Anteroventral Periventricular Nucleus Research Articles

Neonatal Aromatase Inhibition Blocked Defeminization of AVPV Kiss1 Neurons and LH Surge-Generating System in Male Rats.

The neuroendocrine system that controls the preovulatory surge of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH), which triggers ovulation in female mammals, is sexually differentiated in rodents. A transient increase in circulating testosterone levels in male rats within a few hours of birth is primarily responsible for the defeminization of anteroventral periventricular nucleus (AVPV) kisspeptin neurons, which are critical regulators of the GnRH/LH surge. The present study aimed to determine whether neonatal estradiol-17β (E2) converted from testosterone by aromatase primarily causes the defeminization of AVPV kisspeptin neurons and the surge of GnRH/LH in male rodents. The results of the present study showed that the neonatal administration of letrozole (LET), a nonsteroidal aromatase inhibitor, within 2 hours of birth rescued AVPV Kiss1 expression and the LH surge in adult male rats, while the neonatal administration of testosterone propionate (TP) irreversibly attenuated AVPV Kiss1 expression and the LH surge in adult female rats. Furthermore, the neonatal LET-treated Kiss1-Cre-activated tdTomato reporter males exhibited a comparable number of AVPV Kiss1-Cre-activated tdTomato-expressing cells to that of vehicle-treated female rats, while neonatal TP-treated females showed fewer AVPV Kiss1-Cre-activated tdTomato-expressing cells than vehicle-treated females. Moreover, neonatal TP administration significantly decreased the number of arcuate Kiss1-expressing and Kiss1-Cre-activated tdTomato-positive cells and suppressed LH pulses in adult gonadectomized female rats; however, neonatal LET administration failed to affect them. These results suggest that E2 converted from neonatal testosterone is primarily responsible for the defeminization of AVPV kisspeptin neurons and the subsequent GnRH/LH surge generation in male rats.

Social isolation and aggression training lead to escalated aggression and hypothalamus-pituitary-gonad axis hyperfunction in mice

AbstractAlthough the participation of sex hormones and sex hormone-responsive neurons in aggressive behavior has been extensively studied, the role of other systems within the hypothalamus-pituitary-gonadal (HPG) axis remains elusive. Here we assessed how the gonadotropin-releasing hormone (GnRH) and kisspeptin systems are impacted by escalated aggression in male mice. We used a combination of social isolation and aggression training (IST) to exacerbate mice’s aggressive behavior. Next, low-aggressive (group-housed, GH) and highly aggressive (IST) mice were compared regarding neuronal activity in the target populations and hormonal levels, using immunohistochemistry and ELISA, respectively. Finally, we used pharmacological and viral approaches to manipulate neuropeptide signaling and expression, subsequently evaluating its effects on behavior. IST mice exhibited enhanced aggressive behavior compared to GH controls, which was accompanied by elevated neuronal activity in GnRH neurons and arcuate nucleus kisspeptin neurons. Remarkably, IST mice presented an increased number of kisspeptin neurons in the anteroventral periventricular nucleus (AVPV). In addition, IST mice exhibited elevated levels of luteinizing hormone (LH) in serum. Accordingly, activation and blockade of GnRH receptors (GnRHR) exacerbated and reduced aggression, respectively. Surprisingly, kisspeptin had intricate effects on aggression, i.e., viral ablation of AVPV-kisspeptin neurons impaired the training-induced rise in aggressive behavior whereas kisspeptin itself strongly reduced aggression in IST mice. Our results indicate that IST enhances aggressive behavior in male mice by exacerbating HPG-axis activity. Particularly, increased GnRH neuron activity and GnRHR signaling were found to underlie aggression whereas the relationship with kisspeptin remains puzzling.

Maternal oral exposure to low-dose BPA accelerates the onset of puberty by promoting prepubertal Kiss1 expression in the AVPV nucleus of female offspring

As the incidence of precocious puberty has risen in recent years and the age at puberty onset is younger, children may be at increased risk for health consequences associated with the early onset of puberty. Bisphenol A (BPA) is recognized as an endocrine disruptor chemical that is reported to induce precocious puberty. The effect of BPA exposure modes, times, and doses (especially low dose) were controversial. In the present study, we evaluated the potential effects of maternal exposure to low-dose BPA on the hypothalamus, particularly on the arcuate (ARC) nucleus and anteroventral periventricular (AVPV) nucleus during peri-puberty in offspring of BPA-treated rats. Pregnant rats were exposed to corn oil vehicle, 0.05 mg·kg−1·day−1 BPA, or 5 mg·kg−1·day−1 from gestation day 1 (GD1) to postnatal day 21 (PND21) by daily gavage. Body weight (BW), vaginal opening (VO), ovarian follicular luteinization, and relevant hormone concentrations were measured; hypothalamic Kiss1 and GnRH1 levels by western immunoblot analysis were also assessed as indices of puberty onset. During or after exposure, low-dose BPA restricted BW after birth (at PND1 and PND5), and subsequently accelerated puberty onset by promoting the expression of prepubertal Kiss1 and GnRH1 in the AVPV nucleus on PND30, leading to advanced VO, an elevation in LH and FSH concentrations (on PND30). We also noted increased BW on PND30 and PND35. Maternal oral exposure to low-dose BPA altered the BW curve during the neonatal and peripubertal periods, and subsequently accelerated puberty onset by promoting prepubertal Kiss1 expression in the AVPV nucleus.

