Evidence of a role for kisspeptin and neurokinin B in puberty of female sheep

Chronic inflammation decreases arcuate kisspeptin expression in male sheep

Lipopolysaccharide (LPS) from Gram-negative bacteria induces an immune response and impairs reproduction through suppression of gonadotropin releasing hormone (GnRH), subsequently luteinizing hormone (LH) secretion. While there is evidence that acute inflammation inhibits kisspeptin, little is known about the impact of chronic inflammation on this key reproductive neuropeptide in livestock species. Thus, we sought to examine a central mechanism whereby LPS suppresses LH secretion in sheep. Twenty wethers were randomly assigned to one of five treatment groups: control (CON; n=4), single acute IV LPS dose (SAD; n=4), daily acute IV LPS dose (DAD; n=4), daily increasing IV LPS dose (DID; n=4), and chronic subcutaneous LPS dose (CSD; n=4). On Days 1 and 7, blood samples were collected every 12 minutes for 360 minutes using jugular venipuncture. Following blood collection on Day 7, all animals were euthanized, brain tissue was perfused with 4% paraformaldehyde, and hypothalamic blocks were removed and processed for immunohistochemistry. On Day 1, LH pulse frequency was significantly lower (p=0.02) in SAD (0.25 ± 0.1 pulses/hour), DAD (0.25 ± 0.1 pulses/hour), DID (0.35 ± 0.1 pulses/hour), and CSD (0.40 ± 0.1 pulses/hour) compared to CON (0.70 ±0.1 pulses/hour). On Day 7, only DID animals (0.35 ± 0.1 pulses/hour) had significantly lower (p=0.049) LH pulse frequency compared to controls (0.85 ± 0.1 pulse/hour). Furthermore, only DID animals (33.3 ± 10.9 cells/section/animal) had significantly fewer (p=0.001) kisspeptin-immunopositive cells compared to controls (82.6 ± 13.6 cells/section/animal). Taken together, we suggest that daily increasing doses of LPS is a powerful inhibitor of kisspeptin neurons in young male sheep and a physiologically relevant model to examine the impact of chronic inflammation on the reproductive axis in livestock.

Estrogen promotes gonadotropin-releasing hormone expression by regulating tachykinin 3 and prodynorphin systems in chicken

The "KNDy neurons" located in the hypothalamic arcuate nucleus (ARC) of mammals are known to co-express kisspeptin, neurokinin B (NKB), and dynorphin (DYN), and have been identified as key mediators of the feedback regulation of steroid hormones on gonadotropin-releasing hormone (GnRH). However, in birds, the genes encoding kisspeptin and its receptor GPR54 are genomic lost, leaving unclear mechanisms for feedback regulation of GnRH by steroid hormones. Here, the genes tachykinin 3 (TAC3) and prodynorphin (PDYN) encoding chicken NKB and DYN neuropeptides were successfully cloned. Temporal expression profiling indicated that TAC3, PDYN and their receptor genes (TACR3, OPRK1) were mainly expressed in the hypothalamus, with significantly higher expression at 30W than at 15W. Furthermore, overexpression or interference of TAC3 and PDYN can regulate the GnRH mRNA expression. In addition, in vivo and in vitro assays showed that estrogen (E2) could promote the mRNA expression of TAC3, PDYN, and GnRH, as well as the secretion of GnRH/LH. Mechanistically, E2 could dimerize the nuclear estrogen receptor 1 (ESR1) to regulate the expression of TAC3 and PDYN, which promoted the mRNA and protein expression of GnRH gene as well as the secretion of GnRH. In conclusion, these results revealed that E2 could regulate the GnRH expression through TAC3 and PDYN systems, providing novel insights for reproductive regulation in chickens.

Clustering of multi-tissue transcriptomes in gilts with normal cyclicity or delayed puberty reveals genes related to pubertal development†

In gilts, puberty is marked by standing estrus in the presence of a boar. Delayed puberty (DP; failure to display pubertal estrus) is a major reason for gilt removal. To investigate the physiological determinants underlying DP in gilts, transcriptomic data from tissues relevant to estrus and puberty, such as mediobasal hypothalamus, anterior pituitary gland, ovarian cortex, olfactory bulb, amygdala, and hippocampus, were obtained from age-matched DP (n = 8) and cyclic control gilts at follicular phase (n = 8) and luteal phase (n = 8) of the estrous cycle. A gene expression module analysis via three-way gene × individual × tissue clustering using tensor decomposition identified pituitary and ovary gene modules contributing to regulation of pubertal development. Analysis of gene expression in the hypothalamic-pituitary-ovary axis identified reduced expression of hypothalamic genes critical for stimulating gonadotropin secretion (KISS1 and TAC3) and reduced expression of LHB in the anterior pituitary of DP gilts compared with their cyclic counterparts. Consequently, luteinizing hormone-induced genes in the ovary important for folliculogenesis (OXTR, RUNX2, and PTX3) were less expressed in DP gilts. Other intrafollicular genes (AHR, PTGS2, PTGFR, and IGFBP7) and genes in the steroidogenesis pathways (STAR and CYP11A1) necessary to complete the ovulatory cascade were also less expressed in DP gilts. This is the first clustering of multi-tissue expression data from DP and cyclic gilts to identify genes differentially expressed in gilts of similar ages but at different levels of sexual development. A critical lack of gonadotropin support and reduced ovarian responsiveness underlie DP in gilts.

The effect of NK3-Saporin injection within the arcuate nucleus on puberty, the LH surge, and the response to Senktide in female sheep†

The timing of puberty onset is reliant on increased gonadotropin-releasing hormone (GnRH). This elicits a corresponding increase in luteinizing hormone (LH) due to a lessening of sensitivity to the inhibitory actions of estradiol (E2). The mechanisms underlying the increase in GnRH release likely involve a subset of neurons within the arcuate (ARC) nucleus of the hypothalamus that contain kisspeptin, neurokinin B (NKB), and dynorphin (KNDy neurons). We aimed to determine if KNDy neurons in female sheep are critical for: timely puberty onset; the LH surge; and the response to an intravenous injection of the neurokinin-3 receptor (NK3R) agonist, senktide. Prepubertal ewes received injections aimed at the ARC containing blank-saporin (control, n = 5) or NK3-saporin (NK3-SAP, n = 6) to ablate neurons expressing NK3R. Blood samples taken 3/week for 65 days following surgery were assessed for progesterone to determine onset of puberty. Control ewes exhibited onset of puberty at 33.2 ± 3.9 days post sampling initiation, whereas 5/6 NK3-SAP treated ewes didn't display an increase in progesterone. After an artificial LH surge protocol, surge amplitude was lower in NK3-SAP ewes. Finally, ewes were treated with senktide to determine if an LH response was elicited. LH pulses were evident in both groups in the absence of injections, but the response to senktide vs saline was similar between groups. These results show that KNDy cells are necessary for timely puberty onset and for full expresson of the LH surge. The occurrence of LH pulses in NK3-SAP treated ewes may indicate a recovery from an apulsatile state.

Integrative proteomic and phosphoproteomic analysis in the female goat hypothalamus to study the onset of puberty

BACKGROUND

Puberty marks the end of childhood and achieve sexual maturation and fertility. The role of hypothalamic proteins in regulating puberty onset is unclear. We performed a comprehensive differential proteomics and phosphoproteomics analysis in prepubertal and pubertal goats to determine the roles of hypothalamic proteins and phosphoproteins during the onset of puberty.

RESULTS

We used peptide and posttranslational modifications peptide quantification and statistical analyses, and identified 69 differentially expressed proteins from 5,057 proteins and 576 differentially expressed phosphopeptides from 1574 phosphorylated proteins. Combined proteomic and phosphoproteomics, 759 correlated proteins were identified, of which 5 were differentially expressed only at the protein level, and 201 were only differentially expressed at the phosphoprotein level. Pathway enrichment analyses revealed that the majority of correlated proteins were associated with glycolysis/gluconeogenesis, Fc gamma R-mediated phagocytosis, focal adhesion, GABAergic synapse, and Rap1 signaling pathway. These pathways are related to cell proliferation, neurocyte migration, and promoting the release of gonadotropin-releasing hormone in the hypothalamus. CTNNB1 occupied important locations in the protein-protein interaction network and is involved in focal adhesion.

CONCLUSION

The results demonstrate that the proteins differentially expression only at the protein level or only differentially expressed at the phosphoprotein level and their related signalling pathways are crucial in regulating puberty in goats. These differentially expressed proteins and phosphorylated proteins may constitute the proteomic backgrounds between the two different stages.

