Ovarian regulation of kisspeptin neurones in the arcuate nucleus of the rhesus monkey (macaca mulatta)

Effects of menopause on temperature regulation

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

Androgen Inhibition of Reproductive Neuroendocrine Function in Females and Transgender Males

Ovarian function is controlled by pituitary secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), which in turn are governed by gonadotropin releasing hormone (GnRH) secreted from the brain. A fundamental principle of reproductive axis regulation is negative feedback signaling by gonadal sex steroids back to the brain to fine-tune GnRH and gonadotropin secretion. Endogenous negative feedback effects can be mimicked by exogenous steroid treatments, including androgens, in both sexes. Indeed, a growing number of clinical and animal studies indicate that high levels of exogenous androgens, in the typically male physiological range, can inhibit LH secretion in females, as occurs in males. However, the mechanisms by which male-level androgens inhibit GnRH and LH secretion still remain poorly understood, and this knowledge gap is particularly pronounced in transgender men (individuals designated female at birth but identifying as male). Indeed, many transgender men take long-term gender-affirming hormone therapy that mimics male-level testosterone levels. The impact of such gender-affirming testosterone on the reproductive axis, both at the ovarian and neuroendocrine level, is a long-understudied area that still requires further investigation. Importantly, the few concepts of androgen actions in females mostly come from studies of polycystic ovary syndrome, which does not recapitulate a similar androgen milieu or a pathophysiology of inhibited LH secretion as occurs in testosterone-treated transgender men. This review summarizes clinical evidence indicating that exogenous androgens can impair neuroendocrine reproductive function in both female individuals and transgender men and highlights emerging experimental data supporting this in recently developed transgender rodent models.

Elinzanetant, a new combined neurokinin-1/-3 receptor antagonist for the treatment of postmenopausal vasomotor symptoms

INTRODUCTION

In many postmenopausal women, quality of life is decreased due to vasomotor symptoms. Efficient and well-tolerated non-hormonal treatment options are needed.

AREAS COVERED

The present review summarizes what is known about the etiology of postmenopausal vasomotor symptoms as a rationale for the mechanism of action of Elinzanetant, a new neurokinin (NK)-1/-3 receptor antagonist, as well as its efficacy and side effect profile.

EXPERT OPINION

Elinzanetant likely exerts an antagonistic effect on the NK-3 receptor in the preoptic thermoregulatory zone, but also an additional antagonistic effect on the NK-1 receptor possibly leading to a reduction in vasodilatation and heat-sensing neuro-activity. Elinzanetant's reported peak drug concentrations are reached within one hour and the terminal elimination half-life is approximately 15 hours. Two phase IIb clinical trials evaluated the safety profile and efficacy of several doses. There were no serious adverse events, which also included a lack of evidence of drug-related hepatotoxicity. Overall, Elinzanetant seems to be well-tolerated. In the SWITCH-1 study, the 120 mg/day and 160 mg/day regimen showed good efficacy for the treatment of vasomotor symptoms and led to significant improvements in quality of life. Thus, 120 mg oral Elinzanetant/day was used in phase III trials, whose results have not yet been published.

Definition of the estrogen negative feedback pathway controlling the GnRH pulse generator in female mice

The mechanisms underlying the homeostatic estrogen negative feedback pathway central to mammalian fertility have remained unresolved. Direct measurement of gonadotropin-releasing hormone (GnRH) pulse generator activity in freely behaving mice with GCaMP photometry demonstrated striking estradiol-dependent plasticity in the frequency, duration, amplitude, and profile of pulse generator synchronization events. Mice with Cre-dependent deletion of ESR1 from all kisspeptin neurons exhibited pulse generator activity identical to that of ovariectomized wild-type mice. An in vivo CRISPR-Cas9 approach was used to knockdown ESR1 expression selectively in arcuate nucleus (ARN) kisspeptin neurons. Mice with >80% deletion of ESR1 in ARN kisspeptin neurons exhibited the ovariectomized pattern of GnRH pulse generator activity and high frequency LH pulses but with very low amplitude due to reduced responsiveness of the pituitary. Together, these studies demonstrate that estrogen utilizes ESR1 in ARN kisspeptin neurons to achieve estrogen negative feedback of the GnRH pulse generator in mice.

