Tachykinins and the hypothalamo-pituitary-gonadal axis: An update

The Biological Properties of the FAS and TACR3 Genes and the Association of Single-Nucleotide Polymorphisms with Milk Quality Traits in Gannan Yak

Fatty acid synthase (FAS) is a fundamental metabolic enzyme that catalyzes the synthesis of endogenous fatty acids; TACR3, also known as tachykinin receptor 3 or NK3R, is an important G-protein-coupled receptor that is primarily responsible for responding to neuropeptides such as neurokinin B (NKB) and plays a crucial role in embryonic development, organ formation, and cell differentiation. This study aimed to explore the association between the single-nucleotide polymorphisms (SNPs) of the FAS and TACR3 genes and the milk quality of Gannan yak and to determine them as potential molecular marker loci for the milk quality of yaks. The genotyping of 162 Gannan yaks was performed using liquid-phase chip technology. Association analyses were conducted between the obtained SNP loci genotypes and milk composition traits, including milk protein, casein, non-fat solids, and acidity. Comparative sequence analysis of two genes (FAS and TACR3) across multiple species revealed that the yak FAS gene exhibited the highest homology with Bos taurus and Bos indicus, while the yak TACR3 gene showed the greatest sequence similarity to Bos taurus. Hardy-Weinberg equilibrium tests were performed on four SNP loci, and the equilibrium indices of the four loci were 0.799, 0.368, 0.689, and 0.948 (p > 0.05), indicating that all of these loci are in Hardy-Weinberg equilibrium state. g.13,276T>C (FAS) was significantly correlated with lactose content traits (p < 0.05); g.74,382C>G (FAS) was significantly correlated with casein, protein, total solids, non-fat solids, and acidity traits (p < 0.05); g.40,529A>G (TACR3) was significantly correlated with protein, non-fat solids, citric acid, and acidity traits (p < 0.05). The influence of g.40,555C>T (TACR3) on these traits did not reach a significant level (p > 0.05). This study suggests that two genes can serve as potential candidate genes affecting the quality of Gannan yak milk, providing reference genes for improving the quality of Gannan yak milk.

Ovarian tachykinin signaling system induces the growth of secondary follicles during the gonadotropin-independent process

Mammalian follicle growth development is mainly regulated by the hypothalamus-pituitary-gonadal axis after puberty. Although pituitary hormones, gonadotropins, are involved in hypothalamus-pituitary-gonadal axis signaling, they are not responsible for the growth of early stage follicles, namely, primordial follicles, primary follicles, and secondary follicles, in both sexually immature and mature individuals. Unlike those of gonadotropin-dependent follicle growth, the specific regulatory factors of gonadotropin-independent follicle growth have yet to be identified. Here, we identified tachykinins (TKs) as inducers of gonadotropin-independent secondary follicle growth. TKs play various roles as neuropeptides or hormones in a wide variety of biological events both in the central nervous system and in peripheral tissues, but a direct effect of TKs on ovarian follicles has yet to investigated. Follicle development was suppressed in sexually immature 3-week-old KO mice of Tac1 gene encoding TKs (substance P and neurokinin A), which is independent of gonadotropins. TKs and their receptors are specifically localized to granulosa cells in mouse secondary follicles. Furthermore, TKs upregulate the prostaglandin (PG) synthase cyclooxygenase 2 via the Janus kinase 1-signal transducers and activators of transcription protein 3 signaling cascade. We also demonstrated that PGE2 and PGF2α are major PGs in the immature ovary, and the secondary follicle growth was enhanced by interaction between PGE2-PGF2α and their receptors, PGE2 receptor localized in the oocyte membrane and PGF2α receptor localized in the oocyte membrane, granulosa cells, and theca cells. Consequently, this study paves the way for exploring gonadotropin-independent early stage follicle growth systems and relevant dysfunctions, including pediatric endocrinological diseases.

The Impact of Methylphenidate on Pubertal Maturation and Bone Age in ADHD Children and Adolescents: Results from the ADHD Drugs Use Chronic Effects (ADDUCE) Project

OBJECTIVE

The short-term safety of methylphenidate (MPH) has been widely demonstrated; however the long-term safety is less clear. The aim of this study was to investigate the safety of MPH in relation to pubertal maturation and to explore the monitoring of bone age.

METHOD

Participants from ADDUCE, a two-year observational longitudinal study with three parallel cohorts (MPH group, no-MPH group, and a non-ADHD control group), were compared with respect to Tanner staging. An Italian subsample of medicated-ADHD was further assessed by the monitoring of bone age.

RESULTS

The medicated and unmedicated ADHD groups did not differ in Tanner stages indicating no higher risk of sexual maturational delay in the MPH-treated patients. The medicated subsample monitored for bone age showed a slight acceleration of the bone maturation after 24 months, however their predicted adult height remained stable.

CONCLUSION

Our results do not suggest safety concerns on long-term treatment with MPH in relation to pubertal maturation and growth.

Role of Neurokinin B in gametogenesis and steroidogenesis of freshwater catfish, Clarias batrachus

Neurokinin B (NKB), a recently discovered neuropeptide, plays a crucial role in regulating the kiss-GnRH neurons in vertebrate's brain. NKB is also characterized in gonadal tissues; however, its role in gonads is poorly understood. Therefore, in the present study, the effects of NKB on gonadal steroidogenesis and gametogenesis through in vivo and in vitro approaches using NKB antagonist MRK-08 were evaluated. The results suggest that the NKB antagonist decreases the development of advanced ovarian follicles and germ cells in the testis. In addition, MRK-08 further reduces the production of 17β-estradiol in the ovary and testosterone in the testis under both in vivo and in vitro conditions in a dose-dependent manner. Furthermore, the in vitro MRK-08 treatment of gonadal explants attenuated the expression of steroidogenic marker proteins, i.e., StAR, 3β-HSD, and 17β-HSD dose-dependently. Moreover, the MAP kinase proteins, pERK1/2 & ERK1/2 and pAkt & Akt were also downregulated by MRK-08. Thus, the study suggests that NKB downregulates steroidogenesis by modulating the expressions of steroidogenic marker proteins involving ERK1/2 & pERK1/2 and Akt/pAkt signalling pathways. NKB also appears to regulate gametogenesis by regulating gonadal steroidogenesis in the catfish.

