[Congenital hyperinsulinism : contributions of chemistry, therapeutic response, genetics and imaging]. / Hyperinsulinisme congénital : apports de la biologie, de la réponse thérapeutique, de la génétique et de l'imagerie.

Congenital hyperinsulinism is the most common cause of recurrent hypoglycemia in newborns and children. Early diagnosis and rapid management are essential to avoid hypoglycaemic brain injury and later neurological complications. Management of those patients involves biological evaluation, molecular genetics, imaging techniques and surgical advances. We report the case of a newborn with recurrent hypoglycemia due to congenital hyperinsulinism (CHI) caused by a new variant in the ABCC8 gene. Fluorine 18-L-3,4 Dihydroxyphenylalanine Positron Emission Tomography (18F-DOPA PET/CT scan) reported a focal lesion at the isthmus of the pancreas which has been removed by laparoscopic surgery with a complete recovery for the patient.

L'hyperinsulinisme congénital est la cause la plus fréquente d'hypoglycémies récidivantes chez le nouveau-né et l'enfant. Un diagnostic et une prise en charge précoces sont primordiaux pour éviter les conséquences potentielles sur le développement neurologique. Ces derniers reposent sur la conjonction d'éléments biologiques, génétiques et d'imagerie. Nous rapportons le cas d'un nouveau-né présentant des hypoglycémies récidivantes. La mise au point mettra en évidence un hyperinsulinisme congénital (CHI) lié à un variant non encore décrit au sein du gène ABCC8. L'imagerie par Fluorine 18-L-3,4 Dihydroxyphenylalanine Positron Emission Tomography/Computed Tomography-scanner (18F-DOPA PET/CT scan) a mis en évidence une forme focale de l'hyperinsulinisme justifiant une prise en charge chirurgicale amenant à une guérison complète et à l'arrêt de tout traitement médicamenteux.

Perinatal exposure to the fungicide ketoconazole alters hypothalamic control of puberty in female rats.

Introduction: Estrogenic endocrine disrupting chemicals (EDCs) such as diethylstilbestrol (DES) are known to alter the timing of puberty onset and reproductive function in females. Accumulating evidence suggests that steroid synthesis inhibitors such as ketoconazole (KTZ) or phthalates may also affect female reproductive health, however their mode of action is poorly understood. Because hypothalamic activity is very sensitive to sex steroids, we aimed at determining whether and how EDCs with different mode of action can alter the hypothalamic transcriptome and GnRH release in female rats. Design: Female rats were exposed to KTZ or DES during perinatal (DES 3-6-12µg/kg.d; KTZ 3-6-12mg/kg.d), pubertal or adult periods (DES 3-12-48µg/kg.d; KTZ 3-12-48mg/kg.d). Results: Ex vivo study of GnRH pulsatility revealed that perinatal exposure to the highest doses of KTZ and DES delayed maturation of GnRH secretion before puberty, whereas pubertal or adult exposure had no effect on GnRH pulsatility. Hypothalamic transcriptome, studied by RNAsequencing in the preoptic area and in the mediobasal hypothalamus, was found to be very sensitive to perinatal exposure to all doses of KTZ before puberty with effects persisting until adulthood. Bioinformatic analysis with Ingenuity Pathway Analysis predicted "Creb signaling in Neurons" and "IGF-1 signaling" among the most downregulated pathways by all doses of KTZ and DES before puberty, and "PPARg" as a common upstream regulator driving gene expression changes. Deeper screening ofRNAseq datasets indicated that a high number of genes regulating the activity of the extrinsic GnRH pulse generator were consistently affected by all the doses of DES and KTZ before puberty. Several, including MKRN3, DNMT3 or Cbx7, showed similar alterations in expression at adulthood. Conclusion: nRH secretion and the hypothalamic transcriptome are highly sensitive to perinatal exposure to both DES and KTZ. The identified pathways should be exploredfurther to identify biomarkers for future testing strategies for EDC identification and when enhancing the current standard information requirements in regulation.

Unusual Cardiac Manifestations of a Pheochromocytoma in a Girl.

