Positive, but not negative feedback actions of estradiol in adult female mice require estrogen receptor α in kisspeptin neurons

Runx3 transcription factor regulates ovarian functions and ovulation in female mice

We previously demonstrated that the Runx3 transcription factor is expressed in the hypothalami, pituitaries, and ovaries of mice, and that Runx3 knockout (Runx3^−/−) mice are anovulatory and their uteri are atrophic. Runx3 mRNA expression was detected in the granulosa cells of ovarian follicles, and in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC). In the present study, we examined the effects of Runx3 knockout on the gene expression of enzymes associated with steroidogenesis. We found decreased Cyp11a1 mRNA expression in Runx3^−/− mouse ovaries compared with that in wild-type (wt) mouse ovaries at the age of 8 weeks. In situ hybridization analysis showed that the percentages of Cyp11a1 mRNA-expressing theca cells in follicles of Runx3^−/− mice were decreased compared with those of wt mice. In accord with the alterations in Runx3^−/− mouse ovaries, Kiss1 mRNA levels in ARC were increased, whereas mRNA levels of kisspeptin in AVPV were decreased, and gonadotropin-releasing hormone in the preoptic area and follicle-stimulating hormone β subunit gene were increased in Runx3^−/− mice. Following an ovarian transplantation experiment between Runx3^−/− mice and wt mice, corpora lutea were observed when ovaries from Runx3^−/− mice were transplanted into wt mice, but not when those from wt mice were transplanted into Runx3^−/− mice, suggesting that Runx3 in the hypothalamo-pituitary system may drive gonadotropin release to induce ovulation in the ovary. These findings indicate that Runx3 plays a crucial role in the hypothalamo-pituitary-gonadal axis.

Excitability and Burst Generation of AVPV Kisspeptin Neurons Are Regulated by the Estrous Cycle Via Multiple Conductances Modulated by Estradiol Action

The preovulatory secretory surge of gonadotropin-releasing hormone (GnRH) is crucial for fertility and is regulated by a switch of estradiol feedback action from negative to positive. GnRH neurons likely receive estradiol feedback signals via ERα-expressing afferents. Kisspeptin neurons in anteroventral periventricular nucleus (AVPV) are thought to be critical for estradiol-positive feedback induction of the GnRH surge. We examined the electrophysiological properties of GFP-identified AVPV kisspeptin neurons in brain slices from mice on the afternoon of diestrus (negative feedback) and proestrus (positive feedback, time of surge). Extracellular recordings revealed increased firing frequency and action potential bursts on proestrus versus diestrus. Whole-cell recordings were used to study the intrinsic mechanisms of bursting. Upon depolarization, AVPV kisspeptin neurons exhibited tonic firing or depolarization-induced bursts (DIB). Both tonic and DIB cells exhibited bursts induced by rebound from hyperpolarization. DIB occurred similarly on both cycle stages, but rebound bursts were observed more often on proestrus. DIB and rebound bursts were both sensitive to Ni²⁺, suggesting that T-type Ca²⁺ currents (I_Ts) are involved. I_T current density was greater on proestrus versus diestrus. In addition to I_T, persistent sodium current (I_NaP) facilitated rebound bursting. On diestrus, 4-aminopyridine-sensitive potassium currents contributed to reduced rebound bursts in both tonic and DIB cells. Manipulation of specific sex steroids suggests that estradiol induces the changes that enhance AVPV kisspeptin neuron excitability on proestrus. These observations indicate cycle-driven changes in circulating estradiol increased overall action potential generation and burst firing in AVPV kisspeptin neurons on proestrus versus diestrus by regulating multiple intrinsic currents.

Kisspeptin across the human lifespan:evidence from animal studies and beyond

Since its first description in 1996, the KISS1 gene and its peptide products, kisspeptins, have increasingly become recognised as key regulators of reproductive health. With kisspeptins acting as ligands for the kisspeptin receptor KISS1R (previously known as GPR54 or KPR54), recent work has consistently shown that administration of kisspeptin across a variety of species stimulates gonadotrophin release through influencing gonadotrophin-releasing hormone secretion. Evidence from both animal and human studies supports the finding that kisspeptins are crucial for ensuring healthy development, with knockout animal models, as well as proband genetic testing in human patients affected by abnormal pubertal development, corroborating the notion that a functional kisspeptin receptor is required for appropriate gonadotrophin secretion. Given the large body of evidence that exists surrounding the influence of kisspeptin in a variety of settings, this review summarises our physiological understanding of the role of these important peptides and their receptors, before proceeding to describe the varying role they play across the reproductive lifespan.

