Deciphering the Contributions of CRH Receptors in the Brain and Pituitary to Stress-Induced Inhibition of the Reproductive Axis

Suppression of Luteinizing Hormone Secretion in Female Mice by a Urocortin 2-CRHR2 Signaling Pathway

Physiologic stress elicits impairment of reproductive function, in part, by the suppression of luteinizing hormone (LH) secretion. Two populations of kisspeptin-synthesizing neurons in the hypothalamus play essential roles in controlling the pulsatile and surge modes of LH secretion and are potential direct targets of stress-activated neural circuits; however, the mechanism(s) for impairment of kisspeptin cells during stress remain unclear. Here, we conducted 4 experiments to test the hypothesis that corticotropin-releasing hormone receptor 2 (CRHR2) signaling contributes to impaired pulsatile and surge LH secretion via direct actions on kisspeptin cells. First, we observed that cells expressing a specific ligand of CRHR2, urocortin 2 (UCN2), show enhanced c-Fos in the paraventricular nucleus (PVN) following acute hypoglycemia, a metabolic stressor that rapidly suppresses LH pulses by impairing arcuate kisspeptin neuron activation. Second, we determined that central injection of UCN2 rapidly inhibits LH pulses. Furthermore, UCN2 disrupts evening expression of the estradiol-induced LH surge and reduces kisspeptin cell activation in the rostral periventricular hypothalamic region (RP3V). Next, we identified CRHR2 in a majority of both arcuate and RP3V kisspeptin cells. Finally, we observed that UCN2 cells in the PVN are activated following chemogenetic stimulation of catecholamine neurons in the nucleus of the solitary tract. Together these data demonstrate that UCN2-CRHR2 signaling disrupts the pulsatile and surge modes of LH secretion via direct suppression of kisspeptin cells. Furthermore, these findings suggest UCN2 cells in the PVN are regulated by metabolic stress and brainstem norepinephrine signaling pathways that convey stress cues to the hypothalamus.

Stress Molecular Signaling in Interaction With Cognition

Exposure to stressful life events is associated with a high risk of developing psychiatric disorders with a wide variety of symptoms. Cognitive symptoms in stress-related psychiatric disorders can be particularly challenging to understand, both for those experiencing them and for health care providers. To gain insights, it is important to capture stress-induced structural, epigenomic, transcriptomic, and proteomic changes in relevant brain regions such as the amygdala, hippocampus, locus coeruleus, and prefrontal cortex that result in long-lasting alterations in brain function. In this review, we will emphasize a subset of stress molecular mechanisms that alter neuroplasticity, neurogenesis, and balance between excitatory and inhibitory neurons. Then, we discuss how to identify genetic risk factors that may accelerate stress-driven or stress-induced cognitive impairment. Despite the development of new technologies such as single-cell resolution sequencing, our understanding of the molecular effects of stress in the brain remains to be deepened. A better understanding of the diversity of stress effects in different brain regions and cell types is a prerequisite to open new avenues for mechanism-informed prevention and treatment of stress-related cognitive symptoms.

Kisspeptin as a test of hypothalamic dysfunction in pubertal and reproductive disorders

The hypothalamic-pituitary-gonadal axis is regulated by the gonadotropin-releasing hormone pulse generator in the hypothalamus. This is comprised of neurons that secrete kisspeptin in a pulsatile manner to stimulate the release of GnRH, and, in turn, downstream gonadotropins from the pituitary gland, and subsequently sex steroids and gametogenesis from the gonads. Many reproductive disorders in both males and females are characterized by hypothalamic dysfunction, including functional disorders (such as age-related hypogonadism, obesity-related secondary hypogonadism, hyperprolactinemia, functional hypothalamic amenorrhea and polycystic ovary syndrome), structural pathologies (such as craniopharyngiomas or radiation or surgery-related hypothalamic dysfunction), and pubertal disorders (constitutional delay of growth and puberty and congenital hypogonadotropic hypogonadism). However, in many of these conditions, the relative contribution of hypothalamic dysfunction to the observed hypogonadism is unclear; as to date, there is no direct method of evaluating hypothalamic reproductive function in humans. Indeed, it is not possible to directly measure gonadotropin-releasing hormone levels in the hypothalamo-pituitary portal vessels, such that secondary (i.e., pituitary dysfunction) and tertiary (i.e., hypothalamic dysfunction) hypogonadism are often conflated as one entity. In this review, we examine the evidence for the use of kisspeptin as a method of directly evaluating hypothalamic reproductive dysfunction, and deliberate its potential future role in the evaluation of pubertal and reproductive disorders.

