Neurokinin B gene expression is increased in the arcuate nucleus of ovariectomized rats

Effects of menopause on temperature regulation

Changes in thermoregulation, notably the emergence of hot flashes, occur during the menopause transition in association with reproductive hormonal changes. Hot flashes constitute the most characteristic symptom of menopause (prevalence of 50-80%), and have a substantial negative effect on quality of life. Here, we review the endocrine changes associated with menopause and the thermoregulatory system and its sensitivity to female sex hormones. We then review current knowledge on the underlying neural mechanisms of hot flashes and how the reproductive and thermoregulatory systems interact in females. We consider the kisspeptin-neurokinin B-dynorphin (KNDy) neuron complex, which becomes hyperactive when estradiol levels decrease. KNDy neurons project from the arcuate nucleus to thermoregulatory areas within the hypothalamic preoptic area, where heat loss mechanisms are triggered, including cutaneous vasodilation and sweating - characteristics of the hot flash. We describe the physiology and measurement of hot flashes and discuss the mixed research findings about thresholds for sweating in symptomatic individuals. We consider the unique situation of hot flashes that arise during sleep, and discuss the relationships between the environment, exercise, and body mass index with hot flashes. We also discuss the unique situation of surgical menopause (with oophorectomy) and cancer therapy, conditions that are associated with frequent, severe, hot flashes. We then provide an overview of treatments of hot flashes, including hormone therapy and targeted neurokinin B-antagonists, recently developed to target the neural mechanism of hot flashes. Finally, we highlight gaps in knowledge about menopausal thermoregulation and hot flashes and suggest future directions for research.

Effects of Integrated Extracts of Trigonella foenum-graecum and Asparagus racemosus on Hot Flash-like Symptoms in Ovariectomized Rats

Vasomotor symptoms, such as hot flashes (HFs), commonly affect women during menopause, leading to a reduced quality of life. The current study evaluates the combined effect of active components Asparagus racemosus (AR) and Trigonella foenum-graecum (TFG) in a single oral formulation (IAT) for alleviating menopausal symptoms in ovariectomized rats. Following bilateral ovariectomy, the animals were randomly assigned to nine groups: (1) Control, (2) Ovariectomy (OVX), (3) OVX+TA1 (TA: Combination of Trigonella and Asparagus; TFG 30 mg/kg + AR 30 mg/kg), (4) OVX+TA2 (TFG 30 mg/kg + AR 15 mg/kg), (5) OVX+TA3 (TFG 15 mg/kg + AR 30 mg/kg), (6) OVX+TA4 (TFG 40 mg/kg + AR 30 mg/kg), (7) OVX+TA5 (TFG 30 mg/kg + AR 40 mg/kg), (8) OVX+IAT1 (IAT: Integrated Asparagus and Trigonella; TFG+AR integrated extract, 30 mg/kg), and (9) OVX+IAT2 (TFG+AR integrated extract, 60 mg/kg). On the 8th day of treatment, tail and skin temperatures were recorded every 30 min for 24 h. Ovariectomized rats exhibited menopausal symptoms, such as hormonal imbalances and elevated skin temperature. Administration of AR, TFG, and IAT significantly decreased serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), and cortisol while increasing estradiol, progesterone, and dopamine (p < 0.0001), effectively alleviating hot flash-like symptoms. Additionally, they mitigated ovariectomy-induced oxidative stress by lowering malondialdehyde (MDA) levels and restoring antioxidant enzyme activity. Ovariectomized rats exhibited increased expression of a proto-oncogene (c-FOS), gonadotropin-releasing hormone (GnRH), Kisspeptin, Neurokinin B (NKB), and Transient receptor potential vanilloid 1 (TRPV1), along with reduced expressing brain-derived neurotrophic factor (BDNF) levels, which were reversed by treatment, especially with the IAT2 combination. The AR and TFG combination, particularly in IAT formulations, showed strong potential in alleviating menopausal symptoms in ovariectomized rats. These findings suggest that the combination of AR and TFG extracts could be a natural alternative for managing postmenopausal symptoms by restoring reproductive hormone levels, regulating lipid profiles, and enhancing antioxidant defense systems.

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.

Malnutrition alters protein expression of KNDy neuropeptides in the arcuate nucleus of mature ewes

The neuropeptides kisspeptin, neurokinin B, and dynorphin A are imperative for the pulsatile secretion of gonadotropin-releasing hormone and luteinizing hormone to ultimately regulate reproductive cyclicity. A population of neurons co-expressing these neuropeptides, KNDy neurons, within the arcuate nucleus of the hypothalamus (ARC) are positioned to integrate energy status from afferent neuronal and glial cells. We hypothesized that KNDy-expressing neurons in the ARC of mature ewes are influenced by energy balance. To test this hypothesis, ovary-intact, mature ewes were fed to lose, maintain, or gain body weight and hypothalamic tissue harvested during the luteal phase of the estrous cycle. Fluorescent, multiplex immunohistochemistry with direct antibody conjugation was employed to identify and quantify neurons expressing a single neuropeptide, as well as for the first time report co-expression of kisspeptin, neurokinin B, and dynorphin A protein in the ARC. Previous reports using this population of ewes demonstrated that concentrations of insulin and leptin differed between ewes fed to achieve different body weights and that ewes fed to gain body weight had increased concentrations of progesterone. Moreover, within this population of ewes tanycyte density and cellular penetration into the ARC was increased in ewes fed to gain body weight. Within the current report we have revealed that the number of neurons in the ARC expressing kisspeptin, neurokinin B, and dynorphin A protein was increased in ewes fed to gain body weight. Moreover, the number of KNDy neurons in the ARC expressing all three neuropeptides within a single neuron was decreased in ewes fed to lose body weight and increased in ewes fed to gain body weight when compared to ewes fed to maintain body weight. The cumulative findings of this experimental model suggest that expression of kisspeptin, neurokinin B, and dynorphin A protein in the ARC during the luteal phase of the estrous cycle are influenced by energy balance-induced alterations in circulating concentrations of progesterone that drive changes in morphology and density of tanycytes to ultimately regulate central perception of global energy status. Moreover, these results demonstrate that changes in KNDy neurons within the ARC occur as an adaptation to energy balance, potentially regulated divergently by metabolic milieu via proopiomelanocortin afferents.

Neurokinin 1/3 receptor antagonists for menopausal women: A current systematic review and insights into the investigational non-hormonal therapy

BACKGROUND

Over 75% of menopausal women experience vasomotor symptoms (VMS), such as night sweats and hot flashes. Despite the prevalence of these symptoms, there is limited data on non-hormonal therapies to alleviate them.

METHODS

PubMed, Cochrane, Scopus, Ovid, Web of Science, and ClinicalTrials.Gov were searched for relevant studies. The search was performed using the following keywords, which were customized to suit the specific databases/registers: menopause, women, neurokinin 3, and/or Fezolinetant. The search was conducted until December 20, 2022. This systematic review was conducted in compliance with the PRISMA Statement 2020 guidelines.

RESULTS

A total of 326 records were found, with 10 studies (enrolling 1993 women) selected for inclusion. The women received 40-mg doses of NK1/3 receptor antagonists twice daily, with follow-ups at 1 to 3 weeks. Moderately strong evidence was found suggesting that NK1/3 receptor antagonists can help limit the frequency and severity of hot flashes in menopausal women.

CONCLUSION

While the results should be interpreted with caution until further clinical trials validate the efficacy and safety of NK1/3 receptor antagonists among menopausal women, these findings suggest that they are promising targets for future pharmacological and clinical studies in addressing vasomotor symptoms.

The Neuropeptide Spexin Promotes the Osteoblast Differentiation of MC3T3-E1 Cells via the MEK/ERK Pathway and Bone Regeneration in a Mouse Calvarial Defect Model

BACKGROUND

The neural regulation of bone regeneration has emerged recently. Spexin (SPX) is a novel neuropeptide and regulates multiple biological functions. However, the effects of SPX on osteogenic differentiation need to be further investigated. Therefore, the aim of this study is to investigate the effects of SPX on osteogenic differentiation, possible underlying mechanisms, and bone regeneration.

METHODS

In this study, MC3T3-E1 cells were treated with various concentrations of SPX. Cell proliferation, osteogenic differentiation marker expressions, alkaline phosphatase (ALP) activity, and mineralization were evaluated using the CCK-8 assay, reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR), ALP staining, and alizarin red S staining, respectively. To determine the underlying molecular mechanism of SPX, the phosphorylation levels of signaling molecules were examined via western blot analysis. Moreover, in vivo bone regeneration by SPX (0.5 and 1 µg/µl) was evaluated in a calvarial defect model. New bone formation was analyzed using micro-computed tomography (micro-CT) and histology.

RESULTS

The results indicated that cell proliferation was not affected by SPX. However, SPX significantly increased ALP activity, mineralization, and the expression of genes for osteogenic differentiation markers, including runt-related transcription factor 2 (Runx2), Alp, collagen alpha-1(I) chain (Col1a1), osteocalcin (Oc), and bone sialoprotein (Bsp). In contrast, SPX downregulated the expression of ectonucleotide pyrophosphatase/phosphodiesterase 1 (Enpp1). Moreover, SPX upregulated phosphorylated mitogen-activated protein kinase kinase (MEK1/2) and extracellular signal-regulated kinase (ERK1/2). In vivo studies, micro-CT and histologic analysis revealed that SPX markedly increased a new bone formation.