ERα in Tac2 Neurons Regulates Puberty Onset in Female Mice

A variety of data suggest that estrogen action on kisspeptin (Kiss1)-containing arcuate nucleus neurons (which coexpress Kiss1, neurokinin B (the product of Tac2) and dynorphin (KNDy) neurons restrains reproductive onset and function, but roles for estrogen action in these Kiss1 neurons relative to a distinct population of rostral hypothalamic Kiss1 neurons (which does not express Tac2 or dynorphin) have not been directly tested. To test the role for estrogen receptor (ER)α in KNDy cells, we thus generated Tac2(Cre) and Kiss1(Cre) knock-in mice and bred them onto the Esr1(flox) background to ablate ERα specifically in Tac2-expressing cells (ERα(Tac2)KO mice) or all Kiss1 cells (ERα(Kiss1)KO mice), respectively. Most ERα-expressing Tac2 neurons represent KNDy cells. Arcuate nucleus Kiss1 expression was elevated in ERα(Tac2)KO and ERα(Kiss1)KO females independent of gonadal hormones, whereas rostral hypothalamic Kiss1 expression was normal in ERα(Tac2)KO but decreased in ERα(Kiss1)KO females; this suggests that ERα in rostral Kiss1 cells is crucial for control of Kiss1 expression in these cells. Both ERα(Kiss1)KO and ERα(Tac2)KO females displayed early vaginal opening, early and persistent vaginal cornification, increased gonadotropins, uterine hypertrophy, and other evidence of estrogen excess. Thus, deletion of ERα in Tac2 neurons suffices to drive precocious gonadal hyperstimulation, demonstrating that ERα in Tac2 neurons typically restrains pubertal onset and hypothalamic reproductive drive.

Estradiol Restrains Prepubertal Gonadotropin Secretion in Female Mice via Activation of ERα in Kisspeptin Neurons

Elimination of estrogen receptorα (ERα) from kisspeptin (Kiss1) neurons results in premature LH release and pubertal onset, implicating these receptors in 17β-estradiol (E2)-mediated negative feedback regulation of GnRH release during the prepubertal period. Here, we tested the dependency of prepubertal negative feedback on ERα in Kiss1 neurons. Prepubertal (postnatal d 14) and peripubertal (postnatal d 34) wild-type (WT) and Kiss1 cell-specific ERα knockout (KERαKO) female mice were sham operated or ovariectomized and treated with either vehicle- or E2-containing capsules. Plasma and tissues were collected 2 days after surgery for analysis. Ovariectomy increased LH and FSH levels, and E2 treatments completely prevented these increases in WT mice of both ages. However, in prepubertal KERαKO mice, basal LH levels were elevated vs WT, and both LH and FSH levels were not further increased by ovariectomy or affected by E2 treatment. Similarly, Kiss1 mRNA levels in the medial basal hypothalamus, which includes the arcuate nucleus, were suppressed with E2 treatment in ovariectomized prepubertal WT mice but remained unaffected by any treatment in KERαKO mice. In peripubertal KERαKO mice, basal LH and FSH levels were not elevated vs WT and were unaffected by ovariectomy or E2. In contrast to our previous findings in adult animals, these results demonstrate that suppression of gonadotropins and Kiss1 mRNA by E2 in prepubertal animals depends upon ERα activation in Kiss1 neurons. Our observations are consistent with the hypothesis that these receptors play a critical role in restraining GnRH release before the onset and completion of puberty.

Visualizing estrogen receptor-α-expressing neurons using a new ERα-ZsGreen reporter mouse line

BACKGROUND

A variety of biological functions of estrogens, including regulation of energy metabolism, are mediated by neurons expressing estrogen receptor-α (ERα) in the brain. However, complex intracellular processes in these ERα-expressing neurons are difficult to unravel, due to the lack of strategy to visualize ERα-expressing neurons, especially in unfixed brain tissues.

RESULTS AND CONCLUSIONS

Here we generated a novel ERα-ZsGreen reporter mouse line in which expression of a green fluorescent reporter protein, ZsGreen, is driven by a 241kb ERα gene promoter. We validated that ZsGreen is highly colocalized with endogenous ERα in the brain. Native ZsGreen signals were visualized in unfixed brain tissue, and were used to assist single cell collection and electrophysiological recordings. Finally, we demonstrated that this ERα-ZsGreen mouse allele can be used in combination with other genetic reporter alleles to allow experiments in highly selective neural populations.