Male-induced early puberty correlates with the maturation of arcuate nucleus kisspeptin neurons in does

In goats, early exposure of spring-born females to sexually active bucks induces an early puberty onset assessed by the first ovulation. This effect is found when females are continuously exposed well before the male breeding season starting in September. The first aim of this study was to evaluate whether a shortened exposure of females to males could also lead to early puberty. We assessed the onset of puberty in Alpine does isolated from bucks (ISOL), exposed to wethers (CAS), exposed to intact bucks from the end of June (INT1), or mid-August (INT2). Intact bucks became sexually active in mid-September. At the beginning of October, 100% of INT1 and 90% of INT2 exposed does ovulated, in contrast to the ISOL (0%) and CAS (20%) groups. This demonstrated that contact with males that become sexually active is the main factor prompting precocious puberty in females. Furthermore, a reduced male exposure during a short window before the breeding season is sufficient to induce this phenomenon. The second aim was to investigate the neuroendocrine changes induced by male exposure. We found a significant increase in kisspeptin immunoreactivity (fiber density and number of cell bodies) in the caudal part of the arcuate nucleus of INT1 and INT2 exposed females. Thus, our results suggest that sensory stimuli from sexually active bucks (e.g., chemosignals) may trigger an early maturation of the ARC kisspeptin neuronal network leading to gonadotropin-releasing hormone secretion and first ovulation.

Developmental sex differences in the peri-pubertal pattern of hypothalamic reproductive gene expression, including Kiss1 and Tac2, may contribute to sex differences in puberty onset

The mechanisms regulating puberty still remain elusive, as do the underlying causes for sex differences in puberty onset (girls before boys) and pubertal disorders. Neuroendocrine puberty onset is signified by increased pulsatile GnRH secretion, yet how and when various upstream reproductive neural circuits change developmentally to govern this process is poorly understood. We previously reported day-by-day peri-pubertal increases (Kiss1, Tac2) or decreases (Rfrp) in hypothalamic gene expression of female mice, with several brain mRNA changes preceding external pubertal markers. However, similar pubertal measures in males were not previously reported. Here, to identify possible neural sex differences underlying sex differences in puberty onset, we analyzed peri-pubertal males and directly compared them with female littermates. Kiss1 expression in male mice increased over the peri-pubertal period in both the AVPV and ARC nuclei but with lower levels than in females at several ages. Likewise, Tac2 expression in the male ARC increased between juvenile and older peri-pubertal stages but with levels lower than females at most ages. By contrast, both DMN Rfrp expressionand Rfrp neuronal activation strongly decreased in males between juvenile and peri-pubertal stages, but with similar levels as females. Neither ARC KNDy neuronal activation nor Kiss1r expression in GnRH neurons differed between males and females or changed with age. These findings delineate several peri-pubertal changes in neural populations in developing males, with notable sex differences in kisspeptin and NKB neuron developmental patterns. Whether these peri-pubertal hypothalamic sex differences underlie sex differences in puberty onset deserves future investigation.

Early juvenile but not mid to late prenatal nutrition controls puberty in heifers but neither impact adult reproductive function

Objectives were to test the hypothesis that pre and postnatal nutrition in the bovine female, independently or interactively, affect age at puberty and functional characteristics of the estrous cycle of sexually mature offspring. Brangus and Braford (n = 97) beef cows bearing a female fetus were fed to achieve body condition scores of 7.5-8 (H, obese), 5.5-6 (M, moderate) or 3-3.5 (L, thin) by the start of the third trimester and maintained until parturition. Heifer offspring were weaned and fed to gain weight at either a high (H; 1 kg/d) or low (L; 0.5 kg/d) rate between 4 and 8 months of age, then fed the same diet during a common feeding period until puberty which resulted in compensatory growth of heifers in the L group. Heifers (n = 95) from the H postnatal diet reached puberty two months earlier (12 ± 0.4 months; P = 0.0002) than those from the L postnatal diet (14 ± 0.4 months). Estrous cycles of a subgroup of postpubertal heifers (n = 53) were synchronized to evaluate antral follicle count (AFC), rate of growth and size of the pre-ovulatory follicle, size of corpus luteum and ovary, endometrial thickness, and plasma concentrations of progesterone and estradiol-17β (E2). Although there was a trend for postnatal H heifers to have greater AFC and plasma concentrations of E2 compared to L heifers, neither pre nor postnatal nutrition affected any other physiological or hormonal variables, including short-term fertility. Postnatal nutritional effects on pubertal age remained the dominant observed feature.

The impact of undernutrition on KNDy (kisspeptin/neurokinin B/dynorphin) neurons in female lambs

Undernutrition limits reproduction through inhibition of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) secretion. Because KNDy neurons coexpress neuropeptides that play stimulatory (kisspeptin and neurokinin B [NKB]) and inhibitory (dynorphin) roles in pulsatile GnRH/LH release, we hypothesized that undernutrition would inhibit kisspeptin and NKB expression at the same time as increasing dynorphin expression. Fifteen ovariectomized lambs were either fed to maintain pre-study body weight (controls) or feed-restricted to lose 20% of pre-study body weight (FR) over 13 weeks. Blood samples were collected and plasma from weeks 0 and 13 were assessed for LH by radioimmunoassay. At week 13, animals were killed, and brain tissue was processed for assessment of KNDy peptide mRNA or protein expression. Mean LH and LH pulse amplitude were lower in FR lambs compared to controls. We observed lower mRNA abundance for kisspeptin within KNDy neurons of FR lambs compared to controls with no significant change in mRNA for NKB or dynorphin. We also observed that FR lambs had fewer numbers of arcuate nucleus kisspeptin and NKB perikarya compared to controls. These findings support the idea that KNDy neurons are important for regulating reproduction during undernutrition in female sheep.

Sheep as a model for neuroendocrinology research

Animal models remain essential to understand the fundamental mechanisms of physiology and pathology. Particularly, the complex and dynamic nature of neuroendocrine cells of the hypothalamus make them difficult to study. The neuroendocrine systems of the hypothalamus are critical for survival and reproduction, and are highly conserved throughout vertebrate evolution. Their roles in controlling body metabolism, growth and body composition, stress, electrolyte balance, and reproduction, have been intensively studied, and have yielded groundbreaking discoveries. Many of these discoveries would not have been feasible without the use of the domestic sheep (Ovis aries). The sheep has been used for decades to study the neuroendocrine systems of the hypothalamus and has become a model for human neuroendocrinology. The aim of this chapter is to review some of the profound biomedical discoveries made possible by the use of sheep. The advantages and limitations of sheep as a neuroendocrine model will be discussed. While no animal model can perfectly recapitulate a human disease or condition, sheep are invaluable for enabling manipulations not possible in human subjects and isolating physiologic variables to garner insight into neuroendocrinology and associated pathologies.

Tachykinins, new players in the control of reproduction and food intake: A comparative review in mammals and teleosts

In vertebrates, the tachykinin system includes tachykinin genes, which encode one or two peptides each, and tachykinin receptors. The complexity of this system is reinforced by the massive conservation of gene duplicates after the whole-genome duplication events that occurred in vertebrates and furthermore in teleosts. Added to this, the expression of the tachykinin system is more widespread than first thought, being found beyond the brain and gut. The discovery of the co-expression of neurokinin B, encoded by the tachykinin 3 gene, and kisspeptin/dynorphin in neurons involved in the generation of GnRH pulse, in mammals, put a spotlight on the tachykinin system in vertebrate reproductive physiology. As food intake and reproduction are linked processes, and considering that hypothalamic hormones classically involved in the control of reproduction are reported to regulate also appetite and energy homeostasis, it is of interest to look at the potential involvement of tachykinins in these two major physiological functions. The purpose of this review is thus to provide first a general overview of the tachykinin system in mammals and teleosts, before giving a state of the art on the different levels of action of tachykinins in the control of reproduction and food intake. This work has been conducted with a comparative point of view, highlighting the major similarities and differences of tachykinin systems and actions between mammals and teleosts.