Kisspeptin in functional hypothalamic amenorrhea: Pathophysiology and therapeutic potential

Functional hypothalamic amenorrhea (FHA) is one of the most common causes of secondary amenorrhea, resulting in anovulation and infertility, and is a low estrogen state that increases the risk of cardiovascular disease and impairs bone health. FHA is characterized by acquired suppression of physiological pulsatile gonadotropin-releasing hormone (GnRH) release by the hypothalamus in the absence of an identifiable structural cause, resulting in a functional hypogonadotropic hypogonadism. FHA results from either decreased energy intake and/or excessive exercise, leading to low energy availability and weight loss-often in combination with psychological stress on top of a background of genetic susceptibility. The hypothalamic neuropeptide kisspeptin is a key component of the GnRH pulse generator, tightly regulating pulsatile GnRH secretion and the downstream reproductive axis. Here, we review the physiological regulation of pulsatile GnRH secretion by hypothalamic kisspeptin neurons and how their activity is modulated by signals of energy status to affect reproductive function. We explore endocrine factors contributing to the suppression of GnRH pulsatility in the pathophysiology of FHA and how hypothalamic kisspeptin neurons likely represent a final common pathway through which these factors affect GnRH pulse generation. Finally, we discuss the therapeutic potential of kisspeptin as a novel treatment for women with FHA.

Gynura procumbens and selected metabolites: Amelioration of depressive-like behaviors in mice and risperidone-induced hyperprolactinemia in rats

Gynura procumbens (Lour.) Merr., utilized in traditional Chinese medicine, is known for its liver-protective, liver-soothing, and depression-alleviating properties. This research examines the antidepressant and anti-hyperprolactinemia potentials of an ethanol extract from G. procumbens stems (EEGS) and specific metabolites. To model depression and hyperprolactinemia, chronic unpredictable mild stress (CUMS) was induced in mice and risperidone was administered to rats, respectively. Treatments involved administering low (5 mg/kg), medium (25 mg/kg), and high (125 mg/kg) doses of EEGS and certain metabolites to both models. Behavioral assessments were conducted in the CUMS-induced mice, while the CA3 neuronal damage in mice and histopathological alterations in rat mammary glands were evaluated using Nissl and Hematoxylin & Eosin staining techniques, respectively. EEGS decreased immobility times in the forced swimming and tail suspension tests in mice, enhancing their exploration of the central zone. It elevated the serum levels of 5-hydroxytryptamine, norepinephrine, estradiol, luteinizing hormone (LH), and testosterone in mice. Moreover, EEGS restored the neuronal cell arrangement in the CA3 area, reduced interleukin-1beta mRNA production, and increased the expression of interleukin-10 and beta-catenin mRNA. In the context of risperidone-induced hyperprolactinemia, EEGS lowered blood prolactin levels, reduced the dimensions of rat nipples, and enhanced LH, progesterone, and dopamine levels, alongside mitigating mammary hyperplasia. Among the EEGS selected metabolites, the combined effect of chlorogenic acid and trans-p-coumaric acid was found to be more effective than the action of each compound in isolation. Collectively, the findings indicate that EEGS and its selected metabolites offer promising antidepressant benefits while counteracting hyperprolactinemia.

Effects of Selective Serotonin Reuptake Inhibitor Treatment on Ovarian Reserves in Patients with Depression

Background and Objectives: The goal of this study was to investigate the effect of selective serotonin reuptake inhibitor treatment on the ovarian reserves of women of reproductive age with major depressive disorder. Materials and Methods: The current study is a prospective controlled trial including 48 women with major depressive disorder and 48 age-matched healthy controls. Ovarian reserve tests are performed prior to treatment and after six cycles of selective serotonin reuptake inhibitor treatment in the major depressive disorder group. Serum follicle-stimulating hormone, luteinizing hormone, estradiol, and anti-Müllerian hormone levels were evaluated from blood samples, and endometrial thickness, total antral follicle count, and volume of both ovaries were assessed using transvaginal ultrasonography. Results: When the first measurements were compared, menstrual duration and menstrual bleeding increased (p = 0.007 and 0.005, respectively) and luteinizing hormone decreased (p = 0.045) in the major depressive disorder group, while follicle-stimulating hormone, estradiol, anti-Müllerian hormone, endometrial thickness, total antral follicle count, and mean ovarian volume did not differ significantly between groups (p > 0.05). When the major depressive disorder group’s first and final measurements were compared, follicle-stimulating hormone, estradiol, and endometrial thickness increased (p = 0.05, 0.0001, and 0.005, respectively), luteinizing hormone remained constant (p = 0.541), and anti-Müllerian hormone and total antral follicle count decreased (p = 0.024 and 0.042, respectively). Conclusions: In this study, we observed that the ovarian reserve test results of patients diagnosed with major depression for the first time after 6 months of SSRI treatment were significantly different from the results of the pretreatment and control groups.

Neuroendocrine pathogenesis of perimenopausal depression

With the development of social economics and the increase of working pressure, more and more women are suffering from long-term serious stress and showing symptoms of perimenopausal depression (PMD). The incidence rate of PMD is increasing, and the physical and mental health are seriously affected. However, due to the lack of accurate knowledge of pathophysiology, its diagnosis and treatment cannot be accurately executed. By consulting the relevant literature in recent years, this paper elaborates the neuroendocrine mechanism of perimenopausal depression from the aspects of epigenetic changes, monoamine neurotransmitter and receptor hypothesis, glial cell-induced neuroinflammation, estrogen receptor, interaction between HPA axis and HPG axis, and micro-organism-brain gut axis. The purpose is to probe into new ways of treatment of PMD by providing new knowledge about the neuroendocrine mechanism and treatment of PMD.