Estrogen Receptor Beta and 2-arachidonoylglycerol Mediate the Suppressive Effects of Estradiol on Frequency of Postsynaptic Currents in Gonadotropin-Releasing Hormone Neurons of Metestrous Mice: An Acute Slice Electrophysiological Study

Gonadotropin-releasing hormone (GnRH) neurons are controlled by 17β-estradiol (E2) contributing to the steroid feedback regulation of the reproductive axis. In rodents, E2 exerts a negative feedback effect upon GnRH neurons throughout the estrus-diestrus phase of the ovarian cycle. The present study was undertaken to reveal the role of estrogen receptor subtypes in the mediation of the E2 signal and elucidate the downstream molecular machinery of suppression. The effect of E2 administration at low physiological concentration (10 pM) on GnRH neurons in acute brain slices obtained from metestrous GnRH-green fluorescent protein (GFP) mice was studied under paradigms of blocking or activating estrogen receptor subtypes and interfering with retrograde 2-arachidonoylglycerol (2-AG) signaling. Whole-cell patch clamp recordings revealed that E2 significantly diminished the frequency of spontaneous postsynaptic currents (sPSCs) in GnRH neurons (49.62 ± 7.6%) which effect was abolished by application of the estrogen receptor (ER) α/β blocker Faslodex (1 μM). Pretreatment of the brain slices with cannabinoid receptor type 1 (CB1) inverse agonist AM251 (1 μM) and intracellularly applied endocannabinoid synthesis blocker THL (10 μM) significantly attenuated the effect of E2 on the sPSCs. E2 remained effective in the presence of tetrodotoxin (TTX) indicating a direct action of E2 on GnRH cells. The ERβ specific agonist DPN (10 pM) also significantly decreased the frequency of miniature postsynaptic currents (mPSCs) in GnRH neurons. In addition, the suppressive effect of E2 was completely blocked by the selective ERβ antagonist PHTPP (1 μM) indicating that ERβ is required for the observed rapid effect of the E2. In contrast, the ERα agonist PPT (10 pM) or the membrane-associated G protein-coupled estrogen receptor (GPR30) agonist G1 (10 pM) had no significant effect on the frequency of mPSCs in these neurons. AM251 and tetrahydrolipstatin (THL) significantly abolished the effect of E2 whereas AM251 eliminated the action of DPN on the mPSCs. These data suggest the involvement of the retrograde endocannabinoid mechanism in the rapid direct effect of E2. These results collectively indicate that estrogen receptor beta and 2-AG/CB1 signaling mechanisms are coupled and play an important role in the mediation of the negative estradiol feedback on GnRH neurons in acute slice preparation obtained from intact, metestrous mice.

Corticosterone Blocks Ovarian Cyclicity and the LH Surge via Decreased Kisspeptin Neuron Activation in Female Mice

Stress elicits activation of the hypothalamic-pituitary-adrenal axis, which leads to enhanced circulating glucocorticoids, as well as impaired gonadotropin secretion and ovarian cyclicity. Here, we tested the hypothesis that elevated, stress-levels of glucocorticoids disrupt ovarian cyclicity by interfering with the preovulatory sequence of endocrine events necessary for the LH surge. Ovarian cyclicity was monitored in female mice implanted with a cholesterol or corticosterone (Cort) pellet. Cort, but not cholesterol, arrested cyclicity in diestrus. Subsequent studies focused on the mechanism whereby Cort stalled the preovulatory sequence by assessing responsiveness to the positive feedback estradiol signal. Ovariectomized mice were treated with an LH surge-inducing estradiol implant, as well as Cort or cholesterol, and assessed several days later for LH levels on the evening of the anticipated surge. All cholesterol females showed a clear LH surge. At the time of the anticipated surge, LH levels were undetectable in Cort-treated females. In situ hybridization analyses the anteroventral periventricular nucleus revealed that Cort robustly suppressed the percentage of Kiss1 cells coexpressing cfos, as well as reduced the number of Kiss1 cells and amount of Kiss1 mRNA per cell, compared with expression in control brains. In addition, Cort blunted pituitary expression of the genes encoding the GnRH receptor and LHβ, indicating inhibition of gonadotropes during the blockage of the LH surge. Collectively, our findings support the hypothesis that physiological stress-levels of Cort disrupts ovarian cyclicity, in part, through disruption of positive feedback mechanisms at both the hypothalamic and pituitary levels which are necessary for generation of the preovulatory LH surge.