Evidence that pubertal status impacts KNDy neurons in the gilt

Puberty onset is a complex physiological process which enables the capacity for reproduction through increased gonadotropin-releasing hormone (GnRH), and subsequently luteinizing hormone (LH), secretion. While cells that coexpress kisspeptin, neurokinin B (NKB), and dynorphin in the hypothalamic arcuate nucleus (ARC) are believed to govern the timing of puberty, the degree to which KNDy neurons exist and are regulated by pubertal status remains to be determined in the gilt. Hypothalamic tissue from prepubertal and postpubertal, early follicular phase gilts was used to determine the expression of kisspeptin, NKB, and dynorphin within the ARC. Fluorescent in situ hybridization revealed that the majority (> 74%) of ARC neurons that express mRNA for kisspeptin coexpressed mRNA for NKB and dynorphin. There were fewer ARC cells that expressed mRNA for dynorphin in postpubertal gilts compared to prepubertal gilts (P < 0.05), but the number of ARC cells expressing mRNA for kisspeptin or NKB was not different between groups. Within KNDy neurons, mRNA abundance for kisspeptin, NKB, and dynorphin of postpubertal gilts was the same as, less than, and greater than, respectively, prepubertal gilts. Immunostaining for kisspeptin did not differ between prepubertal and postpubertal gilts, but there were fewer NKB immunoreactive fibers in postpubertal gilts compared to prepubertal gilts (P < 0.05). Together, these data reveal novel information about KNDy neurons in gilts and supports the idea that NKB and dynorphin play a role in puberty onset in the female pig.

Kisspeptin, Neurokinin B, and Dynorphin Expression during Pubertal Development in Female Sheep

The neural mechanisms underlying increases in gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion that drive puberty onset are unknown. Neurons coexpressing kisspeptin, neurokinin B (NKB), and dynorphin, i.e., KNDy neurons, are important as kisspeptin and NKB are stimulatory, and dynorphin inhibitory, to GnRH secretion. Given this, we hypothesized that kisspeptin and NKB expression would increase, but that dynorphin expression would decrease, with puberty. We collected blood and hypothalamic tissue from ovariectomized lambs implanted with estradiol at five, six, seven, eight (puberty), and ten months of age. Mean LH values and LH pulse frequency were the lowest at five to seven months, intermediate at eight months, and highest at ten months. Kisspeptin and NKB immunopositive cell numbers did not change with age. Numbers of cells expressing mRNA for kisspeptin, NKB, or dynorphin were similar at five, eight, and ten months of age. Age did not affect mRNA expression per cell for kisspeptin or NKB, but dynorphin mRNA expression per cell was elevated at ten months versus five months. Thus, neither KNDy protein nor mRNA expression changed in a predictable manner during pubertal development. These data raise the possibility that KNDy neurons, while critical, may await other inputs for the initiation of puberty.

How alcohol affects insulin-like growth factor-1's influences on the onset of puberty: A critical review

Alcohol (ALC) is capable of delaying signs associated with pubertal development in laboratory animals, as well as in humans. The normal onset of puberty results from a timely increase in gonadotropin‐releasing hormone (GnRH) secretion, which is associated with a gradual decline in prepubertal inhibitory influences, and the establishment of excitatory inputs that increase GnRH release, which together drive pubertal development. In recent years, insulin‐like growth factor‐1 (IGF‐1) has emerged as a pivotal contributor to prepubertal GnRH secretion and pubertal development, whose critical actions are interfered with by ALC abuse. Here we review the neuroendocrine research demonstrating the important role that IGF‐1 plays in pubertal development, and describe the detrimental effects and mechanisms of action of ALC on the onset and progression of pubertal maturation.

Localization of kisspeptin, NKB, and NK3R in the hypothalamus of gilts treated with the progestin altrenogest

Mechanisms in the brain controlling secretion of gonadotropin hormones in pigs, particularly luteinizing hormone (LH), are poorly understood. Kisspeptin is a potent LH stimulant that is essential for fertility in many species, including pigs. Neurokinin B (NKB) acting through neurokinin 3 receptor (NK3R) is involved in kisspeptin-stimulated LH release, but organization of NKB and NK3R within the porcine hypothalamus is unknown. Hypothalamic tissue from ovariectomized (OVX) gilts was used to determine the distribution of immunoreactive kisspeptin, NKB, and NK3R cells in the arcuate nucleus (ARC). Almost all kisspeptin neurons coexpressed NKB in the porcine ARC. Immunostaining for NK3R was distributed throughout the preoptic area (POA) and in several hypothalamic areas including the periventricular and retrochiasmatic areas but was not detected within the ARC. There was no colocalization of NK3R with gonadotropin-releasing hormone (GnRH), but NK3R-positive fibers in the POA were in close apposition to GnRH neurons. Treating OVX gilts with the progestin altrenogest decreased LH pulse frequency and reduced mean circulating concentrations of LH compared with OVX control gilts (P < 0.01), but the number of kisspeptin and NKB cells in the ARC did not differ between treatments. The neuroanatomical arrangement of kisspeptin, NKB, and NK3R within the porcine hypothalamus confirm they are positioned to stimulate GnRH and LH secretion in gilts, though differences with other species exist. Altrenogest suppression of LH secretion in the OVX gilt does not appear to involve decreased peptide expression of kisspeptin or NKB.

Expression of genes for Kisspeptin (KISS1), Neurokinin B (TAC3), Prodynorphin (PDYN), and gonadotropin inhibitory hormone (RFRP) across natural puberty in ewes

Expression of particular genes in hypothami of ewes was measured across the natural pubertal transition by in situ hybridization. The ewes were allocated to three groups (n = 4); prepubertal, postpubertal and postpubertally gonadectomized (GDX). Prepubertal sheep were euthanized at 20 weeks of age and postpubertal animals at 32 weeks. GDX sheep were also euthanized at 32 weeks, 1 week after surgery. Expression of KISS1, TAC3, PDYN in the arcuate nucleus (ARC), RFRP in the dorsomedial hypothalamus and GNRH1 in the preoptic area was quantified on a cellular basis. KISS1R expression by GNRH1 cells was quantified by double-label in situ hybridization. Across puberty, detectable KISS1 cell number increased in the caudal ARC and whilst PDYN cell numbers were low, numbers increased in the rostral ARC. TAC3 expression did not change but RFRP expression/cell was reduced across puberty. There was no change across puberty in the number of GNRH1 cells that expressed the kisspeptin receptor (KISS1R). GDX shortly after puberty did not increase expression of any of the genes of interest. We conclude that KISS1 expression in the ARC increases during puberty in ewes and this may be a causative factor in the pubertal activation of the reproductive axis. A reduction in expression of RFRP may be a factor in the onset of puberty, removing negative tone on GNRH1 cells. The lack of changes in expression of genes following GDX suggest that the effects of gonadal hormones may differ in young and mature animals.

IGF-1 Influences Gonadotropin-Releasing Hormone Regulation of Puberty

The pubertal process is initiated as a result of complex neuroendocrine interactions within the preoptic and hypothalamic regions of the brain. These interactions ultimately result in a timely increase in the secretion of gonadotropin-releasing hormone (GnRH). Researchers for years have believed that this increase is due to a diminished inhibitory tone which has applied a prepubertal brake on GnRH secretion, as well as to the gradual development of excitatory inputs driving the increased release of the peptide. Over the years, insulin-like growth factor-1 (IGF-1) has emerged as a prime candidate for playing an important role in the onset of puberty. This review will first present initial research demonstrating that IGF-1 increases in circulation as puberty approaches, is able to induce the release of prepubertal GnRH, and can advance the timing of puberty. More recent findings depict an early action of IGF-1 to activate a pathway that releases the inhibitory brake on prepubertal GnRH secretion provided by dynorphin, as well as demonstrating that IGF-1 can also act later in the process to regulate the synthesis and release of kisspeptin, a potent stimulator of GnRH at puberty.

Mating-induced increase in Kiss1 mRNA expression in the anteroventral periventricular nucleus prior to an increase in LH and testosterone release in male rats

Kisspeptin has an indispensable role in gonadotropin-releasing hormone/gonadotropin secretion in mammals. In rodents, kisspeptin neurons are located in distinct brain regions, namely the anteroventral periventricular nucleus-periventricular nucleus continuum (AVPV/PeN), arcuate nucleus (ARC), and medial amygdala (MeA). Among them, the physiological role of AVPV/PeN kisspeptin neurons in males has not been clarified yet. The present study aims to investigate the acute effects of the olfactory and/or mating stimulus with a female rat on hypothalamic and MeA Kiss1 mRNA expression, plasma luteinizing hormone (LH) and testosterone levels in male rats. Intact male rats were exposed to the following stimuli: exposure to clean bedding; exposure to female-soiled bedding as a female-olfactory stimulus; exposure to female-soiled bedding and mating stimulus with a female rat. The mating stimulus significantly increased the number of the AVPV/PeN Kiss1 mRNA-expressing cells in males within 5 minutes after the exposure, and significantly increased LH and testosterone levels, followed by an increase in male sexual behavior. Whereas, the males exposed to female-soiled bedding showed a moderate increase in LH levels and no significant change in testosterone levels and the number of the AVPV/PeN Kiss1 mRNA-expressing cells. Importantly, none of the stimuli affected the number of Kiss1 mRNA-expressing cells in the ARC and MeA. These results suggest that the mating-induced increase in AVPV/PeN Kiss1 mRNA expression may be, at least partly, involved in stimulating LH and testosterone release, and might consequently ensure male mating behavior. This study would be the first report suggesting that the AVPV/PeN kisspeptin neurons in males may play a physiological role in ensuring male reproductive performance.