Orexin antagonism and substance-P: Effects and interactions on polycystic ovary syndrome in the wistar rats

BACKGROUND

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder without definitive treatments. Orexin and Substance-P (SP) neuropeptides can affect the ovarian steroidogenesis. Moreover, there are limited studies about the role of these neuropeptides in PCOS. We aimed here to clarify the effects of orexins and SP in PCOS as well as any possible interactions between them.

METHODS

For this purpose, the animals (n = five rats per group) received intraperitoneally a single dose of SB-334,867-A (orexin-1 receptor antagonist; OX1Ra), JNJ-10,397,049 (orexin-2 receptor antagonist; OX2Ra), and CP-96,345 (neurokinin-1 receptor antagonist; NK1Ra), alone or in combination with each other after two months of PCOS induction. The blocking of orexin and SP receptors was studied in terms of ovarian histology, hormonal changes, and gene expression of ovarian steroidogenic enzymes.

RESULTS

The antagonists' treatment did not significantly affect the formation of ovarian cysts. In the PCOS groups, the co-administration of OX1Ra and OX2Ra as well as their simultaneous injections with NK1Ra significantly reversed testosterone levels and Cyp19a1 gene expression when compared to the PCOS control group. There were no significant interactions between the PCOS groups that received NK1Ra together with one or both OX1R- and OX2R-antagonists.

CONCLUSION

The blocking of the orexin receptors modulates abnormal ovarian steroidogenesis in the PCOS model of rats. This suggests that the binding of orexin-A and -B to their receptors reduces Cyp19a1 gene expression while increasing testosterone levels.

Tachykinin receptor 3 in the lateral habenula alleviates pain and anxiety comorbidity in mice

The coexistence of chronic pain and anxiety is a common clinical phenomenon. Here, the role of tachykinin receptor 3 (NK3R) in the lateral habenula (LHb) in trigeminal neuralgia and in pain-associated anxiety was systematically investigated. First, electrophysiological recording showed that bilateral LHb neurons are hyperactive in a mouse model of trigeminal neuralgia made by partial transection of the infraorbital nerve (pT-ION). Chemicogenetic activation of bilateral LHb glutamatergic neurons in naive mice induced orofacial allodynia and anxiety-like behaviors, and pharmacological activation of NK3R in the LHb attenuated allodynia and anxiety-like behaviors induced by pT-ION. Electrophysiological recording showed that pharmacological activation of NK3R suppressed the abnormal excitation of LHb neurons. In parallel, pharmacological inhibition of NK3R induced orofacial allodynia and anxiety-like behavior in naive mice. The electrophysiological recording showed that pharmacological inhibition of NK3R activates LHb neurons. Neurokinin B (NKB) is an endogenous high-affinity ligand of NK3R, which binds NK3R and activates it to perform physiological functions, and further neuron projection tracing showed that the front section of the periaqueductal gray (fPAG) projects NKB-positive nerve fibers to the LHb. Optogenetics combined with electrophysiology recordings characterize the functional connections in this fPAG ^NKB → LHb pathway. In addition, electrophysiological recording showed that NKB-positive neurons in the fPAG were more active than NKB-negative neurons in pT-ION mice. Finally, inhibition of NKB release from the fPAG reversed the analgesic and anxiolytic effects of LHb Tacr3 overexpression in pT-ION mice, indicating that fPAG ^NKB → LHb regulates orofacial allodynia and pain-induced anxious behaviors. These findings for NK3R suggest the cellular mechanism behind pT-ION in the LHb and suggest that the fPAG ^NKB → LHb circuit is involved in pain and anxiety comorbidity. This previously unrecognized pathway might provide a potential approach for relieving the pain and anxiety associated with trigeminal neuralgia by targeting NK3R.

Female Infertility Is Associated with an Altered Expression Profile of Different Members of the Tachykinin Family in Human Granulosa Cells

Neurokinin B (NKB) and its cognate receptor, NK3R, play a key role in the regulation of reproduction. NKB belongs to the family of tachykinins, which also includes substance P and neurokinin A, both encoded by the by the gene TAC1, and hemokinin-1, encoded by the TAC4 gene. In addition to NK3R, tachykinin effects are mediated by NK1R and NK2R, encoded by the genes TACR1 and TACR2, respectively. The role of these other tachykinins and receptors in the regulation of women infertility is mainly unknown. We have analyzed the expression profile of TAC1, TAC4, TACR1, and TACR2 in mural granulosa and cumulus cells from women presenting different infertility etiologies, including polycystic ovarian syndrome, advanced maternal age, low ovarian response, and endometriosis. We also studied the expression of MME, the gene encoding neprilysin, the most important enzyme involved in tachykinin degradation. Our data show that TAC1, TAC4, TACR1, TACR2, and MME expression is dysregulated in a different manner depending on the etiology of women infertility. The abnormal expression of these tachykinins and their receptors might be involved in the decreased fertility of these patients, offering a new insight regarding the diagnosis and treatment of women infertility.

Substance P-Immunoreactive Fiber Varicosities Appear to Innervate Galaninergic Perikarya in the Human Hypothalamus

Introduction: Substance P (SP) is a member of the tachykinin family. In the central nervous system, SP participates among others, in the regulation of pain, learning, memory, emotion, and sexual functions. In the periphery, SP affects the gastrointestinal, cardiovascular, and urinary systems. Galanin, similarly to SP, appears to be involved in wide range of physiologic functions, including cognition, waking and sleep, feeding, mood, blood pressure, reproduction, and development, where acts as a trophic factor. The similar distribution of SP-immunoreactive (SP-IR) fibers and galanin-IR perikarya in the human hypothalamus suggests functional interaction between these neuropeptides. Methods: We have utilized double-label immunohistochemistry to reveal these putative juxtapositions. Results: The majority of galanin-IR neurons receive contacting SP-IR fibers that often cover a significant area of the galaninergic perikarya forming multiple en passant type contacts. These SP-galanin juxtapositions are located mainly in the basal part of the infundibulum/median eminence, populating the basal periventricular region as well as the basal perifornical area. Discussion: The density and the morphology of these associations suggest that these contacts are functional synapses and therefore may represent the morphological substrate of the control of SP on multiple functions regulated/modulated by galanin. SP via galanin may modulate anterior pituitary hormone secretion, as contrary to SP, high density of galanin immunoreactivity is present in the median eminence, and by innervating galanin-IR neurons projecting to other parts of the brain, SP can modulate indirectly their activities. Impact statement The present study is the first describing juxtapositions between the substance P (SP)-immunoreactive (IR) and galanin-IR neurons in the human hypothalamus. These juxtapositions may be functional synapses and they may represent the morphological substrate of the control of SP on the galaninergic system. SP via galanin may modulate anterior pituitary hormone secretion, as contrary to SP, high density of galanin immunoreactivity is present in the median eminence. Galanin, released into the hypothalamo-hypophyseal circulation, can reach the anterior pituitary and function as a hypophysiotropic substance and regulates anterior pituitary hormone secretion. SP by innervating galanin-IR neurons, which project to other parts of the brain, can modulate indirectly their activities.

