Control of puberty by excitatory amino acid neurotransmitters and its clinical implications

Natural sweetener glycyrrhizin protects against precocious puberty by modulating the gut microbiome

AIMS

Precocious puberty (PP) may lead to many adverse outcomes. Recent evidence suggests that PP is a gut-brain disease. On the other hand, the use of glycyrrhizin, a natural sweetener, has become popular in the past decade. Glycyrrhizin possesses various health benefits, but its impact on PP has yet to be investigated. We aimed to explore the protective effects of glycyrrhizin against PP in both humans (observational) and animals (interventional).

MATERIALS AND METHODS

In the human cohort, we investigated the association between glycyrrhizin consumption and risk of PP. In the animal experiment, we observed puberty onset after feeding danazol-induced PP rats with glycyrrizin. Blood, fecal, and hypothalamic samples were harvested to evaluate potential mechanistic pathways. We also performed a fecal microbiota transplantation to confirm to causal relationship between glycyrrhizin and PP risk.

KEY FINDINGS

Glycyrrhizin exhibited a protective effect against PP in children (OR 0.60, 95%CI: 0.39-0.89, p = 0.013), primarily driven by its significance in girls, while no significant effect was observed in boys. This effect was consistent with findings in rodents. These benefits were achieved through the modulation of the gut microbiome, which functionally suppressed the hypothalamic-pituitary-gonadal axis and prevented PP progression. A fecal microbiota transplantation indicated that the causal correlation between glycyrrhizin intake and PP is mediated by the gut microbiome alterations.

SIGNIFICANCE

Our findings suggest that glycyrrhizin can protect against PP by altering the gut microbiome. Long term use of glycyrrhizin is safe and tolerable. Therefore, glycyrrhizin can serve as a safe and affordable complementary therapy for PP.

Kisspeptin control of hypothalamus-pituitary-ovarian functions

The discovery of Kisspeptin (Kiss) has opened a new direction in research on neuroendocrine control of reproduction in vertebrates. Belonging to the RF amide family of peptides, Kiss and its cognate receptor Gpr54 (Kissr) have a long and complex evolutionary history. Multiple forms of Kiss and Kissr are identified in non-mammalian vertebrates, with the exception of birds, and monotreme mammals. However, only a single form of the ligand (KISS1/Kiss1) and receptor (KISS1R/Kiss1r) is retained in higher mammals. Kiss1 is distributed in the hypothalamus-pituitary-gonadal (HPG) axis and its primary function is to stimulate gonadotropin-releasing hormone (GnRH) secretion. Kiss1 neurons are distributed in the rostral periventricular area of the third ventricle (RP3V) and arcuate/infundibular nucleus (ARN/IFN). The ARN/IFN is considered the GnRH pulse generator controlled by steroid negative feedback, and the RP3V neurons is concerned with GnRH surge induced by steroid positive feedback in females. The Kiss1-Kiss1r signaling is important in all aspects of reproduction: puberty onset, maintenance of adult gonadal functions and reproductive aging, and hence assumes therapeutic potentials in the treatment of reproductive dysfunctions and induction of artificial reproduction. This chapter reviews involvement of Kiss1 in the control of the HPG axis functions in female mammals.

The Role of Genetics in Central Precocious Puberty: Confirmed and Potential Neuroendocrine Genetic and Epigenetic Contributors and Their Interactions with Endocrine Disrupting Chemicals (EDCs)

Despite the growing prevalence of central precocious puberty (CPP), most cases are still diagnosed as “idiopathic” due to the lack of identifiable findings of other diagnostic etiology. We are gaining greater insight into some key genes affecting neurotransmitters and receptors and how they stimulate or inhibit gonadotropin-releasing hormone (GnRH) secretion, as well as transcriptional and epigenetic influences. Although the genetic contributions to pubertal regulation are more established in the hypogonadotropic hypogonadism (HH) literature, cases of CPP have provided the opportunity to learn more about its own genetic influences. There have been clinically confirmed cases of CPP associated with gene mutations in kisspeptin and its receptor (KISS1, KISS1R), Delta-like noncanonical Notch ligand 1 (DLK1), and the now most commonly identified genetic cause of CPP, makorin ring finger protein (MKRN3). In addition to these proven genetic causes, a number of other candidates continue to be evaluated. After reviewing the basic clinical aspects of puberty, we summarize what is known about the various genetic and epigenetic causes of CPP as well as discuss some of the potential effects of endocrine disrupting chemicals (EDCs) on some of these processes.