Conditional Oprk1-dependent Kiss1 deletion in kisspeptin neurons caused estrogen-dependent LH pulse disruption and LH surge attenuation in female rats

The gonadotropin-releasing hormone (GnRH) pulse and surge are considered to be generated by arcuate kisspeptin/neurokinin B/dynorphin A (KNDy) neurons and anteroventral periventricular nucleus (AVPV) kisspeptin neurons, respectively, in female rodents. The majority of KNDy and AVPV kisspeptin neurons express κ-opioid receptors (KORs, encoded by Oprk1) in female rodents. Thus, this study aimed to investigate the effect of a conditional Oprk1-dependent Kiss1 deletion in kisspeptin neurons on the luteinizing hormone (LH) pulse/surge and fertility using Kiss1-floxed/Oprk1-Cre rats, in which Kiss1 was deleted in cells expressing or once expressed the Oprk1/Cre. The Kiss1-floxed/Oprk1-Cre female rats, with Kiss1 deleted in a majority of KNDy neurons, showed normal puberty while having a one-day longer estrous cycle and fewer pups than Kiss1-floxed controls. Notably, ovariectomized (OVX) Kiss1-floxed/Oprk1-Cre rats showed profound disruption of LH pulses in the presence of a diestrous level of estrogen but showed apparent LH pulses without estrogen treatment. Furthermore, Kiss1-floxed/Oprk1-Cre rats, with Kiss1 deleted in approximately half of AVPV kisspeptin neurons, showed a lower peak of the estrogen-induced LH surge than controls. These results suggest that arcuate and AVPV kisspeptin neurons expressing or having expressed Oprk1 have a role in maintaining normal GnRH pulse and surge generation, the normal length of the estrous cycle, and the normal offspring number in female rats.

Changes in pituitary gonadotropin subunits and hypothalamic Kiss-1 gene expression by administration of sex steroids in ovary-intact female rats.

We examined how the sex steroids influence the synthesis of gonadotropins. The effects of sex steroids estradiol (E2), progesterone (P4), and dihydrotestosterone (DHT) in pituitary gonadotroph cell model (LβT2 cells) in vitro and ovary-intact rats in vivo were examined. The effects of sex steroids on Kiss1 gene expression in the hypothalamus were also examined in ovary-intact rats. In LβT2 cells, E2 increased common glycoprotein alpha (Cga) and luteinizing hormone beta (Lhb) subunit promoter activity as well as their mRNA expression. Although gonadotropin subunit promoter activity was not modulated by P4, Cga and Lhb mRNA expression was increased by P4. DHT inhibited Cga and Lhb mRNA expression with a concomitant decrease in their promoter activity. During the 2-week administration of exogenous E2 to ovary-intact rats, the estrous cycle determined by vaginal smears was disrupted. P4 or DHT administration completely eliminated the estrous cycle. Protein expression of all three gonadotropin subunits within the pituitary gland was inhibited by E2 or P4 treatment in vivo; however, DHT reduced Cga expression but did not modulate Lhb or follicle-stimulating hormone beta subunit expression. E2 administration significantly repressed Kiss1 mRNA expression in a posterior hypothalamic region that included the arcuate nucleus. P4 and DHT did not modulate Kiss1 mRNA expression in this region. In contrast, P4 administration significantly inhibited Kiss1 mRNA expression in the anterior region of the hypothalamus that included the anteroventral periventricular nucleus. The expression of gonadotropin-releasing hormone (Gnrh) mRNA in the anterior hypothalamic region, where the preoptic area is located, appeared to be decreased by treatment with E2 and P4. Our findings suggest that sex steroids have different effects in the hypothalamus and pituitary gland.

28 Melanocortin 3 Receptor in Neural Circuits Linking Metabolic State with Reproduction and Growth

Abstract Metabolic state must be communicated to the brain to regulate behavior, growth, nutrient partitioning and development to meet energetic demands. While it is clearly evident that reproduction and energy balance are closely intertwined, the neural circuits integrating these two processes are poorly understood. Recent functional data suggests the melanocortin 3 receptor (MC3R) mediates the exchange of information between reproductive and metabolic state. Additionally, females exhibit uniquely aberrant metabolic and reproductive phenotypes after deletion of MC3R. In this work, we aimed to characterize the role of MC3R neural circuits in linking metabolic state with reproduction and growth in females. We found that MC3R is expressed in brain regions known to have a role in the control of reproductive and metabolic state, including the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARH). In the ARH of female mice, significant differences in overall levels of Mc3r mRNA were not observed at postnatal day 16 (P16), P28 or P48, nor did the percentage of ARH Kiss1, Esr1, Sst, Pomc or Agrp neurons doubly-labeled for Mc3r appear to change during postnatal development. However, the percentage of ARH Ghrh neurons labeled for Mc3r significantly increased from P16 to P48. Thus, MC3R in the ARH may play a potential role in conveying metabolic signals critical for growth during development. In the AVPV of female mice, overall abundance of Mc3r mRNA was low at P16, but increased significantly by P28, and was further elevated in mature mice (P48). Additionally, the percentage of Kiss1- and Esr1-expressing neurons in the AVPV labeled for Mc3r increased significantly between P16 and P48, suggesting that Mc3r may have an important role in the timing of sexual maturation. In addition to the direct regulatory action of MC3R expressed in KISS1 neurons in the AVPV, the impact of MC3R signaling may also be transmitted transynaptically via direct neural projections from MC3R neurons to KISS1 neurons in the AVPV, or to GnRH neurons in the rostral preoptic area. Clearly labeled MC3R terminals were observed in close apposition to both KISS1 neurons in the AVPV, and GnRH neurons in the rostral medial preoptic area. Although both the GnRH and KISS1 neuronal populations appeared heavily innervated by MC3R neurons, the density of MC3R terminals onto KISS1 neurons appeared to be substantially greater than that onto GnRH neurons, suggesting that inputs to AVPV neurons may be particularly impactful on reproduction. Thus, MC3R may not only regulate the activity of KISS1 neurons in the AVPV directly, but may also function transynaptically as an important neurobiological substrate for coordination of metabolic state with sexual maturation and reproductive function.