We report the case of an 11-year-old girl who complained about severe asthenia, orthostatic dizziness and abdominal pain for 4 weeks. The primary investigation concluded on febrile urinary tract infection treated by antibiotics. Symptom persistence prompted cardiological and endocrinological investigations. A fluctuation in blood pressure, long QT interval, dilation of the aortic root and left ventricular hypertrophy were documented. Elevated levels of urinary catecholamines together with the presence of a right-sided adrenal mass shown via abdominal ultrasound and magnetic resonance imaging were highly suggestive of a pheochromocytoma. This was confirmed by through iodine-123-metaiodobenzylguathdine ([123I]-mIBG) scintigraphy. Genetic analysis allowed for the exclusion of pathogenic mutations in genes implicated in hereditary paragangliomas and pheochromocytomas but showed a rare somatic mutation in exon 3 of the von Hippel-Lindau gene. The patient was treated with a ß-blocker and calcium channel antagonist and underwent laparoscopic right-sided adrenalectomy. Cardiac manifestations resolved soon after surgery indicating that they were secondary to the pheochromocytoma. After 5 years of follow-up, the patient remains asymptomatic without any sign of tumor recurrence. The presence of aortic root dilation, a prolonged QT-interval and left ventricular hypertrophy may be early cardiac manifestations of a pheochromocytoma in a child and should prompt this diagnosis to be evoked.

Male minipuberty involves the gonad-independent activation of preoptic nNOS neurons.

BACKGROUND: The maturation of the hypothalamic-pituitary-gonadal (HPG) axis is crucial for the establishment of reproductive function. In female mice, neuronal nitric oxide synthase (nNOS) activity appears to be key for the first postnatal activation of the neural network promoting the release of gonadotropin-releasing hormone (GnRH), i.e. minipuberty. However, in males, the profile of minipuberty as well as the role of nNOS-expressing neurons remain unexplored. METHODS: nNOS-deficient and wild-type mice were studied during postnatal development. The expression of androgen (AR) and estrogen receptor alpha (ERα) as well as nNOS phosphorylation were evaluated by immunohistochemistry in nNOS neurons in the median preoptic nucleus (MePO), where most GnRH neuronal cell bodies reside, and the hormonal profile of nNOS-deficient male mice was assessed using previously established radioimmunoassay and ELISA methods. Gonadectomy and pharmacological manipulation of ERα were used to elucidate the mechanism of minipubertal nNOS activation and the maturation of the HPG axis. RESULTS: In male mice, minipubertal FSH release occurred at P23, preceding the LH surge at P30, when balanopreputial separation occurs. Progesterone and testosterone remained low during minipuberty, increasing around puberty, whereas estrogen levels were high throughout postnatal development. nNOS neurons showed a sharp increase in Ser1412 phosphorylation of nNOS at P23, a phenomenon that occurred even in the absence of the gonads. In male mice, nNOS neurons did not appear to express AR, but abundantly expressed ERα throughout postnatal development. Selective pharmacological blockade of ERα during the infantile period blunted Ser1412 phosphorylation of nNOS at P23. CONCLUSIONS: Our results show that the timing of minipuberty differs in male mice when compared to females, but as in the latter, nNOS activity in the preoptic region plays a role in this process. Additionally, akin to male non-human primates, the profile of minipuberty in male mice is shaped by sex-independent mechanisms, and possibly involves extragonadal estrogen sources.

Exposure to the pesticides linuron, dimethomorph and imazalil alters steroid hormone profiles and gene expression in developing rat ovaries.