CONCLUSION

Overall, these results demonstrated that SPX stimulated osteogenic differentiation in vitro and increased in vivo bone regeneration via the MEK/ERK pathway.

RNA-sequencing of AVPV and ARH reveals vastly different temporal and transcriptomic responses to estradiol in the female rat hypothalamus

In females, estrogens have two main modes of action relating to gonadotropin secretion: positive feedback and negative feedback. Estrogen positive and negative feedback are controlled by different regions of the hypothalamus: the preoptic area/anterior portion (mainly the anteroventral periventricular nucleus, AVPV) of the hypothalamus is associated with estrogen positive feedback while the mediobasal hypothalamus (mainly the arcuate nucleus of the hypothalamus, ARH), is associated with estrogen negative feedback. In this study, we examined the temporal pattern of gene transcription in these two regions following estrogen treatment. Adult, ovariectomized, Long Evans rats received doses of estradiol benzoate (EB) or oil every 4 days for 3 cycles. On the last EB priming cycle, hypothalamic tissues were dissected into the AVPV+ and ARH+ at 0 hrs (baseline/oil control), 6 hrs, or 24 hrs after EB treatment. RNA was extracted and sequenced using bulk RNA sequencing. Differential gene analysis, gene ontology, and weighted correlation network analysis (WGCNA) was performed. Overall, we found that the AVPV+ and ARH+ respond differently to estradiol stimulation. In both regions, estradiol treatment resulted in more gene up-regulation than down-regulation. S100g was very strongly up-regulated by estradiol in both regions at 6 and 24 hrs after EB treatment. In the AVPV+ the highest number of differentially expressed genes occurred 24 hrs after EB. In the ARH+, the highest number of genes differentially expressed by EB occurred between 6 and 24 hrs after EB, while in the AVPV+, the fewest genes changed their expression between these time points, demonstrating a temporal difference in the way that EB regulates transcription these two areas. Several genes strongly implicated in gonadotropin release were differentially affected by estradiol including Esr1, encoding estrogen receptor-α and Kiss1, encoding kisspeptin. As an internal validation, Kiss1 was up-regulated in the AVPV+ and down-regulated in the ARH+. Gene network analysis revealed the vastly different clustering of genes modulated by estradiol in the AVPV+ compared with the ARH+. These results indicate that gene expression in these two hypothalamic regions have specific responses to estradiol in timing and direction.

Fezolinetant in the treatment of vasomotor symptoms associated with menopause

Introduction: Although international clinical practice guidelines recognize a continued role for menopausal hormone therapy (HT), particularly for symptomatic women <60 years of age or within 10 years of menopause, safety and tolerability concerns have discouraged HT use due to potential links with a perceived increased risk of hormone-dependent cancers, and an established risk of stroke and venous thromboembolism. There is therefore a need for safe, effective non-hormonal therapy for relief of menopausal vasomotor symptoms (VMS).Areas covered: This narrative review summarizes the dataset accrued for fezolinetant, a neurokinin-3 receptor (NK3R) antagonist in clinical development for menopause-associated VMS.Expert opinion: Altered signaling in neuroendocrine circuits at menopause leads to VMS wherein NK3R activity plays a key role to modulate the thermoregulatory center in a manner conducive to triggering the 'hot flash' response. Thus, a new generation of NK3R antagonists has entered clinical development to specifically target the mechanistic basis of VMS. Fezolinetant is the most advanced NK3R antagonist in terms of stage of clinical development. Results to date have demonstrated rapid and substantial reduction in VMS frequency and severity and associated improvements in health-related quality of life. NK3R antagonists offer a non-hormonal alternative to HT for the treatment of menopause-related VMS.

Genetic variants predictive of reproductive aging are associated with vasomotor symptoms in a multiracial/ethnic cohort

OBJECTIVE

Vasomotor symptoms (VMS), hot flashes, and night sweats are cardinal symptoms of the menopausal transition. Little is known about genetic influences on VMS. This study evaluated whether previously identified genetic factors predictive of VMS, age at menarche, and age at menopause were associated with VMS in a multiracial/ethnic cohort.

METHODS

For 702 White, 306 Black, 126 Chinese, and 129 Japanese women from the Study of Women's Health Across the Nation (SWAN) Genomic Substudy, we created polygenic risk scores (PRSs) from genome-wide association studies of VMS and ages at menarche and menopause. PRSs and single nucleotide polymorphisms (SNPs) from a previously identified VMS locus (tachykinin receptor 3 [TACR3]) were evaluated for associations with frequent VMS (VMS ≥6 days in the past 2 weeks at any visit) and with VMS trajectories (persistently low, early onset, final menstrual period onset, persistently high).

RESULTS

The C-allele of rs74827081 in TACR3 was associated with reduced likelihood of frequent VMS in White women (odds ratio [OR] = 0.49 [95% CI, 0.29-0.83]). With higher menarche PRS (later menarche), Black women were less likely (OR = 0.55 [95% CI, 0.38-0.78]) to report frequent VMS. With higher PRS for age at menarche, Black women were also less likely to have a persistently high VMS trajectory (OR = 0.55 [95% CI, 0.34-0.91]), whereas White women (OR = 0.75 [95% CI, 0.58-0.98]) were less likely to have a final menstrual period onset trajectory (vs persistently low). Chinese women with higher menopause PRS were more likely to have frequent VMS (OR = 2.29 [95% CI, 1.39-3.78]). Associations were substantively similar after excluding rs74827081 C-allele carriers.

CONCLUSIONS

Genetic factors predictive of reproductive aging are also associated with VMS, suggesting that VMS have a polygenic architecture. Further study in this area may help to identify new targets for novel VMS therapies.

Genetic Variation and Hot Flashes: A Systematic Review

CONTEXT

Approximately 70% of women report experiencing vasomotor symptoms (VMS, hot flashes and/or night sweats). The etiology of VMS is not clearly understood but may include genetic factors.

EVIDENCE ACQUISITION

We searched PubMed and Embase in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidance. We included studies on associations between genetic variation and VMS. We excluded studies focused on medication interventions or prevention or treatment of breast cancer.

EVIDENCE SYNTHESIS

Of 202 unique citations, 18 citations met the inclusion criteria. Study sample sizes ranged from 51 to 17 695. Eleven of the 18 studies had fewer than 500 participants; 2 studies had 1000 or more. Overall, statistically significant associations with VMS were found for variants in 14 of the 26 genes assessed in candidate gene studies. The cytochrome P450 family 1 subfamily A member 1 (CYP1B1) gene was the focus of the largest number (n = 7) of studies, but strength and statistical significance of associations of CYP1B1 variants with VMS were inconsistent. A genome-wide association study reported statistically significant associations between 14 single-nucleotide variants in the tachykinin receptor 3 gene and VMS. Heterogeneity across trials regarding VMS measurement methods and effect measures precluded quantitative meta-analysis; there were few studies of each specific genetic variant.

CONCLUSIONS

Genetic variants are associated with VMS. The associations are not limited to variations in sex-steroid metabolism genes. However, studies were few and future studies are needed to confirm and extend these findings.

Establishment of immortalised cell lines derived from female Shiba goat KNDy and GnRH neurones

Kisspeptin plays a critical role in governing gonadotrophin-releasing hormone (GnRH)/gonadotrophin secretion and subsequent reproductive function in mammals. The hypothalamic arcuate nucleus (ARC) kisspeptin neurones, which co-express neurokinin B (NKB) and dynorphin A (Dyn) and are referred to as KNDy neurones, are considered to be involved in GnRH generation. The present study aimed to establish cell lines derived from goat KNDy and GnRH neurones. Primary-cultured cells of female Shiba goat foetal hypothalamic ARC and preoptic area (POA) tissues were immortalised with the infection of lentivirus containing the simian virus 40 large T-antigen gene. Clones of the immortalised cells were selected by the gene expression of a neuronal marker, and then the neurone-derived cell clones were further selected by the gene expression of KNDy or GnRH neurone markers. As a result, we obtained a KNDy neurone cell line (GA28) from the ARC, as well as two GnRH neurone cell lines (GP11 and GP31) from the POA. Immunocytochemistry revealed the expression of kisspeptin, NKB and Dyn in GA28 cells, as well as GnRH in GP11 and GP31 cells. GnRH secretion from GP11 and GP31 cells into the media was confirmed by an enzyme immunoassay. Moreover, kisspeptin challenge increased intracellular Ca2+ levels in subsets of both GP11 and GP31 cells. Kisspeptin mRNA expression in GA28 cells, which expressed the oestrogen receptor alpha gene, was significantly reduced by 17β-oestradiol treatment. Furthermore, the transcriptional core promoter and repressive regions of the goat NKB gene were detected using GA28 cells. In conclusion, we have established goat KNDy and GnRH neurone cell lines that could be used to analyse molecular and cellular mechanisms regulating KNDy and GnRH neurones in vitro, facilitating the clarification of reproductive neuroendocrine mechanisms in ruminants.

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.

Characterization of the Role of NKA in the Control of Puberty Onset and Gonadotropin Release in the Female Mouse

The tachykinin neurokinin B (NKB, Tac2) is critical for proper GnRH release in mammals, however, the role of the other tachykinins, such as substance P (SP) and neurokinin A (NKA) in reproduction, is still not well understood. In this study, we demonstrate that NKA controls the timing of puberty onset (similar to NKB and SP) and stimulates LH release in adulthood through NKB-independent (but kisspeptin-dependent) mechanisms in the presence of sex steroids. Furthermore, this is achieved, at least in part, through the autosynaptic activation of Tac1 neurons, which express NK2R (Tacr2), the receptor for NKA. Conversely, in the absence of sex steroids, as observed in ovariectomy, NKA inhibits LH through a mechanism that requires the presence of functional receptors for NKB and dynorphin (NK3R and KOR, respectively). Moreover, the ability of NKA to modulate LH secretion is absent in Kiss1KO mice, suggesting that its action occurs upstream of Kiss1 neurons. Overall, we demonstrate that NKA signaling is a critical component in the central control of reproduction, by contributing to the indirect regulation of kisspeptin release.

