Pulsatile Luteinizing Hormone Secretion Research Articles

Central δ/κ opioid receptor signaling pathways mediate chronic and/or acute suckling-induced LH suppression in rats during late lactation.

In mammals, secretion of tonic (pulsatile) gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH) is often suppressed during lactation. Suppression of GnRH/LH pulses in lactating dams is assumed to be caused by suckling stimuli and a chronic negative energy balance due to milk production. The present study aimed to investigate whether the central enkephalin-δ opioid receptor (DOR) signaling mediated the suppression of LH secretion by acute suckling stimuli and/or chronic negative energy balance due to milk production in rats during late lactation when dams were under a heavy energy demand. On postpartum day 16, the number of Penk (enkephalin mRNA)-expressing cells in the arcuate nucleus was significantly higher in lactating rats than in non-lactating control rats. Pulsatile LH secretion was suppressed in rats with chronic suckling or acute 1-h suckling stimuli 6 h after pup removal on day 16 of lactation. Central DOR antagonism significantly increased the mean LH concentrations and the baseline of LH pulses in rats with chronic suckling but not with acute suckling stimuli on day 16 of lactation. Besides, central κ opioid receptor (KOR) antagonism increased the amplitude of LH pulses in rats with the acute suckling stimuli on day 16 of lactation. These results suggest that central DOR signaling mediates the suppression of LH secretion caused by a negative energy balance in rats receiving chronic suckling during late lactation. On the other hand, central KOR signaling likely mediates acute suckling stimuli-induced suppression of LH secretion in rats during late lactation.

Absence of sex differences in diabetes-induced suppression of KNDy neurons in rats.

Diabetes mellitus disturbs kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the arcuate nucleus (ARC), which regulate pulsatile luteinizing hormone (LH) secretion in both sexes. However, it remains unclear whether a sex-specific association with the negative effects of diabetes on KNDy neurons exists. Therefore, we examined mRNA expression in KNDy neurons of diabetic male and female rats 7 weeks after streptozotocin (STZ) injection using histochemistry. In gonad-intact rats, the numbers of Kiss1 and Pdyn mRNA-expressing cells in the ARC decreased in an STZ-dose-dependent manner; moreover, no sex-dependent association with STZ treatment was observed. In males, plasma LH and sex steroid levels decreased in diabetic rats. Conversely, those of females did not vary significantly between the control and diabetic rats. Kiss1 expression in the anteroventral periventricular nucleus was slightly affected in diabetic animals, but did not exhibit sex-dependent differences. In gonadectomized rats, the numbers of KNDy mRNA-expressing cells in the ARC and plasma LH levels decreased in diabetic male and female rats; however, sex-dependent differences did not exist. These results demonstrated that a sex-specific association with the negative effects of diabetes on KNDy neurons did not exist. Therefore, the stage of diabetes that induces the suppression of the hypothalamus may not vary according to sex.

Chemogenetic Activation of RFRP Neurons Reduces LH Pulse Frequency in Female but not Male Mice.

The neuropeptide RFRP-3 (RFamide-related peptide-3) is thought to play a role in the negative regulation of fertility. However, the exogenous administration of RFRP-3 yields varying results depending on the dose and route of administration, sex of the subject, and many other variables. Manipulation of in vivo neuronal activity using DREADDs (designer receptor exclusively activated by designer drugs) technology enables investigation of cell type-specific neuronal activation in a manner that better reflects endogenous neuronal activity. To test the effects of RFRP neuronal activation on pulsatile luteinizing hormone (LH) secretion. We generated mice expressing the stimulatory hM3Dq designer receptor exclusively in RFRP cells using 2 different Cre-loxP-mediated approaches: (1) we bred mice to express hM3Dq in all Rfrp-Cre-expressing cells, including some that transiently expressed Rfrp-Cre neonatally (RFRP × hM3Dq mice), and (2) we stereotaxically injected Cre-dependent hM3Dq into the dorsomedial nucleus of RFRP-Cre mice to drive hM3Dq expression exclusively in a subpopulation of adult Rfrp-Cre neurons (RFRP-AAV-hM3Dq mice). We then investigated the effects of acute hM3Dq activation on LH pulse frequency in RFRP × hM3Dq mice, RFRP-AAV-hM3Dq mice, and their respective controls. In both female RFRP × hM3Dq and RFRP-AAV-hM3Dq mice, chemogenetic activation of Cre-driven hM3Dq led to a significant 35% to 50% reduction in LH pulse frequency compared with controls, while no differences in pulse amplitude or mean LH concentration were observed. In marked contrast, RFRP activation did not cause any changes to LH pulse dynamics in male mice. These data show for the first time that activation of neurons that have expressed Rfrp, or of a subset of adult RFRP neurons, can independently suppress LH pulsatility in female, but not male mice.