DLG2 Mutations in the Etiology of Pubertal Delay and Idiopathic Hypogonadotropic Hypogonadism

INTRODUCTION

Idiopathic hypogonadotropic hypogonadism (IHH) is caused by dysfunction of the hypothalamic-pituitary-gonadal axis. DLG2 was recently implicated as a gene associated with delayed puberty and which may also contribute to IHH. The confirmation of the candidate puberty genes in independent IHH cohorts has become crucial due to the lack of proper genotype-phenotype segregations in reported pedigrees. Therefore, we aimed to screen DLG2 in patient variants in a large cohort of IHH patients.

METHODS

The present study included a total of 336 IHH patients from 290 independent families. The coding and flanking regions of DLG2 were screened for potentially important variants in the WES data. Candidate variants were evaluated in the -gnomAD and GME databases according to their allele frequencies, and only those with a frequency <0.0001 were considered rare. Detected variants were classified according to the ACMG/AMP criteria.

RESULTS

We found 1 homozygous and 2 heterozygous missense variants in 3 independent pedigrees. Identified variants were found extremely rare or not reported in gnomAD. Two variants were categorized as "uncertain significance," and the other one was "likely pathogenic" according to the ACMG criteria. All patients were normosmic, and in 2 of the 3 families, there were no causal variants in other IHH-related genes.

CONCLUSION

We detected 3 rare sequencing variants in DLG2 in 5 patients with IHH or delayed puberty in a large IHH cohort. Our results support the contention that the DLG2 mutations are associated with IHH in human puberty.

Transcriptome-scale spatial gene expression in rat arcuate nucleus during puberty

Background

A variety of neurons in hypothalamus undergo a complicated regulation on transcription activity of multiple genes for hypothalamic–pituitary–gonadal axis activation during pubertal development. Identification of puberty-associated cell composition and characterization of the unique transcriptional signatures across different cells are beneficial to isolation of specific neurons and advanced understanding of their functions.

Methods

The hypothalamus of female Sprague–Dawley rats in postnatal day-25, 35 and 45 were used to define the dynamic spatial atlas of gene expression in the arcuate nucleus (ARC) by 10× Genomics Visium platform. A surface protein expressed selectively by kisspeptin neurons was used to sort neurons by flow cytometric assay in vitro. The transcriptome of the isolated cells was examined using Smart sequencing.

Results

Four subclusters of neurons with similar gene expression signatures in ARC were identified. Only one subcluster showed the robust expression of Kiss1, which could be isolated by a unique membrane surface biomarker Solute carrier family 18 member A3 (SLC18A3). Moreover, genes in different subclusters presenting three expression modules distinctly functioned in each pubertal stage. Different types of cells representing distinct functions on glial or neuron differentiation, hormone secretion as well as estradiol response precisely affect and coordinate with each other, resulting in a complicated regulatory network for hypothalamic–pituitary–gonadal axis initiation and modulation.

Conclusion

Our data revealed a comprehensive transcriptomic overview of ARC within different pubertal stages, which could serve as a valuable resource for the study of puberty and sexual development disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00745-2.

A Putative Adverse Outcome Pathway Network for Disrupted Female Pubertal Onset to Improve Testing and Regulation of Endocrine Disrupting Chemicals

The average age for pubertal onset in girls has declined over recent decades. Epidemiological studies in humans and experimental studies in animals suggest a causal role for endocrine disrupting chemicals (EDCs) that are present in our environment. Of concern, current testing and screening regimens are inadequate in identifying EDCs that may affect pubertal maturation, not least because they do not consider early-life exposure. Also, the causal relationship between EDC exposure and pubertal timing is still a matter of debate. To address this issue, we have used current knowledge to elaborate a network of putative adverse outcome pathways (pAOPs) to identify how chemicals can affect pubertal onset. By using the AOP framework, we highlight current gaps in mechanistic understanding that need to be addressed and simultaneously point towards events causative of pubertal disturbance that could be exploited for alternative test methods. We propose 6 pAOPs that could explain the disruption of pubertal timing by interfering with the central hypothalamic trigger of puberty, GnRH neurons, and by so doing highlight specific modes of action that could be targeted for alternative test method development.

Cellular and molecular features of EDC exposure: consequences for the GnRH network

The onset of puberty and the female ovulatory cycle are important developmental milestones of the reproductive system. These processes are controlled by a tightly organized network of neurotransmitters and neuropeptides, as well as genetic, epigenetic and hormonal factors, which ultimately drive the pulsatile secretion of gonadotropin-releasing hormone. They also strongly depend on organizational processes that take place during fetal and early postnatal life. Therefore, exposure to environmental pollutants such as endocrine-disrupting chemicals (EDCs) during critical periods of development can result in altered brain development, delayed or advanced puberty and long-term reproductive consequences, such as impaired fertility. The gonads and peripheral organs are targets of EDCs, and research from the past few years suggests that the organization of the neuroendocrine control of reproduction is also sensitive to environmental cues and disruption. Among other mechanisms, EDCs interfere with the action of steroidal and non-steroidal receptors, and alter enzymatic, metabolic and epigenetic pathways during development. In this Review, we discuss the cellular and molecular consequences of perinatal exposure (mostly in rodents) to representative EDCs with a focus on the neuroendocrine control of reproduction, pubertal timing and the female ovulatory cycle.