Methylprednisolone acetate mitigates IL1β induced changes in matrix metalloproteinase gene expression in skeletally immature ovine explant knee tissues

OBJECTIVE AND DESIGN

This study aimed at evaluating the effect of methylprednisolone (MPA) on messenger ribonucleic acid (mRNA) expression levels in immature ovine knee joint tissue explants following interleukin (IL)1β induction and to assess responsiveness of the explants.

MATERIAL OR SUBJECTS

Explants were harvested from the articular cartilage, synovium, and infrapatellar fat pad (IPFP) from immature female sheep.

TREATMENT

Methylprednisolone.

METHODS

The samples were allocated into six groups: (1) control, (2) MPA (10^-3 M), (3) MPA (10^-4 M), (4) IL1β, (5) IL1β + 10^-3 M MPA, or (6) IL1β + 10^-4 M MPA. mRNA expression levels for molecules relevant to inflammation, cartilage degradation/anabolism, activation of innate immunity, and adipose tissue/hormones were quantified. Fold changes with MPA treatment were compared via the comparative C_T method.

RESULTS

Methylprednisolone treatment significantly suppressed MMPs consistently across the cartilage (MMP1, MMP3, and MMP13), synovium (MMP1 and MMP3), and IPFP (MMP13) (all p < 0.05). Other genes that were less consistently suppressed include endogenous IL1β (cartilage) and IL6 (IPFP) (all p < 0.05), and others not affected either by IL-1 exposure or subsequent MPA include TGFβ1, TLR4, and adipose-related molecules.

CONCLUSIONS

Methylprednisolone significantly mitigated IL1β induced mRNA expression for MMPs in the immature cartilage, synovium, and IPFP, but the extent of the responsiveness was tissue-, location-, and gene-specific.

Physiological and genomic insight into neuroendocrine regulation of puberty in gilts

The timing of pubertal attainment in gilts is a critical factor for pork production and is an early indicator of future reproductive potential. Puberty, defined as age at first standing estrus in the presence of a boar, is brought about by an escape from estrogen inhibition of the GnRH pulse generator, which allows for increasing LH pulses leading to the onset of cyclicity. The biological mechanisms that control the timing of these events is related to decreasing inhibitory signals with a concomitant increase in stimulatory signals within the hypothalamus. The roles of gamma-aminobutyric acid, endogenous opioid peptides, and gonadotropin-inhibitory hormone in negatively regulating gonadotropin secretion in gilts is explored. Developmental changes in stimulatory mechanisms of glutamatergic and kisspeptin neurons are important for increased LH pulsatility required for the occurrence of puberty in pigs. Age at first estrus of gilts is metabolically gated, and numerous metabolites, metabolic hormones, and appetite-regulating neurotransmitters have been implicated in the nutritional regulation of gonadotropin secretion. Leptin is an important metabolic signal linking body energy reserves with age at puberty in gilts. Leptin acting through neuropeptide Y and proopiomelanocortin neurons in the hypothalamus has important impacts on the function of the reproductive neurosecretory axis of gilts. Age at puberty in swine is heritable, and genomic analyses reveal it to be a polygenic trait. Genome-wide association studies for pubertal age in gilts have revealed several genomic regions in common with those identified for age at menarche in humans. Candidate genes have been identified that have important functions in growth and adiposity. Numerous genes regulating hypothalamic neuronal function, gonadotropes in the adenohypophysis, and ovarian follicular development have been identified and illustrate the complex maturational changes occurring in the hypothalamic-pituitary-ovarian axis during puberty in gilts.

Neuronal networks that regulate gonadotropin-releasing hormone/luteinizing hormone secretion during undernutrition: evidence from sheep

Gonadotropin-releasing hormone (GnRH) neurons are the final common conduit from the central nervous system in the reproductive axis, controlling luteinizing hormone (LH) secretion from the gonadotropes of the anterior pituitary. Although it is generally accepted that undernutrition inhibits GnRH/LH secretion, the central mechanisms that underlie the link between energy balance and reproduction remain to be fully elucidated. Sheep have been a longstanding and invaluable animal model for examination of the nutritional regulation of GnRH/LH secretion, given their ability to serve a biomedical and agricultural purpose. In this review, we summarize work that has used the ovine model to examine the central mechanisms whereby undernutrition regulates GnRH/LH secretion. Specifically, we focus our attention to the arcuate nucleus of the hypothalamus and on neurons that express kisspeptin, neurokinin B, dynorphin, proopiomelanocortin, and neuropeptide y/agouti-related peptide (NPY/AgRP). We examine their roles in mediating the effects of leptin and insulin and their effects on LH during undernutrition, as well as their regulation under conditions of undernutrition. This review will also highlight the interactions between the aforementioned neuronal networks themselves, which may be important for our understanding of the roles each play in relaying information regarding energy status during times of undernutrition to ultimately regulate GnRH/LH secretion.

Role of neurokinin B in ovine puberty

Puberty is the process whereby an individual acquires the ability to reproduce, and the attainment of puberty in a timely manner is critical for both humans and livestock. For livestock, the initiation of puberty at the appropriate time aids in increasing lifetime productivity, thus maximizing profitability for producers. For humans, particularly females, early or late puberty is associated with several adverse health outcomes, including polycystic ovary syndrome, obesity, metabolic syndrome, osteoporosis, and psychosocial distress. Therefore, characterizing the mechanisms responsible for puberty onset would have a significant impact on human and animal health. It has been postulated that a group of neurons in the arcuate nucleus of the hypothalamus may play a role in puberty onset. These neurons contain kisspeptin, neurokinin B (NKB), and dynorphin and are often called KNDy neurons. Although the role of kisspeptin in puberty onset has been heavily researched, the involvement of NKB and dynorphin is not well defined. This mini-review focuses on the role of NKB in the initiation of puberty in female sheep. Stimulation of the receptor for NKB, NK3R, elicits LH secretion in a GnRH-dependent manner in prepubertal ewes, and both functional and neuroanatomical changes to the NKB system, particularly within the preoptic area, appear to occur as female sheep transition from a prepubertal to an adult state. Thus, NKB is likely an important component of puberty onset in sheep, although its integration with other systems that impact the pubertal process, such as photoperiod and nutrition, remains to be elucidated.

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.

Tachykinin signaling in the control of puberty onset

The tachykinin family of peptides has emerged as a critical component of the central control of the reproductive axis. Mounting evidence suggests that neurokinin B (NKB) plays an essential role in sexual maturation and fertility by directly stimulating the release of kisspeptin, with the contribution of additional tachykinins (neurokinin A [NKA] and substance P [SP]) in the fine tuning of the activity of Kiss1 neurons. The expression of tachykinins increases in the hypothalamus before puberty and, therefore, they are considered as initiators of pubertal development by stimulating the awakening of Kiss1 neurons. This is supported by studies showing delayed or absent puberty onset in humans and mice devoid of tachykinin signaling, and the advancement of puberty onset in rodents subjected to chronic activation of tachykinin receptors. This review compiles the current knowledge on the role of tachykinins in the control of puberty onset.