Inhibition of androgen signaling during critical stages of ovary development can disrupt folliculogenesis with potential consequences for reproductive function later in life. Many environmental chemicals can inhibit the androgen signaling pathway, which raises the question if developmental exposure to anti-androgenic chemicals can negatively impact female fertility. Here, we report on altered reproductive hormone profiles in prepubertal female rats following developmental exposure to three pesticides with anti-androgenic potential: linuron (25 and 50 mg/kg bw/d), dimethomorph (60 and 180 mg/kg bw/d) and imazalil (8 and 24 mg/kg bw/d). Dams were orally exposed from gestational day 7 (dimethomorph and imazalil) or 13 (linuron) until birth, then until end of dosing at early postnatal life. Linuron and dimethomorph induced dose-related reductions to plasma corticosterone levels, whereas imazalil mainly suppressed gonadotropin levels. In the ovaries, expression levels of target genes were affected by linuron and dimethomorph, suggesting impaired follicle growth. Based on our results, we propose that anti-androgenic chemicals can negatively impact female reproductive development. This highlights a need to integrate data from all levels of the hypothalamic-pituitary-gonadal axis, as well as the hypothalamic-pituitary-adrenal axis, when investigating the potential impact of endocrine disruptors on female reproductive development and function.

GnRH neurons recruit astrocytes in infancy to facilitate network integration and sexual maturation.

Neurons that produce gonadotropin-releasing hormone (GnRH), which control fertility, complete their nose-to-brain migration by birth. However, their function depends on integration within a complex neuroglial network during postnatal development. Here, we show that rodent GnRH neurons use a prostaglandin D2 receptor DP1 signaling mechanism during infancy to recruit newborn astrocytes that 'escort' them into adulthood, and that the impairment of postnatal hypothalamic gliogenesis markedly alters sexual maturation by preventing this recruitment, a process mimicked by the endocrine disruptor bisphenol A. Inhibition of DP1 signaling in the infantile preoptic region, where GnRH cell bodies reside, disrupts the correct wiring and firing of GnRH neurons, alters minipuberty or the first activation of the hypothalamic-pituitary-gonadal axis during infancy, and delays the timely acquisition of reproductive capacity. These findings uncover a previously unknown neuron-to-neural-progenitor communication pathway and demonstrate that postnatal astrogenesis is a basic component of a complex set of mechanisms used by the neuroendocrine brain to control sexual maturation.

Myocardial Expression of Estrogen Receptor-mRNA Is Associated With Lower Markers of Post-operative Organ Damage in Young Patients With Congenital Cardiac Defect.

Background: Estrogen receptors (ERs) relate to cardio-protection in adults, but their role in younger patients is not known. We aimed to assess the myocardial expression of ERα- and ERß- mRNA in young patients with congenital cardiac disease and to analyze their putative protective role. Patients and Methods: Twenty children and young adults (seven females and 13 males) with a median age of 13.8 years (interquartile range: 12.3 years) were enrolled in this prospective study. The myocardial expression of ER-mRNA and genes involved in inflammation, growth, and stress response was assessed by real-time PCR and was correlated to post-operative (po) outcome. Results: ER-mRNA was detected in the myocardium of all patients, independently of gender and age. The expression of ER-mRNA correlated with that of mRNA coding for brain natriuretic peptide and for all cytokines tested. A higher ERα-mRNA expression correlated with lower troponin T concentrations at 24 h po (p = 0.032), higher PaO2/FiO2 ratio at 4 h po (p = 0.059), lower fluid retention at 4 h po (p = 0.048), and lower aspartate aminotransferase (AST) levels at 24 h po (p = 0.047). A higher ERß-mRNA expression was also correlated with lower fluid retention at 24 h po (p = 0.048). Patients in whom the levels of ERα- and ERß-mRNA were >P50 had lower troponin T (p = 0.003, respectively) and lower AST concentrations at 24 h po (p = 0.043, respectively) than the others. Conclusions: The expression of ERα- and ERß-mRNA is present in the myocardium of children and young adults with congenital cardiac defect and is associated with lower markers of po organ damage. This suggests that ERs may provide perioperative organ protection in this population.

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.

Rationale for Environmental Hygiene towards global protection of fetuses and young children from adverse lifestyle factors.