Characterization of Genome-Wide DNA Methylation and Hydroxymethylation in Mouse Arcuate Nucleus of Hypothalamus During Puberty Process

Background: Pulsatile pituitary gonadotropin secretion governed by hypothalamic gonadotropin-releasing hormone (GnRH) is essential for the pubertal onset. The epigenetic mechanism underlying the activation of GnRH-dependent regulatory axis in hypothalamus remains elusive. This study aims to explore the potential correlation between the signature of DNA (hydroxyl)methylation and pubertal process.

Methods: Hypothalamic arcuate nucleus (ARC) of mouse at early (4-weeks) and late pubertal (8-weeks) stages underwent RNA-, RRBS-, and RRHP-seq to investigate the genome-wide profiles of transcriptome, differential DNA methylation and hydroxymethylation.

Results: A series of differential expressed genes (DEGs) involved in sexual development could be separated into three subgroups with the significant difference of DNA methylation or hydroxymethylation or both in promoter regions. Compared to DNA methylation, DNA hydroxymethylation partook in more signaling pathways including synapse morphology, channel activity and glial development, which could enhance transsynaptic change and glia-to-neuron communication to faciliate GnRH release. The correlation between transcription and these epigenetic modifications indicated that DNA hydroxymethylation impacted with gene transcription independently of DNA methylation spanning puberty.

Conclusion: Our results characterized the hydroxymethylation pattern and provided an insight into the novel epigenetic regulation on gene expression during pubertal process.

Precocious Puberty and Covid-19 Into Perspective: Potential Increased Frequency, Possible Causes, and a Potential Emergency to Be Addressed

A significant increase in precocious puberty, rapidly progressive puberty and precocious menarche has been reported in Italy since the initial lockdown because of the pandemic, and this could represent a new emergency to be addressed during this pandemic. There is a need, therefore, for further understanding and research. Many causes could account for this. Initially, it was thought that the changes in life-style, in screen time, and sleeping habits could be the cause but if considered individually these are insufficient to explain this phenomenon. Likely, changes in central nervous mediators, and an increase in catecholamines could contribute as a trigger, however, these aspects are poorly studied and understood as well as the real perceptions of these children. Finally, staying more indoors has certainly exposed these children to specific contaminants working as endocrine disruptors which could also have had an effect. It would be of utmost importance to compare this phenomenon worldwide with appropriate studies in order to verify what is happening, and gain a new insight into the consequences of the covid-19 pandemic and into precocious puberty and for future prevention.

Melatonin Suppresses the Kainate Receptor-Mediated Excitation on Gonadotropin-Releasing Hormone Neurons in Female and Male Prepubertal Mice

Melatonin, a pineal gland secretion, is an amphiphilic neurohormone involved in the biological and physiologic regulation of bodily functions. Numerous studies have shown the effects of melatonin on the release of gonadotropins and their actions at one or several levels of the hypothalamic–pituitary–gonadal axis. However, direct melatonin action on gonadotropin-releasing hormone (GnRH) neurons and its mechanism of action remain unclear. Here, plasma melatonin levels were measured and the effect of melatonin on GnRH neurons was assessed using brain slice patch clamp techniques. The plasma melatonin levels in prepubertal mice were higher than those in the adults. Melatonin itself did not change the firing activity of GnRH neurons. Interestingly, the kainate receptor-mediated responses but not the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)- and N-methyl-D-aspartic acid (NMDA)-induced responses were suppressed by melatonin in both the voltage clamp and current clamp modes. The inhibitory effects of the kainate-induced response by melatonin tended to increase with higher melatonin concentrations and persisted in the presence of tetrodotoxin, a voltage-sensitive Na⁺ channel blocker, or luzindole, a non-selective melatonin receptor antagonist. However, the response was completely abolished by pretreatment with pertussis toxin. These results suggest that melatonin can regulate GnRH neuronal activities in prepubertal mice by partially suppressing the excitatory signaling mediated by kainate receptors through pertussis toxin-sensitive G-protein-coupled receptors.

DLG2 variants in patients with pubertal disorders

PURPOSE

Impaired function of gonadotropin-releasing hormone (GnRH) neurons can cause a phenotypic spectrum ranging from delayed puberty to isolated hypogonadotropic hypogonadism (IHH). We sought to identify a new genetic etiology for these conditions.