FRI282 Sexually Dimorphic Responses Of Kisspeptin Expression To Neonatal Exposure To Estrogen In Rats

Abstract Disclosure: B. Marzbanabbasabadi: None. P. Lin: None. C. Park: None. C. Ko: None. Kisspeptin neurons (Kiss1 neurons) are located mainly in anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) of hypothalamus and play a key role as regulators of GnRH secretion in all mammalian species. In both females and males, ARC contains more Kiss1 neurons than AVPV. Importantly, unlike ARC, AVPV displays sexual dimorphism; female AVPV contains significantly more Kiss1 neurons than males’. Recent studies showed that neonatal exposure to estrogen decreased Kiss1 expression in the hypothalamus, impacting fertility, in both sexes. However, whether such impact was driven by decreased number of Kiss1 neurons or expression of Kiss1 gene is not known. In this study, we tested our hypothesis that neonatal estrogen exposure decreases both the number of Kiss1 neurons and the Kiss1 gene expression in AVPV, in a gender-dependent manner. This hypothesis was tested in rats by treating them with estradiol benzoate (EB, a prodrug that is converted to estradiol) and measuring the effect by counting the number of Kiss1 neurons (Kiss1 mRNA expressing cells) and comparing Kiss1 mRNA expression levels between EB-exposed and control hypothalami. Male and female rat pups were injected, on postnatal day 1, subcutaneously with 0.3 mg EB via microsphere that was designed to release EB for 2 weeks; unexposed age matching pups were used as controls (n=6-7/group). Male rats were euthanized at 2.5 months of age and their entire brains were collected. Female brains were also sampled at 2.5 months of age, but after synchronizing their estrous cycle by injecting them with PMSG and hCG following an established superovulation protocol. The brains were serially sectioned and the sections from AVPV and caudal region of ARC where Kiss1 neurons most highly populated were identified and used for localizing Kiss1 neurons and quantitating Kiss1 mRNA expression level, using RNAscope. Results showed that in the AVPV, EB-exposed rats had less Kiss1 neurons both in males (8.7±1.9 vs. 42.2±7.9 Kiss1 neurons/section in control, p=0.02) and females (26.0±5.65 vs. 141.6±15.8 Kiss1 neurons/section in control, p=0.03) and showed lower Kiss1 mRNA expression in males (0.33 folds, p=0.03) and in females (0.44 folds, p=0.04) as well. In the ARC, EB-exposed rats had less Kiss1 neurons in females (27.5±4.3 vs. 56.0±2.4/section in control, p=0.00), but had same number in males (31.7±2.3 vs. 42.8±7.6 kiss1 neurons/section in control, p=0.22). EB exposure increased Kiss1 mRNA expression in both males (2.39 folds, p=0.00) and females (1.55 folds, p=0.05). In conclusion, this study showed that neonatal exposure to estrogen alters the number of Kiss1 neurons and Kiss1 mRNA expression in AVPV in a gender-dependent manner. In addition, neonatal estrogen exposure also alters Kiss1 neuron numbers and Kiss1 gene expression in the ARC as well. Presentation: Friday, June 16, 2023

FRI274 Dopamine Transporter-Expressing Leptin-Sensitive Neurons In The Ventral Premammillary Nucleus Innervate Kiss1 Neurons