BACKGROUND: The regulatory management of chemicals and toxicants in the EU addresses hundreds of different chemicals and health hazards individually, one by one. An issue is that, so far, the possible interactions among chemicals or hazards are not considered as such. Another issue is the anticipated delay of several decades before effective protection of public health by regulatory decisions due to a time consuming process. Prenatal and early postnatal life is highly vulnerable to environmental health hazards with lifelong consequences, and a priority period for reduction of exposure. There are some initiatives regarding recommendations for pregnant women aiming at protection against one or another category of health hazard, however not validated by intervention studies. HYPOTHESIS: Here, we aim at strengthening the management of exposure to individual health hazards during pregnancy and lactation, with protective measures in a global strategy of Environmental Hygiene. We hypothesize that such a strategy could reduce both the individual effects of harmful agents in complex mixtures and the possible interactions among them. A panel of experts should develop and endorse implementable measures towards a protective behavior. Their application is meant to be preferably as a package of measures in order to maximize protection and minimize interactions in causing adverse effects. Testing our hypothesis requires biomonitoring studies and longitudinal evaluation of health endpoints in the offspring. Favorable effects would legitimate further action towards equal opportunity access to improved environmental health. CONCLUSION: Environmental Hygiene is proposed as a global strategy aiming at effective protection of pregnant women, unborn children and infants against lifelong consequences of exposure to combinations of adverse lifestyle factors.

Loss of oocytes due to conditional ablation of Murine double minute 2 (Mdm2) gene is p53-dependent and results in female sterility.

Murine double minute 2 and 4 (Mdm2, Mdm4) are major p53-negative regulators, preventing thus uncontrolled apoptosis induction in numerous cell types, although their function in the female germ line has received little attention. In the present work, we have generated mice with specific invalidation of Mdm2 and Mdm4 genes in the mouse oocyte (Mdm2(Ocko) and Mdm4(Ocko) mice), to test their implication in survival of these germ cells. Most of the Mdm2(Ocko) but not Mdm4(Ocko) mice were sterile, with a dramatic reduction of the weight of ovaries and genital tract, a strong increase in follicle-stimulating hormone and luteinizing hormone serum levels, and a reduction of anti-mullerian hormone serum levels. Histological analyses revealed an obvious decrease of the number of growing follicles beyond the primary stage in Mdm2(Ocko) ovaries in comparison to controls, with a pronounced increase in the apparition of primary atretic follicles, most being devoid of oocyte. Similar phenotypes were observed with Mdm2(Ocko) Mdm4(Ocko) ovaries, with no worsening of the phenotype. However, we failed to detect any increase in p53 level in mutant oocytes, nor any other apoptotic marker, introgression of this targeted invalidation in p53-/- mice restored the fertility of females. This study is the first to show that Mdm2, but not Mdm4, has a critical role in oocyte survival and would be involved in premature ovarian insufficiency phenotype.

Delayed Neuroendocrine Sexual Maturation in Female Rats After a Very Low Dose of Bisphenol A Through Altered GABAergic Neurotransmission and Opposing Effects of a High Dose.

Rat sexual maturation is preceded by a reduction of the interpulse interval (IPI) of GnRH neurosecretion. This work aims at studying disruption of that neuroendocrine event in females after early exposure to a very low dose of bisphenol A (BPA), a ubiquitous endocrine disrupting chemical. Female rats were exposed to vehicle or BPA 25 ng/kg·d, 25 µg/kg·d, or 5 mg/kg·d from postnatal day (PND)1 to PND5 or PND15. Exposure to 25 ng/kg·d of BPA for 5 or 15 days was followed by a delay in developmental reduction of GnRH IPI studied ex vivo on PND20. After 15 days of exposure to that low dose of BPA, vaginal opening tended to be delayed. In contrast, exposure to BPA 5 mg/kg·d for 15 days resulted in a premature reduction in GnRH IPI and a trend toward early vaginal opening. RNA sequencing analysis on PND20 indicated that exposure to BPA resulted in opposing dose effects on the mRNA expression of hypothalamic genes involved in gamma aminobutyric acid A (GABAA) neurotransmission. The study of GnRH secretion in vitro in the presence of GABAA receptor agonist/antagonist confirmed an increased or a reduced GABAergic tone after in vivo exposure to the very low or the high dose of BPA, respectively. Overall, we show for the first time that neonatal exposure to BPA leads to opposing dose-dependent effects on the neuroendocrine control of puberty in the female rat. A very low and environmentally relevant dose of BPA delays neuroendocrine maturation related to puberty through increased inhibitory GABAergic neurotransmission.

