnRH pulse generator activity. Although three NKR agonists dose-dependently induced an MUA volley and an accompanying increase in LH secretion, the efficacy in inducing the volley markedly differed. As little as 10 nmol of senktide induced an MUA volley in all goats, whereas a dose of 1000 nmol was only effective for the NK1R and NK2R agonists in two and four goats, respectively. When the treatment failed to evoke an MUA volley, no apparent change was observed in the MUA or LH secretion. Similar effects of the NK2R and NK3R agonists were observed in the presence of estradiol. The results demonstrated that NK3R plays a predominant role in GnRH pulse generation and suggested that the contributions of NK1R and NK2R to this mechanism may be few, if any, in goats.

Neonatal exposure to 17α-ethinyl estradiol affects kisspeptin expression and LH-surge level in female rats

Contamination of estrogenic compounds disrupts endocrinological and neurological reproductive systems in animals. Neonatal exposure to 17α-ethinyl estradiol (EE) induced an abnormal estrous cycle at postnatal day (PND) 180, but not at PND90. We found that serum level of luteinizing hormone (LH) at the latter half of proestrus in EE-treated rats was lower than in the controls at PND90 when there was no significant difference on estrous cyclicity. Additionally, kiss1 mRNA levels in the anteroventral periventricular nucleus-preoptic area (AVPV/POA) were lower in EE-treated rats than in the controls. The expression of GnRH precursor (GNRH1) mRNA in the AVPV/POA and that of LH beta subunit (LHb) mRNA in the pituitary were similar in the control- and EE-treated groups. Our results indicated that neonatal exposure to EE leads to reduced expression of kiss1 mRNA in AVPV/POA and LH-surge, which is likely related to the delayed reproductive dysfunction seen in adult female rats.

Looking for the bird Kiss: evolutionary scenario in sauropsids

Background

The neuropeptide Kiss and its receptor KissR are key-actors in the brain control of reproduction in mammals, where they are responsible for the stimulation of the activity of GnRH neurones. Investigation in other vertebrates revealed up to 3 Kiss and 4 KissR paralogs, originating from the two rounds of whole genome duplication in early vertebrates. In contrast, the absence of Kiss and KissR has been suggested in birds, as no homologs of these genes could be found in current genomic databases. This study aims at addressing the question of the existence, from an evolutionary perspective, of the Kisspeptin system in birds. It provides the first large-scale investigation of the Kisspeptin system in the sauropsid lineage, including ophidian, chelonian, crocodilian, and avian lineages.

Results

Sauropsid Kiss and KissR genes were predicted from multiple genome and transcriptome databases by TBLASTN. Phylogenetic and syntenic analyses were performed to classify predicted sauropsid Kiss and KissR genes and to re-construct the evolutionary scenarios of both gene families across the sauropsid radiation.

Genome search, phylogenetic and synteny analyses, demonstrated the presence of two Kiss genes (Kiss1 and Kiss2 types) and of two KissR genes (KissR1 and KissR4 types) in the sauropsid lineage. These four genes, also present in the mammalian lineage, would have been inherited from their common amniote ancestor. In contrast, synteny analyses supported that the other Kiss and KissR paralogs are missing in sauropsids as in mammals, indicating their absence in the amniote lineage. Among sauropsids, in the avian lineage, we demonstrated the existence of a Kiss2-like gene in three bird genomes. The divergence of these avian Kiss2-like sequences from those of other vertebrates, as well as their absence in the genomes of some other birds, revealed the processes of Kiss2 gene degeneration and loss in the avian lineage.

Conclusion

These findings contribute to trace back the evolutionary history of the Kisspeptin system in amniotes and sauropsids, and provide the first molecular evidence of the existence and fate of a Kiss gene in birds.

The effects of chronic subcutaneous administration of an investigational kisspeptin analog, TAK-683, on gonadotropin-releasing hormone pulse generator activity in goats

The continuous activation of the kisspeptin receptor by its agonists causes the abrogation of kisspeptin signaling, leading to decreased pulsatile luteinizing hormone (LH) secretion. Employing this phenomenon as a tool for probing kisspeptin action, this study aimed to clarify the role of kisspeptin in gonadotropin-releasing hormone (GnRH) pulse generation in goats. We examined the effects of chronic administration of TAK-683, an investigational kisspeptin analog, on LH secretion, GnRH immunostaining, pituitary responses to exogenous GnRH, and GnRH pulse generator activity, reflected by a characteristic increase in multiple-unit activity (MUA volley). An osmotic pump containing TAK-683 was subcutaneously implanted on day 0. TAK-683 treatment dose-dependently suppressed pulsatile LH secretion on day 1. Higher doses of chronic TAK-683 profoundly suppressed pulsatile LH secretion but had little effect on GnRH immunostaining patterns and pituitary responses to GnRH on day 5. In ovariectomized goats, MUA volleys occurred at approximately every 30 min on day -1. On day 5 of chronic TAK-683 administration, pulsatile LH secretion was markedly suppressed, whereas MUA volleys were similar to those observed on day -1. Male pheromones and senktide (neurokinin B receptor agonist) induced an MUA volley but had no effect on LH secretion during chronic TAK-683 administration. The results indicate that the chronic administration of a kisspeptin analog profoundly suppresses pulsatile LH secretion without affecting GnRH content, pituitary function or GnRH pulse generator activity, and they suggest an indispensable role for kisspeptin signaling in the cascade driving GnRH/LH pulses by the GnRH pulse generator.