Morphological and functional evidence for sexual dimorphism in neurokinin B signalling in the retrochiasmatic area of sheep

Neurokinin B (NKB) is critical for fertility in humans and stimulates gonadotrophin-releasing hormone/luteinising hormone (LH) secretion in several species, including sheep. There is increasing evidence that the actions of NKB in the retrochiasmatic area (RCh) contribute to the induction of the preovulatory LH surge in sheep. In the present study, we determined whether there are sex differences in the response to RCh administration of senktide, an agonist to the NKB receptor (neurokinin receptor-3 [NK3R]), and in NKB and NK3R expression in the RCh of sheep. To normalise endogenous hormone concentrations, animals were gonadectomised and given implants to mimic the pattern of ovarian steroids seen in the oestrous cycle. In females, senktide microimplants in the RCh produced an increase in LH concentrations that lasted for at least 8 hours after the start of treatment, whereas a much shorter increment (approximately 2 hours) was seen in males. We next collected tissue from gonadectomised lambs 18 hours after the insertion of oestradiol implants that produce an LH surge in female, but not male, sheep for immunohistochemical analysis of NKB and NK3R expression. As expected, there were more NKB-containing neurones in the arcuate nucleus of females than males. Interestingly, there was a similar sexual dimorphism in NK3R-containing neurones in the RCh, NKB-containing close contacts onto these RCh NK3R neurones, and overall NKB-positive fibres in this region. These data demonstrate that there are both functional and morphological sex differences in NKB-NK3R signalling in the RCh and raise the possibility that this dimorphism contributes to the sex-dependent ability of oestradiol to induce an LH surge in female sheep.

Undernutrition reduces kisspeptin and neurokinin B expression in castrated male sheep

Undernutrition impairs reproductive success through suppression of gonadotropin-releasing hormone (GnRH), and subsequently luteinizing hormone (LH), secretion. Given that kisspeptin and neurokinin B (NKB) neurons in the arcuate nucleus (ARC) of the hypothalamus are thought to play key stimulatory roles in the generation of GnRH/LH pulses, we hypothesized that feed restriction would reduce the ARC mRNA abundance and protein expression of kisspeptin and NKB in young, male sheep. Fourteen wethers (castrated male sheep five months of age) were either fed to maintain (FM; n = 6) pre-study body weight or feed-restricted (FR; n = 8) to lose 20% of pre-study body weight over 13 weeks. Throughout the study, weekly blood samples were collected and assessed for LH concentration using RIA. At Week 13 of the experiment, animals were killed, heads were perfused with 4% paraformaldehyde, and brain tissue containing the hypothalamus was collected, sectioned, and processed for detection of mRNA (RNAscope) and protein (immunohistochemistry) for kisspeptin and NKB. Mean LH was significantly lower and LH inter-pulse interval was significantly higher in FR wethers compared to FM wethers at the end of the experiment (Week 13). RNAscope analysis revealed significantly fewer cells expressing mRNA for kisspeptin and NKB in FR wethers compared to FM controls, and immunohistochemical analysis revealed significantly fewer immunopositive kisspeptin and NKB cells in FR wethers compared to FM wethers. Taken together, this data supports the idea that long-term feed restriction regulates GnRH/LH secretion through central suppression of kisspeptin and NKB in male sheep.

LAY SUMMARY

While undernutrition is known to impair reproduction at the level of the brain, the components responsible for this in the brain remain to be fully understood. Using male sheep we examined the effect of undernutrition on two stimulatory molecules in the brain critical for reproduction: kisspeptin and neurokinin B. Feed restriction for several weeks resulted in decreased luteinizing hormone in the blood indicating reproductive function was suppressed. In addition, undernutrition also reduced both kisspeptin and neurokinin B levels within a region of the brain involved in reproduction, the hypothalamus. Given that they have stimulatory roles in reproduction, we believe that undernutrition acts in the brain to reduce kisspeptin and neurokinin B levels leading to the reduction in luteinizing hormone secretion. In summary, long-term undernutrition inhibits reproductive function in sheep through suppression of kisspeptin and neurokinin B within the brain.

Peripheral administration of SB223412, a selective neurokinin-3 receptor antagonist, suppresses pulsatile luteinizing hormone secretion by acting on the gonadotropin-releasing hormone pulse generator in estrogen-treated ovariectomized female goats

Accumulating evidence suggests that KNDy neurons located in the hypothalamic arcuate nucleus (ARC), which are reported to express kisspeptin, neurokinin B, and dynorphin A, are indispensable for the gonadotropin-releasing hormone (GnRH) pulse generation that results in rhythmic GnRH secretion. The aims of the present study were to investigate the effects of peripheral administration of the neurokinin 3 receptor (NK3R/TACR3, a receptor for neurokinin B) antagonist, SB223412, on GnRH pulse-generating activity and pulsatile luteinizing hormone (LH) secretion in ovariectomized Shiba goats treated with luteal phase levels of estrogen. The NK3R antagonist was infused intravenously for 4 h {0.16 or 1.6 mg/(kg body weight [BW]·4 h)} during which multiple unit activity (MUA) in the ARC was recorded, an electrophysiological technique commonly employed to monitor GnRH pulse generator activity. In a separate experiment, the NK3R antagonist (40 or 200 mg/[kg BW·day]) was administered orally for 7 days to determine whether the NK3R antagonist could modulate pulsatile LH secretion when administered via the oral route. Intravenous infusion of the NK3R antagonist significantly increased the interval of episodic bursts of MUA compared with that of the controls. Oral administration of the antagonist for 7 days also significantly prolonged the interpulse interval of LH pulses. The results of this study demonstrate that peripheral administration of an NK3R antagonist suppresses pulsatile LH secretion by acting on the GnRH pulse generator, suggesting that NK3R antagonist administration could be used to modulate reproductive functions in ruminants.

Role for Kisspeptin and Neurokinin B in Regulation of Luteinizing Hormone and Testosterone Secretion in the Fetal Sheep

Evidence suggests that the hypothalamic-pituitary-gonadal (HPG) axis is active during the critical period for sexual differentiation of the ovine sexually dimorphic nucleus, which occurs between gestational day (GD) 60 and 90. Two possible neuropeptides that could activate the fetal HPG axis are kisspeptin and neurokinin B (NKB). We used GD85 fetal lambs to determine whether intravenous administration of kisspeptin-10 (KP-10) or senktide (NKB agonist) could elicit luteinizing hormone (LH) release. Immunohistochemistry and fluorescent in situ hybridization (FISH) were employed to localize these peptides in brains of GD60 and GD85 lamb fetuses. In anesthetized fetuses, KP-10 elicited robust release of LH that was accompanied by a delayed rise in serum testosterone in males. Pretreatment with the GnRH receptor antagonist (acyline) abolished the LH response to KP-10, confirming a hypothalamic site of action. In unanesthetized fetuses, senktide, as well as KP-10, elicited LH release. The senktide response of females was greater than that of males, indicating a difference in NKB sensitivity between sexes. Gonadotropin-releasing hormone also induced a greater LH discharge in females than in males, indicating that testosterone negative feedback is mediated through pituitary gonadotrophs. Kisspeptin and NKB immunoreactive cells in the arcuate nucleus were more abundant in females than in males. Greater than 85% of arcuate kisspeptin cells costained for NKB. FISH revealed that the majority of these were kisspeptin/NKB/dynorphin (KNDy) neurons. These results support the hypothesis that kisspeptin-GnRH signaling regulates the reproductive axis of the ovine fetus during the prenatal critical period acting to maintain a stable androgen milieu necessary for brain masculinization.

Molecular Characterization and Expression Profiles of the Ovine LHβ Gene and Its Association with Litter Size in Chinese Indigenous Small-Tailed Han Sheep

Simple Summary

Litter size is one of the most important reproductive traits in sheep, and the luteinizing hormone beta polypeptide (LHβ) plays an important role in mammalian follicular development. In this study, we cloned and analyzed the cDNA sequence of the ovine LHβ gene, and the expression patterns of LHβ were determined. Furthermore, the synonymous mutation g.727C > T detected in the LHβ gene was confirmed to be significantly associated with litter size (p < 0.01). These findings support LHβ g.727C > T as a genetic marker for litter size in sheep.

Abstract

The luteinizing hormone beta polypeptide (LHβ) is a glycoprotein hormone secreted by basophilic granular cells of the adenohypophysis, and plays an important role in mammalian follicular development. In this study, we cloned and analyzed the cDNA sequence of the ovine LHβ gene. RT-qPCR analysis showed that ovine LHβ was widely expressed in tissues, with significantly higher expression in the hypophysis than that in other tissues (heart, liver, spleen, lung, kidney, rumen, duodenum, muscle, fat, hypothalamus, and sex glands) (p < 0.01). Hypophyseal expression of LHβ mRNA in lamb increased with age and reached a peak at 70 days, although a slight decrease was observed at 84 days of age. In addition, the synonymous mutation g.727C > T detected in the LHβ gene was confirmed to be significantly associated with the litter size (p < 0.01). Ewes carrying the TT genotype produced more lambs than those carrying the TC and CC genotypes (0.42 and 0.39 per delivery, respectively; p < 0.05). Our results confirm the association of ovine LHβ with litter size in Small-Tailed Han Sheep and implicate LHβ as a candidate for improving reproductive traits in agricultural sheep breeding programs.