Distinct dynorphin expression patterns with low- and high-dose estrogen treatment in the arcuate nucleus of female rats

Kisspeptin (KISS1; encoded by Kiss1) neurons in the arcuate nucleus (ARC) coexpress tachykinin 3 (TAC3; also known as neurokinin B) and dynorphin A (PDYN). Accordingly, they are termed KNDy neurons and considered to be crucial in generating pulsatile release of gonadotropin-releasing hormone. Accumulating evidence suggests that Kiss1 and Tac3 are negatively regulated by estrogen. However, it has not been fully determined whether and how estrogen modulates Pdyn and PDYN. Here, we examined the expression of Pdyn mRNA and PDYN by in situ hybridization and immunohistochemistry, respectively, in the ARC of female rats after ovariectomy (OVX) and OVX plus low- or high-dose beta-estradiol (E2) replacement. We also investigated the effect of E2 on expression of Kiss1, KISS1, Tac3, and TAC3. Furthermore, colocalization of PDYN and estrogen receptor alpha (ESR1) was determined. Subsequently, we found that low-dose E2 treatment had no effect on Pdyn mRNA-expressing cells, but increased PDYN-immunoreactive (ir) cell numbers. In contrast, high-dose E2 treatment resulted in prominent reductions in both Pdyn mRNA-expressing and PDYN-ir cell numbers. Changes induced by low or high doses of E2 were similarly observed in the expression of Kiss1, KISS1, Tac3, and TAC3. The majority of PDYN-ir neurons coexpressed ESR1 in all groups. Our results indicate that E2 regulates the expression of PDYN, as well as KISS1 and TAC3, with regulation by E2 differing according to its levels.

Disentangling puberty: novel neuroendocrine pathways and mechanisms for the control of mammalian puberty

BACKGROUND

Puberty is a complex developmental event, controlled by sophisticated regulatory networks that integrate peripheral and internal cues and impinge at the brain centers driving the reproductive axis. The tempo of puberty is genetically determined but is also sensitive to numerous modifiers, from metabolic and sex steroid signals to environmental factors. Recent epidemiological evidence suggests that the onset of puberty is advancing in humans, through as yet unknown mechanisms. In fact, while much knowledge has been gleaned recently on the mechanisms responsible for the control of mammalian puberty, fundamental questions regarding the intimate molecular and neuroendocrine pathways responsible for the precise timing of puberty and its deviations remain unsolved.

OBJECTIVE AND RATIONALE

By combining data from suitable model species and humans, we aim to provide a comprehensive summary of our current understanding of the neuroendocrine mechanisms governing puberty, with particular focus on its central regulatory pathways, underlying molecular basis and mechanisms for metabolic control.

SEARCH METHODS

A comprehensive MEDLINE search of articles published mostly from 2003 to 2017 has been carried out. Data from cellular and animal models (including our own results) as well as clinical studies focusing on the pathophysiology of puberty in mammals were considered and cross-referenced with terms related with central neuroendocrine mechanisms, metabolic control and epigenetic/miRNA regulation.

OUTCOMES

Studies conducted during the last decade have revealed the essential role of novel central neuroendocrine pathways in the control of puberty, with a prominent role of kisspeptins in the precise regulation of the pubertal activation of GnRH neurosecretory activity. In addition, different transmitters, including neurokinin-B (NKB) and, possibly, melanocortins, have been shown to interplay with kisspeptins in tuning puberty onset. Alike, recent studies have documented the role of epigenetic mechanisms, involving mainly modulation of repressors that target kisspeptins and NKB pathways, as well as microRNAs and the related binding protein, Lin28B, in the central control of puberty. These novel pathways provide the molecular and neuroendocrine basis for the modulation of puberty by different endogenous and environmental cues, including nutritional and metabolic factors, such as leptin, ghrelin and insulin, which are known to play an important role in pubertal timing.

WIDER IMPLICATIONS

Despite recent advancements, our understanding of the basis of mammalian puberty remains incomplete. Complete elucidation of the novel neuropeptidergic and molecular mechanisms summarized in this review will not only expand our knowledge of the intimate mechanisms responsible for puberty onset in humans, but might also provide new tools and targets for better prevention and management of pubertal deviations in the clinical setting.

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.

Transcriptome profiles in peripheral white blood cells at the time of artificial insemination discriminate beef heifers with different fertility potential

Background

Infertility is a longstanding limitation in livestock production with important economic impact for the cattle industry. Female reproductive traits are polygenic and lowly heritable in nature, thus selection for fertility is challenging. Beef cattle operations leverage estrous synchronization in combination with artificial insemination (AI) to breed heifers and benefit from an early and uniform calving season. A couple of weeks following AI, heifers are exposed to bulls for an opportunity to become pregnant by natural breeding (NB), but they may also not become pregnant during this time period. Focusing on beef heifers, in their first breeding season, we hypothesized that: a- at the time of AI, the transcriptome of peripheral white blood cells (PWBC) differs between heifers that become pregnant to AI and heifers that become pregnant late in the breeding season by NB or do not become pregnant during the breeding season; and b- the ratio of transcript abundance between genes in PWBC classifies heifers according to pregnancy by AI, NB, or failure to become pregnant.

Results

We generated RNA-sequencing data from 23 heifers from two locations (A: six AI-pregnant and five NB-pregnant; and B: six AI-pregnant and six non-pregnant). After filtering out lowly expressed genes, we quantified transcript abundance for 12,538 genes. The comparison of gene expression levels between AI-pregnant and NB-pregnant heifers yielded 18 differentially expressed genes (DEGs) (ADAM20, ALDH5A1, ANG, BOLA-DQB, DMBT1, FCER1A, GSTM3, KIR3DL1, LOC107131247, LOC618633, LYZ, MNS1, P2RY12, PPP1R1B, SIGLEC14, TPPP, TTLL1, UGT8, eFDR≤0.02). The comparison of gene expression levels between AI-pregnant and non-pregnant heifers yielded six DEGs (ALAS2, CNKSR3, LOC522763, SAXO2, TAC3, TFF2, eFDR≤0.05). We calculated the ratio of expression levels between all gene pairs and assessed their potential to classify samples according to experimental groups. Considering all samples, relative expression from two gene pairs correctly classified 10 out of 12 AI-pregnant heifers (P = 0.0028) separately from the other 11 heifers (NB-pregnant, or non-pregnant).

Conclusion

The transcriptome profile in PWBC, at the time of AI, is associated with the fertility potential of beef heifers. Transcript levels of specific genes may be further explored as potential classifiers, and thus selection tools, of heifer fertility.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4505-4) contains supplementary material, which is available to authorized users.

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.

Association of genetic variation in the tachykinin receptor 3 locus with hot flashes and night sweats in the Women's Health Initiative Study

OBJECTIVE

Vasomotor symptoms (VMS, ie, hot flashes or night sweats) are reported by many, but not all, women. The extent to which VMS are genetically determined is unknown. We evaluated the relationship of genetic variation and VMS.

METHODS

In this observational study, we accessed data from three genome-wide association studies (GWAS) (SNP Health Association Resource cohort [SHARe], WHI Memory Study cohort [WHIMS+], and Genome-Wide Association Studies of Treatment Response in Randomized Clinical Trials [GARNET] studies, total n = 17,695) of European American, African American, and Hispanic American postmenopausal women aged 50 to 79 years at baseline in the Women's Health Initiative Study. We examined genetic variation in relation to VMS (yes/no) in each study and using trans-ethnic inverse variance fixed-effects meta-analysis. A total of 11,078,977 single-nucleotide polymorphisms (SNPs) met the quality criteria.

RESULTS

After adjustment for covariates and population structure, three SNPs (on chromosomes 3 and 11) were associated with VMS at the genome-wide threshold of 5 × 10 in the African American SHARe GWAS, but were not associated in the other cohorts. In the meta-analysis, 14 SNPs, all located on chromosome 4 in the tachykinin receptor 3 (TACR3) locus, however, had P < 5 × 10. These SNPs' effect sizes were similar across studies/participants' ancestry (odds ratio ∼1.5).

CONCLUSIONS

Genetic variation in TACR3 may contribute to the risk of VMS. To our knowledge, this is the first GWAS to examine SNPs associated with VMS. These results support the biological hypothesis of a role for TACR3 in VMS, which was previously hypothesized from animal and human studies. Further study of these variants may lead to new insights into the biological pathways involved in VMS, which are poorly understood.