Pubertal timing after neonatal diethylstilbestrol exposure in female rats: neuroendocrine vs peripheral effects and additive role of prenatal food restriction.

We studied the effects of neonatal exposure to diethylstilbestrol (DES) on pubertal timing in female rats. We examined associated neuroendocrine changes and effects of prenatal food restriction. Age at vaginal opening was advanced after exposure to 10 µg/kg/d of DES and delayed after 1 µg/kg/d (subcutaneous injections). Using this lower dose, pulsatile GnRH secretion was slower at 25 days of age. Both doses reduced KiSS1 mRNA levels at 15 days of age. Using functional Kisspeptin promoter assay, 1 or 10 µM DES reduced or increased KISS1 transcription, respectively. Leptin stimulatory effect on GnRH secretion in vitro (15 days of age) was reduced after prenatal food restriction and neonatal DES exposure (higher dose), both effects being cumulative. Thus, alterations in pubertal timing by DES neonatally are not unequivocally toward precocity, the level of exposure being critical. We provide evidence of neuroendocrine disruption and interaction with prenatal food availability.

Depletion of the p43 mitochondrial T3 receptor increases Sertoli cell proliferation in mice.

Among T3 receptors, TRα1 is ubiquitous and its deletion or a specific expression of a dominant-negative TRα1 isoform in Sertoli cell leads to an increase in testis weight and sperm production. The identification of a 43-kDa truncated form of the nuclear receptor TRα1 (p43) in the mitochondrial matrix led us to test the hypothesis that this mitochondrial transcription factor could regulate Sertoli cell proliferation. Here we report that p43 depletion in mice increases testis weight and sperm reserve. In addition, we found that p43 deletion increases Sertoli cell proliferation in postnatal testis at 3 days of development. Electron microscopy studies evidence an alteration of mitochondrial morphology observed specifically in Sertoli cells of p43-/- mice. Moreover, gene expression studies indicate that the lack of p43 in testis induced an alteration of the mitochondrial-nuclear cross-talk. In particular, the up-regulation of Cdk4 and c-myc pathway in p43-/- probably explain the extended proliferation recorded in Sertoli cells of these mice. Our finding suggests that T3 limits post-natal Sertoli cell proliferation mainly through its mitochondrial T3 receptor p43.

SynCAM1, a synaptic adhesion molecule, is expressed in astrocytes and contributes to erbB4 receptor-mediated control of female sexual development.

Female sexual maturation requires erythroblastosis B (erbB)4 signaling in hypothalamic astrocytes; however, the mechanisms by which erbB4 contributes to this process are incompletely understood. Here we show that SynCAM1, a synaptic adhesion molecule with signaling capabilities, is not only expressed highly in neurons, but also in hypothalamic astrocytes and is functionally associated with erbB4 receptor activity. Whereas SynCAM1 expression is diminished in astrocytes with impaired erbB4 signaling, ligand-dependent activation of astroglial erbB4 receptors results in rapid association of erbB4 with SynCAM1 and activation of SynCAM1 gene transcription. To determine whether astrocytic SynCAM1-dependent intracellular signaling is required for normal female reproductive function, we generated transgenic mice that express in an astrocyte-specific manner a dominant-negative form of SynCAM1 lacking the intracellular domain. The mutant protein was correctly targeted to the cell membrane and was functionally viable as shown by its ability to block intracellular calcium/calmodulin-dependent serine protein kinase redistribution, a major SynCAM1-mediated event. Dominant-negative-SynCAM1 female mice had a delayed onset of puberty, disrupted estrous cyclicity, and reduced fecundity. These deficits were associated with a reduced capacity of neuregulin-dependent erbB4 receptor activation to elicit prostaglandin E2 release from astrocytes and GnRH release from the hypothalamus. We conclude that one of the mechanisms underlying erbB4 receptor-mediated facilitation of glial-neuronal interactions in the neuroendocrine brain involves SynCAM1-dependent signaling and that this interaction is required for normal female reproductive function.

Early homeostatic disturbances of human growth and maturation by endocrine disrupters.