METHODS

Exome sequencing was performed in an extended family with autosomal dominant, markedly delayed puberty. The effects of the variant were studied in a GnRH neuronal cell line. Variants in the same gene were sought in a large cohort of individuals with IHH.

RESULTS

We identified a rare missense variant (F900V) in DLG2 (which encodes PSD-93) that cosegregated with the delayed puberty. The variant decreased GnRH expression in vitro. PSD-93 is an anchoring protein of NMDA receptors, a type of glutamate receptor that has been implicated in the control of puberty in laboratory animals. The F900V variant impaired the interaction between PSD-93 and a known binding partner, Fyn, which phosphorylates NMDA receptors. Variants in DLG2 that also decreased GnRH expression were identified in three unrelated families with IHH.

CONCLUSION

The findings indicate that variants in DLG2/PSD-93 cause autosomal dominant delayed puberty and may also contribute to IHH. The findings also suggest that the pathogenesis involves impaired NMDA receptor signaling and consequently decreased GnRH secretion.

Glutamate Supply Reactivates Ovarian Function while Increases Serum Insulin and Triiodothyronine Concentrations in Criollo x Saanen-Alpine Yearlings' Goats during the Anestrous Season

The possible effect of glutamate supplementation upon ovarian reactivation and serum concentrations of insulin (INS) and triiodothyronine (T3) in anestrous yearling goats was evaluated. Goats (n = 32, 12 mo., 26° North, 1117 m) with a similar live weight (LW) and body condition score (BCS) were blood sampled twice per week for two weeks (2 × 1 week × 2 weeks) to confirm the anestrus status (<1 ng P4/mL; RIA). Thereafter, goats were randomly assigned to either 1) Glutamate (GLUT; n = 16, LW = 27.1 ± 1.09 kg, 3.5 ± 0.18 units, IV-supplemented with 7 mg of glutamate kg^-1 LW), or 2) Control (CONT; n = 16; LW = 29.2 ± 1.09 kg; BCS = 3.5 ± 0.18, IV saline). During the treatment period, 16 goats (eight/group) were blood sampled twice per week for six weeks. Such serum samples (2 × 1 week × 6 weeks) were quantified by their P4 content to evaluate the ovarian-luteal activity, whereas a sample subset (1 × 1 week × 6 weeks) was used to quantify their INS & T3 content to evaluate their metabolic status. Neither LW (28.19 kg; p > 0.05) nor BCS (3.51 units; p > 0.05) differed between treatments. Goats depicting ovarian reactivation favored the GLUT group (50 vs. 12.5%; p < 0.05). Neither INS (1.72 ± 0.15 ng mL^-1) nor T3 (2.32 ± 0.11 ng mL^-1) differed between treatments, yet a treatment x time interaction regarding INS & T3 concentration across time favored (p < 0.05) the GLUT group. The results unveil exogenous glutamate as an interesting modulator not only of ovarian reactivation, but of metabolic hormone synthesis.

Non-genomic action of vitamin D3 on N-methyl-D-aspartate and kainate receptor-mediated actions in juvenile gonadotrophin-releasing hormone neurons

Vitamin D is a versatile signalling molecule that plays a critical role in calcium homeostasis. There are several studies showing the genomic action of vitamin D in the control of reproduction; however, the quick non-genomic action of vitamin D at the hypothalamic level is not well understood. Therefore, to investigate the effect of vitamin D on juvenile gonadotrophin-releasing hormone (GnRH) neurons, excitatory neurotransmitter receptor agonists N-methyl-D-aspartate (NMDA, 30μM) and kainate (10μM) were applied in the absence or in the presence of vitamin D3 (VitaD3, 10nM). The NMDA-mediated responses were decreased by VitaD3 in the absence and in the presence of tetrodotoxin (TTX), a sodium-channel blocker, with the mean relative inward current being 0.56±0.07 and 0.66±0.07 (P<0.05), respectively. In addition, VitaD3 induced a decrease in the frequency of gamma-aminobutyric acid mediated (GABAergic) spontaneous postsynaptic currents and spontaneous postsynaptic currents induced by NMDA application with a mean relative frequency of 0.595±0.07 and 0.56±0.09, respectively. Further, VitaD3 decreased the kainate-induced inward currents in the absence and in the presence of TTX with a relative inward current of 0.64±0.06 and 0.68±0.06, respectively (P<0.05). These results suggest that VitaD3 has a non-genomic action and partially inhibits the NMDA and kainate receptor-mediated actions of GnRH neurons, suggesting that VitaD3 may regulate the hypothalamic-pituitary-gonadal (HPG) axis at the time of pubertal development.