Abstract Disclosure: C. Sáenz de Miera: None. L. Heikkinen: None. C. Broberger: None. C.F. Elias: None. Pubertal development is tightly regulated by energy balance, and easily disrupted in states of excess or negative energy reserves. This crosstalk between metabolism and reproduction is orchestrated by complex neural networks coordinated by circulating hormones, notably, leptin action in the hypothalamus plays a critical role. The ventral premammillary nucleus (PMv) is rich in leptin receptor (LepRb) neurons, and acts as an essential relay for leptin action on reproduction. Here, we describe a novel subpopulation of leptin sensitive neurons within the PMv that express dopamine transporter (DATPMv). We observed that in both prepubertal and adult females in diestrous, virtually all DATPMv neurons express LepRb mRNA and respond to acute leptin treatment with phosphorylation of the intracellular marker signal transducer and activator of transcription 3 (pSTAT3). Electrophyisological recordings from DAT-CRE;R26tdTomato (DAT-tdTom) mice show that DATPMv cells in adult females have a higher resting membrane potential than those in prepubertal females. DAT mRNA expression in the PMv is higher in prepubertal than in adult females. However, DAT mRNA expression was similar in adult females in diestrous, ovariectomized (OVX), and OVX treated with estradiol, indicating that the age difference observed is not due to the increase in estradiol during pubertal maturation. To trace DATPMv projections, we injected an adenoassociated virus expressing Cre-dependent channelrhodopsin (ChR2-mCherry) in the PMv of adult female DAT-Cre;Kiss1-hrGFP mice, which express GFP driven by kiss1 regulatory elements. ChR2-mCherry projections were observed in the anteroventral periventricular nucleus (AVPV) surrounding Kiss1-hrGFP neurons, a population critical for sexual maturation and positive estrogen feedback in females. No projections were observed near arcuate nucleus Kiss1-hrGFP neurons, in the medial preoptic area (MPOA) or near GnRH neurons. This contrasts with previous observations of dense projections from the overall PMv LepRb population to the MPOA, surrounding GnRH cell bodies suggesting the DATPMv subpopulation has different target areas than the non-DAT LepRb neurons. Using DAT-tdTOM females we observed that overall tdTom projections to the AVPV are denser in adult diestrous than in prepubertal females. Overall, these findings suggest that the DAT expressing LepR subpopulation in the PMv play a role in leptin regulation of sexual maturation via actions on AVPV kisspeptin neurons. Presentation: Friday, June 16, 2023

SAT424 Neuroendocrine And Developmental Impacts Of Early Exposure To Estrogenic Endocrine Disruptors

Abstract Disclosure: M. Streifer: None. S. Mendez: None. R. Raval: None. L. Thompson: None. A.C. Gore: None. Polychlorinated biphenyls (PCBs) are a class of endocrine disrupting chemical (EDC), exposure to which during early development can result in a variety of neuroendocrine and reproductive abnormalities. Hypothalamic kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) and KNDy (Kisspeptin-Neurokinin B-Dynorphin expressing) neurons in the arcuate nucleus (ARC) are involved in reproductive development, maturation, and success; dysfunctions in kisspeptin signaling can lead to hypogonadotropic hypogonadism and sub- or infertility. KNDy and kisspeptin neurons develop under the influence of gonadal hormones, notably estradiol, and are vulnerable to early exposure to estrogenic EDCs. In this experiment male and female rats were perinatally exposed to the weakly estrogenic PCB mixture Aroclor 1221 (A1221) to determine if and how altered kisspeptin signaling in the ARC and AVPV affects reproductive development. Using RNAscope, a novel in situ hybridization technique, we are exploring if changes in the number of KNDy and kisspeptin neurons or RNA expression of kisspeptin and regulatory peptides neurokinin B and dynorphin are potential mechanisms of the increased incidence of reproductive disorders associated with estrogenic PCB exposure. A1221 exposure did not alter the number of kisspeptin-expressing neurons in the AVPV, though quantification of RNA expression and analysis in the ARC are still ongoing. Serum LH, FSH, estradiol, and testosterone were measured as they are involved in the kisspeptin signaling pathway. In A1221 exposed females, serum LH and FSH were decreased, and estradiol was increased in early life (postnatal day 8). A1221 exposed males had decreased serum LH at a prepubertal time point (postnatal day 30), but FSH and testosterone were unaffected by treatment. Developmental markers that could be indicative of dysfunctions in kisspeptin and KNDy neuron function were monitored. A1221 exposure did not cause any obvious abnormal developmental delays in males or females. Moving forward, we plan on further exploring the effects of developmental A1221 exposure in the AVPV and ARC through gene expression profiling. Presentation: Saturday, June 17, 2023

OR09-01 Mini-Puberty Could Be A Key Phase Regulating Reproductive Function In Female Mice

Abstract Disclosure: M. Chester: None. M. Devillers: None. L. Naule: None. F. Souaré: None. R. Corre: None. D. Quintas: None. C. Petrovic: None. J. Cohen-Tannoudji: None. S. Mhaouty-Kodja: None. C.J. Guigon: None. After birth, there is a transient activation of the hypothalamic-pituitary-ovary (HPO) axis, with high secretion of LH and FSH acting on the ovary to promote the secretion of sex steroids and in particular that of estradiol (E2). This period, called mini-puberty, occurs between 10-17 days postnatal (dpn) in mice. During reproductive life, E2 plays an important role on the HPO axis by regulating GnRH pulsatility and, thus, the cyclic fluctuations of gonadotropin hormone levels required for follicular development and ovulation. E2 acts on hypothalamic kisspeptin neurons of the arcuate (ARC) and the anteroventral periventricular nucleus (AVPV), which project to GnRH neurons and regulate their activity by negative and positive feedbacks, respectively. The possibility that E2 contributes, during mini-puberty, to the maturation of hypothalamic structures involved in puberty onset and reproductive function, has never been investigated. The aim of this study was to elucidate the putative roles of mini-puberty on reproduction. We developed a mouse model injected with a GnRH receptor antagonist (GonadoSTOP mice) suppressing LH and FSH surges to cause a 50% decrease in E2 levels during mini-puberty. Our results show that GonadoSTOP mice exhibited later first diestrus 2 (D2) (31.0 dpn versus 29.9 dpn in CTR; n=55-56 mice/group; P=0.0285), suggesting a possible delay in the timing of puberty. During reproductive life, GonadoSTOP mice spent a longer % of time in D2 than control mice, with no alteration in total estrous cycle time (64.4% versus 56% in CTR; n=18-19 mice/group; P=0.0350). Immunohistochemical analysis of kisspeptin neurons in ARC and AVPV of ovariectomized and hormonally-primed mice showed that their numbers were significantly lower in AVPV from GonadoSTOP mice than in control mice (n=5-6 brains/group; P=0.038). In fertility studies, we observed no difference in the time to conception or % of pregnant mice between the two groups at early reproductive life (3, 4 and 5 months). Contrary to these results, at the time of reproductive decline in control mice (11 months), a substantial % of GonadoSTOP mice could still be pregnant (47% versus 18% of CTR mice; P=0.0017). At this age, GonadoSTOP mice had lower LH levels than control mice (P=0.0074), but similar levels to young control mice at 4 months (P>0.05). RT-qPCR analyses of markers reflecting ovarian activity (Cyp19a1, Inhbb, Amh, Gdf9) at 4 and 11 months revealed that ovarian aging occurred similarly in both groups, suggesting that reproductive longevity in GonadoSTOP mice does not have an ovarian origin. Taken together these data suggest that transient and sustained activation of the HPO axis at mini-puberty may regulate key aspects of reproductive function with long-term impact on fertility, possibly by acting on the hypothalamus. Presentation: Friday, June 16, 2023