Tacr3/NK3R: Beyond Their Roles in Reproduction

The Tacr3 gene encodes tachykinin receptor 3 (NK3R), which belongs to the tachykinin receptor family. This family of proteins includes typical G protein-coupled receptors and belongs to the rhodopsin subfamily. NK3R functions by binding to its high-affinity ligand, neurokinin B(NKB). The role of Tacr3/NK3R in growth and reproduction has been extensively studied, but Tacr3/NK3R is also widely expressed in the nervous system from the spinal cord to the brain and is involved in both physiological and pathological processes in the nervous system, including mood disorders, chronic pain, learning and memory deficiencies, Alzheimer's disease, Parkinson's disease, addiction-related processes, hypoxic-ischemic encephalopathy, body fluid management, neural development, and schizophrenia. Here, we summarize the structure of NK3R/NKB and its cellular signaling as well as the expression of Tacr3/NK3R in the nervous system, and we provide a comprehensive summary of the role of Tacr3/NK3R in neurological diseases, including reproduction-related disorders and other neurological diseases. At the end of this review, we propose the hypothesis that Tacr3/NK3R mediates a variety of brain functions by affecting the excitability of different neurons with specific functions. On the basis of this "excited or not" hypothesis, more studies related to Tacr3 should be carried out in other nervous system diseases in order to better understand the biological roles of Tacr3.

Sexual Dimorphic Distribution of Hypothalamic Tachykinin1 Cells and Their Innervations to GnRH Neurons in the Zebrafish

Substance P (SP) and neurokinin A (NKA), encoded by TAC1/Tac1 gene are members of the tachykinin family, which exert their neuromodulatory roles in vertebrate reproduction. In mammals, SP and NKA have been shown to regulate gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion via kisspeptin neurons. On the other hand, the role of SP/NKA in the regulation of reproduction in non-mammalian vertebrates is not well known. In the present study, we first localized expression of tac1 mRNA in the brain of male and female zebrafish, Danio rerio. Next, using an antibody against zebrafish tachykinin1 (Tac1), we examined the neural association of SP/NKA neural processes with GnRH3 neurons, and with kisspeptin (kiss2) neurons, in the brains of male and female zebrafish. In situ hybridization showed an apparent male-dominant tac1 expression in the ventral telencephalic area, the anterior and posterior parts of the parvocellular preoptic nucleus, and the suprachiasmatic nucleus. On the other hand, there was female-dominant tac1 expression in the ventral periventricular hypothalamus. Confocal images of double-labeled zebrafish Tac1 and GnRH3 showed associations between Tac1-immunoreactive processes and GnRH3 neurons in the ventral telencephalic area. In contrast, there was no apparent proximity of Tac1 processes to kiss2 mRNA-expressing neurons in the hypothalamus. Lastly, to elucidate possible direct action of SP/NKA on GnRH3 or Kiss2 neurons, expression of SP/NKA receptor, tacr1a mRNA was examined in regions containing GnRH3 or Kiss2 neurons by in situ hybridization. Expression of tacr1a mRNA was seen in several brain regions including the olfactory bulb, preoptic area and hypothalamus, where GnRH3 and Kiss2 cells are present. These results suggest that unlike in mammals, Tac1 may be involved in male reproductive functions via direct action on GnRH3 neurons but independent of kisspeptin in the zebrafish.

Tachykinins and Kisspeptins in the Regulation of Human Male Fertility

Infertility is a global disease affecting one out of six couples of reproductive age in the world, with a male factor involved in half the cases. There is still much to know about the regulation of human male fertility and thus we decided to focus on two peptide families that seem to play a key role in this function: tachykinins and kisspeptins. With this aim, we conducted an exhaustive review in order to describe the role of tachykinins and kisspeptins in human fertility and their possible implications in infertility etiopathogenesis. Many advances have been made to elucidate the roles of these two families in infertility, and multiple animal species have been studied, including humans. All of this knowledge could lead to new advances in male infertility diagnosis and treatment, but further research is needed to clarify all the implications of tachykinins and kisspeptins in fertility.

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.

Central Substance P Attenuates RF-amid-related Peptide-3 Impacts on the Serum Level of Luteinizing Hormone in Wistar Rats

Introduction: It is well-established that gonadotropin-inhibitory hormone (GnIH) and its mammalian orthologues (RFRP: RF-amid related peptides) can decrease gonadotrophin secretion. Moreover, substance P (SP) is another modulator of the secretion of gonadotropins in a species-dependent manner. This study aimed to find out the impacts of concomitant infusion of RFRP-3 and SP on luteinizing hormone (LH) concentration. Methods: Forty-two rats were arbitrarily assigned to 7 groups (n=6 per group). Animals in the experimental groups were intracerebroventricularly injected with saline +DMSO, SP, RFRP-3, SP + RFRP-3, SP + RF9 (RFRP-3 receptor antagonist), SP + P234 (kisspeptin receptor antagonist) + RFRP-3 and SP + CP-96,345 (SP receptor antagonist) + RFRP-3 in a final volume of 3 µL. Blood samples were collected at 30-minute intervals after injections, and serum was used to measure the LH concentration by radioimmunoassay. Results: According to the results, injections led to the elevation of LH serum concentration at 30-minute post injection (P<0.05) in the SP and SP+RF9 groups. Moreover, administration of either RFRP-3 or SP + RFRP-3 + SP receptor antagonist strikingly decreased the LH mean serum concentration at 30-minute after injections (P<0.05). On the contrary, the infusion of SP+RFRP-3 and SP+RFRP-3+P234 caused no dramatic changes in the LH mean serum concentration. Conclusion: In general, the data showed that SP suppresses the impacts of RFRP-3 on the serum levels of LH.