Neuro-pharmacological reinstatement of ovulation and associated neurobiology in a macaque model of functional hypothalamic amenorrhoea

STUDY QUESTION

What is the underlying neuropathology in a cynomolgus macaque model of functional hypothalamic amenorrhoea (FHA) and can it be normalized to restore ovulation?

SUMMARY ANSWER

Anovulatory monkeys exhibited increased hypothalamic norepinephrine (NE), kisspeptin and gonadotropin-releasing hormone (GnRH) in the early follicular phase, but administration of the NE reuptake inhibitor (NRI), reboxetine (REB), restored ovulation during stress and normalized NE, kisspeptin and GnRH.

WHAT IS KNOWN ALREADY

Female cynomolgus macaques, like women, show individual reproductive sensitivity to modest psychosocial and metabolic stress. During stress, resilient females ovulate through two menstrual cycles whereas stress-sensitive (SS) macaques immediately cease ovulation. On Day 5 of a non-stressed menstrual cycle, resilient macaques have less NE synthesizing enzyme [dopamine β-hydroxylase (DBH)], kisspeptin and GnRH innervation of the medial basal hypothalamus but more endogenous serotonin than SS macaques. Stress increased DBH/NE, kisspeptin and GnRH but did not alter serotonin.

STUDY DESIGN, SIZE, DURATION

In a longitudinal design, 27 adult (7-13 years) female cynomolgus macaques (Macaca fascicularis) with three different levels of sensitivity to stress were monitored with daily vaginal swabs and frequent serum progesterone (P) measurements. Three 90-day experimental periods called 'Cycle Sets' were monitored. A Cycle Set consisted of one ovulatory menstrual cycle without stress, and two cycles, or 60 days, with modest stress. Each Cycle Set was followed by a rest period. During a Cycle Set, individuals were either untreated (placebo) or administered escitalopram (CIT) or REB. Ultimately, half of each sensitivity group was euthanized during stress with CIT or REB treatment and the hypothalamus was obtained. Neurobiological endpoints were compared between CIT and REB treatment groups in stress resilient and SS monkeys.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The monkeys were housed at the University of Pittsburgh primate facility for the duration of the experiments. Upon euthanasia, their brains and serum samples were shipped to the Oregon National Primate Research Center. The hypothalamus was examined with immunohistochemistry for the expression of DBH (a marker for NE axons), kisspeptin and GnRH. P was measured in the serum samples by radioimmunoassay.

MAIN RESULTS AND THE ROLE OF CHANCE

Daily administration of REB restored ovulation in 9 of 10 SS animals during stress. Of note, REB significantly increased P secretion during stress in the most sensitive group (P = 0.032), which indicates ovulation. CIT lacked efficacy. REB significantly reduced DBH/NE, kisspeptin and GnRH axon density in the hypothalamus relative to CIT treatment (P = 0.003. 0.018 and 0.0001, respectively) on Day 5 of the menstrual cycle in resilient and sensitive groups.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The US FDA has not approved REB for human use, although it is used in Europe for the treatment of depression/anxiety as EdronaxTR. Whether REB could be useful for the treatment of FHA in women has not been determined.

WIDER IMPLICATIONS FOR THE FINDINGS

The use of an NRI to treat FHA is a novel approach and the potential reinstatement of ovulation could be straightforward compared to current treatment protocols. The underlying neurobiology provides a compelling case for treating the origin of the pathology, i.e. elevated NE, rather than circumventing the hypothalamus altogether with gonadotropins, which have associated risks such as hyperstimulation syndrome or multiple births.

STUDY FUNDING/COMPETING INTEREST(S)

Portions of this study were supported by NIH grant HD062864 to C.L.B., NIH grant HD62618 to J.L.C. and C.L.B. and 1P51 OD011092 for the operation of the Oregon National Primate Research Center. There were no competing interests.