PURPOSE OF REVIEW: We attempt to delineate and integrate aspects of growth and development that could be affected by endocrine disrupters [endocrine-disrupting compounds (EDC)], an increasing public health concern. RECENT FINDINGS: Epidemiological and experimental data substantiate that fetal and early postnatal life are critical periods of exposure to endocrine disrupters, with possible transgenerational effects. The EDC effects include several disorders of the reproductive system throughout life (abnormalities of sexual differentiation, infertility or subfertility and some neoplasia) and disorders of energy balance (obesity and metabolic syndrome). The mechanisms are consistent with the concept of 'developmental origin of adult disease'. They could involve cross-talk between the factors controlling reproduction and those controlling energy balance, both in the hypothalamus and peripherally. SUMMARY: Due to ubiquity of endocrine disrupters and lifelong stakes of early exposure, individual families should be provided by pediatricians with recommendations following the precautionary principle, that is prevention or attenuation of conditions possibly detrimental to health before the evidence of such adverse effects is complete and undisputable.

Gene expression profiling of hypothalamic hamartomas: a search for genes associated with central precocious puberty.

BACKGROUND: Hypothalamic hamartomas (HHs) are congenital lesions composed of neurons and astroglia. Frequently, HHs cause central precocious puberty (CPP) and/or gelastic seizures. Because HHs might express genes similar to those required for the initiation of normal puberty, we used cDNA arrays to compare the gene expression profile of an HH associated with CPP with three HHs not accompanied by sexual precocity. METHODS: Global changes in gene expression were detected using Affymetrix arrays. The results were confirmed by semiquantitative PCR, which also served to examine the expression of selected genes in the hypothalamus of female monkeys undergoing puberty. RESULTS: All HHs were associated with seizures. Ten genes whose expression was increased in the HH with CPP were identified. They encode proteins involved in three key cellular processes: transcriptional regulation, cell-cell signaling, and cell adhesiveness. They include IA-1 and MEF2A, two transcription factors required for neuronal development; mGluR1 and VILIP-1, which encode proteins involved in neuronal communication, and TSG-6 that encodes a protein involved in cell adhesiveness. Of these, expression of mGluR1 also increases in the female monkey hypothalamus at puberty. CONCLUSIONS: Increased expression of these genes in HHs may be relevant to the ability of some HHs to induce sexual precocity.

Oxytocin facilitates female sexual maturation through a glia-to-neuron signaling pathway.

It has been earlier proposed that oxytocin could play a facilitatory role in the preovulatory LH surge in both rats and humans. We here provide evidence that oxytocin also facilitates sexual maturation in female rats. The administration of an oxytocin antagonist for 6 d to immature female rats decreased GnRH pulse frequency ex vivo and delayed the age at vaginal opening and first estrus. The in vitro reduction in GnRH pulse frequency required chronic blockade of oxytocin receptors, because it was not acutely observed after a single injection of the antagonist. Hypothalamic explants exposed to the antagonist in vitro showed a reduced GnRH pulse frequency and failed to respond to oxytocin with GnRH release. Prostaglandin E(2) (PGE(2)) mimicked the stimulatory effect of oxytocin on GnRH pulse frequency, and inhibition of PG synthesis blocked the effect of oxytocin, suggesting that oxytocin accelerates pulsatile GnRH release via PGE(2). The source of PGE(2) appears to be astrocytes, because oxytocin stimulates PGE(2) release from cultured hypothalamic astrocytes. Moreover, astrocytes express oxytocin receptors, whereas GnRH neurons do not. These results suggest that oxytocin facilitates female sexual development and that this effect is mediated by a mechanism involving glial production of PGE(2).

Mechanisms of interaction of endocrine-disrupting chemicals with glutamate-evoked secretion of gonadotropin-releasing hormone.