Posterodorsal Medial Amygdala Urocortin-3, GABA, and Glutamate Mediate Suppression of LH Pulsatility in Female Mice

The posterodorsal subnucleus of the medial amygdala (MePD) is an upstream modulator of the hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-adrenal (HPA) axes. Inhibition of MePD urocortin-3 (Ucn3) neurons prevents psychological stress-induced suppression of luteinizing hormone (LH) pulsatility while blocking the stress-induced elevations in corticosterone (CORT) secretion in female mice. We explore the neurotransmission and neural circuitry suppressing the gonadotropin-releasing hormone (GnRH) pulse generator by MePD Ucn3 neurons and we further investigate whether MePD Ucn3 efferent projections to the hypothalamic paraventricular nucleus (PVN) control CORT secretion and LH pulsatility. Ucn3-cre-tdTomato female ovariectomized (OVX) mice were unilaterally injected with adeno-associated virus (AAV)-channelrhodopsin 2 (ChR2) and implanted with optofluid cannulae targeting the MePD. We optically activated Ucn3 neurons in the MePD with blue light at 10 Hz and monitored the effect on LH pulses. Next, we combined optogenetic stimulation of MePD Ucn3 neurons with pharmacological antagonism of GABAA or GABAB receptors with bicuculline or CGP-35348, respectively, as well as a combination of NMDA and AMPA receptor antagonists, AP5 and CNQX, respectively, and observed the effect on pulsatile LH secretion. A separate group of Ucn3-cre-tdTomato OVX mice with 17β-estradiol replacement were unilaterally injected with AAV-ChR2 in the MePD and implanted with fiber-optic cannulae targeting the PVN. We optically stimulated the MePD Ucn3 efferent projections in the PVN with blue light at 20 Hz and monitored the effect on CORT secretion and LH pulses. We reveal for the first time that activation of Ucn3 neurons in the MePD inhibits GnRH pulse generator frequency via GABA and glutamate signaling within the MePD, while MePD Ucn3 projections to the PVN modulate the HPG and HPA axes.

Social isolation exacerbates acute ozone inhalation induced pulmonary and systemic health outcomes

Psychosocially-stressed individuals might have exacerbated responses to air pollution exposure. Acute ozone exposure activates the neuroendocrine stress response leading to systemic metabolic and lung inflammatory changes. We hypothesized chronic mild stress (CS) and/or social isolation (SI) would cause neuroendocrine, inflammatory, and metabolic phenotypes that would be exacerbated by an acute ozone exposure. Male 5-week-old Wistar-Kyoto rats were randomly assigned into 3 groups: no stress (NS) (pair-housed, regular-handling); SI (single-housed, minimal-handling); CS (single-housed, subjected to mild unpredicted-randomized stressors [restraint-1 h, tilted cage-1 h, shaking-1 h, intermittent noise-6 h, and predator odor-1 h], 1-stressor/day*5-days/week*8-weeks. All animals then 13-week-old were subsequently exposed to filtered-air or ozone (0.8-ppm) for 4 h and immediately necropsied. CS, but not SI animals had increased adrenal weights. However, relative to NS, both CS and SI had lower circulating luteinizing hormone, prolactin, and follicle-stimulating hormone regardless of exposure (SI > CS), and only CS demonstrated lower thyroid-stimulating hormone levels. SI caused more severe systemic inflammation than CS, as evidenced by higher circulating cytokines and cholesterol. Ozone exposure increased urine corticosterone and catecholamine metabolites with no significant stressor effect. Ozone-induced lung injury, and increases in lavage-fluid neutrophils and IL-6, were exacerbated by SI. Ozone severely lowered circulating thyroid-stimulating hormone, prolactin, and luteinizing hormone in all groups and exacerbated systemic inflammation in SI. Ozone-induced increases in serum glucose, leptin, and triglycerides were consistent across stressors; however, increases in cholesterol were exacerbated by SI. Collectively, psychosocial stressors, especially SI, affected the neuroendocrine system and induced adverse metabolic and inflammatory effects that were exacerbated by ozone exposure.

Regulation of the gonadotropin-releasing hormone neuron during stress

The effect of stress on reproduction and gonadal function has captivated investigators for almost 100 years. Following the identification of gonadotropin-releasing hormone (GnRH) 50 years ago, a niche research field emerged fixated on how stress impairs this central node controlling downstream pituitary and gonadal function. It is now clear that both episodic GnRH secretion in males and females and surge GnRH secretion in females are inhibited during a variety of stress types. There has been considerable advancement in our understanding of numerous stress-related signaling molecules and their ability to impair reproductive neuroendocrine activity during stress. Recently, much attention has turned to the effects of stress on two populations of kisspeptin neurons: the stimulatory afferents to GnRH neurons that regulate pulsatile and surge-type gonadotropin secretion. Indeed, future work is still required to fully construct the neuroanatomical framework underlying stress effects, directly or indirectly, on GnRH neuron function. The present review evaluates and synthesizes evidence related to stress-related signaling molecules acting directly on GnRH neurons. Here, we review the evidence for and against the action of a handful of signaling molecules as inhibitors of GnRH neuron function, including corticotropin-releasing hormone, urocortins, norepinephrine, cortisol/corticosterone, calcitonin gene-related peptide and arginine-phenylalanine-amide-related peptide-3.