Regulation of arcuate genes by developmental exposures to endocrine-disrupting compounds in female rats

Developmental exposure to endocrine-disrupting compounds (EDCs) alters reproduction and energy homeostasis, both of which are regulated by the arcuate nucleus (ARC). Little is known about the effects of EDC on ARC gene expression. In Experiment #1, pregnant dams were treated with either two doses of bisphenol A (BPA) or oil from embryonic day (E)18-21. Neonates were injected from postnatal day (PND)0-7. Vaginal opening, body weights, and ARC gene expression were measured. Chrm3 (muscarinic receptor 3) and Adipor1 (adiponectin receptor 1) were decreased by BPA. Bdnf (brain-derived neurotropic factor), Igf1 (insulin-like growth factor 1), Htr2c (5-hydroxytryptamine receptor), and Cck2r (cholescystokinin 2 receptor) were impacted. In Experiment #2, females were exposed to BPA, diethylstilbestrol (DES), di(2-ethylhexyl)phthalate, or methoxychlor (MXC) during E11-PND7. MXC and DES advanced the age of vaginal opening and ARC gene expression was impacted. These data indicate that EDCs alter ARC genes involved in reproduction and energy homeostasis in females.

Social opportunity rapidly regulates expression of CRF and CRF receptors in the brain during social ascent of a teleost fish, Astatotilapia burtoni

In social animals, hierarchical rank governs food availability, territorial rights and breeding access. Rank order can change rapidly and typically depends on dynamic aggressive interactions. Since the neuromodulator corticotrophin releasing factor (CRF) integrates internal and external cues to regulate the hypothalamic-pituitary adrenal (HPA) axis, we analyzed the CRF system during social encounters related to status. We used a particularly suitable animal model, African cichlid fish, Astatotilapia burtoni, whose social status regulates reproduction. When presented with an opportunity to rise in rank, subordinate A. burtoni males rapidly change coloration, behavior, and their physiology to support a new role as dominant, reproductively active fish. Although changes in gonadotropin-releasing hormone (GnRH1), the key reproductive molecular actor, have been analyzed during social ascent, little is known about the roles of CRF and the HPA axis during transitions. Experimentally enabling males to ascend in social rank, we measured changes in plasma cortisol and the CRF system in specific brain regions 15 minutes after onset of social ascent. Plasma cortisol levels in ascending fish were lower than subordinate conspecifics, but similar to levels in dominant animals. In the preoptic area (POA), where GnRH1 cells are located, and in the pituitary gland, CRF and CRF₁ receptor mRNA levels are rapidly down regulated in ascending males compared to subordinates. In the Vc/Vl, a forebrain region where CRF cell bodies are located, mRNA coding for both CRFR₁ and CRFR₂ receptors is lower in ascending fish compared to stable subordinate conspecifics. The rapid time course of these changes (within minutes) suggests that the CRF system is involved in the physiological changes associated with shifts in social status. Since CRF typically has inhibitory effects on the neuroendocrine reproductive axis in vertebrates, this attenuation of CRF activity may allow rapid activation of the reproductive axis and facilitate the transition to dominance.

Puberty and adolescence as a time of vulnerability to stressors that alter neurobehavioral processes

Puberty and adolescence are major life transitions during which an individual's physiology and behavior changes from that of a juvenile to that of an adult. Here we review studies documenting the effects of stressors during pubertal and adolescent development on the adult brain and behavior. The experience of complex or compound stressors during puberty/adolescence generally increases stress reactivity, increases anxiety and depression, and decreases cognitive performance in adulthood. These behavioral changes correlate with decreased hippocampal volumes and alterations in neural plasticity. Moreover, stressful experiences during puberty disrupt behavioral responses to gonadal hormones both in sexual performance and on cognition and emotionality. These behavioral changes correlate with altered estrogen receptor densities in some estrogen-concentrating brain areas, suggesting a remodeling of the brain's response to hormones. A hypothesis is presented that activation of the immune system results in chronic neuroinflammation that may mediate the alterations of hormone-modulated behaviors in adulthood.

Perinatal exposure to low doses of tributyltin chloride advances puberty and affects patterns of estrous cyclicity in female mice

Tributyltin (TBT), a proven endocrine-disrupting chemical, is well known to induce imposex in female gastropods. Herein we demonstrate the effects of low doses of tributyltin chloride (TBTCl) on the female offspring of KM mice. Pregnant mice were administered by gavage with 0, 1, 10, or 100 μg TBTCl/kg body weight/day from day 6 of pregnancy through the period of lactation. TBTCl dramatically advanced the age of onset of vaginal opening (VO) and first vaginal estrus, and reduced body weights at VO and first estrus. Furthermore, perinatal treatment with TBTCl significantly reduced the number of days between VO and first estrus. In addition, female offspring from dams exposed to 10 and 100 μg kg(-1) TBTCl exhibited altered patterns of estrous cyclicity in adulthood. In conclusion, perinatal exposure to low doses TBTCl result in early puberty and impaired estrous cyclicity in female mice, which suggest that TBTCl might act as an estrogen agonist or/and a disruptor on hypothalamic-pituitary function in the present study.