Expression of ESR1 in Glutamatergic and GABAergic Neurons Is Essential for Normal Puberty Onset, Estrogen Feedback, and Fertility in Female Mice

Circulating estradiol exerts a profound influence on the activity of the gonadotropin-releasing hormone (GnRH) neuronal network controlling fertility. Using genetic strategies enabling neuron-specific deletion of estrogen receptor α (Esr1), we examine here whether estradiol-modulated GABA and glutamate transmission are critical for the functioning of the GnRH neuron network in the female mouse. Using Vgat- and Vglut2-ires-Cre knock-in mice and ESR1 immunohistochemistry, we demonstrate that subpopulations of GABA and glutamate neurons throughout the limbic forebrain express ESR1, with ESR1-GABAergic neurons being more widespread and numerous than ESR1-glutamatergic neurons. We crossed Vgat- and Vglut2-ires-Cre mice with an Esr1(lox/lox) line to generate animals with GABA-neuron-specific or glutamate-neuron-specific deletion of Esr1. Vgat-ires-Cre;Esr1(lox/lox) mice were infertile, with abnormal estrous cycles, and exhibited a complete failure of the estrogen positive feedback mechanism responsible for the preovulatory GnRH surge. However, puberty onset and estrogen negative feedback were normal. Vglut2-ires-Cre;Esr1(lox/lox) mice were also infertile but displayed a wider range of deficits, including advanced puberty onset, abnormal negative feedback, and abolished positive feedback. Whereas <25% of preoptic kisspeptin neurons expressed Cre in Vgat- and Vglut2-ires-Cre lines, ∼70% of arcuate kisspeptin neurons were targeted in Vglut2-ires-Cre;Esr1(lox/lox) mice, possibly contributing to their advanced puberty phenotype. These observations show that, unexpectedly, ESR1-GABA neurons are only essential for the positive feedback mechanism. In contrast, we reveal the key importance of ESR1 in glutamatergic neurons for multiple estrogen feedback loops within the GnRH neuronal network required for fertility in the female mouse.

EP24.15 as a Potential Regulator of Kisspeptin Within the Neuroendocrine Hypothalamus

The neuropeptide kisspeptin (Kiss1) is integral to the advent of puberty and the generation of cyclical LH surges. Although many complex actions of Kiss1 are known, the mechanisms governing the processing/regulation of this peptide have not been unveiled. The metallo enzyme, endopeptidase 24.15 (thimet oligopeptidase), has been demonstrated to play a key role in the processing and thus the duration of action of the reproductive neuropeptide, GnRH, which signals downstream of Kiss1. Initial in silico modeling implied that Kiss1 could also be a putative substrate for EP24.15. Coincubation of Kiss1 and EP24.15 demonstrated multiple cleavages of the peptide predominantly between Arg29-Gly30 and Ser47-Phe48 (corresponding to Ser5-Phe6 in Kiss-10; Kiss-10 as a substrate had an additional cleavage between Phe6-Gly7) as determined by mass spectrometry. Vmax for the reaction was 2.37±0.09 pmol/min · ng with a Km of 19.68 ± 2.53μM, which is comparable with other known substrates of EP24.15. EP24.15 immunoreactivity, as previously demonstrated, is distributed in cell bodies, nuclei, and processes throughout the hypothalamus. Kiss1 immunoreactivity is localized primarily to cell bodies and fibers within the mediobasal and anteroventral-periventricular hypothalamus. Double-label immunohistochemistry indicated coexpression of EP24.15 and Kiss1, implicating that the regulation of Kiss1 by EP24.15 could occur in vivo. Further studies will be directed at determining the precise temporal sequence of EP24.15 effects on Kiss1 as it relates to the control of reproductive hormone secretion and treatment of fertility issues.