The Testicular Protection Effect of Thiamine Pyrophosphate Against Cisplatin-treated Male Rats

Infertility is a worldwide problem affecting both genders, it can be defined as the inability of the adult males to make a fertile woman pregnant after one year of regular intercourse. Cisplatin considers one of the most potent antineoplastic drugs that is extensively   used, alone or in combination with other antitumor agents, to manage solid and germ cell cancer. The major drawback in cisplatin treatment is its damaging consequence on various body tissue, including the testis, liver, renal and others. One of its pronounced adverse effects is testicular injury, which may proceed to end with infertility. Thiamine pyrophosphate is the active form of thiamine which has an important role in the oxidative phosphorylation pathway. It acts as a co-factor and energy source for many cellular enzymes, also it utilizes by pentose-phosphate shut that elevates NADPH and improves antioxidants level. This study aimed to evaluate the effect of thiamine pyrophosphate on sperm parameters and gonadotropic hormones (luteal and follicle-stimulating hormone) of male rats exposed to a single dose of cisplatin. Twenty-eight albino male rats were randomly grouped into four groups. Control group: received normal saline, Cisplatin group: received normal saline and cisplatin, TPP50 group: received thiamine pyrophosphate (50mg/kg) with cisplatin, and TPP100 group: as third group (TPP50) but thiamine pyrophosphate dose was 100 mg/kg. Semen samples used to measure the sperms viability and morphology, while serum samples were gathered to measure the levels of gonadotropic hormones (FSH and LH). This study revealed that rat’s testicular function was notably deteriorated by cisplatin administration, represented by a reduction in sperm parameters (viability and normal morphology), and serum gonadotropic hormones (FSH and LH). In this work, thiamine pyrophosphate was act as a protective agent that ameliorates rat’s testicular damage induced by cisplatin in a dose-dependent manner. The suggested mechanism may attribute to its antioxidant and anti-apoptotic action

How exposure to chronic stress contributes to the development of type 2 diabetes: A complexity science approach

Chronic stress contributes to the onset of type 2 diabetes (T2D), yet the underlying etiological mechanisms are not fully understood. Responses to stress are influenced by earlier experiences, sex, emotions and cognition, and involve a complex network of neurotransmitters and hormones, that affect multiple biological systems. In addition, the systems activated by stress can be altered by behavioral, metabolic and environmental factors. The impact of stress on metabolic health can thus be considered an emergent process, involving different types of interactions between multiple variables, that are driven by non-linear dynamics at different spatiotemporal scales. To obtain a more comprehensive picture of the links between chronic stress and T2D, we followed a complexity science approach to build a causal loop diagram (CLD) connecting the various mediators and processes involved in stress responses relevant for T2D pathogenesis. This CLD could help develop novel computational models and formulate new hypotheses regarding disease etiology.

Regulation of the kiss2 promoter in yellowtail clownfish (Amphiprion clarkii) by cortisol via GRE-dependent GR pathway

Kisspeptin plays a vital role in mediating the stress-induced reproductive regulation. Cortisol, known as a stress-related hormone, is involved in gonadal development and sexual differentiation by binding with glucocorticoid receptor (GR) to regulate the expression of kiss gene. In the present study, cortisol treatment in yellowtail clownfish (Amphiprion clarkii) showed that the expression of kiss (kiss1 and kiss2) and gr (gr1 and gr2) genes were increased significantly. We demonstrated that the yellowtail clownfish Kiss neurons co-express the glucocorticoid receptors in the telencephalon, mesencephalon, cerebellum, and hypothalamus. We further cloned the promoter of kiss2 gene in yellowtail clownfish and identified the presence of putative binding sites for glucocorticoid receptors, estrogen receptors, androgen receptors, progesterone receptors, AP1, and C/EBP. Applying transient transfection in HEK293T cells of the yellowtail clownfish kiss2 promoter, cortisol (dexamethasone) treatment was shown to enhance the promoter activities of the yellowtail clownfish kiss2 gene in the presence of GRs. Deletion analysis of kiss2 promoter indicated that cortisol-induced promoter activities were located between position -660 and -433 with GR1, and -912 and -775 with GR2, respectively. Finally, point mutation studies on the kiss2 promoter showed that cortisol-stimulated promoter activity was mediated by one GRE site located at position -573 in the presence of GR1 and by each GRE site located at position -883, -860, -851, and -843 in the presence of GR2. Results of the present study provide novel evidence that cortisol could regulate the transcription of kiss2 gene in the yellowtail clownfish via GRE-dependent GR pathway.

Heterogeneity in GnRH and kisspeptin neurons and their significance in vertebrate reproductive biology

Vertebrate reproduction is essentially controlled by the hypothalamus-pituitary-gonadal (HPG) axis, which is a central dogma of reproductive biology. Two major hypothalamic neuroendocrine cell groups containing gonadotropin-releasing hormone (GnRH) and kisspeptin are crucial for control of the HPG axis in vertebrates. GnRH and kisspeptin neurons exhibit high levels of heterogeneity including their cellular morphology, biochemistry, neurophysiology and functions. However, the molecular foundation underlying heterogeneities in GnRH and kisspeptin neurons remains unknown. More importantly, the biological and physiological significance of their heterogeneity in reproductive biology is poorly understood. In this review, we first describe the recent advances in the neuroendocrine functions of kisspeptin-GnRH pathways. We then view the recent emerging progress in the heterogeneity of GnRH and kisspeptin neurons using morphological and single-cell transcriptomic analyses. Finally, we discuss our views on the significance of functional heterogeneity of reproductive endocrine cells and their potential relevance to reproductive health.