Localization of kisspeptin, NKB, and NK3R in the hypothalamus of gilts treated with the progestin altrenogest

Mechanisms in the brain controlling secretion of gonadotropin hormones in pigs, particularly luteinizing hormone (LH), are poorly understood. Kisspeptin is a potent LH stimulant that is essential for fertility in many species, including pigs. Neurokinin B (NKB) acting through neurokinin 3 receptor (NK3R) is involved in kisspeptin-stimulated LH release, but organization of NKB and NK3R within the porcine hypothalamus is unknown. Hypothalamic tissue from ovariectomized (OVX) gilts was used to determine the distribution of immunoreactive kisspeptin, NKB, and NK3R cells in the arcuate nucleus (ARC). Almost all kisspeptin neurons coexpressed NKB in the porcine ARC. Immunostaining for NK3R was distributed throughout the preoptic area (POA) and in several hypothalamic areas including the periventricular and retrochiasmatic areas but was not detected within the ARC. There was no colocalization of NK3R with gonadotropin-releasing hormone (GnRH), but NK3R-positive fibers in the POA were in close apposition to GnRH neurons. Treating OVX gilts with the progestin altrenogest decreased LH pulse frequency and reduced mean circulating concentrations of LH compared with OVX control gilts (P < 0.01), but the number of kisspeptin and NKB cells in the ARC did not differ between treatments. The neuroanatomical arrangement of kisspeptin, NKB, and NK3R within the porcine hypothalamus confirm they are positioned to stimulate GnRH and LH secretion in gilts, though differences with other species exist. Altrenogest suppression of LH secretion in the OVX gilt does not appear to involve decreased peptide expression of kisspeptin or NKB.

Serum kisspeptin levels in polycystic ovary syndrome: A meta-analysis

AIM

To clarify the association of serum kisspeptin levels in women with polycystic ovary syndrome (PCOS) by meta-analysis.

METHODS

Two English databases and two Chinese databases were searched for the relationship between kisspeptin and PCOS published from 2009. After the studies screening according to specific principles, we used STATA 12.0 for meta-analysis. Standardized mean difference (SMD) and its 95% confidence intervals (95% CIs) were used as the effect size and STATA 12.0 software was performed by this meta-analysis.

RESULTS

Nine articles were included in the end, with a total of 1282 participants (699 patients and 583 controls). Heterogeneity between studies was statistically significant. Therefore, the random effects model was used to combine the effects. Meta-analysis showed statistically significant differences in serum kisspeptin levels between the PCOS patients and controls (SMD = 0.57, 95% CI [0.32, 0.82]), which indicated that there is a strong association between serum kisspeptin levels and PCOS. The source of high heterogeneity between the inclusion studies (I²  = 73.2%) might be due to the small sample size. The larger variation of kisspeptin concentration might be caused by different diagnosis criteria of PCOS and short half-time period of kisspeptin combined with nonstandard testing process.

CONCLUSION

Serum kisspeptin levels in PCOS patients were higher than non-PCOS patients. It is a hint to indicate us that kisspeptin might be an independent biomarker of PCOS patients.

The role of kisspeptin/neurokinin B/dynorphin neurons in pathomechanism of vasomotor symptoms in postmenopausal women: from physiology to potential therapeutic applications

Women during perimenopausal period experience a range of symptoms, which interfere with physical, sexual, and social life. About 65-75% of symptoms connected with postmenopausal period are vasomotor symptoms (VMS), such as hot flushes and night sweats. Hot flushes are subjective sensation of heat associated with cutaneous vasodilatation and drop in core temperature. It is suspected that VMS are strongly correlated with pulsatile oversecretion of gonadotropin-releasing hormone (GnRH) and subsequently luteinizing hormone (LH). Evidence has accumulated in parallel showing that lack of negative feedback of steroid hormones synthesized in ovary causes overactivation of hypertrophied kisspeptin/neurokinin B/dynorphin (KNDy) neurons, located in infundibular nucleus. Oversecretion of both kisspeptin (KISS1) and neurokinin B (NKB), as well as downregulation of dynorphin, plays dominant role in creation of GnRH pulses. This in turn causes VMS. Administration of senktide, highly potent and selective NK3R agonist, resulted in increase of serum LH concentration, induction of VMS, increase in heart rate, and skin temperature in postmenopausal women. These finding suggest that modulation of KNDy neurons may become new therapeutic approach in the treatment of VMS.