Expanding the Role of Tachykinins in the Neuroendocrine Control of Reproduction

Reproductive function is driven by the hormonal interplay between the gonads and brain-pituitary axis. Gonadotropin-releasing hormone (GnRH) is released in a pulsatile manner, which is critical for the attainment and maintenance of fertility, however, GnRH neurons lack the ability to directly respond to most regulatory factors, and a hierarchical upstream neuronal network governs its secretion. We and others proposed a model in which Kiss1 neurons in the arcuate nucleus (ARC), so called KNDy neurons, release kisspeptin (a potent GnRH secretagogue) in a pulsatile manner to drive GnRH pulses under the coordinated autosynaptic action of its cotransmitters, the tachykinin neurokinin B (NKB, stimulatory) and dynorphin (inhibitory). Numerous genetic and pharmacological studies support this model; however, additional regulatory mechanisms (upstream of KNDy neurons) and alternative pathways of GnRH secretion (kisspeptin-independent) exist, but remain ill defined. In this aspect, attention to other members of the tachykinin family, namely substance P (SP) and neurokinin A (NKA), has recently been rekindled. Even though there are still major gaps in our knowledge about the functional significance of these systems, substantial evidence, as discussed below, is placing tachykinin signaling as an important pathway for the awakening of the reproductive axis and the onset of puberty to physiological GnRH secretion and maintenance of fertility in adulthood.

Ablation of KNDy Neurons Results in Hypogonadotropic Hypogonadism and Amplifies the Steroid-Induced LH Surge in Female Rats

In the human infundibular (arcuate) nucleus, a subpopulation of neurons coexpress kisspeptin and neurokinin B (NKB), 2 peptides required for normal reproductive function. A homologous group of neurons exists in the arcuate nucleus of rodents, termed KNDy neurons based on the coexpression of kisspeptin, NKB, and dynorphin. To study their function, we recently developed a method to selectively ablate KNDy neurons using NK3-SAP, a neurokinin 3 receptor agonist conjugated to saporin (SAP). Here, we ablated KNDy neurons in female rats to determine whether these neurons are required for estrous cyclicity and the steroid induced LH surge. NK3-SAP or Blank-SAP (control) was microinjected into the arcuate nucleus using stereotaxic surgery. After monitoring vaginal smears for 3-4 weeks, rats were ovariectomized and given 17β-estradiol and progesterone in a regimen that induced an afternoon LH surge. Rats were killed at the time of peak LH levels, and brains were harvested for NKB and dual labeled GnRH/Fos immunohistochemistry. In ovary-intact rats, ablation of KNDy neurons resulted in hypogonadotropic hypogonadism, characterized by low levels of serum LH, constant diestrus, ovarian atrophy with increased follicular atresia, and uterine atrophy. Surprisingly, the 17β-estradiol and progesterone-induced LH surge was 3 times higher in KNDy-ablated rats. Despite the marked increase in the magnitude of the LH surge, the number of GnRH or anterior ventral periventricular nucleus neurons expressing Fos was not significantly different between groups. Our studies show that KNDy neurons are essential for tonic levels of serum LH and estrous cyclicity and may play a role in limiting the magnitude of the LH surge.

Estradiol Membrane-Initiated Signaling and Female Reproduction

The discoveries of rapid, membrane-initiated steroid actions and central nervous system steroidogenesis have changed our understanding of the neuroendocrinology of reproduction. Classical nuclear actions of estradiol and progesterone steroids affecting transcription are essential. However, with the discoveries of membrane-associated steroid receptors, it is becoming clear that estradiol and progesterone have neurotransmitter-like actions activating intracellular events. Ultimately, membrane-initiated actions can influence transcription. Estradiol membrane-initiated signaling (EMS) modulates female sexual receptivity and estrogen feedback regulating the luteinizing hormone (LH) surge. In the arcuate nucleus, EMS activates a lordosis-regulating circuit that extends to the medial preoptic nucleus and subsequently to the ventromedial nucleus (VMH)--the output from the limbic and hypothalamic regions. Here, we discuss how EMS leads to an active inhibition of lordosis behavior. To stimulate ovulation, EMS facilitates astrocyte synthesis of progesterone (neuroP) in the hypothalamus. Regulation of GnRH release driving the LH surge is dependent on estradiol-sensitive kisspeptin (Kiss1) expression in the rostral periventricular nucleus of the third ventricle (RP3V). NeuroP activation of the LH surge depends on Kiss1, but the specifics of signaling have not been well elucidated. RP3V Kiss1 neurons appear to integrate estradiol and progesterone information which feeds back onto GnRH neurons to stimulate the LH surge. In a second population of Kiss1 neurons, estradiol suppresses the surge but maintains tonic LH release, another critical component of the estrous cycle. Together, evidence suggests that regulation of reproduction involves membrane action of steroids, some of which are synthesized in the brain.

Prenatal Testosterone Treatment Leads to Changes in the Morphology of KNDy Neurons, Their Inputs, and Projections to GnRH Cells in Female Sheep

Prenatal testosterone (T)-treated ewes display a constellation of reproductive defects that closely mirror those seen in PCOS women, including altered hormonal feedback control of GnRH. Kisspeptin/neurokinin B/dynorphin (KNDy) neurons of the arcuate nucleus (ARC) play a key role in steroid feedback control of GnRH secretion, and prenatal T treatment in sheep causes an imbalance of KNDy peptide expression within the ARC. In the present study, we tested the hypothesis that prenatal T exposure, in addition to altering KNDy peptides, leads to changes in the morphology and synaptic inputs of this population, kisspeptin cells of the preoptic area (POA), and GnRH cells. Prenatal T treatment significantly increased the size of KNDy cell somas, whereas POA kisspeptin, GnRH, agouti-related peptide, and proopiomelanocortin neurons were each unchanged in size. Prenatal T treatment also significantly reduced the total number of synaptic inputs onto KNDy neurons and POA kisspeptin neurons; for KNDy neurons, the decrease was partly due to a decrease in KNDy-KNDy synapses, whereas KNDy inputs to POA kisspeptin cells were unaltered. Finally, prenatal T reduced the total number of inputs to GnRH cells in both the POA and medial basal hypothalamus, and this change was in part due to a decreased number of inputs from KNDy neurons. The hypertrophy of KNDy cells in prenatal T sheep resembles that seen in ARC kisspeptin cells of postmenopausal women, and together with changes in their synaptic inputs and projections to GnRH neurons, may contribute to defects in steroidal control of GnRH observed in this animal model.

Testing the Critical Window Hypothesis of Timing and Duration of Estradiol Treatment on Hypothalamic Gene Networks in Reproductively Mature and Aging Female Rats

At menopause, the dramatic loss of ovarian estradiol (E2) necessitates the adaptation of estrogen-sensitive neurons in the hypothalamus to an estrogen-depleted environment. We developed a rat model to test the "critical window" hypothesis of the effects of timing and duration of E2 treatment after deprivation on the hypothalamic neuronal gene network in the arcuate nucleus and the medial preoptic area. Rats at 2 ages (reproductively mature or aging) were ovariectomized and given E2 or vehicle replacement regimes of differing timing and duration. Using a 48-gene quantitative low-density PCR array and weighted gene coexpression network analysis, we identified gene modules differentially regulated by age, timing, and duration of E2 treatment. Of particular interest, E2 status differentially affected suites of genes in the hypothalamus involved in energy balance, circadian rhythms, and reproduction. In fact, E2 status was the dominant factor in determining gene modules and hormone levels; age, timing, and duration had more subtle effects. Our results highlight the plasticity of hypothalamic neuroendocrine systems during reproductive aging and its surprising ability to adapt to diverse E2 replacement regimes.

Neurokinin 3 Receptor-Expressing Neurons in the Median Preoptic Nucleus Modulate Heat-Dissipation Effectors in the Female Rat

KNDy neurons facilitate tail skin vasodilation and modulate the effects of estradiol on thermoregulation. We hypothesize that KNDy neurons influence cutaneous vasodilation via projections to neurons in the median preoptic nucleus (MnPO) that express the neurokinin 3 receptor (NK3R). In support of this hypothesis, focal microinjections of senktide, an NK3R agonist, into the MnPO lowers core temperature (TCORE) in the female rat. To further study the role of MnPO NK3R neurons in thermoregulation, these neurons were specifically ablated using a conjugate of a selective NK3R agonist and saporin (NK3-SAP). NK3-SAP or blank-SAP (control) was injected into the MnPO/medial septum. Tail skin temperature (TSKIN) and TCORE were measured in ovariectomized rats exposed to 3 ambient temperatures (TAMBIENT) before and after estradiol-17β (E2) treatment. Before killing, we injected senktide (sc), monitored TCORE for 70 minutes, and harvested brains for Fos immunohistochemistry. Ablation of MnPO NK3R neurons lowered TSKIN at neutral and subneutral TAMBIENT regardless of E2 treatment. However, ablation did not prevent the effects of E2 on TCORE and TSKIN. In control rats, senktide injections induced hypothermia with numerous Fos-immunoreactive cells in the MnPO. In contrast, in NK3-SAP rats, senktide did not alter TCORE and minimal Fos-immunoreactive neurons were identified in the MnPO. These data show that NK3R neurons in the MnPO are required for the hypothermic effects of senktide but not for the E2 modulation of thermoregulation. The lower TSKIN in NK3-SAP-injected rats suggests that MnPO NK3R neurons, like KNDy neurons, facilitate cutaneous vasodilation, an important heat-dissipation effector.