Peripheral administration of a κ-opioid receptor agonist nalfurafine inactivates gonadotropin-releasing hormone pulse generator activity in goats

Neurons co-expressing kisspeptin, neurokinin B, and dynorphin A (KNDy neurons), located in the arcuate nucleus (ARC) of the hypothalamus, are indicated to be the gonadotropin-releasing hormone (GnRH) pulse generator. Dynorphin A is reported to suppress GnRH pulse generator activity. Nalfurafine is a selective agonist of the κ-opioid receptor (KOR), a receptor for dynorphin A, clinically used as an anti-pruritic drug. This study aimed to evaluate the effects of nalfurafine on GnRH pulse generator activity and luteinizing hormone (LH) pulses using female goats. Nalfurafine (0, 2, 4, 8, or 16 μg/head) was intravenously injected into ovariectomized Shiba goats. The multiple unit activity (MUA) in the ARC area was recorded, and plasma LH concentrations were measured 2 and 48 h before and after injection, respectively. The MUA volley interval during 0–2 h after injection was significantly increased in the nalfurafine 8 and 16 μg groups compared with the vehicle group. In 0–2 h after injection, the number of LH pulses was significantly decreased in the nalfurafine 8 and 16 μg groups, and the mean and baseline LH were significantly decreased in all nalfurafine-treated groups (2, 4, 8, and 16 μg) compared with the vehicle group. These results suggest that nalfurafine inhibits the activity of the GnRH pulse generator in the ARC, thus suppressing pulsatile LH secretion. Therefore, nalfurafine could be used as a reproductive inhibitor in mammals.

Norepinephrine Neurons in the Nucleus of the Solitary Tract Suppress Luteinizing Hormone Secretion in Female Mice.

Stress impairs fertility, at least in part, via inhibition of gonadotropin secretion. Luteinizing hormone (LH) is an important gonadotropin that is released in a pulsatile pattern in males and in females throughout the majority of the ovarian cycle. Several models of stress, including acute metabolic stress, suppress LH pulses via inhibition of neurons in the arcuate nucleus of the hypothalamus that coexpress kisspeptin, neurokinin B, and dynorphin (termed KNDy cells) which form the pulse generator. The mechanism for inhibition of KNDy neurons during stress, however, remains a significant outstanding question. Here, we investigated a population of catecholamine neurons in the nucleus of the solitary tract (NTS), marked by expression of the enzyme dopamine beta-hydroxylase (DBH), in female mice. First, we found that a subpopulation of DBH neurons in the NTS is activated (express c-Fos) during metabolic stress. Then, using chemogenetics, we determined that activation of these cells is sufficient to suppress LH pulses, augment corticosterone secretion, and induce sickness-like behavior. In subsequent studies, we identified evidence for suppression of KNDy cells (rather than downstream signaling pathways) and determined that the suppression of LH pulses was not dependent on the acute rise in glucocorticoids. Together these data support the hypothesis that DBH cells in the NTS are important for regulation of neuroendocrine and behavioral responses to stress.

Estrogen receptor-α signaling in tanycytes lies at the crossroads of fertility and metabolism

BackgroundEstrogen secretion by the ovaries regulates the hypothalamic-pituitary-gonadal axis during the reproductive cycle, influencing gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion, and also plays a role in regulating metabolism. Here, we establish that hypothalamic tanycytes—specialized glia lining the floor and walls of the third ventricle—integrate estrogenic feedback signals from the gonads and couple reproduction with metabolism by relaying this information to orexigenic neuropeptide Y (NPY) neurons. MethodsUsing mouse models, including mice floxed for Esr1 (encoding estrogen receptor alpha, ERα) and those with Cre-dependent expression of designer receptors exclusively activated by designer drugs (DREADDs), along with viral-mediated, pharmacological and indirect calorimetric approaches, we evaluated the role of tanycytes and tanycytic estrogen signaling in pulsatile LH secretion, cFos expression in NPY neurons, estrous cyclicity, body-weight changes and metabolic parameters in adult females. ResultsIn ovariectomized mice, chemogenetic activation of tanycytes significantly reduced LH pulsatile release, mimicking the effects of direct NPY neuron activation. In intact mice, tanycytes were crucial for the estrogen-mediated control of GnRH/LH release, with tanycytic ERα activation suppressing fasting-induced NPY neuron activation. Selective knockout of Esr1 in tanycytes altered estrous cyclicity and fertility in female mice and affected estrogen's ability to inhibit refeeding in fasting mice. The absence of ERα signaling in tanycytes increased Npy transcripts and body weight in intact mice and prevented the estrogen-mediated decrease in food intake as well as increase in energy expenditure and fatty acid oxidation in ovariectomized mice. ConclusionsOur findings underscore the pivotal role of tanycytes in the neuroendocrine coupling of reproduction and metabolism, with potential implications for its age-related deregulation after menopause. Significance statementOur investigation reveals that tanycytes, specialized glial cells in the brain, are key interpreters of estrogen signals for orexigenic NPY neurons in the hypothalamus. Disrupting tanycytic estrogen receptors not only alters fertility in female mice but also impairs the ability of estrogens to suppress appetite. This work thus sheds light on the critical role played by tanycytes in bridging the hormonal regulation of cyclic reproductive function and appetite/feeding behavior. This understanding may have potential implications for age-related metabolic deregulation after menopause.