Analysis of gonadotrophin-releasing hormone-1 and kisspeptin neuronal systems in the nonphotoregulated seasonally breeding eastern rock elephant-shrew (Elephantulus myurus)

Of the 18 sub-Saharan elephant-shrew species, only eastern rock elephant-shrews reproduce seasonally throughout their distribution, a process seemingly independent of photoperiod. The present study characterizes gonadal status and location/intensity of gonadotrophin-releasing hormone-1 (GnRH-1) and kisspeptin immunoreactivities in this polyovulating species in the breeding and nonbreeding seasons. GnRH-1-immunoreactive (ir) cell bodies are predominantly in the medial septum, diagonal band, and medial preoptic area; processes are generally sparse except in the external median eminence. Kisspeptin-ir cell bodies are detected only within the arcuate nucleus; the density of processes is generally low, except in the septohypothalamic nucleus, ventromedial bed nucleus of the stria terminalis, arcuate nucleus, and internal and external median eminence. Kisspeptin-ir processes are negligible at locations containing GnRH-1-ir cell bodies. The external median eminence is the only site with conspicuously overlapping distributions of the respective immunoreactivities and, accordingly, a putative site for kisspeptin's regulation of GnRH-1 release in this species. In the nonbreeding season in males, there is an increase in the rostral population of GnRH-1-ir cell bodies and density of GnRH-1-ir processes in the median eminence. In both sexes, the breeding season is associated with increased kisspeptin-ir process density in the rostral periventricular area of the third ventricle and arcuate nucleus; at the latter site, this is positively correlated with gonadal mass. Cross-species comparisons lead us to hypothesize differential mechanisms within these peptidergic systems: that increased GnRH-1 immunoreactivity during the nonbreeding season reflects increased accumulation with reduced release; that increased kisspeptin immunoreactivity during the breeding season reflects increased synthesis with increased release.

The Roles of Neurokinins and Endogenous Opioid Peptides in Control of Pulsatile LH Secretion

Work over the last 15 years on the control of pulsatile LH secretion has focused largely on a set of neurons in the arcuate nucleus (ARC) that contains two stimulatory neuropeptides, critical for fertility in humans (kisspeptin and neurokinin B (NKB)) and the inhibitory endogenous opioid peptide (EOP), dynorphin, and are now known as KNDy (kisspeptin-NKB-dynorphin) neurons. In this review, we consider the role of each of the KNDy peptides in the generation of GnRH pulses and the negative feedback actions of ovarian steroids, with an emphasis on NKB and dynorphin. With regard to negative feedback, there appear to be important species differences. In sheep, progesterone inhibits GnRH pulse frequency by stimulating dynorphin release, and estradiol inhibits pulse amplitude by suppressing kisspeptin. In rodents, the role of KNDy neurons in estrogen negative feedback remains controversial, progesterone may inhibit GnRH via dynorphin, but the physiological significance of this action is unclear. In primates, an EOP, probably dynorphin, mediates progesterone negative feedback, and estrogen inhibits kisspeptin expression. In contrast, there is now compelling evidence from several species that kisspeptin is the output signal from KNDy neurons that drives GnRH release during a pulse and may also act within the KNDy network to affect pulse frequency. NKB is thought to act within this network to initiate each pulse, although there is some redundancy in tachykinin signaling in rodents. In ruminants, dynorphin terminates GnRH secretion at the end of pulse, most likely acting on both KNDy and GnRH neurons, but the data on the role of this EOP in rodents are conflicting.