Both Estrogen and Androgen Modify the Response to Activation of Neurokinin-3 and κ-Opioid Receptors in Arcuate Kisspeptin Neurons From Male Mice

Gonadal steroids regulate the pattern of GnRH secretion. Arcuate kisspeptin (kisspeptin, neurokinin B, and dynorphin [KNDy]) neurons may convey steroid feedback to GnRH neurons. KNDy neurons increase action potential firing upon the activation of neurokinin B receptors (neurokinin-3 receptor [NK3R]) and decrease firing upon the activation of dynorphin receptors (κ-opioid receptor [KOR]). In KNDy neurons from intact vs castrated male mice, NK3R-mediated stimulation is attenuated and KOR-mediated inhibition enhanced, suggesting gonadal secretions are involved. Estradiol suppresses spontaneous GnRH neuron firing in male mice, but the mediators of the effects on firing in KNDy neurons are unknown. We hypothesized the same gonadal steroids affecting GnRH firing pattern would regulate KNDy neuron response to NK3R and KOR agonists. To test this possibility, extracellular recordings were made from KNDy neurons in brain slices from intact, untreated castrated or castrated adult male mice treated in vivo with steroid receptor agonists. As observed previously, the stimulation of KNDy neurons by the NK3R agonist senktide was attenuated in intact vs castrated mice and suppression by dynorphin was enhanced. In contrast to observations of steroid effects on the GnRH neuron firing pattern, both estradiol and DHT suppressed senktide-induced KNDy neuron firing and enhanced the inhibition caused by dynorphin. An estrogen receptor-α agonist but not an estrogen receptor-β agonist mimicked the effects of estradiol on NK3R activation. These observations suggest the steroid modulation of responses to activation of NK3R and KOR as mechanisms for negative feedback in KNDy neurons and support the contribution of these neurons to steroid-sensitive elements of a GnRH pulse generator.

Divergent Regulation of ER and Kiss Genes by 17β-Estradiol in Hypothalamic ARC Versus AVPV Models

Kisspeptin (Kiss) and G-protein-coupled receptor (Gpr)54 have emerged as key regulators of reproduction. 17β-estradiol (E2)-mediated regulation of these neurons is nuclei specific, where anteroventral periventricular (AVPV) Kiss neurons are positively regulated by E2, whereas arcuate nucleus (ARC) neurons are inhibited. We have generated immortalized Kiss cell lines from male and female adult-derived murine hypothalamic primary culture, as well as cell lines from microdissected AVPV and ARC from female Kiss-green fluorescent protein (GFP) mice. All exhibit endogenous Kiss-1 expression, estrogen receptors (ER)s (ERα, ERβ, and Gpr30), as well as known markers of AVPV Kiss neurons in the mHypoA-50 and mHypoA-Kiss/GFP-4, vs markers of ARC Kiss neurons in the mHypoA-55 and the mHypoA-Kiss/GFP-3 lines. There was an increase in Kiss-1 mRNA expression at 24 hours in the AVPV lines and a repression of Kiss-1 mRNA at 4 hours in the ARC lines. An E2-mediated decrease in ERα mRNA expression at 24 hours in the AVPV cell lines was detected, and a significant decrease in Gpr30, ERα, and ERβ mRNA levels at 4 hours in the ARC cell lines was evident. ER agonists and antagonists determined the specific ERs responsible for mediating changes in gene expression. In the AVPV, ERα is required but not ERβ or GPR30, vs the ARC Kiss-expressing cell lines that require GPR30, and either ERα and/or ERβ. We determined cAMP response element-binding protein 1 was necessary for the down-regulation of Kiss-1 mRNA expression using small interfering RNA knockdown in the ARC cell model. These studies elucidate some of the molecular events involved in the differential E2-mediated regulation of unique and specific Kiss neuronal models.

A "Timed" Kiss Is Essential for Reproduction: Lessons from Mammalian Studies

Reproduction is associated with the circadian system, primarily as a result of the connectivity between the biological clock in the suprachiasmatic nucleus (SCN) and reproduction-regulating brain regions, such as preoptic area (POA), anteroventral periventricular nucleus (AVPV), and arcuate nucleus (ARC). Networking of the central pacemaker to these hypothalamic brain regions is partly represented by close fiber appositions to specialized neurons, such as kisspeptin and gonadotropin-releasing hormone (GnRH) neurons; accounting for rhythmic release of gonadotropins and sex steroids. Numerous studies have attempted to dissect the neurochemical properties of GnRH neurons, which possess intrinsic oscillatory features through the presence of clock genes to regulate the pulsatile and circadian secretion. However, less attention has been given to kisspeptin, the upstream regulator of GnRH and a potent mediator of reproductive functions including puberty. Kisspeptin exerts its stimulatory effects on GnRH secretion via its cognate Kiss-1R receptor that is co-expressed on GnRH neurons. Emerging studies have found that kisspeptin neurons oscillate on a circadian basis and that these neurons also express clock genes that are thought to regulate its rhythmic activities. Based on the fiber networks between the SCN and reproductive nuclei such as the POA, AVPV, and ARC, it is suggested that interactions among the central biological clock and reproductive neurons ensure optimal reproductive functionality. Within this neuronal circuitry, kisspeptin neuronal system is likely to "time" reproduction in a long term during development and aging, in a medium term to regulate circadian or estrus cycle, and in a short term to regulate pulsatile GnRH secretion.