Evidence that Nitric Oxide Is Critical for LH Surge Generation in Female Sheep

Elevated and sustained estradiol concentrations cause a gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) surge that is necessary for ovulation. In sheep, several different neural systems have been implicated in this stimulatory action of estradiol and this study focused on somatostatin (SST) neurons in the ventral lateral region of the ventral medial nucleus (vlVMN) which express c-Fos during the surge. First, we determined if increased activity of SST neurons could be related to elevated GnRH secretion by assessing SST synapses onto GnRH neurons and neurons coexpressing kisspeptin, neurokinin B, dynorphin (KNDy). We found that the percentage of preoptic area GnRH neurons that receive SST input increased during the surge compared with other phases of the cycle. However, since SST is generally inhibitory, and pharmacological manipulation of SST signaling did not alter the LH surge in sheep, we hypothesized that nitric oxide (NO) was also produced by these neurons to account for their activation during the surge. In support of this hypothesis we found that (1) the majority of SST cells in the vlVMN (>80%) contained neuronal nitric oxide synthase (nNOS); (2) the expression of c-Fos in dual-labeled SST-nNOS cells, but not in single-labeled cells, increased during the surge compared with other phases of the cycle; and (3) intracerebroventricular (ICV) infusion of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester, completely blocked the estrogen-induced LH surge. These data support the hypothesis that the population of SST-nNOS cells in the vlVMN are a source of NO that is critical for the LH surge, and we propose that they are an important site of estradiol positive feedback in sheep.

The Correlation between Hormonal Disturbance in PCOS Women and Serum Level of Kisspeptin

BACKGROUND

Kisspeptin is a neuropeptide that upregulates gonadotropin-releasing hormone (GnRH) secretion. It is an essential element for the luteinizing hormone (LH) surge and ovulation. Women with polycystic ovary syndrome (PCOS) expose alteration in both GnRH and LH secretion levels.

OBJECTIVE

This paper aims to evaluate serum kisspeptin levels in healthy and polycystic ovarian syndrome women. Furthermore, it investigates the effect of obesity and age on circulating kisspeptin levels in both normal and PCOS women. Moreover, it points out the correlation between kisspeptin and other hormonal parameters. Methods and Patients. One hundred women (60 are with PCOS and 40 are normal) were enrolled in the study. Five milliliter samples of blood from all the patients and control women were obtained twice during the menstrual cycle. All the study samples were classified depending on the age factor for several subgroups.

RESULTS

Kisspeptin levels were higher in PCOS patients than those in the normal group. Kisspeptin correlated with serum free testosterone level (r=0.26). In healthy women, preovulatory kisspeptin levels were higher than follicular kisspeptin levels (P < 0.05), while this difference was insignificant in PCOS patients. The variation in serum kisspeptin levels between overweight/obese and normal-weight women was insignificant. In normal women, serum kisspeptin levels were higher in women >35 years than those <24 years at (P=0.03).

CONCLUSION

The serum kisspeptin level is higher in PCOS women. Its levels fluctuate during the menstrual cycle, but these fluctuations are disturbed in PCOS women. The effect of BMI on serum kisspeptin levels is insignificant, and kisspeptin serum levels increase with age.

Regulation of prepubertal dynorphin secretion in the medial basal hypothalamus of the female rat

The onset of puberty is the result of an increase in secretion of hypothalamic gonadotrophin-releasing hormone (GnRH). This action is a result of not only the development of stimulatory inputs to its release, but also the gradual decrease in inhibitory inputs that restrain release of the peptide prior to pubertal onset. Dynorphin (DYN) is one of the inhibitory inputs produced in the medial basal hypothalamus (MBH); however, little is known about what substance(s) control its prepubertal synthesis and release. Because neurokinin B (NKB) increases in the hypothalamus as puberty approaches, we considered it a candidate for such a role. An initial study investigated the acute effects of an NKB agonist, senktide, on the secretion of DYN from MBH tissues incubated in vitro. In other experiments, central injections of senktide were administered to animals for 4 days then MBHs were collected for assessment of DYN synthesis or for the in vitro secretion of both DYN and GnRH. Because insulin-like growth factor (IGF)-1 has been shown to play an important role at puberty, additional animals received central injections of this peptide for 4 days to assess NKB and DYN synthesis or the in vitro secretion of NKB. The results obtained show that senktide administration up-regulates the NKB receptor protein, at the same time as suppressing the DYN and its receptor. Senktide consistently suppressed DYN and elevated GnRH secretion in the same tissue incubates from both the acute and chronic studies. IGF-1 administration caused an increase in NKB protein, at the same time as decreasing DYN protein. Furthermore, the central administration of IGF-1 caused an increase in NKB release, an action blocked by the IGF-1 receptor blocker, JB-1. These results indicate that the IGF-1/NKB pathway contributes to suppressing the DYN inhibitory tone on prepubertal GnRH secretion and thus facilitates the puberty-related increase in the release of GnRH to accelerate the onset of puberty.

Expression of kisspeptin protein in hypothalamus and LH profile of growing female lambs

Kisspeptin (kp) is considered to be one of the major regulators of the induction of pubertal events via the activation of the gonadotrophin-releasing hormone-LH system. The aim of the present study was to analyse expression of immunoreactive (ir) kp in the hypothalamic neurons of female lambs from the neonatal to the peripubertal period (5 days to 32 weeks) in relation to the plasma LH pattern using immunohistochemistry and image analysis. Hypothalami were collected from female lambs (n=33) from the infantile, juvenile, prepubertal and peripubertal periods. The population of kp-ir perikarya was detected mainly in the arcuate nucleus and their number increased gradually from 5 to 16 weeks of age and was maintained at a high level up to the peripubertal stage. This was reflected by the significant (P<0.05) gradual increase in the percentage of hypothalamic area occupied by kp-ir neurons and increase in the number of kp-ir perikarya within the arcuate nucleus. The same pattern of kp immunoreactivity was observed in the median eminence. Plasma LH concentration increased from Week 5 to Weeks 12-16 and further increased at Week 32. LH pulse frequency increased from Week 5 to 32 (P<0.05). Thus, changes in kp expression reflected changes in the LH pattern during lamb growth. The data obtained provide evidence about the participation of kp in the mechanisms of ontogenic development of ovine reproductive processes.

Preclinical Models of Altered Early Life Nutrition and Development of Reproductive Disorders in Female Offspring

Early epidemiology studies in humans have and continue to offer valuable insight into the Developmental Origins of Health and Disease (DOHaD) hypothesis, which emphasises the importance of early-life nutritional and environmental changes on the increased risk of metabolic and reproductive disease in later life. Human studies are limited and constrained by a range of factors which do not apply to preclinical research. Animal models therefore offer a unique opportunity to fully investigate the mechanisms associated with developmental programming, helping to elucidate the developmental processes which influence reproductive diseases, and highlight potential biomarkers which can be translated back to the human condition. This review covers the use and limitations of a number of animal models frequently utilised in developmental programming investigations, with an emphasis on dietary manipulations which can lead to reproductive dysfunction in offspring.

Central Mechanism Controlling Pubertal Onset in Mammals: A Triggering Role of Kisspeptin

Pubertal onset is thought to be timed by an increase in pulsatile gonadotropin-releasing hormone (GnRH)/gonadotropin secretion in mammals. The underlying mechanism of pubertal onset in mammals is still an open question. Evidence accumulated in the last 15 years suggests that kisspeptin/neurokinin B/dynorphin A (KNDy) neurons in the hypothalamic arcuate nucleus play a key role in pubertal onset by triggering pulsatile GnRH/gonadotropin secretin in mammals. Specifically, KNDy neurons are now considered a part of GnRH pulse generator, in which neurokinin B facilitates and dynorphin A inhibits, the synchronized discharge of KNDy neurons in autocrine and/or paracrine manners. Kisspeptin serves as a potent secretagogue of GnRH secretion and thus its release is fundamental to pubertal increase in GnRH/gonadotropin secretion in mammals. Proposed mechanisms inhibiting Kiss1 (kisspeptin gene) expression during childhood to juvenile varies from species to species: we envisage that negative feedback action of estrogen plays a key role in the inhibition of Kiss1 expression in KNDy neurons in rodents and sheep, whereas estrogen-independent inhibition of kisspeptin secretion by γ-amino butyric acid or neuropeptide Y are suggested to be responsible for the pre-pubertal suppression of GnRH/gonadotropin secretion in primates. Taken together, the timing of pubertal onset is postulated to be controlled by upstream regulators for kisspeptin biosynthesis and secretion in mammals.