Control of the onset of puberty

PURPOSE OF REVIEW

The mechanism of puberty initiation remains an enigma, despite extensive research in the field. Pulsatile pituitary gonadotropin secretion under the guidance of hypothalamic gonadotropin-releasing hormone (GnRH) constitutes a sine qua non for pubertal onset. In turn, the secretion of GnRH in the human hypothalamus is regulated by kisspeptin and its receptor as well as by permissive or opposing signals mediated by neurokinin B and dynorphin acting on their respective receptors. These three supra-GnRH regulators compose the Kisspeptin, Neurokinin B and Dynorhin neurons (KNDy) system, a key player in pubertal onset and progression.

RECENT FINDINGS

The recent discovery that makorin ring finger protein 3 is also involved in puberty initiation provided further insights into the regulation of the KNDy pathway. In fact, the inhibitory (γ-amino butyric acid, neuropeptide Y, and RFamide-related peptide-3) and stimulatory signals (glutamate) acting upstream of KNDy called into question the role of makorin ring finger protein 3 as the gatekeeper of puberty. Meanwhile, the findings that 'neuroestradiol' produced locally and endocrine disruptors from the environment may influence GnRH secretion is intriguing. Finally, epigenetic mechanisms have been implicated in pubertal onset through recently discovered mechanisms.

SUMMARY

The exact molecular machinery underlying puberty initiation in humans is under intensive investigation. In this review, we summarize research evidence in the field, while emphasizing the areas of uncertainty and underlining the impact of current information on the evolving theory regarding this fascinating phenomenon.

Estradiol Upregulates Kisspeptin Expression in the Preoptic Area of both the Male and Female Rhesus Monkey (Macaca mulatta): Implications for the Hypothalamic Control of Ovulation in Highly Evolved Primates

The aim of this immunohistochemical study was to evaluate the distribution of kisspeptin neurons in the preoptic area (POA) of gonadally intact adult male and female rhesus monkeys, and to determine whether imposition of an estradiol (E2)-positive feedback signal in the castrate male increased kisspeptin in the POA. Additionally, kisspeptin in the POA of the intact female was examined during an LH surge induced prematurely by E2 administered in the early follicular phase. The number of kisspeptin neurons in the POA of males and females was similar. Immunoactive kisspeptin perikarya were not observed in the POA of castrate adult males, but such neurons in these animals were present within 12 h of imposing an increment in circulating E2 concentrations that in a screening study conducted 4-6 weeks earlier had elicited an LH surge. As expected, premature induction of an LH surge by E2 early in the follicular phase was associated with upregulation of kisspeptin in the POA. These results represent the first description of immunoreactive kisspeptin cell bodies in the POA of the macaque brain and provide further support for the view that (1) kisspeptin neurons in the POA of the female monkey are a target for the positive feedback action of E2 and (2) the hypothalamic mechanism which mediates this action of E2 in primates is not subjected to perinatal programming by testicular testosterone. Moreover, our findings indicate that maintenance of the kisspeptin content in the POA of intact male monkeys requires the action of E2, presumably generated by aromatization of testicular testosterone at the hypothalamic level.

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

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

Acute Influences of Bisphenol A Exposure on Hypothalamic Release of Gonadotropin-Releasing Hormone and Kisspeptin in Female Rhesus Monkeys

Bisphenol A (BPA) is an industrial compound with pervasive distribution in the environments of industrialized countries. The U.S. Centers for Disease Control recently found that greater than 90% of Americans carry detectable levels of BPA, raising concern over the direct influences of this compound on human physiology. Epidemiologic evidence links elevated BPA serum concentrations to human reproductive dysfunction, although controlled studies on the acute effect of BPA exposure on reproductive function are limited, particularly in primates. We evaluated the effect of direct BPA exposure on female primate hypothalamic peptide release. Specifically, using a microdialysis method, we examined the effects of BPA (0.1, 1, and 10nM) directly infused to the stalk-median eminence on the release of GnRH and kisspeptin (KP) in mid to late pubertal ovarian intact female rhesus monkeys. We found that the highest level of BPA exposure (10nM) suppressed both GnRH and KP release, whereas BPA at lower concentrations (0.1 and 1nM) had no apparent effects. In addition, we measured BPA in plasma and hypothalamic dialysates after an iv bolus injection of BPA (100 μg/kg). We found a relatively stable distribution of BPA between the blood and brain (plasma:brain ≅ 5:1) persists across a wide range of blood BPA concentrations (1-620 ng/mL). Findings of this study suggest that persistent, high-level exposures to BPA could impair female reproductive function by directly influencing hypothalamic neuroendocrine function.