Altered expression of the kisspeptin/KISS1R and neurokinin B/NK3R systems in mural granulosa and cumulus cells of patients with polycystic ovarian syndrome

PURPOSE

The neurokinin B (NKB)/NK₃ receptor (NK3R) and kisspeptin (KISS1)/kisspeptin receptor (KISS1R), two systems essential for reproduction, are present in human granulosa cells (GCs) of healthy women and contribute to the control of fertility, at least partially, by acting on the gonads. However, little is known about the expression of these systems in GCs of women with polycystic ovarian syndrome (PCOS). The aim of this study was to analyze the expression of NKB/NK3R and KISS1/KISS1R in mural granulosa (MGCs) and cumulus cells (CCs) of PCOS women.

METHODS

A cross-sectional study was performed in 46 healthy women and 43 PCOS women undergoing controlled ovarian stimulation. MGCs and CCs were collected from pre-ovulatory follicles after transvaginal ultrasound-guided oocyte retrieval and the expression of the genes encoding NKB (TAC3), NK3R (TACR3), KISS1, and its receptor (KISS1R) was analyzed using real-time quantitative RT-PCR.

RESULTS

TAC3, TACR3, and KISS1 mRNA levels were decreased in MGCs and CCs of PCOS women. TAC3 positively correlated with KISS1 in MGCs of healthy women and TACR3 was positively associated with KISS1R in CCs from healthy women. These associations were not observed in PCOS women.

CONCLUSION

The NKB/NK3R and KISS1/KISS1R systems are dysregulated in MGCs and CCs of PCOS women. The lower expression of these systems in GCs could contribute to the abnormal follicle development and defective ovulation that characterize the pathogenesis of PCOS.

The role of neuropeptides and neurotransmitters on kisspeptin/kiss1r-signaling in female reproduction

Reproductive function is regulated by the hypothalamic-pituitary-gonads (HPG) axis. Hypothalamic neurons synthesizing kisspeptin play a fundamental role in the central regulation of the timing of puberty onset and reproduction in mammals. Kisspeptin is a regulator of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH). In female rodent, the kisspeptin (encoded by kiss1 gene), neurokinin B (Tac3) and dynorphin neurons form the basis for the "KNDy neurons" in the arcuate nucleus and play a fundamental role in the regulation of GnRH/LH release. Furthermore, various factors including neurotransmitters and neuropeptides may cooperate with kisspeptin signaling to modulate GnRH function. Many neuropeptides including proopiomelanocortin, neuropeptide Y, agouti-related protein, and other neuropeptides, as well as neurotransmitters, dopamine, norepinephrine and γ-aminobutyric acid are suggested to control feeding and HPG axis, the underlying mechanisms are not well known. Nonetheless, to date, information about the neurochemical factors of kisspeptin neurons remains incomplete in rodent. This review is intended to provide an overview of KNDy neurons; major neuropeptides and neurotransmitters interfere in kisspeptin signaling to modulate GnRH function for regulation of puberty onset and reproduction, with a focus on the female rodent.

The usefulness of circulating levels of leptin, kisspeptin, and neurokinin B in obese girls with precocious puberty

This study investigated the relationships of circulating leptin, kisspeptin, and neurokinin B (NKB) levels with precocious puberty (PP) in overweight/obese girls and evaluated the usefulness of these markers in the initiation of puberty. One hundred and twenty-eight girls aged 7.0-8.9 years with PP (group A, normal-weight; group B, overweight/obese) and 30 age-matched normal controls (NC) were enrolled. Serum levels of leptin, kisspeptin, and NKB were measured by commercial kits. Serum leptin levels were higher in group A (4.21 ng/mL) and B (5.64 ng/mL) compared to the NC (2.35 ng/mL, p < .001). Serum kisspeptin levels were lower in group A (0.59 ng/mL) than in group B (0.66 ng/mL, p = .018). Serum NKB levels were not different among the three groups. The predictive value of leptin (AUC =0.791) was lower than that of IGF-1 (AUC =0.917, p = .009), although both were significant markers for PP in the regression analysis. BMI z-score (AUC =0.806) was a predictive factor of PP. In conclusion, a higher level of leptin, IGF-1, and fatness in overweight/obese girls with PP compared to the NC confirms their roles in the regulation of puberty. Further research is needed if the effects of kisspeptin and NKB on puberty are limited at the levels of neurons or target tissue.

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

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

Tac1 Signaling Is Required for Sexual Maturation and Responsiveness of GnRH Neurons to Kisspeptin in the Male Mouse

The tachykinins substance P (SP) and neurokinin A (Tac1) have emerged as novel regulators of kisspeptin/GnRH release. Recently, we documented that SP modulates reproductive function in the female mouse. Here, we extended this characterization to the male mouse. Tac1-/- male mice showed delayed puberty onset. They also presented significantly decreased expression levels of Pdyn (dynorphin) and Nos1 (nitric oxide synthase) in the mediobasal hypothalamus and elevated Gnrh1 levels. Unexpectedly, the response of Tac1-/- mice to central kisspeptin or senktide (neurokinin B receptor-agonist) administration was significantly decreased compared with controls, despite the preserved ability of GnRH neurons to stimulate luteinizing hormone release as demonstrated by central N-methyl-D-aspartate receptor administration, suggesting a deficit at the GnRH neuron level. Importantly, we demonstrated that kisspeptin receptor and SP receptor (NK1R) heterodimerize, indicating that changes in the SP tone could alter the responsiveness of GnRH neurons to kisspeptin. Finally, electrophysiological recordings from arcuate Kiss1 neurons showed that, although virtually all Kiss1 neurons responded to NKB and senktide, only half responded to an NK1R agonist and none to the neurokinin A receptor agonist at a 1-μM dose. In summary, we provide compelling evidence for a role of Tac1 in the control of reproductive function in the male mouse, suggesting a predominant central action that may involve a change in the balance of neural factors that control GnRH expression.