Sexually active bucks are a critical social cue that activates the gonadotrope axis and early puberty onset in does

In rodents, early exposure to adult male is well known to induce an early puberty in females (Vandenbergh effect). This phenomenon has been less studied in other mammals. In goats, despite our extensive knowledge about the "male-effect" phenomenon in adults (i.e. ovulation induced by the introduction of the male during the anestrous), there are few data on the consequences of an early exposure of females to males. Here, we evaluated the puberty onset of young alpine goats when raised since weaning with intact bucks (INT), with castrated bucks (CAS) or isolated from bucks (ISOL). The INT group had the first ovulation 1.5 month before the two other groups. Despite the earlier puberty the INT group of females had normal and regular ovarian cycles. Morphological study of the genital tract showed that at 6 months, uterus of INT goats was 40% heavier than CAS and ISOL goats. Moreover, INT females had a myometrium significantly thicker and INT was the only group having corpora lutea. In our study, INT females were pubescent in the month following the entry of bucks into the breeding season, suggesting that only sexually active bucks provide the signal responsible for puberty acceleration. By removing direct contact with the bucks, we showed that somatosensory interactions were dispensable for an early puberty induction. Finally, no difference in the GnRH network (fiber density and number of synaptic appositions) can be detected between pubescent and non-pubescent females, suggesting that the male stimulations triggering puberty onset act probably on upstream neuronal networks, potentially on kisspeptin neurons.

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.

Regulation of GnRH pulsatility in ewes

Early work in ewes provided a wealth of information on the physiological regulation of pulsatile gonadotropin-releasing hormone (GnRH) secretion by internal and external inputs. Identification of the neural systems involved, however, was limited by the lack of information on neural mechanisms underlying generation of GnRH pulses. Over the last decade, considerable evidence supported the hypothesis that a group of neurons in the arcuate nucleus that contain kisspeptin, neurokinin B and dynorphin (KNDy neurons) are responsible for synchronizing secretion of GnRH during each pulse in ewes. In this review, we describe our current understanding of the neural systems mediating the actions of ovarian steroids and three external inputs on GnRH pulsatility in light of the hypothesis that KNDy neurons play a key role in GnRH pulse generation. In breeding season adults, estradiol (E₂) and progesterone decrease GnRH pulse amplitude and frequency, respectively, by actions on KNDy neurons, with E₂ decreasing kisspeptin and progesterone increasing dynorphin release onto GnRH neurons. In pre-pubertal lambs, E₂ inhibits GnRH pulse frequency by decreasing kisspeptin and increasing dynorphin release, actions that wane as the lamb matures to allow increased pulsatile GnRH secretion at puberty. Less is known about mediators of undernutrition and stress, although some evidence implicates kisspeptin and dynorphin, respectively, in the inhibition of GnRH pulse frequency by these factors. During the anoestrus, inhibitory photoperiod acting via melatonin activates A15 dopaminergic neurons that innervate KNDy neurons; E₂ increases dopamine release from these neurons to inhibit KNDy neurons and suppress the frequency of kisspeptin and GnRH release.

The Roles of Neurokinins and Endogenous Opioid Peptides in Control of Pulsatile LH Secretion

Work over the last 15 years on the control of pulsatile LH secretion has focused largely on a set of neurons in the arcuate nucleus (ARC) that contains two stimulatory neuropeptides, critical for fertility in humans (kisspeptin and neurokinin B (NKB)) and the inhibitory endogenous opioid peptide (EOP), dynorphin, and are now known as KNDy (kisspeptin-NKB-dynorphin) neurons. In this review, we consider the role of each of the KNDy peptides in the generation of GnRH pulses and the negative feedback actions of ovarian steroids, with an emphasis on NKB and dynorphin. With regard to negative feedback, there appear to be important species differences. In sheep, progesterone inhibits GnRH pulse frequency by stimulating dynorphin release, and estradiol inhibits pulse amplitude by suppressing kisspeptin. In rodents, the role of KNDy neurons in estrogen negative feedback remains controversial, progesterone may inhibit GnRH via dynorphin, but the physiological significance of this action is unclear. In primates, an EOP, probably dynorphin, mediates progesterone negative feedback, and estrogen inhibits kisspeptin expression. In contrast, there is now compelling evidence from several species that kisspeptin is the output signal from KNDy neurons that drives GnRH release during a pulse and may also act within the KNDy network to affect pulse frequency. NKB is thought to act within this network to initiate each pulse, although there is some redundancy in tachykinin signaling in rodents. In ruminants, dynorphin terminates GnRH secretion at the end of pulse, most likely acting on both KNDy and GnRH neurons, but the data on the role of this EOP in rodents are conflicting.

Three-dimensional imaging of KNDy neurons in the mammalian brain using optical tissue clearing and multiple-label immunocytochemistry

Kisspeptin/Neurokinin B/Dynorphin (KNDy) neurons of the arcuate nucleus (ARC) play a key role in the regulation of fertility. The ability to detect features of KNDy neurons that are essential for fertility may require three-dimensional (3D) imaging of the complete population. Recently developed protocols for optical tissue clearing permits 3D imaging of neuronal populations in un-sectioned brains. However, these techniques have largely been described in the mouse brain. We report 3D imaging of the KNDy cell population in the whole rat brain and sheep hypothalamus using immunolabelling and modification of a solvent-based clearing protocol, iDISCO. This study expands the use of optical tissue clearing for multiple mammalian models and provides versatile analysis of KNDy neurons across species. Additionally, we detected a small population of previously unreported kisspeptin neurons in the lateral region of the ovine mediobasal hypothalamus, demonstrating the ability of this technique to detect novel features of the kisspeptin system.

Role of Kisspeptin and Neurokinin B in Puberty in Female Non-Human Primates

In human patients, loss-of-function mutations in the genes encoding kisspeptin (KISS1) and neurokinin B (NKB) and their receptors (KISS1R and NK3R, respectively) result in an abnormal timing of puberty or the absence of puberty. To understand the neuroendocrine mechanism of puberty, we investigated the contribution of kisspeptin and NKB signaling to the pubertal increase in GnRH release using rhesus monkeys as a model. Direct measurements of GnRH and kisspeptin in the median eminence of the hypothalamus with infusion of agonists and antagonists for kisspeptin and NKB reveal that kisspeptin and NKB signaling stimulate GnRH release independently or collaboratively by forming kisspeptin and NKB neuronal networks depending on the developmental age. For example, while in prepubertal females, kisspeptin and NKB signaling independently stimulate GnRH release, in pubertal females, the formation of a collaborative kisspeptin and NKB network further accelerates the pubertal increase in GnRH release. It is speculated that the collaborative mechanism between kisspeptin and NKB signaling to GnRH neurons is necessary for the complex reproductive function in females.

Tachykinin-3 Genes and Peptides Characterized in a Basal Teleost, the European Eel: Evolutionary Perspective and Pituitary Role

In mammals, neurokinin B (NKB) is a short peptide encoded by the gene tac3. It is involved in the brain control of reproduction by stimulating gonadotropin-releasing hormone (GnRH) neurons, mainly via kisspeptin. We investigated tac3 genes and peptides in a basal teleost, the European eel, which shows an atypical blockade of the sexual maturation at a prepubertal stage. Two tac3 paralogous genes (tac3a and tac3b) were identified in the eel genome, each encoding two peptides (NKBa or b and NKB-related peptide NKB-RPa or b). Amino acid sequence of eel NKBa is identical to human NKB, and the three others are novel peptide sequences. The four eel peptides present the characteristic C-terminal tachykinin sequence, as well as a similar alpha helix 3D structure. Tac3 genes were identified in silico in 52 species of vertebrates, and a phylogeny analysis was performed on the predicted TAC3 pre-pro-peptide sequences. A synteny analysis was also done to further assess the evolutionary history of tac3 genes. Duplicated tac3 genes in teleosts likely result from the teleost-specific whole genome duplication (3R). Among teleosts, TAC3b precursor sequences are more divergent than TAC3a, and a loss of tac3b gene would have even occurred in some teleost lineages. NKB-RP peptide, encoded beside NKB by tac3 gene in actinopterygians and basal sarcopterygians, would have been lost in ancestral amniotes. Tissue distribution of eel tac3a and tac3b mRNAs showed major expression of both transcripts in the brain especially in the diencephalon, as analyzed by specific qPCRs. Human NKB has been tested in vitro on primary culture of eel pituitary cells. Human NKB dose-dependently inhibited the expression of lhβ, while having no effect on other glycoprotein hormone subunits (fshβ, tshβ, and gpα) nor on gh. Human NKB also dose-dependently inhibited the expression of GnRH receptor (gnrh-r2). The four eel peptides have been synthesized and also tested in vitro. They all inhibited the expression of both lhβ and of gnrh-r2. This reveals a potential dual inhibitory role of the four peptides encoded by the two tac3 genes in eel reproduction, exerted at the pituitary level on both luteinizing hormone and GnRH receptor.