P-708 melatonin alleviates circadian rhythm disruption-induced enhanced luteinizing hormone pulsatility and ovarian dysfunction in vivo and in vitro

Abstract Study question Is melatonin deficiency a reversible cause of abnormal pattern of luteinizing hormone (LH) pulsatility and ovarian dysfunction caused by circadian rhythm disruption (CRD)? Summary answer Melatonin could rescue the augmented LH pulsatility and reproductive abnormalities caused by CRD. What is known already Melatonin, mainly synthesized and released by pineal gland, engages in regulating circadian rhythms. When circadian rhythms are disrupted, the nocturnal productions of melatonin are suppressed. Evidence suggests that circadian rhythm disruption (CRD) is associated with reproductive dysfunctions, while melatonin plays a vital role for female reproduction as a free radical scavenger and a neuroendocrine regulator. The gonadotrophin-releasing hormone (GnRH) drives pulsatile luteinizing hormone (LH) secretion, which is also essential for fertility. Study design, size, duration We used 90 CBA/CaJ mice to establish the chronic jet-lag model in which mice were exposed to an 8 hr time shift every 3 days. After 8 weeks of jet-lag induction, some of the mice were given melatonin treatment for 4 weeks. Furthermore, we used a perfusion system in vitro to mimic the process of CRD-induce high-frequency GnRH pulses stimulation of LβT2 gonadotrope cells. Participants/materials, setting, methods Repetitive tail-tip blood collection was used to evaluate the pattern of LH pulsatility. Blood plasma samples were collected from 4 mice at 4-hour intervals to measure levels of melatonin. Follicular development was evaluated by ovarian histology. Reproductive hormones was detected by ELISA. Immunohistochemistry and western blot were used to detect the expression of melatonin receptor 1A (MT1). The LβT2 cells were exposed to pulsatile GnRH at high pulse frequencies to mimic augmented pulsatile GnRH stimulation. Main results and the role of chance CRD mice exhibited reproductive-endocrine dysfunction, including irregular estrous cycles, reduced number of corpus lutea (CL), and decreased levels of estradiol and progesterone. Additionally, CRD enhanced the frequency and amplitude of LH pulsatility and pituitary LH beta-subunit expression. Melatonin administration alleviated these CRD-induced reproductive abnormalities and reversed the augmented LH pulsatility. The expression of MT1 decreased in the anterior pituitaries of CRD mice but increased after melatonin treatment, indicating the essential role of MT1 in melatonin’s reversal of CRD-induced enhanced LH pulsatility. Limitations, reasons for caution Further research is needed to validate the applicability and safety of these findings in humans. Wider implications of the findings The results suggest that melatonin may be a beneficial option for patients with reproductive-endocrine abnormalities, particularly those with circadian rhythm disruption. Trial registration number 82101719

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

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

NK3R signalling in the posterodorsal medial amygdala is involved in stress-induced suppression of pulsatile LH secretion in female mice.