SAT592 Sexually Dimorphic Modulation Of Arcuate Kisspeptin Neurons Activity In Response To NPY

Abstract Disclosure: N.D. Mansano: None. R. Frazao: None. Kisspeptin neurons are part of an intricate brain circuit that receives neuronal inputs related tonutritional status from at least three neuronal populations, including NPY/AgRP and POMC neurons of the arcuate nucleus of the hypothalamus (ARH) and cells in the ventral premammillary nucleus. Its well-known action on the HPG axis, hypothalamic kisspeptin neurons also modulate the activity of specific neurons of the paraventricular and the dorsomedial nuclei of the hypothalamus, regions involved in the regulation of appetite and energy expenditure. However, it is not completely elucidated if NPY can influence the HPG axis through the modulation of kisspeptin neuron activity. To determine the NPY effect in the hypothalamic kisspeptin neurons we performed whole-cell patch-clamp recordings. The hypothalamic slices were obtained from the adult Kiss1/hrGFP female (diestrus-stage) or male mice. Kisspeptin cells located in the arcuate nucleus of the hypothalamus (ARHkisspeptin) and at the anteroventral periventricular and rostral periventricular nuclei (AVPV/PeNkisspeptin) were recorded. On female mice, ARHkisspeptin neurons exhibited a rest membrane potential (RMP) average of -52.5±2.5 mV (-40 to -62 mV) and 1.3±0.2 GΩ input resistance (IR). NPY induced the hyperpolarization of 45% of the ARHkisspeptin neurons (n= 9 of 20 cells, out of 9 mice). ARHkisspeptin neuron’s RMP hyperpolarization was followed by a significant decrease in IR and frequency of action potentials (fAPS). In the AVPV/PeNkisspeptin neurons showed RMP average of -69.6±1.9 mV (-51 to - 88 mV) and IR of 0.8±0.09 GΩ (n=18 cells out of 9 mice). No significant NPY-induced effect was noted when recordings were performed on AVPV/PeNkisspeptin cells from female mice. To elucidate if the ARHkisspeptin neuron’s hyperpolarization depends on action potentials (APs) mediated by synaptic transmission we further evaluated NPY effects in the presence of TTX and amino acid receptor antagonists (6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10μM), DL-2-amino-5-phosphonopentanoic acid (AP5, 50μM), and picrotoxin (50μM). NPY induced no effect on ARHkisspeptin neuron’s RMP, and IR in the presence of TTX and amino acid receptor antagonists. Suggesting that NPY-induced hyperpolarization of ARHkisspeptin neurons is an indirect effect. To further verify whether sex must be considered as a biological variable to study the NPY effect, we recorded ARHkisspeptin cells from male mice. ARHkisspeptin neurons recorded from male mice exhibited RPM average of -55.6±1.5 (-45 to -66 mV) and IR of 1.5±0.15 GΩ (n= 13 cells out of 10 mice). Interestingly, NPY induced no effect on RMP, IR, or fAPs in male animals. In conclusion, our results suggest that NPY-induced hyperpolarization of ARHkisspeptin cells depends on AP’s mediate synaptic transmission, as a sex-specific effect. Presentation: Saturday, June 17, 2023

Sexually dimorphic oxytocin receptor-expressing (OXTR) neurons in the anteroventral periventricular nucleus (AVPV) in the postpartum female mouse are involved in maternal behavior.