Chronic oestradiol reduces the dendritic spine density of KNDy (kisspeptin/neurokinin B/dynorphin) neurones in the arcuate nucleus of ovariectomised Tac2-enhanced green fluorescent protein transgenic mice

Neurones in the arcuate nucleus that express neurokinin B (NKB), kisspeptin and dynorphin (KNDy) play an important role in the reproductive axis. Oestradiol modulates the gene expression and somatic size of these neurones, although there is limited information available about whether their dendritic structure, a correlate of cellular plasticity, is altered by oestrogens. In the present study, we investigated the morphology of KNDy neurones by filling fluorescent neurones in the arcuate nucleus of Tac2-enhanced green fluorescent protein (EGFP) transgenic mice with biocytin. Filled neurones from ovariectomised (OVX) or OVX plus 17β-oestradiol (E2)-treated mice were visualised with anti-biotin immunohistochemistry and reconstructed in three dimensions with computer-assisted microscopy. KNDy neurones exhibited two primary dendrites, each with a few branches confined to the arcuate nucleus. Quantitative analysis revealed that E2 treatment of OVX mice decreased the cell size and dendritic spine density of KNDy neurones. The axons of KNDy neurones originated from the cell body or proximal dendrite and gave rise to local branches that appeared to terminate within the arcuate nucleus. Numerous terminal boutons were also visualised within the ependymal layer of the third ventricle adjacent to the arcuate nucleus. Axonal branches also projected to the adjacent median eminence and exited the arcuate nucleus. Confocal microscopy revealed close apposition of EGFP and gonadotrophin-releasing hormone-immunoreactive fibres within the median eminence and confirmed the presence of KNDy axon terminals in the ependymal layer of the third ventricle. The axonal branching pattern of KNDy neurones suggests that a single KNDy neurone could influence multiple arcuate neurones, tanycytes in the wall of the third ventricle, axon terminals in the median eminence and numerous areas outside of the arcuate nucleus. In parallel with its inhibitory effects on electrical excitability, E2 treatment of OVX Tac2-EGFP mice induces structural changes in the somata and dendrites of KNDy neurones.

Neurokinin B is critical for normal timing of sexual maturation but dispensable for adult reproductive function in female mice

Humans carrying mutations in neurokinin B (NKB) or the NKB receptor fail to undergo puberty due to decreased secretion of GnRH. Despite this pubertal delay, many of these patients go on to achieve activation of their hypothalamic-pituitary-gonadal axis in adulthood, a phenomenon termed reversal, indicating that NKB signaling may play a more critical role for the timing of pubertal development than adult reproductive function. NKB receptor-deficient mice are hypogonadotropic but have no defects in the timing of sexual maturation. The current study has performed the first phenotypic evaluation of mice bearing mutations in Tac2, the gene encoding the NKB ligand, to determine whether they have impaired sexual development similar to their human counterparts. Male Tac2-/- mice showed no difference in the timing of sexual maturation or fertility compared with wild-type littermates and were fertile. In contrast, Tac2-/- females had profound delays in sexual maturation, with time to vaginal opening and first estrus occurring significantly later than controls, and initial abnormalities in estrous cycles. However, cycling recovered in adulthood and Tac2-/- females were fertile, although they produced fewer pups per litter. Thus, female Tac2-/- mice parallel humans harboring NKB pathway mutations, with delayed sexual maturation and activation of the reproductive cascade later in life. Moreover, direct comparison of NKB ligand and receptor-deficient females confirmed that only NKB ligand-deficient animals have delayed sexual maturation, suggesting that in the absence of the NKB receptor, NKB may regulate the timing of sexual maturation through other tachykinin receptors.

Daily successive changes in reproductive gene expression and neuronal activation in the brains of pubertal female mice

Puberty is governed by the secretion of gonadotropin releasing hormone (GnRH), but the roles and identities of upstream neuropeptides that control and time puberty remain poorly understood. Indeed, how various reproductive neural gene systems change before and during puberty, and in relation to one another, is not well-characterized. We detailed the daily pubertal profile (from postnatal day [PND] 15 to PND 30) of neural Kiss1 (encoding kisspeptin), Kiss1r (kisspeptin receptor), Tac2 (neurokinin B), and Rfrp (RFRP-3, mammalian GnIH) gene expression and day-to-day c-fos induction in each of these cell types in developing female mice. Kiss1 expression in the AVPV/PeN increased substantially over the pubertal transition, reaching adult levels around vaginal opening (PND 27.5), a pubertal marker. However, AVPV/PeN Kiss1 neurons were not highly activated, as measured by c-fos co-expression, at any pubertal age. In the ARC, Kiss1 and Tac2 cell numbers showed moderate increases across the pubertal period, and neuronal activation of Tac2/Kiss1 cells was moderately elevated at all pubertal ages. Additionally, Kiss1r expression specifically in GnRH neurons was already maximal by PND 15 and did not change with puberty. Conversely, both Rfrp expression and Rfrp/c-fos co-expression in the DMN decreased markedly in the early pre-pubertal stage. This robust decrease of the inhibitory RFRP-3 population may diminish inhibition of GnRH neurons during early puberty. Collectively, our data identify the precise timing of important developmental changes - and in some cases, lack thereof - in gene expression and neuronal activation of key reproductive neuropeptides during puberty, with several changes occurring well before vaginal opening.

The integrated hypothalamic tachykinin-kisspeptin system as a central coordinator for reproduction

Tachykinins are comprised of the family of related peptides, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB). NKB has emerged as regulator of kisspeptin release in the arcuate nucleus (ARC), whereas the roles of SP and NKA in reproduction remain unknown. This work explores the roles of SP and NKA in the central regulation of GnRH release. First, central infusion of specific agonists for the receptors of SP (neurokinin receptor 1, NK1R), NKA (NK2R) and NKB (NK3R) each induced gonadotropin release in adult male and ovariectomized, estradiol-replaced female mice, which was absent in Kiss1r(-/-) mice, indicating a kisspeptin-dependent action. The NK2R agonist, however, decreased LH release in ovariectomized-sham replaced females, as documented for NK3R agonists but in contrast to the NK1R agonist, which further increased LH release. Second, Tac1 (encoding SP and NKA) expression in the ARC and ventromedial nucleus was inhibited by circulating estradiol but did not colocalize with Kiss1 mRNA. Third, about half of isolated ARC Kiss1 neurons expressed Tacr1 (NK1R) and 100% Tacr3 (NK3R); for anteroventral-periventricular Kiss1 neurons and GnRH neurons, approximately one-fourth expressed Tacr1 and one-tenth Tacr3; Tacr2 (NK2R) expression was absent in all cases. Overall, these results identify a potent regulation of gonadotropin release by the SP/NK1R and NKA/NK2R systems in the presence of kisspeptin-Kiss1r signaling, indicating that they may, along with NKB/NK3R, control GnRH release, at least in part through actions on Kiss1 neurons.

Effects and interactions of tachykinins and dynorphin on FSH and LH secretion in developing and adult rats

Kisspeptin/neurokinin B/dynorphin (KNDy) neurons, which coexpress kisspeptins (Kps), neurokinin B (NKB), and dynorphin (Dyn), regulate gonadotropin secretion. The KNDy model proposes that NKB (a stimulator, through NK3R) and Dyn (an inhibitor, through κ-opioid receptor) shape Kp secretion onto GnRH neurons. However, some aspects of this paradigm remain ill defined. Here we aimed to characterize the following: 1) the effects of NKB signaling on FSH secretion and 2) the role of Dyn in gonadotropin secretion after NK3R activation; 3) additionally, we explored the roles of other tachykinin receptors, NK1R and NK2R, on gonadotropin release. Thus, the effects of the NK3R agonist, senktide, on FSH release were explored across postnatal development in male and female rats; gonadotropin responses to agonists of NK1R substance P and NK2R [neurokinin A (NKA)] were also monitored. Moreover, the effects of senktide on gonadotropin secretion were assessed after antagonizing Dyn actions by nor-binaltorphimine didydrochloride. Before puberty, rats of both sexes showed increased FSH secretion to senktide (and Kp-10). Conversely, adult female rats were irresponsive to senktide in terms of FSH, despite proven LH responses, whereas the adult males did not display FSH or LH responses to senktide, even at high doses. In turn, substance P and NKA stimulated gonadotropin secretion in prepubertal rats, whereas in adults modest gonadotropin responses to NKA were detected. By pretreatment with a Dyn antagonist, adult males became responsive to senktide in terms of LH secretion and displayed elevated basal LH and FSH levels; nor-binaltorphimine didydrochloride treatment uncovered FSH responses to senktide in adult females. Furthermore, the expression of Pdyn and Opkr1 (encoding Dyn and κ-opioid receptor, respectively) in the mediobasal hypothalamus was greater in males than in females at prepubertal ages. Overall, our data contribute to refining our understanding on how the elements of the KNDy node and related factors (ie, other tachykinins) differentially participate in the control of gonadotropins at different stages of rat postnatal maturation.

Androgen Receptors Expression in Pituitary of Male Viscacha in relation to Growth and Reproductive Cycle

The aim of this work was to study the androgen receptors (AR) expression in pituitary pars distalis (PD) of male viscachas in relation to growth and reproductive cycle. AR were detected by immunocytochemistry and quantified by image analysis. Pituitary glands from fetus, immature, prepubertal, and adult viscachas during their reproductive cycle were used. In the fetal PD, the immunoreactivity (ir) was mainly cytoplasmic. In immature and prepubertal animals, AR-ir was cytoplasmic (ARc-ir) and nuclear (ARn-ir) in medial region. In adult animals, ARn-ir cells were numerous at caudal end. AR regionalization varied between the PD zones in relation to growth. In immature animals, the ARn-ir increased whereas the cytoplasmic expression decreased in relation to the fetal glands. The percentage of ARc-ir cells increased in prepubertal animals whereas the nuclear AR expression was predominant in adult viscachas. The AR expression changed in adults, showing minimum percentage in the gonadal regression period. The variation of nuclear AR expression was directly related with testosterone concentration. These results demonstrated variations in the immunostaining pattern, regionalization, and number of AR-ir cells throughout development, growth, and reproductive cycle, suggesting the involvement of AR in the regulation of the pituitary activity of male viscacha.