Relative Importance of the Arcuate and Anteroventral Periventricular Kisspeptin Neurons in Control of Puberty and Reproductive Function in Female Rats

Kisspeptin plays a critical role in pubertal timing and reproductive function. In rodents, kisspeptin perikarya within the hypothalamic arcuate (ARC) and anteroventral periventricular (AVPV) nuclei are thought to be involved in LH pulse and surge generation, respectively. Using bilateral microinjections of recombinant adeno-associated virus encoding kisspeptin antisense into the ARC or AVPV of female rats at postnatal day 10, we investigated the relative importance of these two kisspeptin populations in the control of pubertal timing, estrous cyclicity, and LH surge and pulse generation. A 37% knockdown of kisspeptin in the AVPV resulted in a significant delay in vaginal opening and first vaginal estrous, abnormal estrous cyclicity, and reduction in the occurrence of spontaneous LH surges, although these retained normal amplitude. This AVPV knockdown had no effect on LH pulse frequency, measured after ovariectomy. A 32% reduction of kisspeptin in the ARC had no effect on the onset of puberty but resulted in abnormal estrous cyclicity and decreased LH pulse frequency. Additionally, the knockdown of kisspeptin in the ARC decreased the amplitude but not the incidence of LH surges. These results might suggest that the role of AVPV kisspeptin in the control of pubertal timing is particularly sensitive to perturbation. In accordance with our previous studies, ARC kisspeptin signaling was critical for normal pulsatile LH secretion in female rats. Despite the widely reported role of AVPV kisspeptin neurons in LH surge generation, this study suggests that both AVPV and ARC populations are essential for normal LH surges and estrous cyclicity.

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

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

Prolonged infusion of estradiol benzoate into the stalk median eminence stimulates release of GnRH and kisspeptin in ovariectomized female rhesus macaques

Our recent study indicates that a brief infusion (20 min) of estradiol (E2) benzoate (EB) into the stalk-median eminence (S-ME) stimulates GnRH release with a latency of approximately 10 minutes. In contrast to the effect induced by a brief infusion of EB, it has previously been shown that systemic EB administration suppresses release of GnRH, kisspeptin, and LH with a latency of several hours, which is known as the negative feedback action of E2. We speculated that the differential results by these 2 modes of EB administration are due to the length of E2 exposure. Therefore, in the present study, the effects of EB infusion for periods of 20 minutes, 4 hours, or 7 hours into the S-ME of ovariectomized female monkeys on the release of GnRH and kisspeptin were examined using a microdialysis method. To assess the effects of the EB infusion on LH release, serum samples were also collected. The results show that similar to the results with 20-minute infusion, both 4- and 7-hour infusions of EB consistently stimulated release of GnRH and kisspeptin from the S-ME accompanied by LH release in the general circulation. In contrast, sc injection of EB suppressed all 3 hormones (GnRH, kisspeptin, and LH) measured. It is concluded that regardless of the exposure period, direct E2 action on GnRH and kisspeptin neurons in the S-ME, where their neuroterminals are present, is stimulatory, and the E2-negative feedback effects do not occur at the S-ME level.

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

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

Oestrogen-induced activation of preoptic kisspeptin neurones may be involved in the luteinising hormone surge in male and female Japanese monkeys