Urinary metabolite markers of precocious puberty

The incidence of precocious puberty (PP, the appearance of signs of pubertal development at an abnormally early age), is rapidly rising, concurrent with changes of diet, lifestyles, and social environment. The current diagnostic methods are based on a hormone (gonadotropin-releasing hormone) stimulation test, which is costly, time-consuming, and uncomfortable for patients. The lack of molecular biomarkers to support simple laboratory tests, such as a blood or urine test, has been a long standing bottleneck in the clinical diagnosis and evaluation of PP. Here we report a metabolomic study using an ultra performance liquid chromatography-quadrupole time of flight mass spectrometry and gas chromatography-time of flight mass spectrometry. Urine metabolites from 163 individuals were profiled, and the metabolic alterations were analyzed after treatment of central precocious puberty (CPP) with triptorelin depot. A panel of biomarkers selected from >70 differentially expressed urinary metabolites by receiver operating characteristic and logistic regression analysis provided excellent predictive power with high sensitivity and specificity for PP. The altered metabolic profile of the PP patients was characterized by three major perturbed metabolic pathways: catecholamine, serotonin metabolism, and tricarboxylic acid cycle, presumably resulting from activation of the sympathetic nervous system and the hypothalamic-pituitary-gonadal axis. Treatment with triptorelin depot was able to normalize these three altered pathways. Additionally, significant changes in the urine levels of 4-hydroxyphenylacetic acid, 5-hydroxyindoleacetic acid, indoleacetic acid, 5-hydroxytryptophan, and 5-hydroxykynurenamine in the CPP group suggest that the development of CPP condition may involve an alteration in symbiotic gut microbial composition.

Kisspeptin signaling is required for peripheral but not central stimulation of gonadotropin-releasing hormone neurons by NMDA

NMDA and kisspeptins can stimulate gonadotropin-releasing hormone (GnRH) release after peripheral or central administration in mice. To determine whether these agonists act independently or through a common pathway, we have examined their ability to stimulate GnRH/luteinizing hormone (LH) release after peripheral or central administration in Kiss1- or Gpr54 (Kiss1r)-null mutant mice. Peripheral injection of NMDA failed to stimulate GnRH/LH release in prepubertal or gonadally intact mutant male mice. Dual-labeling experiments indicated a direct activation of Kiss1-expressing neurons in the arcuate nucleus. In contrast, central injection of NMDA into the lateral ventricle increased plasma LH levels in both Kiss1 and Gpr54 mutant male mice similar to the responses in wild-type mice. Central injection of NMDA stimulated c-Fos expression throughout the hypothalamus but not in GnRH neurons, suggesting an action at the nerve terminals only. In contrast, kisspeptin-10 stimulated LH release after both central and peripheral injection but induced c-Fos expression in GnRH neurons only after central administration. Finally, central injection of NMDA induces c-Fos expression in catecholamine- and nitric oxide-producing neurons in the hypothalamus of mutant mice, indicating a possible kisspeptin-independent GnRH/LH release by NMDA through activation of these neurons. Thus, NMDA may act at both GnRH cell bodies (kisspeptin-independent) and nerve terminals (kisspeptin-dependent) in a dual way to participate in the GnRH/LH secretion in the male mouse.

[Neuronal LHRH system activity in an animal model of growth retardation]

OBJECTIVE

Mild and chronic energy restriction results in growth retardation with puberal delay, a nutritional disease known as nutritional dwarfing (ND). The aim of the present study was to assess the profile of hypothalamic luteinizing hormone-releasing hormone (LHRH) release, at baseline and under glutamate stimulation, in ND rats to elucidate gonadotrophic dysfunction. Reproductive ability during refeeding was also studied.

MATERIAL AND METHODS

At weaning, 60 male rats were assigned to two groups of 30 animals each: a control and an experimental group. Control rats were fed ad libitum with a balanced rodent diet. The experimental group received 80% of the diet consumed by the control group for 4 weeks. After 4 weeks of food restriction, the ND group was fed freely for 8 weeks. Ten rats from each group were sacrificed every 4 weeks for assays.