Hypothalamic Effects of Tamoxifen on Oestrogen Regulation of Luteinising Hormone and Prolactin Secretion in Female Rats

Oestradiol (E2) acts in the hypothalamus to regulate luteinising hormone (LH) and prolactin (PRL) secretion. Tamoxifen (TX) has been extensively used as a selective oestrogen receptor modulator, although its neuroendocrine effects remain poorly understood. In the present study, we investigated the hypothalamic effects of TX in rats under low or high circulating E2 levels. Ovariectomised (OVX) rats treated with oil, E2 or TX, or E2 plus TX, were evaluated for hormonal secretion and immunohistochemical analyses in hypothalamic areas. Both E2 and TX reduced LH levels, whereas TX blocked the E2 -induced surges of LH and PRL. TX prevented the E2 -induced expression of progesterone receptor (PR) in the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC), although it did not alter PR expression in OVX rats. TX blocked the E2 induction of c-Fos in AVPV neurones, consistent with the suppression of LH surge. However, TX failed to prevent E2 inhibition of kisspeptin expression in the ARC. In association with the blockade of PRL surge, TX increased the phosphorylation of tyrosine hydroxylase (TH) in the median eminence of OVX, E2 -treated rats. TX also precluded the E2 -induced increase in TH expression in the ARC. In all immunohistochemical analyses, TX treatment in OVX rats caused no measurable effect on the hypothalamus. Thus, TX is able to prevent the positive- but not negative-feedback effect of E2 on the hypothalamus. TX also blocks the effects of E2 on tuberoinfundibular dopaminergic neurones and PRL secretion. These findings further characterise the anti-oestrogenic actions of TX in the hypothalamus and provide new information on the oestrogenic regulation of LH and PRL.

The Increase in Signaling by Kisspeptin Neurons in the Preoptic Area and Associated Changes in Clock Gene Expression That Trigger the LH Surge in Female Rats Are Dependent on the Facilitatory Action of a Noradrenaline Input

In rodents, kisspeptin neurons in the rostral periventricular area of the third ventricle (RP3V) of the preoptic area are considered to provide a major stimulatory input to the GnRH neuronal network that is responsible for triggering the preovulatory LH surge. Noradrenaline (NA) is one of the main modulators of GnRH release, and NA fibers are found in close apposition to kisspeptin neurons in the RP3V. Our objective was to interrogate the role of NA signaling in the kisspeptin control of GnRH secretion during the estradiol induced LH surge in ovariectomized rats, using prazosin, an α1-adrenergic receptor antagonist. In control rats, the estradiol-induced LH surge at 17 hours was associated with a significant increase in GnRH and kisspeptin content in the median eminence with the increase in kisspeptin preceding that of GnRH and LH. Prazosin, administered 5 and 3 hours prior to the predicted time of the LH surge truncated the LH surge and abolished the rise in GnRH and kisspeptin in the median eminence. In the preoptic area, prazosin blocked the increases in Kiss1 gene expression and kisspeptin content in association with a disruption in the expression of the clock genes, Per1 and Bmal1. Together these findings demonstrate for the first time that NA modulates kisspeptin synthesis in the RP3V through the activation of α1-adrenergic receptors prior to the initiation of the LH surge and indicate a potential role of α1-adrenergic signaling in the circadian-controlled pathway timing of the preovulatory LH surge.