The oestrogen-induced luteinising hormone (LH) surge is evident in male primates, including humans, whereas male rodents never show the LH surge, even when treated with a preovulatory level of oestrogen. This suggests that the central mechanism governing reproductive hormones in primates is different from that in rodents. The present study aimed to investigate whether male Japanese monkeys conserve a brain mechanism mediating the oestrogen-induced LH surge via activation of kisspeptin neurones. Adult male and female Japanese monkeys were gonadectomised and then were treated with oestradiol-17β for 2 weeks followed by a bolus injection of oestradiol benzoate. Both male and female monkeys showed an oestrogen-induced LH surge. In gonadectomised monkeys sacrificed just before the anticipated time of the LH surge, oestrogen treatment significantly increased the number of KISS1-expressing cells in the preoptic area (POA) and enhanced the expression of c-fos in POA KISS1-positive cells of males and females. The oestrogen treatment failed to induce c-fos expression in the arcuate nucleus (ARC) kisspeptin neurones in both sexes just prior to LH surge onset. Thus, kisspeptin neurones in the POA but not in the ARC might be involved in the positive-feedback action of oestrogen that induces LH surge in male Japanese monkeys, as well as female monkeys. The present results indicate that oestrogen-induced activation of POA kisspeptin neurones may contribute to the LH surge generation in both sexes. The conservation of the LH surge generating system found in adult male primates, unlike rodents, could be a result of the capability of oestrogen to induce POA kisspeptin expression and activation.

Disparate changes in kisspeptin and neurokinin B expression in the arcuate nucleus after sex steroid manipulation reveal differential regulation of the two KNDy peptides in rats

Kisspeptin, neurokinin B (NKB) and dynorphin A are coexpressed in a population of neurons in the arcuate nucleus (ARC), termed KNDy neurons, which were recently recognized as important elements for the generation of GnRH pulses. However, the topographic distribution of these peptides and their regulated expression by sex steroids are still not well understood. In this study, detailed examination of NKB and kisspeptin immunoreactivity in the rat ARC was carried out, including comparison between sexes, with and without sex steroid replacement. Neurons expressing kisspeptin and NKB were more prominent in the caudal ARC of females, whereas neurons expressing NKB, but not kisspeptin, were the most abundant in the male. Sex steroid manipulation revealed differential regulation of kisspeptin and NKB; although kisspeptin immunoreactive (ir) cells increased in response to gonadectomy, NKB remained unchanged. Furthermore, the number of NKB-ir cells increased upon sex steroid replacement compared with gonadectomy, whereas kisspeptin did not, suggesting that sex steroids differently regulate these peptides. In addition, only in females did the density of kisspeptin- and NKB-ir fibers in the ARC increase upon sex steroid replacement in relation to sham and ovariectomy, respectively, suggesting sex-specific regulation of release. In conclusion, our observations reveal sex differences in the number of kisspeptin- and NKB-ir cells, which are more prominent in the caudal ARC. The divergent regulation of kisspeptin and NKB peptide contents in the ARC as a function of sex and steroid milieu enlarge our understanding on how these neuropeptides are posttranscriptionally regulated in KNDy neurons.

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

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

Hypothalamic KISS1 expression, gonadotrophin-releasing hormone and neurotransmitter innervation vary with stress and sensitivity in macaques

The present study examined the effect of short-term psychosocial and metabolic stress in a monkey model of stress-induced amenorrhaea on the hypothalamic-pituitary-gonadal axis. KISS1 expression was determined by in situ hybridisation in the infundibular arcuate nucleus. Downstream of KISS1, gonadotrophin-releasing hormone (GnRH) axons in lateral areas rostral to the infundibular recess, serum luteinising hormone (LH) and serum oestradiol were measured by immunohistochemistry and radioimmunoassay. Upstream of KISS1, norepinephrine axons in the rostral arcuate nucleus and serotonin axons in the anterior hypothalamus and periaqueductal grey were measured by immunohistochemistry. Female cynomolgus macaques (Macaca fascicularis) characterised as highly stress resilient (HSR) or stress sensitive (SS) were examined. After characterisation of stress sensitivity, monkeys were either not stressed, or mildly stressed for 5 days before euthanasia in the early follicular phase. Stress consisted of 5 days of 20% food reduction in a novel room with unfamiliar conspecifics. There was a significant increase in KISS1 expression in HSR and SS animals in the presence versus absence of stress (P = 0.005). GnRH axon density increased with stress in HSR and SS animals (P = 0.015), whereas LH showed a gradual but nonsignificant increase with stress. Oestradiol trended higher in HSR animals and there was no effect of stress (P = 0.83). Norepinephrine axon density (marked with dopamine β-hydroxylase) increased with stress in both HSR and SS groups (P ≤ 0.002), whereas serotonin axon density was higher in HSR compared to SS animals and there was no effect of stress (P = 0.03). The ratio of dopamine β-hydroxylase/oestradiol correlated with KISS1 (P = 0.052) and GnRH correlated with serum LH (P = 0.039). In conclusion, oestradiol inhibited KISS1 in the absence of stress, although stress increased norepinephrine, which may over-ride oestradiol inhibition of KISS1 expression. We speculate that neural pathways transduce stress to KISS1 neurones, which changes their sensitivity to oestradiol.