TAC1 Gene Products Regulate Pituitary Hormone Secretion and Gene Expression in Prepubertal Grass Carp Pituitary Cells

Tachykinin-1 (TAC1) is known to have diverse functions in mammals, but similar information is scarce in fish species. Using grass carp as a model, the pituitary actions, receptor specificity and postreceptor signaling of TAC1 gene products, namely substance P (SP) and neurokinin A (NKA), were examined. TAC1 encoding SP and NKA as well as tachykinin receptors NK1R and NK2R were cloned in the carp pituitary. The newly cloned receptors were shown to be functional with properties similar to mammalian counterparts. In carp pituitary cells, SP and NKA could trigger luteinizing hormone (LH), prolactin (PRL), and somatolactin α (SLα) secretion, with parallel rises in PRL and SLα transcripts. Short-term SP treatment (3 hours) induced LH release, whereas prolonged induction (24 hours) could attenuate LHβ messenger RNA (mRNA) expression. At pituitary cell level, LH, PRL, and SLα regulation by TAC1 gene products were mediated by NK1R, NK2R, and NK3R, respectively. Apparently, SP- and NKA-induced LH and SLα secretion and transcript expression were mediated by adenylyl cyclase/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA), phospholiphase C (PLC)/inositol 1,4,5-triphosphate/protein kinase C (PKC), and Ca2+/calmodulin (CaM)/CaM-dependent protein kinase-II pathways. The signal transduction for PRL responses was similar, except for the absence of a PKC component. Regarding SP inhibition of LHβ mRNA expression, the cAMP/PKA- and PLC/PKC-dependent (but not Ca2+/CaM-dependent) cascades were involved. These results, as a whole, suggest that TAC1 gene products play a role in LH, PRL, and SLα regulation via overlapping postreceptor signaling coupled to different subtypes of tachykinin receptor expressed in the carp pituitary.

Do Substance P and Neurokinin A Play Important Roles in the Control of LH Secretion in Ewes?

There is now general agreement that neurokinin B (NKB) acts via neurokinin-3-receptor (NK3R) to stimulate secretion of GnRH and LH in several species, including rats, mice, sheep, and humans. However, the roles of two other tachykinins, substance P (SP) and neurokinin A, which act primarily via NK1R and NK2R, respectively, are less clear. In rodents, these signaling pathways can stimulate LH release and substitute for NKB signaling; in humans, SP is colocalized with kisspeptin and NKB in the mediobasal hypothalamus. In this study, we examined the possible role of these tachykinins in control of the reproductive axis in sheep. Immunohistochemistry was used to describe the expression of SP and NK1R in the ovine diencephalon and determine whether these proteins are colocalized in kisspeptin or GnRH neurons. SP-containing cell bodies were largely confined to the arcuate nucleus, but NK1R-immunoreactivity was more widespread. However, there was very low coexpression of SP or NK1R in kisspeptin cells and none in GnRH neurons. We next determined the minimal effective dose of these three tachykinins that would stimulate LH secretion when administered into the third ventricle of ovary-intact anestrous sheep. A much lower dose of NKB (0.2 nmol) than of neurokinin A (2 nmol) or SP (10 nmol) consistently stimulated LH secretion. Moreover, the relative potency of these three neuropeptides parallels the relative selectivity of NK3R. Based on these anatomical and pharmacological data, we conclude that NKB-NK3R signaling is the primary pathway for the control of GnRH secretion by tachykinins in ewes.

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.

Expression of Tachykinins and Tachykinin Receptors and Interaction with Kisspeptin in Human Granulosa and Cumulus Cells1

The neurokinin B/NK3 receptor (NK3R) and kisspeptin/kisspeptin receptor (KISS1R), two systems which are essential for reproduction, are coexpressed in human mural granulosa (MGC) and cumulus cells (CCs). However, little is known about the presence of other members of the tachykinin family in the human ovary. In the present study, we analyzed the expression of substance P (SP), hemokinin-1 (HK-1), NK1 receptor (NK1R), and NK2 receptor (NK2R) in MGCs and CCs collected from preovulatory follicles of oocyte donors at the time of oocyte retrieval. RT-PCR, quantitative RT-PCR, immunocytochemistry, and Western blotting were used to investigate the patterns of expression of tachykinin and tachykinin receptor mRNAs and proteins and the possible interaction between the tachykinin family and kisspeptin. Intracellular free Ca2+ levels ([Ca2+]i) in MGCs after exposure to SP or kisspeptin in the presence of SP were also measured. We found that SP, HK-1, the truncated NK1R isoform NK1R-Tr, and NK2R were all expressed in MGCs and CCs. NK1R-Tr mRNA and NK2R mRNA and protein levels were higher in MGCs than in CCs from the same patients. Treatment of cells with kisspeptin modulated the expression of HK-1, NK3R, and KISS1R mRNAs, whereas treatment with SP regulated kisspeptin mRNA levels and reduced the [Ca2+]i response produced by kisspeptin. These data demonstrate that the whole tachykinin system is expressed and acts in coordination with kisspeptin to regulate granulosa cell function in the human ovary.

Transcriptome analysis reveals differentially expressed genes associated with germ cell and gonad development in the Southern bluefin tuna (Thunnus maccoyii)

BACKGROUND

Controlling and managing the breeding of bluefin tuna (Thunnus spp.) in captivity is an imperative step towards obtaining a sustainable supply of these fish in aquaculture production systems. Germ cell transplantation (GCT) is an innovative technology for the production of inter-species surrogates, by transplanting undifferentiated germ cells derived from a donor species into larvae of a host species. The transplanted surrogates will then grow and mature to produce donor-derived seed, thus providing a simpler alternative to maintaining large-bodied broodstock such as the bluefin tuna. Implementation of GCT for new species requires the development of molecular tools to follow the fate of the transplanted germ cells. These tools are based on key reproductive and germ cell-specific genes. RNA-Sequencing (RNA-Seq) provides a rapid, cost-effective method for high throughput gene identification in non-model species. This study utilized RNA-Seq to identify key genes expressed in the gonads of Southern bluefin tuna (Thunnus maccoyii, SBT) and their specific expression patterns in male and female gonad cells.

RESULTS

Key genes involved in the reproductive molecular pathway and specifically, germ cell development in gonads, were identified using analysis of RNA-Seq transcriptomes of male and female SBT gonad cells. Expression profiles of transcripts from ovary and testis cells were compared, as well as testis germ cell-enriched fraction prepared with Percoll gradient, as used in GCT studies. Ovary cells demonstrated over-expression of genes related to stem cell maintenance, while in testis cells, transcripts encoding for reproduction-associated receptors, sex steroids and hormone synthesis and signaling genes were over-expressed. Within the testis cells, the Percoll-enriched fraction showed over-expression of genes that are related to post-meiosis germ cell populations.

CONCLUSIONS

Gonad development and germ cell related genes were identified from SBT gonads and their expression patterns in ovary and testis cells were determined. These expression patterns correlate with the reproductive developmental stage of the sampled fish. The majority of the genes described in this study were sequenced for the first time in T. maccoyii. The wealth of SBT gonadal and germ cell-related gene sequences made publicly available by this study provides an extensive resource for further GCT and reproductive molecular biology studies of this commercially valuable fish.