Evidence that Neurokinin B Controls Basal Gonadotropin-Releasing Hormone Secretion but Is Not Critical for Estrogen-Positive Feedback in Sheep

BACKGROUND

Loss-of-function mutations in genes encoding kisspeptin or neurokinin B (NKB) or their receptors cause infertility. NKB is coproduced in kisspeptin neurons in the arcuate nucleus (ARC), and these neurons also produce the NKB receptor (NK3R), allowing autosynaptic function. We tested the hypothesis that NKB action in ARC kisspeptin neurons is aligned with increased pulsatile secretion of luteinizing hormone (LH) and/or activation of the estrogen-induced LH surge in ewes.

METHODS

Using in situ hybridization and immunohistochemistry, we examined NKB expression in kisspeptin neurons during the ovine estrous cycle. We infused kisspeptin, senktide (an NK3R agonist), or dynorphin into the lateral ventricle during the luteal phase of the estrous cycle to determine effects on pulsatile LH secretion. Finally, we examined the effect of an NK3R antagonist (MRK-08) in ovariectomized ewes.

RESULTS

NKB (Tac3) mRNA expression in mid-ARC kisspeptin neurons was elevated during the mid-to-late follicular phase of the estrous cycle. The number of NKB-immunoreactive cells and NKB/kisspeptin terminals in the median eminence was similar during the estrous cycle. Kisspeptin and senktide increased LH pulse frequency and mean LH levels. Central MRK-08 infusion eliminated the LH pulses but did not prevent an estrogen-positive feedback on LH secretion.

CONCLUSIONS

NKB expression in ARC kisspeptin neurons is upregulated during the late follicular phase of the estrous cycle, when the pulsatile secretion of gonadotropin-releasing hormone (GnRH)/LH is maximal. When GnRH/LH secretion is minimal, central senktide infusion induces LH secretion, similar to the response to kisspeptin. Although the increase in LH in response to senktide appeared surge-like, we did not observe any change in the surge following NK3R antagonist treatment. We conclude that NKB plays a role in increasing basal GnRH/LH pulsatility in the follicular phase of the cycle but is not essential for estrogen-induced positive feedback.

Neurokinin-3 receptor activation in the retrochiasmatic area is essential for the full pre-ovulatory luteinising hormone surge in ewes

Neurokinin B (NKB) is essential for human reproduction and has been shown to stimulate luteinising hormone (LH) secretion in several species, including sheep. Ewes express the neurokinin-3 receptor (NK3R) in the retrochiasmatic area (RCh) and there is one report that placement of senktide, an NK3R agonist, therein stimulates LH secretion that resembles an LH surge in ewes. In the present study, we first confirmed that local administration of senktide to the RCh produced a surge-like increase in LH secretion, and then tested the effects of this agonist in two other areas implicated in the control of LH secretion and where NK3R is found in high abundance: the preoptic area (POA) and arcuate nucleus (ARC). Bilateral microimplants containing senktide induced a dramatic surge-like increase in LH when given in the POA similar to that seen with RCh treatment. By contrast, senktide treatment in the ARC resulted in a much smaller but significant increase in LH concentrations suggestive of an effect on tonic secretion. The possible role of POA and RCh NK3R activation in the LH surge was next tested by treating ewes with SB222200, an NK3R antagonist, in each area during an oestradiol-induced LH surge. SB222200 in the RCh, but not in the POA, reduced the LH surge amplitude by approximately 40% compared to controls, indicating that NK3R activation in the former region is essential for full expression of the pre-ovulatory LH surge. Based on these data, we propose that the actions of NKB in the RCh are an important component of the pre-ovulatory LH surge in ewes.

Neurokinin B and reproductive functions: "KNDy neuron" model in mammals and the emerging story in fish

In mammals, neurokinin B (NKB), the gene product of the tachykinin family member TAC3, is known to be a key regulator for episodic release of luteinizing hormone (LH). Its regulatory actions are mediated by a subpopulation of kisspeptin neurons within the arcuate nucleus with co-expression of NKB and dynorphin A (commonly called the "KNDy neurons"). By forming an "autosynaptic feedback loop" within the hypothalamus, the KNDy neurons can modulate gonadotropin-releasing hormone (GnRH) pulsatility and subsequent LH release in the pituitary. NKB regulation of LH secretion has been recently demonstrated in zebrafish, suggesting that the reproductive functions of NKB may be conserved from fish to mammals. Interestingly, the TAC3 genes in fish not only encode the mature peptide of NKB but also a novel tachykinin-like peptide, namely NKB-related peptide (or neurokinin F). Recent studies in zebrafish also reveal that the neuroanatomy of TAC3/kisspeptin system within the fish brain is quite different from that of mammals. In this article, the current ideas of "KNDy neuron" model for GnRH regulation and steroid feedback, other reproductive functions of NKB including its local actions in the gonad and placenta, the revised model of tachykinin evolution from invertebrates to vertebrates, as well as the emerging story of the two TAC3 gene products in fish, NKB and NKB-related peptide, will be reviewed with stress on the areas with interesting questions for future investigations.

Electrophysiology of arcuate neurokinin B neurons in female Tac2-EGFP transgenic mice

Neurons in the arcuate nucleus that coexpress kisspeptin, neurokinin B (NKB), and dynorphin (KNDy neurons) play an important role in the modulation of reproduction by estrogens. Here, we study the anatomical and electrophysiological properties of arcuate NKB neurons in heterozygous female transgenic mice with enhanced green fluorescent protein (EGFP) under the control of the Tac2 (NKB) promoter (Tac2-EGFP mice). The onset of puberty, estrous cyclicity, and serum LH were comparable between Tac2-EGFP and wild-type mice. The location of EGFP-immunoreactive neurons was consistent with previous descriptions of Tac2 mRNA-expressing neurons in the rodent. In the arcuate nucleus, nearly 80% of EGFP neurons expressed pro-NKB-immunoreactivity. Moreover, EGFP fluorescent intensity in arcuate neurons was increased by ovariectomy and reduced by 17β-estradiol (E2) treatment. Electrophysiology of single cells in tissue slices was used to examine the effects of chronic E2 treatment on Tac2-EGFP neurons in the arcuate nucleus of ovariectomized mice. Whole-cell recordings revealed arcuate NKB neurons to be either spontaneously active or silent in both groups. E2 had no significant effect on the basic electrophysiological properties or spontaneous firing frequencies. Arcuate NKB neurons exhibited either tonic or phasic firing patterns in response to a series of square-pulse current injections. Notably, E2 reduced the number of action potentials evoked by depolarizing current injections. This study demonstrates the utility of the Tac2-EGFP mouse for electrophysiological and morphological studies of KNDy neurons in tissue slices. In parallel to E2 negative feedback on LH secretion, E2 decreased the intensity of the EGFP signal and reduced the excitability of NKB neurons in the arcuate nucleus of ovariectomized Tac2-EGFP mice.

A role for neurokinin B in pulsatile GnRH secretion in the ewe

The recent description of infertility in humans with loss-of-function mutations in genes for neurokinin B (NKB) or its receptor (NK3R) has focused attention on the importance of this tachykinin in the control of GnRH secretion. In a number of species, NKB neurons in the arcuate nucleus also produce two other neuropeptides implicated in the control of GnRH secretion: (1) kisspeptin, which is also essential for fertility in humans, and (2) dynorphin, an inhibitory endogenous opioid peptide. A number of characteristics of this neuronal population led to the hypothesis that they may be responsible for driving synchronous release of GnRH during episodic secretion of this hormone, and there is now considerable evidence to support this hypothesis in sheep and goats. In this article, we briefly review the history of work on the NKB system in sheep and then review the anatomy of NKB signaling in the ewe. We next describe evidence from a number of species that led to development of a model for the role of these neurons in episodic GnRH secretion. Finally, we discuss recent experiments in sheep and goats that tested this hypothesis and led to a modified version of the model, and then broaden our focus to briefly consider the possible roles of NKB in other species and systems.

Kisspeptin neurones do not directly signal to RFRP-3 neurones but RFRP-3 may directly modulate a subset of hypothalamic kisspeptin cells in mice

The neuropeptides kisspeptin (encoded by Kiss1) and RFamide-related peptide-3 (also known as GnIH; encoded by Rfrp) are potent stimulators and inhibitors, respectively, of reproduction. Whether kisspeptin or RFRP-3 might act directly on each other's neuronal populations to indirectly modulate reproductive status is unknown. To examine possible interconnectivity of the kisspeptin and RFRP-3 systems, we performed double-label in situ hybridisation (ISH) for the RFRP-3 receptors, Gpr147 and Gpr74, in hypothalamic Kiss1 neurones of adult male and female mice, as well as double-label ISH for the kisspeptin receptor, Kiss1r, in Rfrp-expressing neurones of the hypothalamic dorsal-medial nucleus (DMN). Only a very small proportion (5-10%) of Kiss1 neurones of the anteroventral periventricular region expressed Gpr147 or Gpr74 in either sex, whereas higher co-expression (approximately 25%) existed in Kiss1 neurones in the arcuate nucleus. Thus, RFRP-3 could signal to a small, primarily arcuate, subset of Kiss1 neurones, a conclusion supported by the finding of approximately 35% of arcuate kisspeptin cells receiving RFRP-3-immunoreactive fibre contacts. By contrast to the former situation, no Rfrp neurones co-expressed Kiss1r in either sex, and Tacr3, the receptor for neurokinin B (NKB; a neuropeptide co-expressed with arcuate kisspeptin neurones) was found in <10% of Rfrp neurones. Moreover, kisspeptin-immunoreactive fibres did not readily appose RFRP-3 cells in either sex, further excluding the likelihood that kisspeptin neurones directly communicate to RFRP-3 neurones. Lastly, despite abundant NKB in the DMN region where RFRP-3 soma reside, NKB was not co-expressed in the majority of Rfrp neurones. Our results suggest that RFRP-3 may modulate a small proportion of kisspeptin-producing neurones in mice, particularly in the arcuate nucleus, whereas kisspeptin neurones are unlikely to have any direct reciprocal actions on RFRP-3 neurones.