Psychosocial stress negatively impacts reproductive function by inhibiting pulsatile luteinizing hormone (LH) secretion. The posterodorsal medial amygdala (MePD) is responsible in part for processing stress and modulating the reproductive axis. Activation of the neurokinin 3 receptor (NK3R) suppresses the gonadotropin-releasing hormone (GnRH) pulse generator, under hypoestrogenic conditions, and NK3R activity in the amygdala has been documented to play a role in stress and anxiety. We investigate whether NK3R activation in the MePD is involved in mediating the inhibitory effect of psychosocial stress on LH pulsatility in ovariectomised female mice. First, we administered senktide, an NK3R agonist, into the MePD and monitored the effect on pulsatile LH secretion. We then delivered SB222200, a selective NK3R antagonist, intra-MePD in the presence of predator odour, 2,4,5-trimethylthiazole (TMT) and examined the effect on LH pulses. Senktide administration into the MePD dose-dependently suppresses pulsatile LH secretion. Moreover, NK3R signalling in the MePD mediates TMT-induced suppression of the GnRH pulse generator, which we verified using a mathematical model. The model verifies our experimental findings: (i) predator odour exposure inhibits LH pulses, (ii) activation of NK3R in the MePD inhibits LH pulses and (iii) NK3R antagonism in the MePD blocks stressor-induced inhibition of LH pulse frequency in the absence of ovarian steroids. These results demonstrate for the first time that NK3R neurons in the MePD mediate psychosocial stress-induced suppression of the GnRH pulse generator.

CRISPR-Cas9 knockdown of ESR1 in preoptic GABA-kisspeptin neurons suppresses the preovulatory surge and estrous cycles in female mice.

Evidence suggests that estradiol-sensing preoptic area GABA neurons are involved in the preovulatory surge mechanism necessary for ovulation. In vivo CRISPR-Cas9 editing was used to achieve a 60-70% knockdown in estrogen receptor alpha (ESR1) expression by GABA neurons located within the regions of the rostral periventricular area of the third ventricle (RP3V) and medial preoptic nuclei (MPN) in adult female mice. Mice exhibited variable reproductive phenotypes with the only significant finding being mice with bilateral ESR1 deletion in RP3V GABA neurons having reduced cFos expression in gonadotropin-releasing hormone (GnRH) neurons at the time of the surge. One sub-population of RP3V GABA neurons expresses kisspeptin. Re-grouping ESR1-edited mice on the basis of their RP3V kisspeptin expression revealed a highly consistent phenotype; mice with a near-complete loss of kisspeptin immunoreactivity displayed constant estrus and failed to exhibit surge activation but retained pulsatile luteinizing hormone (LH) secretion. These observations demonstrate that ESR1-expressing GABA-kisspeptin neurons in the RP3V are essential for the murine preovulatory LH surge mechanism.

New methods to investigate the GnRH pulse generator.

The exact neural construct underlying the dynamic secretion of gonadotrophin-releasing hormone (GnRH) has only recently been identified despite the detection of multiunit electrical activity volleys associated with pulsatile luteinising hormone (LH) secretion four decades ago. Since the discovery of kisspeptin/neurokinin B/dynorphin neurons in the mammalian hypothalamus, there has been much research into the role of this neuronal network in controlling the oscillatory secretion of gonadotrophin hormones. In this review, we provide an update of the progressive application of cutting-edge techniques combined with mathematical modelling by the neuroendocrine community, which are transforming the functional investigation of the GnRH pulse generator. Understanding the nature and function of the GnRH pulse generator can greatly inform a wide range of clinical studies investigating infertility treatments.

25 Role of Kndy and Arcuate Kiss1r-Containing Neurons in the Preovulatory Luteinizing Hormone Surge and Puberty Onset of Female sheep

Abstract Neurons within the arcuate nucleus (ARC) of the hypothalamus containing kisspeptin, neurokinin B (NKB), and dynorphin (KNDy neurons) have an important role in regulating the pulsatile secretion of gonadotropin releasing hormone (GnRH) and luteinizing hormone (LH). In sheep, kisspeptin neurons also contribute to the LH surge, as kisspeptin receptor (Kiss1r) antagonist administration reduces surge amplitude by 50% and KNDy neurons are likely involved, based on increased Fos expression at the time of the surge. However, the extent to which kisspeptin acts within the ARC regulate the GnRH/LH surge remains unclear. Thus, herein we tested the hypothesis that deletion of KNDy or ARC Kiss1r-containing neurons would impair the LH surge. Adult female sheep received bilateral injections targeting the ARC of NKB-saporin (NKB-SAP, n = 8), kisspeptin-saporin (Kiss-SAP, n = 10), or blank-saporin (Blank-SAP, n = 7) as a control. In other work, NKB-SAP lesioned over 90% of ovine KNDy neurons, while Kiss-SAP lesioned 67% of Kiss1r-containing cells without affecting KNDy or GnRH cell number. Ewes were also ovariectomized and a subcutaneous silastic estradiol (E2) implant was inserted at the time of neurosurgery. Two artificial luteal phases were simulated with progesterone-containing CIDRs, immediately followed by E2 treatment via implants to induce an LH surge. Blood samples were collected every two to four hours over two days and analyzed for LH via radioimmunoassay. LH surge amplitude in six of eight NKB-SAP ewes (49.5 ± 11.7 ng/mL) was significantly reduced compared with Blank-SAP control ewes (156.7 ± 20.2 ng/mL, p = 0.0001), a reduction similar to that produced by treatment with a Kiss1r antagonist. Nine of ten Kiss-SAP treated ewes displayed little to no increase of LH at the time of the expected surge (16.6 ± 5.3 ng/mL, p < 0.0001). Lesion effectiveness is currently being assessed by RNAscope, however all Kiss-SAP animals examined to date have significantly reduced ARC Kiss1r cell numbers except a single ewe which exhibited a normal LH surge. Based on these data, we propose that in ewes, KNDy neurons contribute to, but are not required for, the LH surge. In contrast, ARC Kiss1r-containing cells are essential for a functional LH surge. Given these results, we are currently assessing the role of ARC Kiss1r neurons in ovine puberty using a similar approach. Our data to date shows that time to puberty onset is similar for Kiss-SAP, Blank-SAP, and non-surgical control animals as measured by an increase in progesterone (p = 0.35). Blood samples to detect LH pulses and the LH surge are currently being analyzed, as are ARC Kiss1r cell numbers.