The ERα-PI3K Cascade in Proopiomelanocortin Progenitor Neurons Regulates Feeding and Glucose Balance in Female Mice

Estrogens act upon estrogen receptor (ER)α to inhibit feeding and improve glucose homeostasis in female animals. However, the intracellular signals that mediate these estrogenic actions remain unknown. Here, we report that anorexigenic effects of estrogens are blunted in female mice that lack ERα specifically in proopiomelanocortin (POMC) progenitor neurons. These mutant mice also develop insulin resistance and are insensitive to the glucose-regulatory effects of estrogens. Moreover, we showed that propyl pyrazole triol (an ERα agonist) stimulates the phosphatidyl inositol 3-kinase (PI3K) pathway specifically in POMC progenitor neurons, and that blockade of PI3K attenuates propyl pyrazole triol-induced activation of POMC neurons. Finally, we show that effects of estrogens to inhibit food intake and to improve insulin sensitivity are significantly attenuated in female mice with PI3K genetically inhibited in POMC progenitor neurons. Together, our results indicate that an ERα-PI3K cascade in POMC progenitor neurons mediates estrogenic actions to suppress food intake and improve insulin sensitivity.

KNDy Neurons Modulate the Magnitude of the Steroid-Induced Luteinizing Hormone Surges in Ovariectomized Rats

Kisspeptin is the most potent stimulator of LH release. There are two kisspeptin neuronal populations in the rodent brain: in the anteroventral periventricular nucleus (AVPV) and in the arcuate nucleus. The arcuate neurons coexpress kisspeptin, neurokinin B, and dynorphin and are called KNDy neurons. Because estradiol increases kisspeptin expression in the AVPV whereas it inhibits KNDy neurons, AVPV and KNDy neurons have been postulated to mediate the positive and negative feedback effects of estradiol on LH secretion, respectively. Yet the role of KNDy neurons during the positive feedback is not clear. In this study, ovariectomized rats were microinjected bilaterally into the arcuate nucleus with a saporin-conjugated neurokinin B receptor agonist for targeted ablation of approximately 70% of KNDy neurons. In oil-treated animals, ablation of KNDy neurons impaired the rise in LH after ovariectomy and kisspeptin content in both populations. In estradiol-treated animals, KNDy ablation did not influence the negative feedback of steroids during the morning. Surprisingly, KNDy ablation increased the steroid-induced LH surges, accompanied by an increase of kisspeptin content in the AVPV. This increase seems to be due to lack of dynorphin input from KNDy neurons to the AVPV as the following: 1) microinjections of a dynorphin antagonist into the AVPV significantly increased the LH surge in estradiol-treated rats, similar to KNDy ablation, and 2) intra-AVPV microinjections of dynorphin in KNDy-ablated rats restored LH surge levels. Our results suggest that KNDy neurons provide inhibition to AVPV kisspeptin neurons through dynorphin and thus regulate the amplitude of the steroid-induced LH surges.

Xenoestrogens Ethinyl Estradiol and Zearalenone Cause Precocious Puberty in Female Rats via Central Kisspeptin Signaling

Xenoestrogens from synthetic or natural origin represent an increasing risk of disrupted endocrine functions including the physiological activity of the hypothalamo-pituitary-gonad axis. Ethinyl estradiol (EE2) is a synthetic estrogen used in contraceptive pills, whereas zearalenone (ZEA) is a natural mycoestrogen found with increasing prevalence in various cereal crops. Both EE2 and ZEA are agonists of estrogen receptor-α and accelerate puberty. However, the neuroendocrine mechanisms that are responsible for this effect remain unknown. Immature female Wistar rats were treated with EE2 (10 μg/kg), ZEA (10 mg/kg), or vehicle for 10 days starting from postnatal day 18. As a marker of puberty, the vaginal opening was recorded and neuropeptide and related transcription factor mRNA levels were measured by quantitative real time PCR and in situ hybridization histochemistry. Both ZEA and EE2 accelerated the vaginal opening, increased the uterine weight and the number of antral follicles in the ovary, and resulted in the increased central expression of gnrh. These changes occurred in parallel with an earlier increase of kiss1 mRNA in the anteroventral and rostral periventricular hypothalamus and an increased kisspeptin (KP) fiber density and KP-GnRH appositions in the preoptic area. These changes are compatible with a mechanism in which xenoestrogens overstimulate the developmentally unprepared reproductive system, which results in an advanced vaginal opening and an enlargement of the uterus at the periphery. Within the hypothalamus, ZEA and EE2 directly activate anteroventral and periventricular KP neurons to stimulate GnRH mRNA. However, GnRH and gonadotropin release and ovulation are disrupted due to xenoestrogen-mediated inhibitory KP signaling in the arcuate nucleus.