Maternal care is crucial for the survival and development of offspring. Oxytocin modulates maternal behavior by binding to oxytocin receptors (OXTRs) in various parts of the brain. Previously, we showed that OXTRs are expressed in the anteroventral periventricular nucleus (AVPV) of female, but not male mice. Because the AVPV is involved in the regulation of maternal behavior and oxytocin enhances its induction, this finding leads to the hypothesis that the female specific population of OXTR neurons in the AVPV regulates maternal behavior. To address this hypothesis, OXTR-Venus reporter mice were used to assess if expression levels of OXTR in the AVPV are changed during the postpartum period. The total number of OXTR-Venus neurons was significantly greater in postpartum dams compared to virgin females. To assess efferent projections of the AVPV-OXTR neurons, a Cre-dependent fluorescent protein (tdTomato) expressing a viral vector was injected into one side of the AVPV of female OXTR-Cre mice. Fibers expressing tdTomato were found in hypothalamic areas containing oxytocin neurons (the supraoptic and paraventricular nuclei) and the midbrain areas (the ventral tegmental area and periaqueductal gray) that are involved in the regulation of maternal motivation. To assess if activity of the AVPV-OXTR neurons is involved in the regulation of maternal behaviors, a chemogenetic approach was employed. Specific inhibition of activity of AVPV-OXTR neurons completely abolished pup retrieval and nest building behaviors. Collectively, these findings demonstrate that AVPV-OXTR neurons in postpartum female mice constitute an important node in the neural circuitry that regulates maternal behavior.

Chronic estradiol exposure suppresses luteinizing hormone surge without affecting kisspeptin neurons and estrogen receptor alpha in anteroventral periventricular nucleus†.

Mammalian ovulation is induced by a luteinizing hormone surge, which is triggered by elevated plasma estrogen levels; however, chronic exposure to high levels of estradiol is known to inhibit luteinizing hormone secretion. In the present study, we hypothesized that the inhibition of the luteinizing hormone surge by chronic estradiol exposure is due to the downregulation of the estrogen receptor alpha in kisspeptin neurons at hypothalamic anteroventral periventricular nucleus, which is known as the gonadotropin-releasing hormone/luteinizing hormone surge generator. Animals exposed to estradiol for 2days showed an luteinizing hormone surge, whereas those exposed for 14days showed a significant suppression of luteinizing hormone. Chronic estradiol exposure did not affect the number of kisspeptin neurons and the percentage of kisspeptin neurons with estrogen receptor alpha or c-Fos in anteroventral periventricular nucleus, but it did affect the number of kisspeptin neurons in arcuate nucleus. Furthermore, chronic estradiol exposure did not affect gonadotropin-releasing hormone neurons. In the pituitary, 14-day estradiol exposure significantly reduced the expression of Lhb mRNA and LHβ-immunoreactive areas. Gonadotropin-releasing hormone-induced luteinizing hormone release was also reduced significantly by 14-day estradiol exposure. We revealed that the suppression of an luteinizing hormone surge by chronic estradiol exposure was induced in association with the significant reduction in kisspeptin neurons in arcuate nucleus, luteinizing hormone expression in the pituitary, and pituitary responsiveness to gonadotropin-releasing hormone, and this was not caused by changes in the estrogen receptor alpha-expressing kisspeptin neurons in anteroventral periventricular nucleus and gonadotropin-releasing hormone neurons, which are responsible for estradiol positive feedback.

Genotypic sex shapes maternal care in the African pygmy mouse, Mus minutoides.

Sexually dimorphic behaviours, such as parental care, have long been thought to be mainly driven by gonadal hormones. In the past two decades, a few studies have challenged this view, highlighting the direct influence of the sex chromosome complement (XX versus XY or ZZ versus ZW). The African pygmy mouse, Mus minutoides, is a wild mouse species with naturally occurring XY sex reversal induced by a third, feminizing X* chromosome, leading to three female genotypes: XX, XX* and X*Y. Here, we show that sex reversal in X*Y females shapes a divergent maternal care strategy (maternal aggression, pup retrieval and nesting behaviours) from both XX and XX* females. Although neuroanatomical investigations were inconclusive, we show that the dopaminergic system in the anteroventral periventricular nucleus of the hypothalamus is worth investigating further as it may support differences in pup retrieval behaviour between females. Combining behaviours and neurobiology in a rodent subject to natural selection, we evaluate potential candidates for the neural basis of maternal behaviours and strengthen the underestimated role of the sex chromosomes in shaping sex differences in brain and behaviours. All things considered, we further highlight the emergence of a third sexual phenotype, challenging the binary view of phenotypic sexes.

Effects of chronic irisin treatment on brain monoamine levels in the hypothalamic and subcortical nuclei of adult male and female rats: An HPLC-ECD study