The Distribution of Substance P and Kisspeptin in the Mediobasal Hypothalamus of the Male Rhesus Monkey and a Comparison of Intravenous Administration of These Peptides to Release GnRH as Reflected by LH Secretion

Substance P (SP) was recently reported to be expressed in human kisspeptin/neurokinin B/dynorphin (KNDy) neurons and to enhance KNDy neuron excitability in the mouse hypothalamus. We therefore examined (1) interactions of SP and kisspeptin in the mediobasal hypothalamus of adult male rhesus monkeys using immunofluorescence, and (2) the ability of SP to induce LH release in GnRH-primed, agonadal juvenile male monkeys. SP cell bodies were observed only occasionally in the arcuate nucleus (Arc), but more frequently dorsal to the Arc in the region of the premammillary nucleus. Castration resulted in an increase in the number of SP cell bodies in the Arc but not in the other regions. SP fibers innervated the Arc, where they were found in close apposition with kisspeptin perikarya in the periphery of this nucleus. Beaded SP axons projected to the median eminence, where they terminated in the external layer and intermingled with beaded kisspeptin axons. Colocalization of the two peptides, however, was not observed. Although close apposition between SP fibers and kisspeptin neurons suggest a role for SP in modulating GnRH pulse generator activity, i.v. injections of SP failed to elicit release of GnRH (as reflected by LH) in the juvenile monkey. Although the finding of structural interactions between SP and kisspeptin neurons is consistent with the notion that this tachykinin may be involved in regulating pulsatile GnRH release, the apparent absence of expression of SP in KNDy neurons suggests that this peptide is unlikely to be a fundamental component of the primate GnRH pulse generator.

15 years on the Editorial Board of PEPTIDES

In this article, part of an issue of PEPTIDES celebrating the many years of dedication of Dr. A.J. Kastin as Editor-in-Chief of the journal, I describe how I first met him and how our friendship and collaboration developed. In 1970 I joined Dr. A.V. Schally's team at the Endocrine and Polypeptide Laboratories of Tulane University and the V.A. Hospital and it was at that time that I met Dr. Kastin for the first time. In 1984 I joined Dr. Schally's team for the second time and I began publishing part of my research findings in PEPTIDES. Afterward many more results from the research work were also published in PEPTIDES. I became a member of the Editorial Board of the same journal in 1999. It was going to be a very interesting experience. Some of my observations as a reviewer for PEPTIDES are described in the present article. Finally, I expressed my warmest congratulations to Dr. A.J. Kastin for the outstanding job that he carried out as Editor-in-Chief of PEPTIDES.

Substance p regulates puberty onset and fertility in the female mouse

Puberty is a tightly regulated process that leads to reproductive capacity. Kiss1 neurons are crucial in this process by stimulating GnRH, yet how Kiss1 neurons are regulated remains unknown. Substance P (SP), an important neuropeptide in pain perception, induces gonadotropin release in adult mice in a kisspeptin-dependent manner. Here, we assessed whether SP, through binding to its receptor NK1R (neurokinin 1 receptor), participates in the timing of puberty onset and fertility in the mouse. We observed that 1) selective NK1R agonists induce gonadotropin release in prepubertal females; 2) the expression of Tac1 (encoding SP) and Tacr1 (NK1R) in the arcuate nucleus is maximal before puberty, suggesting increased SP tone; 3) repeated exposure to NK1R agonists prepubertally advances puberty onset; and 4) female Tac1(-/-) mice display delayed puberty; moreover, 5) SP deficiency leads to subfertility in females, showing fewer corpora lutea and antral follicles and leading to decreased litter size. Thus, our findings support a role for SP in the stimulation of gonadotropins before puberty, acting via Kiss1 neurons to stimulate GnRH release, and its involvement in the attainment of full reproductive capabilities in female mice.

Neuropeptide co-expression in hypothalamic kisspeptin neurons of laboratory animals and the human

Hypothalamic peptidergic neurons using kisspeptin (KP) and its co-transmitters for communication are critically involved in the regulation of mammalian reproduction and puberty. This article provides an overview of neuropeptides present in KP neurons, with a focus on the human species. Immunohistochemical studies reveal that large subsets of human KP neurons synthesize neurokinin B, as also shown in laboratory animals. In contrast, dynorphin described in KP neurons of rodents and sheep is found rarely in KP cells of human males and postmenopausal females. Similarly, galanin is detectable in mouse, but not human, KP cells, whereas substance P, cocaine- and amphetamine-regulated transcript and proenkephalin-derived opioids are expressed in varying subsets of KP neurons in humans, but not reported in ARC of other species. Human KP neurons do not contain neurotensin, cholecystokinin, proopiomelanocortin-derivatives, agouti-related protein, neuropeptide Y, somatostatin or tyrosine hydroxylase (dopamine). These data identify the possible co-transmitters of human KP cells. Neurochemical properties distinct from those of laboratory species indicate that humans use considerably different neurotransmitter mechanisms to regulate fertility.

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.

Presynaptic partners of dorsal raphe serotonergic and GABAergic neurons

The serotonin system powerfully modulates physiology and behavior in health and disease, yet the circuit mechanisms underlying serotonin neuron activity are poorly understood. The major source of forebrain serotonergic innervation is from the dorsal raphe nucleus (DR), which contains both serotonin and GABA neurons. Using viral tracing combined with electrophysiology, we found that GABA and serotonin neurons in the DR receive excitatory, inhibitory, and peptidergic inputs from the same specific brain regions. Embedded in this overall similarity are important differences. Serotonin neurons are more likely to receive synaptic inputs from anterior neocortex while GABA neurons receive disproportionally higher input from the central amygdala. Local input mapping revealed extensive serotonin-serotonin as well as GABA-serotonin connectivity with a distinct spatial organization. Covariance analysis suggests heterogeneity of both serotonin and GABA neurons with respect to the inputs they receive. These analyses provide a foundation for further functional dissection of the serotonin system.

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.