Neuroendocrine interactions of the stress and reproductive axes

Reproduction is controlled by a sequential regulation of the hypothalamo-pituitary-gonadal (HPG) axis. The HPG axis integrates multiple inputs to maintain proper reproductive functions. It has long been demonstrated that stress alters fertility. Nonetheless, the central mechanisms of how stress interacts with the reproductive system are not fully understood. One of the major pathways that is activated during the stress response is the hypothalamo-pituitary-adrenal (HPA) axis. In this review, we discuss several aspects of the interactions between these two neuroendocrine systems to offer insights to mechanisms of how the HPA and HPG axes interact. We have also included discussions of other systems, for example GABA-producing neurons, where they are informative to the overall picture of stress effects on reproduction.

Depression and Its Effect on the Menstrual Cycle

A strong association is noted between depression and early perimenopause as well as menopause. The association was found to be the greatest in women with natural menopause at the age less than 40 years. Excessive corticotropin-releasing hormone (CRH) levels in depression lead to inhibition of the hypothalamic-pituitary-gonadal (HPG) axis and increased cortisol levels which further inhibits the action of gonadotropin-releasing hormone (GnRH) neurons, gonadotrophs, and gonads. The resulting changes in luteinizing hormone (LH) amplitude, follicle-stimulating hormone (FSH) levels, and LH pulse frequency were noted in patients with depression.

Besides depression, earlier surgical menopause is associated with cognitive decline. In addition, it is seen that menopausal changes predisposed females to an increased risk of depression. The association between dysmenorrhea and depression was found to be bidirectional and congruent in most studies. Patients with dysmenorrhea and coexisting depression had enhanced pain perception along with a poor response to pain relief measures. Even the treatment of underlying depression has been shown to cause menorrhagia. On the other hand, amenorrhea has also been reported as a side effect of sertraline and electroconvulsive therapy. Menstrual disorders contribute to a significant number of outpatient gynecological visits per year in the United States. Co-existing or history of depression can either be the cause of or interfere in the treatment of these disorders. Furthermore, the treatment of depression can be the etiology of various menstrual abnormalities, while menstrual disorders themselves could be the cause of depression. The increasing prevalence of depression, women’s health, multiple female-specific subtypes, and the preexisting burden of menstrual disorders necessitates more detailed studies on the effects of depression on the menstrual cycle. 

Neuroendocrine regulation of pubertal suppression in the naked mole-rat: What we know and what comes next

Puberty is a key developmental milestone that marks an individual's maturation in several ways including, but not limited to, reproductive maturation, changes in behaviors and neural organization. The timing at which puberty occurs is variable both within individuals of the same species and between species. These variations can be aligned with ecological cues that delay or suppress puberty. Naked mole-rats are colony-living rodents where reproduction is restricted to a few animals; all other animals are pubertally-suppressed. Animals removed from suppressive colony cues can reproductively mature, presenting the unique opportunity to study adult-onset puberty. Recently, we found that RFRP-3 administration sustains pubertal delay in naked mole-rats removed from colony. In this review, we explore what is known about regulators that control puberty onset, the role of stress/social status in pubertal timing, the status of knowledge of pubertal suppression in naked mole-rats and what comes next.

An Inhibitory Circuit From Brainstem to GnRH Neurons in Male Mice: A New Role for the RFRP Receptor

RFamide-related peptides (RFRPs, mammalian orthologs of gonadotropin-inhibitory hormone) convey circadian, seasonal, and social cues to the reproductive system. They regulate gonadotropin secretion by modulating gonadotropin-releasing hormone (GnRH) neurons via the RFRP receptor. Mice lacking this receptor are fertile but exhibit abnormal gonadotropin responses during metabolic challenges, such as acute fasting, when the normal drop in gonadotropin levels is delayed. Although it is known that these food intake signals to the reproductive circuit originate in the nucleus tractus solitarius (NTS) in the brainstem, the phenotype of the neurons conveying the signal remains unknown. Given that neuropeptide FF (NPFF), another RFamide peptide, resides in the NTS and can bind to the RFRP receptor, we hypothesized that NPFF may regulate GnRH neurons. To address this question, we used a combination of techniques: cell-attached electrophysiology on GnRH-driven green fluorescent protein-tagged neurons in acute brain slices; calcium imaging on cultured GnRH neurons; and immunostaining on adult brain tissue. We found (1) NPFF inhibits GnRH neuron excitability via the RFRP receptor and its canonical signaling pathway (Gi/o protein and G protein-coupled inwardly rectifying potassium channels), (2) NPFF-like fibers in the vicinity of GnRH neurons coexpress neuropeptide Y, (3) the majority of NPFF-like cell bodies in the NTS also coexpress neuropeptide Y, and (4) acute fasting increased NPFF-like immunoreactivity in the NTS. Together these data indicate that NPFF neurons within the NTS inhibit GnRH neurons, and thus reproduction, during fasting but prior to the energy deficit.