SAT601 The Role Of The Melanocortin System In Ovine Puberty

Abstract Disclosure: E.G. Aerts: None. M.J. Griesgraber: None. A. Thomson: None. M. Brown: None. A. Seman: None. S.L. Hardy: None. R.L. Goodman: None. C. Nestor: None. S.M. Hileman: None. The neural mechanisms that regulate the timing of puberty onset are not completely known. In several species, including sheep, puberty onset relies on an increase in gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion as a result of decreased sensitivity to estradiol (E2) inhibition. Additionally, it is unclear how E2 acts in the hypothalamus to inhibit GnRH/LH secretion, as GnRH neurons do not contain estrogen receptor alpha (ERα). Neurons within the arcuate nucleus (ARC) of the hypothalamus that contain kisspeptin, neurokinin B, and dynorphin (KNDy neurons) are critical for the generation of GnRH pulses and contain ERα. Data from our laboratory suggests that KNDy neurons, while critical, may be responding to other inputs that time puberty onset. Proopiomelanocortin (POMC) and Agouti-related peptide (AgRP) neurons in the ARC have been shown to contain ERα and provide input to KNDy neurons, which contain the melanocortin 3 and 4 receptor (MC3R, MC4R). The goal of this work was to assess POMC- and AgRP-positive cell numbers, input onto KNDy neurons, and neuronal activity changes in a puberty-specific manner. Female sheep were ovariectomized and given subcutaneous E2 implants at 5 months (prepubertal, n=4), 8 months (peripubertal, n=5), and 10 months (postpubertal, n=5) of age. Two weeks after surgery, blood samples were collected via jugular venipuncture every 12 minutes for 4 hours and assessed for LH. The sheep were then sacrificed and hypothalamic tissue was perfused, collected, and prepared for staining. The tissue was assessed via immunohistochemistry for POMC, AgRP, kisspeptin, NKB, and c-Fos, a known marker of neuronal activity. Pulsatile LH secretion was, as expected, reduced at 5 months and highest at 10 months. ARC POMC cell numbers did not significantly change over development (p>0.10). The number of ARC POMC close contacts onto ARC kisspeptin neurons increased significantly with development (p<0.05), as well as the percentage of ARC POMC neurons expressing c-Fos (p<0.05). ARC AgRP cell numbers and the percentage of AgRP cells colocalized with c-Fos decreased significantly over time (p<0.05). The number of AgRP close contacts onto ARC NKB cells is currently being analyzed. The percentage of NKB cells colocalizing c-Fos throughout pubertal development also increased significantly (p<0.05). This data supports the hypothesis that the ARC melanocortin system impacts KNDy neurons to regulate GnRH/LH secretion throughout pubertal development. Presentation: Saturday, June 17, 2023

SAT375 Impact of Flutamide on Wake vs. Sleep LH Pulse Frequency in PCOS: An Interim Analysis