Novel pituitary actions of TAC3 gene products in fish model: receptor specificity and signal transduction for prolactin and somatolactin α regulation by neurokinin B (NKB) and NKB-related peptide in carp pituitary cells

TAC3 is a member of tachykinins, and its gene product neurokinin B (NKB) has recently emerged as a key regulator for LH through modulation of kisspeptin/GnRH system within the hypothalamus. In fish models, TAC3 not only encodes NKB but also a novel tachykinin-like peptide called NKB-related peptide (NKBRP), and the pituitary actions of these TAC3 gene products are still unknown. Using grass carp as a model, the direct effects and postreceptor signaling for the 2 TAC3 products were examined at the pituitary level. Grass carp TAC3 was cloned and confirmed to encode NKB and NKBRP similar to that of other fish species. In carp pituitary cells, NKB and NKBRP treatment did not affect LH release and gene expression but up-regulated prolactin (PRL) and somatolactin (SL)α secretion, protein production, and transcript expression. The stimulation by these 2 TAC3 gene products on PRL and SLα release and mRNA levels were mediated by pituitary NK2 and NK3 receptors, respectively. Apparently, NKB- and NKBRP-induced SLα secretion and transcript expression were caused by adenylate cyclase/cAMP/protein kinase A, phospholipase C/inositol 1,4,5-triphosphate/protein kinase C and Ca(2+)/calmodulin/Ca(2+)/calmodulin-dependent protein kinase II activation. The signal transduction for the corresponding responses on PRL release and mRNA expression were also similar, except that the protein kinase C component was not involved. These findings suggest that the 2 TAC3 gene products do not play a role in LH regulation at the pituitary level in carp species but may serve as novel stimulators for PRL and SLα synthesis and secretion via overlapping postreceptor signaling mechanisms coupled to NK2 and NK3 receptors, respectively.

Comparing label-free quantitative peptidomics approaches to characterize diurnal variation of peptides in the rat suprachiasmatic nucleus

Mammalian circadian rhythm is maintained by the suprachiasmatic nucleus (SCN) via an intricate set of neuropeptides and other signaling molecules. In this work, peptidomic analyses from two times of day were examined to characterize variation in SCN peptides using three different label-free quantitation approaches: spectral count, spectra index and SIEVE. Of the 448 identified peptides, 207 peptides were analyzed by two label-free methods, spectral count and spectral index. There were 24 peptides with significant (adjusted p-value < 0.01) differential peptide abundances between daytime and nighttime, including multiple peptides derived from secretogranin II, cocaine and amphetamine regulated transcript, and proprotein convertase subtilisin/kexin type 1 inhibitor. Interestingly, more peptides were analyzable and had significantly different abundances between the two time points using the spectral count and spectral index methods than with a prior analysis using the SIEVE method with the same data. The results of this study reveal the importance of using the appropriate data analysis approaches for label-free relative quantitation of peptides. The detection of significant changes in so rich a set of neuropeptides reflects the dynamic nature of the SCN and the number of influences such as feeding behavior on circadian rhythm. Using spectral count and spectral index, peptide level changes are correlated to time of day, suggesting their key role in circadian function.

Agouti-related peptide plays a critical role in leptin's effects on female puberty and reproduction

Deficient leptin signaling causes infertility via reduced activity of GnRH neurons, causing a hypogonadal state in both rodents and humans. Because GnRH neurons do not express leptin receptors, leptin's effect on GnRH neurons must be indirect. Neurons within the hypothalamic arcuate nucleus that coexpress AGRP and NPY are considered to be important intermediate neurons involved in leptin regulation of GnRH neurons. Previously, we reported that the absence of AGRP and haploinsufficiency of MC4R in leptin receptor mutant (Lepr(db/db)) females result in restoration of fertility and lactation despite the persistence of obesity and insulin resistance. The overarching hypothesis in the present study is that the absence or reduction of leptin's inhibition of AGRP/NPY neurons leads to suppression of GnRH release in cases of leptin signaling deficiency. Since TAC2 (NKB)-TAC3R signaling plays a role in puberty maturation and is modulated by metabolic status, the other aim of this study is to test whether TAC2/NKB neurons in ARC regulated by melanocortinergic signals herein affect leptin's action on puberty and reproduction. Our data showed that AGRP deficiency in Lepr(db/db) females restores normal timing of vaginal opening and estrous cycling, although uterine weight gain and mammary gland development are morphologically delayed. Nonetheless, Agrp(-/-) Lepr(db/db) females are fertile and sustain adequate nutrition of pups with lactation to weaning age. AGRP deficiency results in advanced vaginal opening in wild-type female mice. The postpubertal increase in hypothalamic TAC2 mRNA was not observed in Lepr(db/db) females, whereas AGRP deficiency restored it in Lepr(db/db) females. Additionally, MC4R activation with MTII induced FOS expression in TAC2 neurons, supporting the concept of melanocortinergic regulation of TAC2 neurons. These studies suggest that AGRP imposes an inhibitory effect on puberty and that TAC2 neurons may transmit melanocortinergic inhibition of GnRH neurons.

Afferent neuronal control of type-I gonadotropin releasing hormone neurons in the human

Understanding the regulation of the human menstrual cycle represents an important ultimate challenge of reproductive neuroendocrine research. However, direct translation of information from laboratory animal experiments to the human is often complicated by strikingly different and unique reproductive strategies and central regulatory mechanisms that can be present in even closely related animal species. In all mammals studied so far, type-I gonadotropin releasing hormone (GnRH) synthesizing neurons form the final common output way from the hypothalamus in the neuroendocrine control of the adenohypophysis. Under various physiological and pathological conditions, hormonal and metabolic signals either regulate GnRH neurons directly or act on upstream neuronal circuitries to influence the pattern of pulsatile GnRH secretion into the hypophysial portal circulation. Neuronal afferents to GnRH cells convey important metabolic-, stress-, sex steroid-, lactational-, and circadian signals to the reproductive axis, among other effects. This article gives an overview of the available neuroanatomical literature that described the afferent regulation of human GnRH neurons by peptidergic, monoaminergic, and amino acidergic neuronal systems. Recent studies of human genetics provided evidence that central peptidergic signaling by kisspeptins and neurokinin B (NKB) play particularly important roles in puberty onset and later, in the sex steroid-dependent feedback regulation of GnRH neurons. This review article places special emphasis on the topographic distribution, sexual dimorphism, aging-dependent neuroanatomical changes, and plastic connectivity to GnRH neurons of the critically important human hypothalamic kisspeptin and NKB systems.

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.