Monoaminergic systems are known to be involved in the pathophysiology of neuropsychiatric disorders and vegetative functions due to their established influence on hypothalamic and subcortical areas. These systems can be modulated by lifestyle factors, especially exercise, which is known to produce several beneficial effects on reproduction, brain health, and mental disorders. The fact that exercise is sensed by the brain shows that muscle-stimulated secretion of myokines allows direct crosstalk between the muscles and the brain. One of such exercise-induced beneficial effects on the brain is exhibited by irisin—a recently discovered PGC-1α-dependent adipo-myokine mainly secreted from skeletal muscle during exercise. Thus, we hypothesized that irisin may affect central monoamine levels and thus play an important role in the muscle–brain endocrine loop. To test this assertion, for 10 weeks, vehicle (deionized water) or 100 ng/kg irisin was injected intraperitoneally once a day to 12 male and 12 female rats after which the levels of monoamines and their metabolites were determined by HPLC-ECD. In the hypothalamic nuclei, irisin significantly decreased dopamine (DA) metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) (p < 0.05), DOPAC/DA ratio (p < 0.01) and noradrenaline (NA, p < 0.05) levels in the anteroventral periventricular nucleus (AVPV), and DOPAC and NA levels in the medial preoptic area (mPOA) (p < 0.05), having a crucial role in reproduction and sexual motivation, respectively. On the other hand, irisin significantly increased DOPAC levels in the lateral hypothalamic area (LHA) (p < 0.05), which acts as a hunger center, while it significantly decreased the levels of DA, NA, and its metabolite 3,4-dihydroxyphenylglycol (DHPG) in the ventromedial hypothalamic nucleus (VMH) as a known satiety center (p < 0.05). In nucleus accumbens (NaC), irisin significantly reduced 5-hydroxyindoleacetic acid (5-HIAA) levels (p < 0.05), which are implicated in autism spectrum disorder (ASD) physiopathology. It also significantly increased DA levels in this area, thus exhibiting positive effects on depression and sexual dysfunction in men. On the other hand, it significantly decreased serotonin (5-HT) (p < 0.01) and its metabolite 5-HIAA levels in the medial amygdala (MeA) (p < 0.05), indicating that it may play a role in social behaviors. Moreover, it significantly attenuated NA levels in the same subcortical area (p < 0.01), which is directly involved in stress-induced activation of the central noradrenergic system. These findings demonstrate for the first time that irisin induces significant changes in monoamine levels in many hypothalamic nuclei involved in feeding behavior and vegetative functions, as well as in subcortical nuclei related to neuropsychiatric disorders.

Hypothalamic Kisspeptin Neurons as a Target for Whole-Cell Patch-Clamp Recordings.

Kisspeptins are essential for the maturation of the hypothalamic-pituitary-gonadal (HPG) axis and fertility. Hypothalamic kisspeptin neurons located in the anteroventral periventricular nucleus and rostral periventricular nucleus, as well as the arcuate nucleus of the hypothalamus, project to gonadotrophin-releasing hormone (GnRH) neurons, among other cells. Previous studies have demonstrated that kisspeptin signaling occurs through the Kiss1 receptor (Kiss1r), ultimately exciting GnRH neuron activity. In humans and experimental animal models, kisspeptins are sufficient for inducing GnRH secretion and, consequently, luteinizing hormone (LH) and follicle stimulant hormone (FSH) release. Since kisspeptins play an essential role in reproductive functions, researchers are working to assess how the intrinsic activity of hypothalamic kisspeptin neurons contributes to reproduction-related actions and identify the primary neurotransmitters/neuromodulators capable of changing these properties. The whole-cell patch-clamp technique has become a valuable tool for investigating kisspeptin neuron activity in rodent cells. This experimental technique allows researchers to record and measure spontaneous excitatory and inhibitory ionic currents, resting membrane potential, action potential firing, and other electrophysiological properties of cell membranes. In the present study, crucial aspects of the whole-cell patch-clamp technique, known as electrophysiological measurements that define hypothalamic kisspeptin neurons, and a discussion of relevant issues about the technique, are reviewed.

Changes in Corticotropin-Releasing Factor Receptor Type 1, Co-Expression with Tyrosine Hydroxylase and Oxytocin Neurons, and Anxiety-Like Behaviors across the Postpartum Period in Mice

Introduction: Corticotropin-releasing factor and its primary receptor (CRFR1) are critical regulators of behavioral and neuroendocrine stress responses. CRFR1 has also been associated with stress-related behavioral changes in postpartum mice. Our previous studies indicate dynamic changes in CRFR1 levels and coupling of CRFR1 with tyrosine hydroxylase (TH) and oxytocin (OT) neurons in postpartum mice. In this study, we aimed to determine the time course of these changes during the postpartum period. Methods: Using a CRFR1-GFP reporter mouse line, we compared postpartum mice at five time points with nulliparous mice. We performed immunohistochemistry to assess changes in CRFR1 levels and changes in co-expression of TH/CRFR1-GFP and OT/CRFR1-GFP across the postpartum period. Mice were also assessed for behavioral stress responses in the open field test. Results: Relative to nulliparous mice, CRFR1 levels were elevated in the anteroventral periventricular nucleus (AVPV/PeN) but were decreased in the medial preoptic area from postpartum day 1 (P1) through P28. In the paraventricular hypothalamus (PVN), there is a transient decline in CRFR1 mid-postpartum with a nadir at P7. Co-localization of CRFR1 with TH-expressing neurons was also altered with a transient decrease found in the AVPV/PeN at P7 and P14. Co-expression of CRFR1 and OT neurons of the PVN and supraoptic nucleus was dramatically altered with virtually no co-expression found in nulliparous mice, but levels increased shortly after parturition and peaked near P21. A transient decrease in open field center time was found at P7, indicating elevated anxiety-like behavior. Conclusion: This study revealed various changes in CRFR1 across the postpartum period, which may contribute to stress-related behavior changes in postpartum mice.

Hindbrain Adenosine 5-Triphosphate (ATP)-Purinergic Signaling Triggers LH Surge and Ovulation via Activation of AVPV Kisspeptin Neurons in Rats.