Abstract Disclosure: C.K. Matingou: None. S. Kim: None. M. Gilrain: None. C.M. Burt Solorzano: None. C.R. McCartney: None. Polycystic ovary syndrome (PCOS) is characterized by hyperandrogenism and ovulatory dysfunction. PCOS is also associated with luteinizing hormone (LH) excess, in part related to persistently high gonadotropin-releasing hormone (GnRH) pulse frequency. Furthermore, late pubertal girls with obesity and hyperandrogenemia did not exhibit sleep-associated decreases in LH (GnRH) pulse frequency when studied during the follicular phase, in contrast to non-hyperandrogenemic controls with or without obesity (JCEM 2014;99:2887-96). We therefore aimed to test two hypotheses: (1) sleep-associated reductions in LH pulse frequency are less pronounced in adult PCOS compared to late-follicular controls; and (2) sleep-associated reductions in LH pulse frequency are normalized in PCOS with 4 weeks of flutamide (androgen-receptor antagonist) pretreatment. To date, we have studied 5 women with PCOS (median age 30 y, BMI 42.6 kg/m2) and 5 ovulatory controls (median age 22 y, BMI 23.2 kg/m2). Subjects underwent two separate 16-hour frequent-blood-sampling studies to characterize pulsatile LH secretion, once after flutamide pretreatment (250 mg BID x 4 weeks) and once after placebo (PBO) pretreatment (BID for 4 weeks). In each study, 1500-2300 h and 2300-0700 h were designated the wake and sleep periods, respectively. The order of flutamide and PBO administration was randomized, and treatment allocation was switched after the first admission per a cross-over design. Controls were studied on cycle days 7-10, while those with PCOS were studied no earlier than cycle day 7. Serum progesterone concentrations were < 1.5 ng/dl for all admissions. With PBO pretreatment, participants with PCOS and controls exhibited the following: wake LH pulse frequency 1.19 (1.08-1.33) (median [interquartile range]) and 1.22 (0.97-1.27) pulses/h, respectively; sleep LH pulse frequency 0.93 (0.78-1.28) and 0.83 (0.78-0.99) pulses/h, respectively; and wake-to-sleep change in LH pulse frequency of -19.4 (-21.9 to +2.9) and -15.5 (-31.8 to -12.0) percent, respectively. For participants with PCOS, pretreatment with flutamide was associated with the following changes compared to PBO: wake LH pulse frequency +0.01 (-0.06 to +0.03) pulses/h; sleep LH pulse frequency +0.06 (+0.01 to +0.07) pulses/h; and wake-to-sleep LH pulse frequency change +5 (+7 to -12) percent. None of these differences were statistically significant by conservative nonparametric testing. We conclude that this interim analysis does not offer any indication that wake- and sleep-associated LH pulse frequencies are different between PCOS and late-follicular controls, nor does it suggest clear differences in wake-to-sleep changes in late-follicular LH pulse frequency between groups. Furthermore, this analysis does not seem to offer any indication that flutamide alone alters wake- and/or sleep-associated LH pulse frequencies in PCOS. Presentation Date: Saturday, June 17, 2023

FRI279 Submaximal Loss Of KNDy Neurons Accelerates And Amplifies Pulsatile LH Secretion In Female Rats

Abstract Disclosure: A.C. Campideli-Santana: None. K.S. da Costa Silva: None. R. Araújo-Lopes: None. L.M. Antunes: None. R.E. Szawka: None. Kisspeptin is a powerful stimulator neuropeptide in the hypothalamus-pituitary-gonadal axis and is essential for fertility. Neurons in the arcuate nucleus (ARC) of the hypothalamus that coexpress kisspeptin, neurokinin B, and dynorphin (KNDy) play a crucial role in the control of luteinizing hormone (LH) secretion, but the neuroendocrine mechanisms involved in this regulation are not fully understood. Our previous study demonstrated that the moderate loss of KNDy neurons amplifies the LH surge induced by estradiol in ovariectomized rats (1). The current study aimed to perform a longitudinal evaluation of female rats in which KNDy neurons were ablated to determine the integrated role of this neuronal population in the control of pulsatile LH secretion. Adult female rats underwent a neurochemical ablation of KNDy neurons via intra-ARC stereotaxic injections of neurokinin-3 receptor agonist conjugated with saporin (NK3-SAP), while control animals received blank-saporin (Control). Estrous cyclicity was monitored over 21 days before and after the stereotaxic surgery. Three weeks after surgery, blood samples (10 µL) were withdrawn from the tail tip at 6-minute intervals for 180 minutes on the day of diestrus. Rats were then ovariectomized and the ovaries were processed for histological analysis. Whole blood LH levels were measured by ELISA and brains were immunohistochemically labeled for neurokinin B in the ARC. NK3-SAP rats bearing a submaximal loss of KNDy neurons (between 55-95%; n = 8) displayed irregular estrous cycles. The ovarian weight and the number of corpora lutea and atretic follicles were unaltered, whereas the number of healthy early antral follicles decreased in NK3-SAP rats. The frequency of LH pulses was increased and both pulse amplitude and mean LH levels were higher in NK3-SAP compared with Control rats. Thus, the submaximal loss of KNDy neurons affects the regularity of estrous cyclicity but does not preclude ovulation, while seems to stimulate the maturation of early antral follicles. Notably, KNDy neuron loss accelerates and amplifies LH pulsatile secretion during the rat estrous cycle. These results suggest a new role for KNDy neurons in restraining the frequency and amplitude of LH pulses in ovary-intact animals, with possible implications in the rate of recruitment of early antral follicles. Reference: Campideli-Santana et al., J Neuroendocrinol. 2022 Nov;34(11):e13204. Support: FAPEMIG, CNPq, CAPES, and Pro-reitoria de Pesquisa-UFMG. Presentation: Friday, June 16, 2023