RESULTS

At week 4, body weight and length were significantly diminished in the experimental group vs. the control group (p<0.001). No changes were observed in LHRH baseline release, pulse frequency or amplitude in the experimental group compared with the control group at any time. However, under glutamate stimulation, LHRH release was significantly higher in ND rats than in control rats at week 4 (p<0.05). Refeeding the ND group allowed the rats to reach overall growth and reproductive ability.

CONCLUSIONS

The results of the present study suggest that the response to the facilitatory effect of glutamate on LHRH release in post-restricted ND rats is probably related to a lesser central nervous system maturation in relation to their chronological age. The adequate somatic growth and normal reproductive ability attained with refeeding suggest the reversibility of the two energetically costly processes compromised by global, mild and chronic food restriction.

KISS1 gene analysis in Korean girls with central precocious puberty: a polymorphism, p.P110T, suggested to exert a protective effect

Mutations in the GPR54 gene have already been identified as a cause of idiopathic hypogonadotrophic hypogonadism and central precocious puberty (CPP) in certain patients. However, currently there is only a limited amount of data available regarding KISS1 gene mutations or polymorphisms. The aim of this study is to identify KISS1 gene mutations or polymorphisms in Korean girls with CPP. 101 Korean girls with CPP were recruited as the patient group, and 51 healthy Korean female adults as the control group. All coding exons and exon-intron boundaries of the KISS1 gene were sequenced. The relationships between identified sequence variations and CPP were evaluated via the comparison of allele frequencies between the two groups. Different clinical characteristics were also compared between the subgroups with or without a certain variation in the patient group. Eight polymorphisms were identified in the KISS1 gene. Although two of them were novel, those polymorphisms could not lead to amino acid changes. p.P110T was detected less frequently in CPP patients than in the controls (P = 0.022). Moreover, the CPP patients with p.P110T evidenced lower peak FSH values under GnRH stimulation than those without p.P110T (P = 0.002). The allele frequencies of several polymorphisms in the Korean population were identified in this study. An infrequent polymorphism in the KISS1 gene, p.P110T, appeared to be meaningful. This polymorphism was suggested to exert a protective effect on pubertal precocity, even though more evidence will be required to confirm the accurate function.

Age-dependent differences in sensitivity and sensitization to cannabinoids and 'club drugs' in male adolescent and adult rats

Lifelong substance abuse is often initiated during adolescence; yet, most pre-clinical research in this area has been conducted in adult animals. Substantial evidence exists that the brain development that continues throughout adolescence may result in pharmacological responses that differ in a crucial manner from those of adults. The goal of this study was to evaluate age differences in motor activity following acute and repeated administration of drugs that are commonly abused by adolescents, including cocaine, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), and the club drugs, ketamine and 3,4-methylenedioxymethamphetamine (MDMA). Adolescent and adult male rats were injected once daily with saline or with a dose of one of the test drugs for two 5-day dosing periods, separated by a 2-day drug holiday during which they remained in their home cages. Following each injection, rats were placed in a locomotor chamber for a 20-minute session. The potencies of cocaine, ketamine and MDMA for producing motor stimulation were less in male adolescents than in male adults. Furthermore, sensitization to the club drug, ketamine, developed after repeated dosing in adults, but not adolescents. In contrast, adolescents were initially more sensitive to the stimulatory effects of low doses of Delta(9)-THC than were adults, although rapid tolerance occurred. These results suggest that adolescents are less sensitive to the acute and repeated stimulant effects of some, but not all, of the drugs that are preferentially abused by this age group. This differential sensitivity may contribute to the different patterns of use that have been noted in adolescent versus adult drug abusers.

Distinct subsets of hypothalamic genes are modulated by two different thermogenesis-inducing stimuli

Obesity results from an imbalance between food intake and energy expenditure, two vital functions that are tightly controlled by specialized neurons of the hypothalamus. The complex mechanisms that integrate these two functions are only beginning to be deciphered. The objective of this study was to determine the effect of two thermogenesis-inducing conditions, i.e., ingestion of a high-fat (HF) diet and exposure to cold environment, on the expression of 1,176 genes in the hypothalamus of Wistar rats. Hypothalamic gene expression was evaluated using a cDNA macroarray approach. mRNA and protein expressions were determined by reverse-transcription PCR (RT-PCR) and immunoblot. Cold exposure led to an increased expression of 43 genes and to a reduced expression of four genes. HF diet promoted an increased expression of 90 genes and a reduced expression of 78 genes. Only two genes (N-methyl-D-aspartate (NMDA) receptor 2B and guanosine triphosphate (GTP)-binding protein G-alpha-i1) were similarly affected by both thermogenesis-inducing conditions, undergoing an increment of expression. RT-PCR and immunoblot evaluations confirmed the modulation of NMDA receptor 2B and GTP-binding protein G-alpha-i1, only. This corresponds to 0.93% of all the responsive genes and 0.17% of the analyzed genes. These results indicate that distinct environmental thermogenic stimuli can modulate predominantly distinct profiles of genes reinforcing the complexity and multiplicity of the hypothalamic mechanisms that regulate energy conservation and expenditure.