Ovulation disorders are a serious problem for humans and livestock. In female rodents, kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) are responsible for generating a luteinizing hormone (LH) surge and consequent ovulation. Here, we report that adenosine 5-triphosphate (ATP), a purinergic receptor ligand, is a possible neurotransmitter that stimulates AVPV kisspeptin neurons to induce an LH surge and consequent ovulation in rodents. Administration of an ATP receptor antagonist (PPADS) into the AVPV blocked the LH surge in ovariectomized (OVX) rats treated with a proestrous level of estrogen (OVX + high E2) and significantly reduced the ovulation rate in proestrous ovary-intact rats. AVPV ATP administration induced a surge-like LH increase in OVX + high E2 rats in the morning. Importantly, AVPV ATP administration could not induce the LH increase in Kiss1 KO rats. Furthermore, ATP significantly increased intracellular Ca2+ levels in immortalized kisspeptin neuronal cell line, and coadministration of PPADS blocked the ATP-induced Ca2+ increase. Histologic analysis revealed that the proestrous level of estrogen significantly increased the number of P2X2 receptor (an ATP receptor)-immunopositive AVPV kisspeptin neurons visualized by tdTomato in Kiss1-tdTomato rats. The proestrous level of estrogen significantly increased varicosity-like vesicular nucleotide transporter (a purinergic marker)-immunopositive fibers projecting to the vicinity of AVPV kisspeptin neurons. Furthermore, we found that some hindbrain vesicular nucleotide transporter-positive neurons projected to the AVPV and expressed estrogen receptor α, and the neurons were activated by the high E2 treatment. These results suggest that hindbrain ATP-purinergic signaling triggers ovulation via activation of AVPV kisspeptin neurons.SIGNIFICANCE STATEMENT Ovulation disorders, which cause infertility and low pregnancy rates, are a serious problem for humans and livestock. The present study provides evidence that adenosine 5-triphosphate, acting as a neurotransmitter in the brain, stimulates kisspeptin neurons in the anteroventral periventricular nucleus, known as the gonadotropin-releasing hormone surge generator, via purinergic receptors to induce the gonadotropin-releasing hormone/luteinizing hormone surge and ovulation in rats. In addition, histologic analyses indicate that adenosine 5-triphosphate is likely to be originated from the purinergic neurons in the A1 and A2 of the hindbrain. These findings may contribute to new therapeutic controls for hypothalamic ovulation disorders in humans and livestock.

Heterozygous mutations in SOX2 may cause idiopathic hypogonadotropic hypogonadism via dominant-negative mechanisms.

Pathogenic SRY-box transcription factor 2 (SOX2) variants typically cause severe ocular defects within a SOX2 disorder spectrum that includes hypogonadotropic hypogonadism. We examined exome-sequencing data from a large, well-phenotyped cohort of patients with idiopathic hypogonadotropic hypogonadism (IHH) for pathogenic SOX2 variants to investigate the underlying pathogenic SOX2 spectrum and its associated phenotypes. We identified 8 IHH individuals harboring heterozygous pathogenic SOX2 variants with variable ocular phenotypes. These variant proteins were tested in vitro to determine whether a causal relationship between IHH and SOX2 exists. We found that Sox2 was highly expressed in the hypothalamus of adult mice and colocalized with kisspeptin 1 (KISS1) expression in the anteroventral periventricular nucleus of adult female mice. In vitro, shRNA suppression of mouse SOX2 protein in Kiss-expressing cell lines increased the levels of human kisspeptin luciferase (hKiss-luc) transcription, while SOX2 overexpression repressed hKiss-luc transcription. Further, 4 of the identified SOX2 variants prevented this SOX2-mediated repression of hKiss-luc. Together, these data suggest that pathogenic SOX2 variants contribute to both anosmic and normosmic forms of IHH, attesting to hypothalamic defects in the SOX2 disorder spectrum. Our study describes potentially novel mechanisms contributing to SOX2-related disease and highlights the necessity of SOX2 screening in IHH genetic evaluation irrespective of associated ocular defects.

Testing the extreme male hypothesis in the valproate mouse model; sex-specific effects on plasma testosterone levels and tyrosine hydroxylase expression in the anteroventral periventricular nucleus, but not on parental behavior.

Autism is a neurodevelopmental disorder with a strong male bias in prevalence and severity. The extreme male hypothesis proposed that autism is a manifestation of extreme male traits as evidenced by increased masculine behaviors, hypermasculinization of some brain regions, and alterations in androgen metabolism. In the present study, the extreme male hypothesis was tested in the valproate (VPA) mouse model. Females of the C57BL/6JOlaHsd mouse strain were treated with 500 mg/kg VPA on gestational day 12. Offspring of both sexes were tested at 3 to 4 months of age in the elevated plus maze (EPM), open field, sociability tests, and for parental behavior. After sacrifice at 5 to 6 months of age, plasma testosterone was measured in males, while the brains of both sexes were examined for tyrosine hydroxylase (TH) expression in the anteroventral periventricular nucleus (AVPV). VPA treatment significantly increased plasma testosterone levels and decreased AVPV TH expression in males, whereas the expression of TH in females remained at the same level. In parental behavior test none of the pup-oriented behavior was affected by VPA treatment in both sexes, the exception was nest quality which was lower after VPA exposure in males, but not in females. Our results suggest a hypermasculinizing effect of VPA that occurred specifically in males but not in females, and this effect could be related to changes in androgen physiology. Nevertheless, a generalized interpretation of the extreme male hypothesis on brain and behavior should be avoided due to the complex effects of VPA.