Impact of chronic variable stress on neuroendocrine hypothalamus and pituitary in male and female C57BL/6J mice

Chronic stress exerts multiple negative effects on the physiology and health of an individual. In the present study, we examined hypothalamic, pituitary and endocrine responses to 14 days of chronic variable stress (CVS) in male and female C57BL/6J mice. In both sexes, CVS induced a significant decrease in body weight and enhanced the acute corticosterone stress response, which was accompanied by a reduction in thymus weight only in females. However, single-point blood measurements of basal prolactin, thyroid-stimulating hormone, luteinising hormone, growth hormone and corticosterone levels taken at the end of the CVS were not different from those of controls. Similarly, pituitary mRNA expression of Fshb, Lhb, Prl and Gh was unchanged by CVS, although Pomc and Tsh were significantly elevated. Within the adrenal medulla, mRNA for Th, Vip and Gal were elevated following CVS. Avp transcript levels within the paraventricular nucleus of the hypothalamus were increased by CVS; however, levels of Gnrh1, Crh, Oxt, Sst, Trh, Ghrh, Th and Kiss1 remained unchanged. Oestrous cycles were lengthened slightly by CVS and ovarian histology revealed a reduction in the number of preovulatory follicles and corpora lutea. Taken together, these observations indicate that 14 days of CVS induces an up-regulation of the neuroendocrine stress axis and creates a mild disruption of female reproductive function. However, the lack of changes in other neuroendocrine axes controlling anterior and posterior pituitary secretion suggest that most neuroendocrine axes are relatively resilient to CVS.

Indirect Suppression of Pulsatile LH Secretion by CRH Neurons in the Female Mouse

Acute stress is a potent suppressor of pulsatile luteinizing hormone (LH) secretion, but the mechanisms through which corticotrophin-releasing hormone (CRH) neurons inhibit gonadotropin-releasing hormone (GnRH) release remain unclear. The activation of paraventricular nucleus (PVN) CRH neurons with Cre-dependent hM3Dq in Crh-Cre female mice resulted in the robust suppression of pulsatile LH secretion. Channelrhodopsin (ChR2)-assisted circuit mapping revealed that PVN CRH neuron projections existed around kisspeptin neurons in the arcuate nucleus (ARN) although many more fibers made close appositions with GnRH neuron distal dendrons in the ventral ARN. Acutely prepared brain slice electrophysiology experiments in GnRH- green fluorescent protein (GFP) mice showed a dose-dependent (30 and 300 nM CRH) activation of firing in ~20% of GnRH neurons in both intact diestrus and ovariectomized mice with inhibitory effects being uncommon (<8%). Confocal GCaMP6 imaging of GnRH neuron distal dendrons in acute para-horizontal brain slices from GnRH-Cre mice injected with Cre-dependent GCaMP6s adeno-associated viruses demonstrated no effects of 30 to 300 nM CRH on GnRH neuron dendron calcium concentrations. Electrophysiological recordings of ARN kisspeptin neurons in Crh-Cre,Kiss1-GFP mice revealed no effects of 30 -300 nM CRH on basal or neurokinin B-stimulated firing rate. Similarly, the optogenetic activation (2-20 Hz) of CRH nerve terminals in the ARN of Crh-Cre,Kiss1-GFP mice injected with Cre-dependent ChR2 had no effect on kisspeptin neuron firing. Together, these studies demonstrate that PVN CRH neurons potently suppress LH pulsatility but do not exert direct inhibitory control over GnRH neurons, at their cell body or dendron, or the ARN kisspeptin neuron pulse generator in the female mouse.

Special features of neuroendocrine interactions between stress and reproduction in teleosts

Stress and reproduction are both essential functions for vertebrate survival, ensuring on one side adaptative responses to environmental changes and potential life threats, and on the other side production of progeny. With more than 25,000 species, teleosts constitute the largest group of extant vertebrates, and exhibit a large diversity of life cycles, environmental conditions and regulatory processes. Interactions between stress and reproduction are a growing concern both for conservation of fish biodiversity in the frame of global changes and for the development of sustainability of aquaculture including fish welfare. In teleosts, as in other vertebrates, adverse effects of stress on reproduction have been largely documented and will be shortly overviewed. Unexpectedly, stress notably via cortisol, may also facilitate reproductive function in some teleost species in relation to their peculiar life cyles and this review will provide some examples. Our review will then mainly address the neuroendocrine axes involved in the control of stress and reproduction, namely the corticotropic and gonadotropic axes, as well as their interactions. After reporting some anatomo-functional specificities of the neuroendocrine systems in teleosts, we will describe the major actors of the corticotropic and gonadotropic axes at the brain-pituitary-peripheral glands (interrenals and gonads) levels, with a special focus on the impact of teleost-specific whole genome duplication (3R) on the number of paralogs and their potential differential functions. We will finally review the current knowledge on the neuroendocrine mechanisms of the various interactions between stress and reproduction at different levels of the two axes in teleosts in a comparative and evolutionary perspective.