OR09-02 Chemogenetic Manipulation Of Brainstem Noradrenergic Neurons Modulates The Activity Of The Kisspeptin GnRH Pulse Generator In Mice

Abstract Disclosure: S. Vas: None. M. Ruiz-Cruz: None. S. Han: None. S. Hwa-Yeo: None. A.E. Herbison: None. The kisspeptin neurons in the arcuate nucleus (ARNKISS) represent the GnRH pulse generator that drives pulsatile luteinizing hormone secretion. These neurons serve as a hub to integrate multiple cues, such as the negative feedback control from steroid hormones, as well as metabolic, and stress-related inputs. Brainstem noradrenergic (NA) neurons have long been implicated in the control of GnRH pulse generator frequency and fertility but the precise mechanisms through which they operate, and their roles remain unclear. Here we used intersectional Cre-lox and FLP-FRT recombination approaches to couple ARNKISS neuron GCaMP6 fiber photometry with the brainstem NA DREADD (Designer Receptor Exclusively Activated by Designer Drug) modulation to investigate the role that NA may play in controlling ARNKISS pulse generator activity. Kiss1-Cre,GCaMP6s mice were crossed with a mouse line in which FLP recombinase is expressed selectively in dopamine β-hydroxylase (NA) neurons. Adult female mice were injected bilaterally with a FLP-dependent retrograde viral vector (AAVrg-hSyn-fDIO-hM3D(Gq)-mCherry-WPREpA) into the mid-caudal ARN to express excitatory (hM3Dq) DREADD receptors selectively in brainstem NA neurons that project to the ARN. An optical fiber was then implanted to detect the calcium-dependent population activity of KISSARN neurons. Histology revealed m-Cherry/DREADD expression in small sub-populations of tyrosine-hydroxylase neurons located in the brainstem A1, A2 and A6, confirming direct innervation from these regions to the ARN. Selective activation of these NA neurons with 1.5 and 3 mg/kg CNO (s.c.) in diestrous-stage mice, dose-dependently inhibited the frequency of the pulse generator synchronization episodes by 48-76% over 4 hours. These observations demonstrate that, when activated, brainstem NA neurons exert an inhibitory influence on the kisspeptin GnRH pulse generator in intact female mice. The new data may help to dissect how key components of the stress-responsive circuitry impact the central regulation of fertility. Presentation: Friday, June 16, 2023

Hypothalamic neuroglial plasticity is regulated by anti-Müllerian hormone and disrupted in polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is the most common reproductive-endocrine disorder affecting between 5 and 18% of women worldwide. An elevated frequency of pulsatile luteinizing hormone (LH) secretion and higher serum levels of anti-Müllerian hormone (AMH) are frequently observed in women with PCOS. The origin of these abnormalities is, however, not well understood. We studied brain structure and function in women with and without PCOS using proton magnetic resonance spectroscopy (MRS) and diffusion tensor imaging combined with fiber tractography. Then, using a mouse model of PCOS, we investigated by electron microscopy whether AMH played a role on the regulation of hypothalamic structural plasticity. Increased AMH serum levels are associated with increased hypothalamic activity/axonal-glial signalling in PCOS patients. Furthermore, we demonstrate that AMH promotes profound micro-structural changes in the murine hypothalamic median eminence (ME), creating a permissive environment for GnRH secretion. These include the retraction of the processes of specialized AMH-sensitive ependymo-glial cells called tanycytes, allowing more GnRH neuron terminals to approach ME blood capillaries both during the run-up to ovulation and in a mouse model of PCOS. We uncovered a central function for AMH in the regulation of fertility by remodeling GnRH terminals and their tanycytic sheaths, and provided insights into the pivotal role of the brain in the establishment and maintenance of neuroendocrine dysfunction in PCOS. INSERM (U1172), European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement n° 725149), CHU de Lille, France (Bonus H).