Pubertal Escape From Estradiol Negative Feedback in Ewe Lambs Is Not Accounted for by Decreased ESR1 mRNA or Protein in Kisspeptin Neurons

In this study, we investigated whether decreased sensitivity to estradiol negative feedback is associated with reduced estrogen receptor α (ESR1) expression in kisspeptin neurons as ewe lambs approach puberty. Lambs were ovariectomized and received no implant (OVX) or an implant containing estradiol (OVX+E). In the middle arcuate nucleus (mARC), ESR1 messenger RNA (mRNA) was greater in OVX than OVX+E lambs but did not differ elsewhere. Post hoc analysis of luteinizing hormone (LH) secretion from OVX+E lambs revealed three patterns of LH pulsatility: low [1 to 2 pulses per 12 hours; low frequency (LF), n = 3], moderate [6 to 7 pulses per 12 hours; moderate frequency (MF), n = 6], and high [>10 pulses per 12 hours; high frequency (HF), n = 5]. The percentage of kisspeptin neurons containing ESR1 mRNA in the preoptic area did not differ among HF, MF, or LF groups. However, the percentage of kisspeptin neurons containing ESR1 mRNA in the mARC was greater in HF (57%) than in MF (36%) or LF (27%) lambs and did not differ from OVX (50%) lambs. A higher percentage of kisspeptin neurons contained ESR1 protein in all regions of the arcuate nucleus (ARC) in OVX compared with OVX+E lambs. There were no differences in ESR1 protein among the HF, MF, or LF groups in the preoptic area or ARC. Contrary to our hypothesis, increases in LH pulsatility were associated with enhanced ESR1 mRNA abundance in kisspeptin neurons in the ARC, and absence of estradiol increased the percentage of kisspeptin neurons containing ESR1 protein in the ARC. Therefore, changes in the expression of ESR1, particularly in kisspeptin neurons in the ARC, do not explain the pubertal escape from estradiol negative feedback in ewe lambs.

Kisspeptin, gonadotrophin-releasing hormone and oestrogen receptor α colocalise with neuronal nitric oxide synthase neurones in prepubertal female sheep

Puberty is a process that integrates multiple inputs ultimately resulting in an increase in gonadotrophin-releasing hormone (GnRH) secretion. Although kisspeptin neurones play an integral role in GnRH secretion and puberty onset, other systems are also likely important. One potential component is nitric oxide (NO), a gaseous neurotransmitter synthesised by nitric oxide synthase (NOS). The present study aimed to neuroanatomically characterise neuronal NOS (nNOS) in prepubertal female sheep and determine whether oestradiol exerts effects on this system. Luteinising hormone secretion was reduced by oestradiol treatment in prepubertal ovariectomised ewes. Neurones immunoreactive for nNOS were identified in several areas, with the greatest number present in the ventrolateral portion of the ventromedial hypothalamus, followed by the ventromedial hypothalamus, preoptic area (POA) and arcuate nucleus (ARC). Next, we determined whether nNOS neurones contained oestrogen receptor (ER)α and could potentially communicate oestradiol (E₂ ) feedback to GnRH neurones. Neuronal NOS neurones contained ERα with the percentage of coexpression (12%-40%) depending upon the area analysed. We next investigated whether a neuroanatomical relationship existed between nNOS and kisspeptin or nNOS and GnRH neurones. A high percentage of kisspeptin neurones in the POA (79%) and ARC (98%) colocalised with nNOS. Kisspeptin close contacts were also associated with nNOS neurones. A greater number of close contacts were observed in the ARC than the POA. A high percentage of POA GnRH neurones (79%) also expressed nNOS, although no GnRH close contacts were observed onto nNOS neurones. Neither the numbers of nNOS neurones in the POA or hypothalamus, nor the percentage of nNOS coexpression with GnRH, kisspeptin or ERα were influenced by oestradiol. These experiments reveal that a neuroanatomical relationship exists between both nNOS and kisspeptin and nNOS and GnRH in prepubertal ewes. Therefore, nNOS may act both directly and indirectly to influence GnRH secretion in prepubertal sheep.

Does Dynorphin Play a Role in the Onset of Puberty in Female Sheep?

Puberty onset involves increased gonadotrophin-release (GnRH) release as a result of decreased sensitivity to oestrogen (E₂ )-negative feedback. Because GnRH neurones lack E₂ receptor α, this pathway must contain interneurones. One likely candidate is KNDy neurones (kisspeptin, neurokinin B, dynorphin). The overarching hypothesis of the present study was that the prepubertal hiatus in luteinising hormone (LH) release involves reduced kisspeptin and/or heightened dynorphin input. We first tested the specific hypothesis that E₂ would reduce kisspeptin-immunopositive cell numbers and increase dynorphin-immunopositive cell numbers. We found that kisspeptin cell numbers were higher in ovariectomised (OVX) lambs than OVX lambs treated with E₂ (OVX+ E₂ ) or those left ovary-intact. Very few arcuate dynorphin cells were identified in any group. Next, we hypothesised that central blockade of κ-opioid receptor (KOR) would increase LH secretion at a prepubertal (6 months) but not postpubertal (10 months) age. Luteinising hormone pulse frequency and mean LH increased during infusion of a KOR antagonist, norbinaltorphimine, in OVX + E₂ lambs at the prepubertal age but not in the same lambs at the postpubertal age. We next hypothesised that E₂ would increase KOR expression in GnRH neurones or alter synaptic input to KNDy neurones in prepubertal ewes. Oestrogen treatment decreased the percentage of GnRH neurones coexpressing KOR (approximately 68%) compared to OVX alone (approximately 78%). No significant differences in synaptic contacts per cell between OVX and OVX + E₂ groups were observed. Although these initial data are consistent with dynorphin inhibiting pulsatile LH release prepubertally, additional work will be necessary to define the source and mechanisms of this inhibition.

Optogenetic Stimulation of Arcuate Nucleus Kiss1 Neurons Reveals a Steroid-Dependent Glutamatergic Input to POMC and AgRP Neurons in Male Mice

Kisspeptin (Kiss1) neurons are essential for reproduction, but their role in the control of energy balance and other homeostatic functions remains unclear. Proopiomelanocortin (POMC) and agouti-related peptide (AgRP) neurons, located in the arcuate nucleus (ARC) of the hypothalamus, integrate numerous excitatory and inhibitory inputs to ultimately regulate energy homeostasis. Given that POMC and AgRP neurons are contacted by Kiss1 neurons in the ARC (Kiss1(ARC)) and they express androgen receptors, Kiss1(ARC) neurons may mediate the orexigenic action of testosterone via POMC and/or AgRP neurons. Quantitative PCR analysis of pooled Kiss1(ARC) neurons revealed that mRNA levels for Kiss1 and vesicular glutamate transporter 2 were higher in castrated male mice compared with gonad-intact males. Single-cell RT-PCR analysis of yellow fluorescent protein (YFP) ARC neurons harvested from males injected with AAV1-EF1α-DIO-ChR2:YFP revealed that 100% and 88% expressed mRNAs for Kiss1 and vesicular glutamate transporter 2, respectively. Whole-cell, voltage-clamp recordings from nonfluorescent postsynaptic ARC neurons showed that low frequency photo-stimulation (0.5 Hz) of Kiss1-ChR2:YFP neurons elicited a fast glutamatergic inward current in POMC and AgRP neurons. Paired-pulse, photo-stimulation revealed paired-pulse depression, which is indicative of greater glutamate release, in the castrated male mice compared with gonad-intact male mice. Group I and group II metabotropic glutamate receptor agonists depolarized and hyperpolarized POMC and AgRP neurons, respectively, which was mimicked by high frequency photo-stimulation (20 Hz) of Kiss1(ARC) neurons. Therefore, POMC and AgRP neurons receive direct steroid- and frequency-dependent glutamatergic synaptic input from Kiss1(ARC) neurons in male mice, which may be a critical pathway for Kiss1 neurons to help coordinate energy homeostasis and reproduction.