The genetic basis for the timing of human puberty

Puberty is a complex, coordinated biological process with multiple levels of regulation. Epidemiological observations suggest that the timing of pubertal events is a heritable trait, although environmental factors can modulate such genetic influence. The study of pathological states of early and late puberty has provided valuable insight into those genes that regulate gonadotrophin-releasing hormone (GnRH) activity. The development of pulsatile release of GnRH secretion mediated through kisspeptin-1 activation of G-protein coupled receptor-54 appears to be a central event at the onset and during progression of puberty. Stimulating and restraining influences (e.g. in the form of glutamatergic and GABAergic neuronal inputs) are likely to influence the timing of this process. The study of extreme variants of 'normality', such as constitutional delay of growth and puberty and early puberty, may lead to the recognition of additional genes and pathways that can modulate both the timing of pubertal onset and its tempo.

Selective role of neuropeptide Y receptor subtype Y2 in the control of gonadotropin secretion in the rat

Different signals with key roles in energy homeostasis regulate the reproductive axis. These include neuropeptide Y and polypeptide YY(3-36), whose type Y(2) receptor is the most abundant of this family in the brain. We evaluated herein the putative roles of Y(2) receptors in the control of gonadotropin secretion by means of central administration of PYY(13-36) (agonist of Y(2) receptors) and BIIE 0246 (antagonist of Y(2) receptors) to intact and orchidectomized male rats. In addition, the ability of PYY(13-36) to elicit GnRH and gonadotropin secretion in vitro and the impact of fasting on LH responses to PYY(13-36) in vivo were also monitored. Central administration of PYY(13-36) significantly decreased the circulating levels of both gonadotropins, an effect that was observed in prepubertal and adult rats. Yet a dual action of Y(2) receptors in the control of male gonadotropic axis was evidenced as their activation induced 1) stimulation of gonadotropin responses to GnRH at the pituitary but 2) inhibition of GnRH secretion at the hypothalamus. Antagonization of Y(2) receptors failed to modify basal LH secretion in intact males either after being fed ad libitum or after being fasted. In contrast, their central blockade in orchidectomized rats evoked a significant increase in circulating LH and FSH level, suggesting the constitutive activation of Y(2) receptor in such stimulated conditions. In summary, our data evidence a complex mode of action of Y(2) receptors in the control of gonadotropic axis, with stimulatory and inhibitory actions at different levels of the system that are sensitive to the gonadal status.

Morphological evidence for direct interaction between gonadotrophin-releasing hormone neurones and astroglial cells in the human hypothalamus

In rodents, there is compelling evidence indicating that dynamic cell-to-cell communications involving cross talk between astroglial cells (such as astrocytes and specialised ependymoglial cells known as tanycytes) and neurones are important in regulating the secretion of gonadotrophin-releasing hormone (GnRH), the neurohormone that controls both sexual maturation and adult reproductive function. However, whether such astroglial cell-GnRH neurone interactions occur in the human brain is not known. In the present study, we used immunofluorescence to examine the anatomical relationship between GnRH neurones and glial cells within the hypothalamus of five women. Double-staining experiments demonstrated the ensheathment of GnRH neurone perikarya by glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte processes in the periventricular zone of the tuberal region of the hypothalamus. GFAP immunoreactivity did not overlap that of GnRH at the GnRH neurone's projection site (i.e. the median eminence of the hypothalamus). Rather, human GnRH neuroendocrine fibres were found to be closely associated with vimentin or nestin-immunopositive radial glial processes likely belonging to tanycytes. In line with these light microscopy data, ultrastructural examination of GnRH-immunoreactive neurones showed numerous glial cells in direct apposition to pre-embedding-labelled GnRH cell bodies and/or dendrites in the infundibular nucleus, whereas postembedding immunogold-labelled GnRH nerve terminals were often seen to be enwrapped by glial cell processes in the median eminence. GnRH nerve button were sometimes visualised in close proximity to fenestrated pituitary portal blood capillaries and/or evaginations of the basal lamina that delineate the pericapillary space. In summary, these data demonstrate that GnRH neurones morphologically interact with astrocytes and tanycytes in the human brain and provide evidence that glial cells may contribute physiologically to the process by which the neuroendocrine brain controls the function of GnRH neurones in humans.