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

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

The Role of Neurotransmitters in Protection against Amyloid- β Toxicity by KiSS-1 Overexpression in SH-SY5Y Neurons

Recent studies have suggested that the kisspeptin (KP) and kissorphin (KSO) peptides have neuroprotective actions against the Alzheimer's amyloid-β (Aβ) peptide. Overexpression of the human KiSS-1 gene that codes for KP and KSO peptides in SH-SY5Y neurons has also been shown to inhibit Aβ neurotoxicity. The in vivo actions of KP include activation of neuroendocrine and neurotransmitter systems. The present study used antagonists of KP, neuropeptide FF (NPFF), opioids, oxytocin, estrogen, adrenergic, cholinergic, dopaminergic, serotonergic, and γ-aminobutyric acid (GABA) receptors plus inhibitors of catalase, cyclooxygenase, nitric oxide synthase, and the mitogen activated protein kinase cascade to characterize the KiSS-1 gene overexpression neuroprotection against Aβ cell model. The results showed that KiSS-1 overexpression is neuroprotective against Aβ and the action appears to involve the KP or KSO peptide products of KiSS-1 processing. The mechanism of neuroprotection does not involve the activation of the KP or NPFF receptors. Opioids play a role in the toxicity of Aβ in the KiSS-1 overexpression system and opioid antagonists naloxone or naltrexone inhibited Aβ toxicity. The mechanism of KiSS-1 overexpression induced protection against Aβ appears to have an oxytocin plus a cyclooxygenase dependent component, with the oxytocin antagonist atosiban and the cyclooxygenase inhibitor SC-560 both enhancing the toxicity of Aβ.

The decline in pulsatile GnRH release, as reflected by circulating LH concentrations, during the infant-juvenile transition in the agonadal male rhesus monkey (Macaca mulatta) is associated with a reduction in kisspeptin content of KNDy neurons of the arcuate nucleus in the hypothalamus

Puberty in primates is timed by 2 hypothalamic events: during late infancy a decline in pulsatile GnRH release occurs, leading to a hypogonadotropic state that maintains quiescence of the prepubertal gonad; and in late juvenile development, pulsatile GnRH release is reactivated and puberty initiated, a phase of development that is dependent on kisspeptin signaling. In the present study, we determined whether the arrest of GnRH pulsatility in infancy was associated with a change in kisspeptin expression in the mediobasal hypothalamus (MBH). Kisspeptin was determined using immunohistochemistry in coronal hypothalamic sections from agonadal male rhesus monkeys during early infancy when GnRH release as reflected by circulating LH concentrations was robust and compared with that in juveniles in which GnRH pulsatility was arrested. The distribution of immunopositive kisspeptin neurons in the arcuate nucleus of the MBH of infants was similar to that previously reported for adults. Kisspeptin cell body number was greater in infants compared with juveniles, and at the middle to posterior level of the arcuate nucleus, this developmental difference was statistically significant. Neurokinin B in the MBH exhibited a similar distribution to that of kisspeptin and was colocalized with kisspeptin in approximately 60% of kisspeptin perikarya at both developmental stages. Intensity of GnRH fiber staining in the median eminence was robust at both stages. These findings indicate that the switch that shuts off pulsatile GnRH release during infancy and that guarantees the subsequent quiescence of the prepubertal gonad involves a reduction in a stimulatory kisspeptin tone to the GnRH neuronal network.