Kisspeptin and GnRH pulse generation

The reproductive neuropeptide gonadotropin-releasing hormone (GnRH) has two modes of secretion. Besides the surge mode, which induces ovulation in females, the pulse mode of GnRH release is essential to cause various reproductive events in both sexes, such as spermatogenesis, follicular development, and sex steroid synthesis. Some environmental cues control gonadal activities through modulating GnRH pulse frequency. Researchers have looked for the anatomical location of the mechanism generating GnRH pulses, the GnRH pulse generator, in the brain, because an artificial manipulation of GnRH pulse frequency is of therapeutic importance to stimulate or suppress gonadal activity. Discoveries of kisspeptin and, consequently, KNDy (kisspeptin/neurokinin B/dynorphin) neurons in the hypothalamus have provided a clue to the possible location of the GnRH pulse generator. Our analyses of hypothalamic multiple-unit activity revealed that KNDy neurons located in the hypothalamic arcuate nucleus might play a central role in the generation of GnRH pulses in goats, and perhaps other mammalian species. This chapter further discusses the possible mechanisms for GnRH pulse generation.

Substance P immunoreactivity exhibits frequent colocalization with kisspeptin and neurokinin B in the human infundibular region

Neurons synthesizing neurokinin B (NKB) and kisspeptin (KP) in the hypothalamic arcuate nucleus represent important upstream regulators of pulsatile gonadotropin-releasing hormone (GnRH) neurosecretion. In search of neuropeptides co-expressed in analogous neurons of the human infundibular nucleus (Inf), we have carried out immunohistochemical studies of the tachykinin peptide Substance P (SP) in autopsy samples from men (21-78 years) and postmenopausal (53-83 years) women. Significantly higher numbers of SP-immunoreactive (IR) neurons and darker labeling were observed in the Inf of postmenopausal women than in age-matched men. Triple-immunofluorescent studies localized SP immunoreactivity to considerable subsets of KP-IR and NKB-IR axons and perikarya in the infundibular region. In postmenopausal women, 25.1% of NKB-IR and 30.6% of KP-IR perikarya contained SP and 16.5% of all immunolabeled cell bodies were triple-labeled. Triple-, double- and single-labeled SP-IR axons innervated densely the portal capillaries of the infundibular stalk. In quadruple-labeled sections, these axons formed occasional contacts with GnRH-IR axons. Presence of SP in NKB and KP neurons increases the functional complexity of the putative pulse generator network. First, it is possible that SP modulates the effects of KP and NKB in axo-somatic and axo-dendritic afferents to GnRH neurons. Intrinsic SP may also affect the activity and/or neuropeptide release of NKB and KP neurons via autocrine/paracrine actions. In the infundibular stalk, SP may influence the KP and NKB secretory output via additional autocrine/paracrine mechanisms or regulate GnRH neurosecretion directly. Finally, possible co-release of SP with KP and NKB into the portal circulation could underlie further actions on adenohypophysial gonadotrophs.

Modulation of body temperature and LH secretion by hypothalamic KNDy (kisspeptin, neurokinin B and dynorphin) neurons: a novel hypothesis on the mechanism of hot flushes

Despite affecting millions of individuals, the etiology of hot flushes remains unknown. Here we review the physiology of hot flushes, CNS pathways regulating heat-dissipation effectors, and effects of estrogen on thermoregulation in animal models. Based on the marked changes in hypothalamic kisspeptin, neurokinin B and dynorphin (KNDy) neurons in postmenopausal women, we hypothesize that KNDy neurons play a role in the mechanism of flushes. In the rat, KNDy neurons project to preoptic thermoregulatory areas that express the neurokinin 3 receptor (NK3R), the primary receptor for NKB. Furthermore, activation of NK₃R in the median preoptic nucleus, part of the heat-defense pathway, reduces body temperature. Finally, ablation of KNDy neurons reduces cutaneous vasodilatation and partially blocks the effects of estrogen on thermoregulation. These data suggest that arcuate KNDy neurons relay estrogen signals to preoptic structures regulating heat-dissipation effectors, supporting the hypothesis that KNDy neurons participate in the generation of flushes.

Regulation of arcuate neurons coexpressing kisspeptin, neurokinin B, and dynorphin by modulators of neurokinin 3 and κ-opioid receptors in adult male mice

Pulsatile GnRH release is essential to fertility and is modulated by gonadal steroids, most likely via steroid-sensitive afferents. Arcuate neurons coexpressing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy neurons) are steroid-sensitive and have been postulated to both generate GnRH pulses and mediate steroid feedback on pulse frequency. KNDy neurons are proposed to interact with one another via NKB and dynorphin to activate and inhibit the KNDy network, respectively, and thus alter kisspeptin output to GnRH neurons. To test the roles of NKB and dynorphin on KNDy neurons and the steroid sensitivity of these actions, targeted extracellular recordings were made of Tac2(NKB)-GFP-identified neurons from castrate and intact male mice. Single-cell PCR confirmed most of these cells had a KNDy phenotype. The neurokinin 3 receptor (NK3R) agonist senktide increased action potential firing activity of KNDy neurons. Dynorphin reduced spontaneous KNDy neuron activity, but antagonism of κ-opioid receptors (KOR) failed to induce firing activity in quiescent KNDy neurons. Senktide-induced activation was greater in KNDy neurons from castrate mice, whereas dynorphin-induced suppression was greater in KNDy neurons from intact mice. Interactions of dynorphin with senktide-induced activity were more complex; dynorphin treatment after senktide had no consistent inhibitory effect, whereas pretreatment with dynorphin decreased senktide-induced activity only in KNDy neurons from intact but not castrate mice. These data suggest dynorphin-mediated inhibition of senktide-induced activity requires gonadal steroid feedback. Together, these observations support the hypotheses that activation of NK3R and KOR, respectively, excites and inhibits KNDy neurons and that gonadal steroids modulate these effects.

Interactions between kisspeptins and neurokinin B

Reproductive function is tightly regulated by an intricate network of central and peripheral factors; however, the precise mechanism triggering critical reproductive events, such as puberty onset, remains largely unknown. Recently, the neuropeptides kisspeptin (encoded by Kiss1) and neurokinin B (NKB, encoded by TAC3 in humans and Tac2 in rodents) have been placed as essential gatekeepers of puberty. Studies in humans and rodents have revealed that loss-of-function mutations in the genes encoding either kisspeptin and NKB or their receptors, Kiss1r and neurokinin 3 receptor (NK3R), lead to impaired sexual maturation and infertility. Kisspeptin, NKB, and dynorphin A are co-expressed in neurons of the arcuate nucleus (ARC), so-called Kisspeptin/NKB/Dyn (KNDy) neurons. Importantly, these neurons also co-express NK3R. Compelling evidence suggests a stimulatory role of NKB (or the NK3R agonist, senktide) on LH release in a number of species. This effect is likely mediated by autosynaptic inputs of NKB on KNDy neurons to induce the secretion of gonadotropin-releasing hormone (GnRH) in a kisspeptin--dependent manner, with the coordinated actions of other neuroendocrine factors, such as dynorphin, glutamate, or GABA. Thus, we have proposed a model in which NKB feeds back to the KNDy neuron to shape the pulsatile release of kisspeptin, and hence GnRH, in a mechanism also dependent on the sex steroid level. Additionally, NKB may contribute to the regulation of the reproductive function by metabolic cues. Investigating how NKB and kisspeptin interact to regulate the gonadotropic axis will offer new insights into the control of GnRH release during puberty onset and the maintenance of the reproductive function in adulthood, offering a platform for the understanding and treatment of a number of reproductive disorders.

Molecular profiling of postnatal development of the hypothalamus in female and male rats

Reproductive function is highly dynamic during postnatal developmental. Here, we performed molecular profiling of gene expression patterns in the hypothalamus of developing male and female rats to identify which genes are sexually dimorphic, to gain insight into a more complex network of hypothalamic genes, and to ascertain dynamic changes in their relationships with one another and with sex steroid hormones during development. Using a low-density PCR platform, we quantified mRNA levels in the preoptic area (POA) and medial basal hypothalamus (MBH), and assayed circulating estradiol, testosterone, and progesterone at six ages from birth through adulthood. Numerous genes underwent developmental change, particularly postnatal increases, decreases, or peaks/plateaus at puberty. Surprisingly, there were few sex differences; only Esr1, Kiss1, and Tac2 were dimorphic (higher in females). Cluster analysis of gene expression revealed sexually dimorphic correlations in the POA but not the MBH from P30 (Postnatal Day 30) to P60. Hormone measurements showed few sex differences in developmental profiles of estradiol; higher levels of progesterone in females only after P30; and a developmental pattern of testosterone with a nadir at P30 followed by a dramatic increase through P60 (males). Furthermore, bionetwork analysis revealed that hypothalamic gene expression profiles and their relationships to hormones undergo dynamic developmental changes that differ considerably from adults. These data underscore the importance of developmental stage in considering the effects of hormones on the regulation of neuroendocrine genes in the hypothalamus. Moreover, the finding that few neuroendocrine genes are sexually dimorphic highlights the need to consider postnatal development from a network approach that allows assessment of interactions and patterns of expression.