Mechanisms of Lactation-induced Infertility in Female Mice.

Lactation in mammals is associated with a period of infertility, which serves to direct maternal metabolic resources toward caring for the newborn offspring rather than supporting another pregnancy. This lactational infertility is characterized by reduced pulsatile luteinizing hormone (LH) secretion and lack of ovulation. The mechanisms mediating suppression of LH secretion during lactation are unclear. There are potential roles for both hormonal cues such as prolactin and progesterone, and pup-derived cues such as suckling, on the inhibition of reproduction. To enable future studies using transgenic animals to investigate these mechanisms, in the present study our aim was to characterize lactational infertility in mice, and to investigate the effect of removing pup-derived cues on LH secretion, time to ovulation, and kisspeptin immunoreactivity. We first confirmed that C57BL/6J mice experience prolonged anestrus during lactation, which is dependent on establishment of lactation, as removal of pups the day of parturition led to immediate resumption of pulsatile LH secretion and normal estrous cycles. Once lactation is established, however, the lactational anestrus persisted for several days even after premature removal of pups. Pharmacological suppression of prolactin following premature weaning significantly reduced this period of lactational infertility. Progesterone does not appear to play a significant role in the suppression of fertility during lactation in mice, as levels measured during lactation were not different from nonpregnant mice. These data suggest that prolactin plays a key role in mediating anestrus during early lactation in mice, even in the absence of the suckling stimulus.

Long-term effects of prenatal undernutrition on female rat hypothalamic KNDy neurons.

The nutritional environment during development periods induces metabolic programming, leading to metabolic disorders and detrimental influences on human reproductive health. This study aimed to determine the long-term adverse effect of intrauterine malnutrition on the reproductive center kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the hypothalamic arcuate nucleus (ARC) of female offspring. Twelve pregnant rats were divided into ad-lib-fed (control, n = 6) and 50% undernutrition (UN, n = 6) groups. The UN group was restricted to 50% daily food intake of the control dams from gestation day 9 until term delivery. Differences between the two groups in terms of various maternal parameters, including body weight (BW), pregnancy duration, and litter size, as well as birth weight, puberty onset, estrous cyclicity, pulsatile luteinizing hormone (LH) secretion, and hypothalamic gene expression of offspring, were determined. Female offspring of UN dams exhibited low BW from birth to 3 weeks, whereas UN offspring showed signs of precocious puberty; hypothalamic Tac3 (a neurokinin B gene) expression was increased in prepubertal UN offspring, and the BW at the virginal opening was lower in UN offspring than that in the control group. Interestingly, the UN offspring showed significant decreases in the number of KNDy gene-expressing cells after 29 weeks of age, but the number of ARC kisspeptin-immunoreactive cells, pulsatile LH secretions, and estrous cyclicity were comparable between the groups. In conclusion, intrauterine undernutrition induced various changes in KNDy gene expression depending on the life stage. Thus, intrauterine undernutrition affected hypothalamic developmental programming in female rats.

Short-term depletion of plasma estrogen affects hypothalamic kisspeptin-neurokinin B-dynorphin A neurons, gonadotrophs, and pulsatile luteinizing hormone secretion in female rats

Kisspeptin-neurokinin B-dynorphin A (KNDy) neurons in the arcuate nucleus (ARC) regulate pulsatile luteinizing hormone (LH) secretion. These neurons express estrogen receptors and are negatively regulated by estrogen. This study aimed to determine whether estrogen supplementation after short-term ovariectomy-induced estrogen depletion has different effects on KNDy neurons depending on the timing of the supplementation. To decrease endogenous estradiol (E2) for a short time, adult female rats received a tube filled with E2 one week after ovariectomy and utilized it one week later (O1w + E). From the results of immunohistochemistry, the response to E2 was attenuated in KNDy neurons of O1w + E rats. Enlarged LH-secreting cells in the anterior pituitary were found in O1w + E rats; however, such enlarged LH cells were not found in ones without previous short-term E2 depletion. From the analysis of LH pulses, plasma LH levels were increased in O1w + E rats relative to ones without previous short-term E2 depletion. These results suggested that once endogenous sex steroids were depleted, the response to E2 in hypothalamic KNDy neurons did not fully recover in one week. Thus, short-term sex steroid depletion due to gonadectomy could alter the response to the sex steroids in KNDy neurons even though the period without sex steroids is only one week, and the alteration is likely to affect plasma hormone levels.