Neuropeptides in sepsis: from brain pathology to systemic inflammation

Septic encephalopathy is frequently diagnosed in critically ill patients and in up to 70% of patients with severe systemic infection [19]. The syndrome is defined by diffuse cerebral dysfunction or structural abnormalities attributed to the effects of systemic infection, rather than a direct central nervous system cause. The clinical characteristics can range from mild delirium to deep coma, but patients are often medically sedated making the diagnosis difficult. Any manifestation, however, is specific and markers of disease are lacking [43]. Sepsis survivors present long term cognitive impairment, including alterations of memory, attention and concentration [10,54]. Here, we propose that neuropeptides may play a key role in septic encephalopathy, leading to a vicious circle characterized by brain disease and systemic inflammation.

Specific needs of dopamine neurons for stimulation in order to survive: implication for Parkinson disease

Parkinson disease (PD) is a degenerative brain disorder characterized by motor symptoms that are unequivocally associated with the loss of dopaminergic (DA) neurons in the substantia nigra (SN). Although our knowledge of the mechanisms that contribute to DA cell death in both hereditary and sporadic forms of the disease has advanced significantly, the nature of the pathogenic process remains poorly understood. In this review, we present evidence that neurodegeneration occurs when the electrical activity and excitability of these neurons is reduced. In particular, we will focus on the specific need these neurons may have for stimulation in order to survive and on the molecular and cellular mechanisms that may be compromised when this need is no longer met in PD.

Changes in pituitary function with ageing and implications for patient care

The pituitary gland has a role in puberty, reproduction, stress-adaptive responses, sodium and water balance, uterine contractions, lactation, thyroid function, growth, body composition and skin pigmentation. Ageing is marked by initially subtle erosion of physiological signalling mechanisms, resulting in lower incremental secretory-burst amplitude, more disorderly patterns of pituitary hormone release and blunted 24 h rhythmic secretion. Almost all pituitary hormones are altered by ageing in humans, often in a manner dependent on sex, body composition, stress, comorbidity, intercurrent illness, medication use, physical frailty, caloric intake, immune status, level of exercise, and neurocognitive decline. The aim of this article is to critically discuss the mechanisms mediating clinical facets of changes in the hypothalamic-pituitary axis during ageing, and the extent to which confounding factors operate to obscure ageing-related effects.

GPCR Heterodimerization in the Reproductive System: Functional Regulation and Implication for Biodiversity

A G protein-coupled receptor (GPCR) functions not only as a monomer or homodimer but also as a heterodimer with another GPCR. GPCR heterodimerization results in the modulation of the molecular functions of the GPCR protomer, including ligand binding affinity, signal transduction, and internalization. There has been a growing body of reports on heterodimerization of multiple GPCRs expressed in the reproductive system and the resultant functional modulation, suggesting that GPCR heterodimerization is closely associated with reproduction including the secretion of hormones and the growth and maturation of follicles and oocytes. Moreover, studies on heterodimerization among paralogs of gonadotropin-releasing hormone (GnRH) receptors of a protochordate, Ciona intestinalis, verified the species-specific regulation of the functions of GPCRs via multiple GnRH receptor pairs. These findings indicate that GPCR heterodimerization is also involved in creating biodiversity. In this review, we provide basic and current knowledge regarding GPCR heterodimers and their functional modulation, and explore the biological significance of GPCR heterodimerization.

Sex-specific modulation of gene expression networks in murine hypothalamus

The hypothalamus contains nuclei and cell populations that are critical in reproduction and that differ significantly between the sexes in structure and function. To examine the molecular and genetic basis for these differences, we quantified gene expression in the hypothalamus of 39 pairs of adult male and female mice belonging to the BXD strains. This experimental design enabled us to define hypothalamic gene coexpression networks and provided robust estimates of absolute expression differences. As expected, sex has the strongest effect on the expression of genes on the X and Y chromosomes (e.g., Uty, Xist, Kdm6a). Transcripts associated with the endocrine system and neuropeptide signaling also differ significantly. Sex-differentiated transcripts often have well delimited expression within specific hypothalamic nuclei that have roles in reproduction. For instance, the estrogen receptor (Esr1) and neurokinin B (Tac2) genes have intense expression in the medial preoptic and arcuate nuclei and comparatively high expression in females. Despite the strong effect of sex on single transcripts, the global pattern of covariance among transcripts is well preserved, and consequently, males and females have well matched coexpression modules. However, there are sex-specific hub genes in functionally equivalent modules. For example, only in males is the Y-linked gene, Uty, a highly connected transcript in a network that regulates chromatin modification and gene transcription. In females, the X chromosome paralog, Kdm6a, takes the place of Uty in the same network. We also find significant effect of sex on genetic regulation and the same network in males and females can be associated with markedly different regulatory loci. With the exception of a few sex-specific modules, our analysis reveals a system in which sets of functionally related transcripts are organized into stable sex-independent networks that are controlled at a higher level by sex-specific modulators.

Analysis of the expression of neurokinin B, kisspeptin, and their cognate receptors NK3R and KISS1R in the human female genital tract

OBJECTIVE

To investigate the presence of neurokinin B (NKB)/NK(3) receptor (NK(3)R) and kisspeptin/KISS1 receptor (KISS1R) messenger RNA (mRNA) and proteins throughout the human female genital tract.

DESIGN

In vitro study.

SETTING

Academic research laboratories and academic hospitals.

PATIENT(S)

Fifteen reproductive-age women and 16 postmenopausal women provided fresh samples of uterus, ovary, or oviduct, and 12 women provided archival samples of endometrium or oviduct.

INTERVENTION(S)

Fresh and archival samples of uterus, ovary, and oviduct obtained from reproductive-age and postmenopausal women.

MAIN OUTCOME MEASURE(S)

Results of reverse-transcription polymerase chain reaction (RT-PCR) and immunohistochemistry to investigate the pattern of expression of NKB/NK(3)R and kisspeptin/KISS1R in target tissues.

RESULT(S)

Expression of the genes encoding NKB (TAC3) and NK(3)R (TACR3), and kisspeptin (KISS1) and its receptor (KISS1R) was found in the uterus, ovary, and oviduct. Both NKB and NK(3)R immunoreactivity was detected in the endometrium, the oviduct, and the ovary, with marked expression in endometrial and oviductal epithelial cells, where intense coexpression of kisspeptin and KISS1R was also detected. Positive staining for NKB and NK(3)R was found in the myometrium where, in contrast, kisspeptin and KISS1R were absent.

CONCLUSION(S)

NKB/NK(3)R and kisspeptin/KISS1R are present in female peripheral reproductive tissues with colocalization of both systems in some non-neuronal cell populations of the human female genital tract. Our findings are compatible with a potential modulatory role of NKB and kisspeptin at peripheral reproductive tissues.