Gonadotropin and kisspeptin gene expression, but not GnRH, are impaired in cFOS deficient mice

cFOS is a pleiotropic transcription factor, which binds to the AP1 site in the promoter of target genes. In the pituitary gonadotropes, cFOS mediates induction of FSHβ and GnRH receptor genes. Herein, we analyzed reproductive function in the cFOS-deficient mice to determine its role in vivo. In the pituitary cFOS is necessary for gonadotropin subunit expression, while TSHβ is unaffected. Additionally, cFOS null animals have the same sex-steroid levels, although gametogenesis is impeded. In the brain, cFOS is not necessary for GnRH neuronal migration, axon targeting, cell number, or mRNA levels. Conversely, cFOS nulls, particularly females, have decreased Kiss1 neuron numbers and lower Kiss1 mRNA levels. Collectively, our novel findings suggest that cFOS plays a cell-specific role at multiple levels of the hypothalamic-pituitary-gonadal axis, affecting gonadotropes but not thyrotropes in the pituitary, and kisspeptin neurons but not GnRH neurons in the hypothalamus, thereby contributing to the overall control of reproduction.

60 YEARS OF NEUROENDOCRINOLOGY: The hypothalamo-pituitary-gonadal axis

This review provides an outline of how our understanding of the neuroendocrine control of the hypothalamo-pituitary-gonadal axis has evolved since the publication of Geoffrey Harris' renowned monograph in 1955. Particular attention is directed to the neurobiology underlying pulsatile GnRH release from the hypothalamus, the neuroendocrine control of ovarian cycles, puberty and seasonality of gonadal function, and to ideas that have emerged as a result of examining the relationship between growth and the reproductive axis. The review closes with i) a brief discussion of how knowledge gained as a result of pursuing the early hypotheses of Harris has led to major clinical and therapeutic applications, and ii) a personal glimpse into the future of research in this fascinating area of biology.

Classical and membrane-initiated estrogen signaling in an in vitro model of anterior hypothalamic kisspeptin neurons

The neuropeptide kisspeptin is essential for sexual maturation and reproductive function. In particular, kisspeptin-expressing neurons in the anterior rostral periventricular area of the third ventricle are generally recognized as mediators of estrogen positive feedback for the surge release of LH, which stimulates ovulation. Estradiol induces kisspeptin expression in the neurons of the rostral periventricular area of the third ventricle but suppresses kisspeptin expression in neurons of the arcuate nucleus that regulate estrogen-negative feedback. To focus on the intracellular signaling and response to estradiol underlying positive feedback, we used mHypoA51 cells, an immortalized line of kisspeptin neurons derived from adult female mouse hypothalamus. mHypoA51 neurons express estrogen receptor (ER)-α, classical progesterone receptor (PR), and kisspeptin, all key elements of estrogen-positive feedback. As with kisspeptin neurons in vivo, 17β-estradiol (E2) induced kisspeptin and PR in mHypoA51s. The ERα agonist, 1,3,5-Tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole, produced similar increases in expression, indicating that these events were mediated by ERα. However, E2-induced PR up-regulation required an intracellular ER, whereas kisspeptin expression was stimulated through a membrane ER activated by E2 coupled to BSA. These data suggest that anterior hypothalamic kisspeptin neurons integrate both membrane-initiated and classical nuclear estrogen signaling to up-regulate kisspeptin and PR, which are essential for the LH surge.

The relationship between circulating kisspeptin and sexual hormones levels in healthy females

The kisspeptin (metastin) is an endogenous peptide, which regulates human reproduction by modulating gonadotropin-releasing hormone (GnRH) secretion. Kisspeptin was detected in peripheral blood, although GnRH was not. Previously, we measured plasma kisspeptin levels in male healthy subjects and patients with hypogonadism using enzyme immunoassay (EIA) to elucidate a normal range in healthy males and clinical implications of kisspeptin in male hypogonadism. We suggested that the plasma kisspeptin levels were received feedback from testosterone. In this study, we focused female subjects and elucidated the relationship between menstrual cycle and plasma kisspeptin levels to understand kisspeptin-hypothalamic-pituitary-gonadal axis. We measured plasma kisspeptin levels in eight female volunteers. The plasma kisspeptin levels in female are significantly higher than those in male. There are no significant correlation between plasma kisspeptin levels and sexual hormones. We revealed that the kisspeptin might stimulate a start of menstruation as a trigger, and progress menstruation covered for weakened ovarian function. We suggest that kisspeptin may be closely related with menstrual cycle and that the measurement of plasma kisspeptin levels is useful for understanding of reproductive system.