The Secretive Liaison of Particulate Matter and SARS-CoV-2. A Hypothesis and Theory Investigation

As the novel coronavirus disease sweeps across the world, there is growing speculation on the role that atmospheric factors may have played on the different distribution of SARS-CoV-2, and on the epidemiological characteristics of COVID-19. Knowing the role that environmental factors play in influenza virus outbreaks, environmental pollution and, in particular, atmospheric airborne (particulate matter, PM) has been considered as a potential key factor in the spread and mortality of COVID-19. A possible role of the PM as the virus carrier has also been debated. The role of PM in exacerbating respiratory and cardiovascular disease has been well recognized. Accumulating evidence support the hypothesis that PM can trigger inflammatory response at molecular, cellular and organ levels. On this basis, we developed the hypothesis that PM may play a role as a booster of COVID-19 rather than as a carrier of SARS-CoV-2. To support our hypothesis, we analyzed the molecular signatures detected in cells exposed to PM samples collected in one of the most affected areas by the COVID-19 outbreak, in Italy. T47D human breast adenocarcinoma cells were chosen to explore the global gene expression changes induced by the treatment with organic extracts of PM 2.5. The analysis of the KEGG's pathways showed modulation of several gene networks related to the leucocyte transendothelial migration, cytoskeleton and adhesion system. Three major biological process were identified, including coagulation, growth control and immune response. The analysis of the modulated genes gave evidence for the involvement of PM in the endothelial disease, coagulation disorders, diabetes and reproductive toxicity, supporting the hypothesis that PM, directly or through molecular interplay, affects the same molecular targets as so far known for SARS-COV-2, contributing to the cytokines storm and to the aggravation of the symptoms triggered by COVID-19. We provide evidence for a plausible cooperation of receptors and transmembrane proteins, targeted by PM and involved in COVID-19, together with new insights into the molecular interplay of chemicals and pathogens that could be of importance for sustaining public health policies and developing new therapeutic approaches.

A CRH Receptor Type 1 Agonist Increases GABA Transmission to GnRH Neurons in a Circulating-Estradiol-Dependent Manner

GnRH neurons are central regulators of reproduction and respond to factors affecting fertility, such as stress. Corticotropin-releasing hormone (CRH) is released during stress response. In brain slices from unstressed controls, CRH has opposite, estradiol-dependent effects on GnRH neuron firing depending on the CRH receptor activated; activating CRHR-1 stimulates whereas activating CRHR-2 suppresses activity. We investigated possible direct and indirect mechanisms. Mice were ovariectomized and either not treated further (OVX) or given a capsule producing high positive feedback (OVX + E) or low negative feedback (OVX + low E) physiologic circulating estradiol levels. We tested possible direct effects on GnRH neurons by altering voltage-gated potassium currents. Two types of voltage-gated potassium currents (transient IA and sustained IK) were measured; neither CRHR-1 nor CRHR-2 agonists altered potassium current density in GnRH neurons from OVX + E mice. Further, neither CRH nor receptor-specific agonists altered action potential generation in response to current injection in GnRH neurons from OVX + E mice. To test the possible indirect actions, GABAergic postsynaptic currents were monitored. A CRHR-1 agonist increased GABAergic transmission frequency to GnRH neurons from OVX + E, but not OVX, mice, whereas a CRHR-2 agonist had no effect. Finally, we tested if CRH alters the firing rate of arcuate kisspeptin neurons, which provide an important excitatory neuromodulatory input to GnRH neurons. CRH did not acutely alter firing activity of these neurons from OVX, OVX + E or OVX + low E mice. These results suggest CRH increases GnRH neuron activity in an estradiol-dependent manner in part by activating GABAergic afferents. Mechanisms underlying inhibitory effects of CRH remain unknown.

Recovery of menses after functional hypothalamic amenorrhoea: if, when and why

BACKGROUND

Prolonged amenorrhoea occurs as a consequence of functional hypothalamic amenorrhoea (FHA) which is most often induced by weight loss, vigorous exercise or emotional stress. Unfortunately, removal of these triggers does not always result in the return of menses. The prevalence and conditions underlying the timing of return of menses vary strongly and some women report amenorrhoea several years after having achieved and maintained normal weight and/or energy balance. A better understanding of these factors would also allow improved counselling in the context of infertility. Although BMI, percentage body fat and hormonal parameters are known to be involved in the initiation of the menstrual cycle, their role in the physiology of return of menses is currently poorly understood. We summarise here the current knowledge on the epidemiology and physiology of return of menses.

OBJECTIVE AND RATIONALE

The aim of this review was to provide an overview of (i) factors determining the recovery of menses and its timing, (ii) how such factors may exert their physiological effects and (iii) whether there are useful therapeutic options to induce recovery.

SEARCH METHODS

We searched articles published in English, French or German language containing keywords related to return of menses after FHA published in PubMed between 1966 and February 2020. Manuscripts reporting data on either the epidemiology or the physiology of recovery of menses were included and bibliographies were reviewed for further relevant literature. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) criteria served to assess quality of observational studies.