Sex differences in the neurokinin B system in the human infundibular nucleus

CONTEXT

The recent report that loss-of-function mutations in either the gene encoding neurokinin B (NKB) or its receptor (NK3R) produce gonadotropin deficiencies in humans strongly points to NKB as a key regulator of GnRH release.

OBJECTIVES

We used NKB immunohistochemistry on postmortem human brain tissue to determine: 1) whether the human NKB system in the infundibular nucleus (INF) is sexually dimorphic; 2) at what stage in development the infundibular NKB system would diverge between men and women; 3) whether this putative structural difference is reversed in male-to-female (MtF) transsexual people; and 4) whether menopause is accompanied by changes in infundibular NKB immunoreactivity.

METHODS

NKB immunohistochemical staining was performed on postmortem hypothalamus material of both sexes from the infant/pubertal period into the elderly period and from MtF transsexuals.

RESULTS

Quantitative analysis demonstrated that the human NKB system exhibits a robust female-dominant sexual dimorphism in the INF. During the first years after birth, both sexes displayed a moderate and equivalent level of NKB immunoreactivity in the INF. The adult features emerged progressively around puberty until adulthood, where the female-dominant sex difference appeared and continued into old age. In MtF transsexuals, a female-typical NKB immunoreactivity was observed. Finally, in postmenopausal women, there was a significant increase in NKB immunoreactivity compared to premenopausal women.

CONCLUSION

Our results indicate that certain sex differences do not emerge until adulthood when activated by sex steroid hormones and the likely involvement of the human infundibular NKB system in the negative and positive feedback of estrogen on GnRH secretion.

Role for kisspeptin/neurokinin B/dynorphin (KNDy) neurons in cutaneous vasodilatation and the estrogen modulation of body temperature

Estrogen withdrawal in menopausal women leads to hot flushes, a syndrome characterized by the episodic activation of heat dissipation effectors. Despite the extraordinary number of individuals affected, the etiology of flushes remains an enigma. Because menopause is accompanied by marked alterations in hypothalamic kisspeptin/neurokinin B/dynorphin (KNDy) neurons, we hypothesized that these neurons could contribute to the generation of flushes. To determine if KNDy neurons participate in the regulation of body temperature, we evaluated the thermoregulatory effects of ablating KNDy neurons by injecting a selective toxin for neurokinin-3 expressing neurons [NK(3)-saporin (SAP)] into the rat arcuate nucleus. Remarkably, KNDy neuron ablation consistently reduced tail-skin temperature (T(SKIN)), indicating that KNDy neurons facilitate cutaneous vasodilatation, an important heat dissipation effector. Moreover, KNDy ablation blocked the reduction of T(SKIN) by 17β-estradiol (E(2)), which occurred in the environmental chamber during the light phase, but did not affect the E(2) suppression of T(SKIN) during the dark phase. At the high ambient temperature of 33 °C, the average core temperature (T(CORE)) of ovariectomized (OVX) control rats was significantly elevated, and this value was reduced by E(2) replacement. In contrast, the average T(CORE) of OVX, KNDy-ablated rats was lower than OVX control rats at 33 °C, and not altered by E(2) replacement. These data provide unique evidence that KNDy neurons promote cutaneous vasodilatation and participate in the E(2) modulation of body temperature. Because cutaneous vasodilatation is a cardinal sign of a hot flush, these results support the hypothesis that KNDy neurons could play a role in the generation of flushes.

Neurokinin B and the control of the gonadotropic axis in the rat: developmental changes, sexual dimorphism, and regulation by gonadal steroids

Neurokinin B (NKB), encoded by Tac2 in rodents, and its receptor, NK3R, have recently emerged as important regulators of reproduction; NKB has been proposed to stimulate kisspeptin output onto GnRH neurons. Accordingly, NKB has been shown to induce gonadotropin release in several species; yet, null or even inhibitory effects of NKB have been also reported. The basis for these discrepant findings, as well as other key aspects of NKB function, remains unknown. We report here that in the rat, LH responses to the NK3R agonist, senktide, display a salient sexual dimorphism, with persistent stimulation in females, regardless of the stage of postnatal development, and lack of LH responses in males from puberty onward. Such dimorphism was independent of the predominant sex steroid after puberty, because testosterone administration to adult females failed to prevent LH responses to senktide, and LH responsiveness was not restored in adult males treated with estradiol or the nonaromatizable androgen, dihydrotestosterone. Yet, removal of sex steroids by gonadectomy switched senktide effects to inhibitory, both in adult male and female rats. Sexual dimorphism was also evident in the numbers of NKB-positive neurons in the arcuate nucleus (ARC), which were higher in adult female rats. This is likely the result of differences in sex steroid milieu during early periods of brain differentiation, because neonatal exposures to high doses of estrogen decreased ARC NKB neurons at later developmental stages. Likewise, neonatal estrogenization resulted in lower serum LH levels that were normalized by senktide administration. Finally, we document that the ability of estrogen to inhibit hypothalamic Tac2 expression seems region specific, because estrogen administration decreased Tac2 levels in the ARC but increased them in the lateral hypothalamus. Altogether, our data provide a deeper insight into relevant aspects of NKB function as major regulator of the gonadotropic axis in the rat, including maturational changes, sexual dimorphism, and differential regulation by sex steroids.

Central administration of neurokinin B activates kisspeptin/NKB neurons in the arcuate nucleus and stimulates luteinizing hormone secretion in ewes during the non-breeding season

Human genetic studies have suggested that kisspeptin and neurokinin B (NKB) play pivotal roles in the control of gonadotropin-releasing hormone (GnRH) secretion. However, the role of NKB in this context is less clear compared with that of kisspeptin. In the present study, we investigated the ratio of colocalization of kisspeptin and NKB in neurons in the arcuate nucleus (ARC), the effects of intracerebroventricular infusion of NKB on luteinizing hormone (LH) secretion and whether the treatment activates ARC kisspeptin/NKB neurons in seasonally anestrous ewes. Double-labeling immunohistochemistry revealed that the majority of kisspeptin neurons coexpressed NKB in the ARC. Infusion of NKB for 2 h into the lateral ventricle elicited a discharge of LH, which resulted in significant increases in LH concentrations between 20 and 50 min after the start of infusion compared with a saline-infused control. Animals were sacrificed immediately after the end of infusion, and Fos expression in ARC kisspeptin neurons was immunohistochemically examined. The NKB treatment activated kisspeptin neurons throughout the ARC, and approximately 70% of kisspeptin neurons expressed Fos immunoreactivity at the caudal portion of the nucleus. The present study demonstrated that a central infusion of NKB elicited a discharge of LH, which was associated with the activation of a large population of ARC kisspeptin/NKB neurons in seasonally anestrous ewes. The results suggest that NKB plays a stimulatory role in the control of pulsatile GnRH secretion and that the population of ARC kisspeptin/NKB neurons is one of sites of the NKB action in sheep.

Arcuate kisspeptin/neurokinin B/dynorphin (KNDy) neurons mediate the estrogen suppression of gonadotropin secretion and body weight

Estrogen withdrawal increases gonadotropin secretion and body weight, but the critical cell populations mediating these effects are not well understood. Recent studies have focused on a subpopulation of hypothalamic arcuate neurons that coexpress estrogen receptor α, neurokinin 3 receptor (NK(3)R), kisspeptin, neurokinin B, and dynorphin for the regulation of reproduction. To investigate the function of kisspeptin/neurokinin B/dynorphin (KNDy) neurons, a novel method was developed to ablate these cells using a selective NK(3)R agonist conjugated to the ribosome-inactivating toxin, saporin (NK(3)-SAP). Stereotaxic injections of NK(3)-SAP in the arcuate nucleus ablated KNDy neurons, as demonstrated by the near-complete loss of NK(3)R, NKB, and kisspeptin-immunoreactive (ir) neurons and depletion of the majority of arcuate dynorphin-ir neurons. Selectivity was demonstrated by the preservation of proopiomelanocortin, neuropeptide Y, and GnRH-ir elements in the arcuate nucleus and median eminence. In control rats, ovariectomy (OVX) markedly increased serum LH, FSH, and body weight, and these parameters were subsequently decreased by treatment with 17β-estradiol. KNDy neuron ablation prevented the rise in serum LH after OVX and attenuated the rise in serum FSH. KNDy neuron ablation did not completely block the suppressive effects of E(2) on gonadotropin secretion, a finding consistent with redundant pathways for estrogen negative feedback. However, regardless of estrogen status, KNDy-ablated rats had lower levels of serum gonadotropins compared with controls. Surprisingly, KNDy neuron ablation prevented the dramatic effects of OVX and 17β-estradiol (E(2)) replacement on body weight and abdominal girth. These data provide evidence that arcuate KNDy neurons are essential for tonic gonadotropin secretion, the rise in LH after removal of E(2), and the E(2) modulation of body weight.