OUTCOMES

Few studies investigate return of menses and most of them have serious qualitative and methodological limitations. These include (i) the lack of precise definitions for FHA or resumption of menses, (ii) the use of short observation periods with unsatisfactory descriptions and (iii) the inclusion of poorly characterised small study groups. The comparison of studies is further hampered by very inhomogeneous study designs. Consequently, the exact prevalence of resumption of menses after FHA is unknown. Also, the timepoint of return of menses varies strongly and reliable prediction models are lacking. While weight, body fat and energy availability are associated with the return of menses, psychological factors also have a strong impact on the menstrual cycle and on behaviour known to increase the risk of FHA. Drug therapies with metreleptin or naltrexone might represent further opportunities to increase the chances of return of menses, but these require further evaluation.

WIDER IMPLICATIONS

Although knowledge on the physiology of return of menses is presently rudimentary, the available data indicate the importance of BMI/weight (gain), energy balance and mental health. The physiological processes and genetics underlying the impact of these factors on the return of menses require further research. Larger prospective studies are necessary to identify clinical parameters for accurate prediction of return of menses as well as reliable therapeutic options.

MAP/ERK Signaling in Developing Cognitive and Emotional Function and Its Effect on Pathological and Neurodegenerative Processes

The signaling pathway of the microtubule-associated protein kinase or extracellular regulated kinase (MAPK/ERK) is a common mechanism of extracellular information transduction from extracellular stimuli to the intracellular space. The transduction of information leads to changes in the ongoing metabolic pathways and the modification of gene expression patterns. In the central nervous system, ERK is expressed ubiquitously, both temporally and spatially. As for the temporal ubiquity, this signaling system participates in three key moments: (i) Embryonic development; (ii) the early postnatal period; and iii) adulthood. During embryonic development, the system is partly responsible for the patterning of segmentation in the encephalic vesicle through the FGF8-ERK pathway. In addition, during this period, ERK directs neurogenesis migration and the final fate of neural progenitors. During the early postnatal period, ERK participates in the maturation process of dendritic trees and synaptogenesis. During adulthood, ERK participates in social and emotional behavior and memory processes, including long-term potentiation. Alterations in mechanisms related to ERK are associated with different pathological outcomes. Genetic alterations in any component of the ERK pathway result in pathologies associated with neural crest derivatives and mental dysfunctions associated with autism spectrum disorders. The MAP-ERK pathway is a key element of the neuroinflammatory pathway triggered by glial cells during the development of neurodegenerative diseases, such as Parkinson's and Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis, as well as prionic diseases. The process triggered by MAPK/ERK activation depends on the stage of development (mature or senescence), the type of cellular element in which the pathway is activated, and the anatomic neural structure. However, extensive gaps exist with regards to the targets of the phosphorylated ERK in many of these processes.

The reproductive stress hypothesis

In this paper, we propose the reproductive stress hypothesis that describes the pregnant females response to reproductive events based upon the activation of the hypothalamic-pituitary-adrenal axis and sympathetic adrenomedullary system. The main components of the reproductive stress hypothesis can be summarized as follows: (1) events unique to reproduction including empathema, pregnancy, parturition and lactation cause non-specific responses in females, called active reproductive stress; (2) the fetus is a special stressor for pregnant females where endocrine hormones, including corticotropin-releasing hormones and fetal glucocorticoids secreted by the fetus and placenta, enter the maternal circulatory system, leading to another stress response referred to as passive reproductive stress and (3) response to uterine tension and intrauterine infection is the third type of stress, called fetal intrauterine stress. Appropriate reproductive stress is a crucial prerequisite in normal reproductive processes. By contrast, excessive or inappropriate reproductive stress may result in dysfunctions of the reproductive system, such as compromised immune function, leading to susceptibility to disease. The novel insights of the reproductive stress hypothesis have important implications for deciphering the pathogenesis of certain diseases in pregnant animals, including humans, which in turn may be applied to preventing and treating their occurrence.

Modulation of Gonadotropin-Releasing Hormone Neuron Activity and Secretion in Mice by Non-peptide Neurotransmitters, Gasotransmitters, and Gliotransmitters

Gonadotropin-releasing hormone (GnRH) neuron activity and GnRH secretion are essential for fertility in mammals. Here, I review findings from mouse studies on the direct modulation of GnRH neuron activity and GnRH secretion by non-peptide neurotransmitters (GABA, glutamate, dopamine, serotonin, norepinephrine, epinephrine, histamine, ATP, adenosine, and acetylcholine), gasotransmitters (nitric oxide and carbon monoxide), and gliotransmitters (prostaglandin E2 and possibly GABA, glutamate, and ATP). These neurotransmitters, gasotransmitters, and gliotransmitters have been shown to directly modulate activity and/or GnRH secretion in GnRH neurons in vivo or ex vivo (brain slices), from postnatal through adult mice, or in embryonic or immortalized mouse GnRH neurons. However, except for GABA, nitric oxide, and prostaglandin E2, which appear to be essential for normal GnRH neuron activity, GnRH secretion, and fertility in males and/or females, the biological significance of their direct modulation of GnRH neuron activity and/or GnRH secretion in the central regulation of reproduction remains largely unknown and requires further exploration.