In previous studies, we detected a dichlorodiphenyltrichloroethane (DDT) derivative in the serum of children with sexual precocity after migration from developing countries. Recently, we reported that DDT stimulated pulsatile gonadotropin-releasing hormone (GnRH) secretion and sexual maturation in the female rat. The aim of this study was to delineate the mechanisms of interaction of endocrine-disrupting chemicals including DDT with GnRH secretion evoked by glutamate in vitro. Using hypothalamic explants obtained from 15-day-old female rats, estradiol (E2) and DDT caused a concentration-related increase in glutamate-evoked GnRH release while p,p'-dichlorodiphenyldichloroethene and methoxychlor had no effect. The effective DDT concentrations in vitro were consistent with the serum concentrations measured in vivo 5 days after exposure of immature rats to 10 mg/kg/day of o,p'-DDT. Bisphenol A induced some stimulatory effect, whereas no change was observed with 4-nonylphenol. The o,p'-DDT effects in vitro were prevented partially by a selective antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) subtype of glutamate receptors. A complete prevention of o,p'-DDT effects was caused by an estrogen receptor (ER) antagonist as well as an aryl hydrocarbon receptor (AHR) antagonist and inhibitors of protein kinases A and C and mitogen-activated kinases. While an intermittent incubation with E2 caused no change in amplification of the glutamate-evoked GnRH release for 4 h, continuous incubation with E2 or o,p'-DDT caused an increase of this amplification after 3.5 h of incubation. In summary, DDT amplifies the glutamate-evoked GnRH secretion in vitro through rapid and slow effects involving ER, AHR, and AMPA receptor mediation.

Early maturation of gonadotropin-releasing hormone secretion and sexual precocity after exposure of infant female rats to estradiol or dichlorodiphenyltrichloroethane.

An increase in the frequency of pulsatile gonadotropin-releasing hormone (GnRH) secretion in vitro and a reduction in LH response to GnRH in vivo characterize hypothalamic-pituitary maturation before puberty in the female rat. In girls migrating for international adoption, sexual precocity is frequent and could implicate former exposure to the insecticide dichlorodiphenyltrichloroethane (DDT), since a long-lasting DDT derivative has been detected in the serum of such children. We aimed at studying the effects of early transient exposure to estradiol (E(2)) or DDT in vitro and in vivo in the infantile female rat. Using a static incubation system of hypothalamic explants from 15-day-old female rats, a concentration- and time-dependent reduction in GnRH interpulse interval (IPI) was seen during incubation with E(2) and DDT isomers. These effects were prevented by antagonists of alpha-amino-3-hydroxy-5-methylisoxazole-4 propionic acid (AMPA)/kainate receptors and estrogen receptor. Also, o,p'-DDT effects were prevented by an antagonist of the aryl hydrocarbon orphan dioxin receptor (AHR). After subcutaneous injections of E(2) or o,p'-DDT between Postnatal Days (PNDs) 6 and 10, a decreased GnRH IPI was observed on PND 15 as an ex vivo effect. After DDT administration, serum LH levels in response to GnRH were not different from controls on PND 15, whereas they tended to be lower on PND 22. Subsequently, early vaginal opening (VO) and first estrus were observed together with a premature age-related decrease in LH response to GnRH. After prolonged exposure to E(2) between PNDs 6 and 40, VO occurred at an earlier age, but first estrus was delayed. We conclude that a transient exposure to E(2) or o,p'-DDT in early postnatal life is followed by early maturation of pulsatile GnRH secretion and, subsequently, early developmental reduction of LH response to GnRH that are possible mechanisms of the subsequent sexual precocity. The early maturation of pulsatile GnRH secretion could involve effects mediated through estrogen receptor and/or AHR as well as AMPA/kainate subtype of glutamate receptors.

Neuroendocrine mechanisms controlling female puberty: new approaches, new concepts.

Sexual development and mature reproductive function are controlled by a handful of neurones that, located in the basal forebrain, produce the decapeptide luteinizing hormone releasing hormone (LHRH). LHRH is released into the portal system that connects the hypothalamus to the pituitary gland and act on the latter to stimulate the synthesis and release of gonadotrophin hormones. The pubertal activation of LHRH release requires coordinated changes in excitatory and inhibitory inputs to LHRH-secreting neurones. These inputs are provided by both transsynaptic and glia-to-neurone communication pathways. Using cellular and molecular approaches, in combination with transgenic animal models and high-throughput procedures for gene discovery, we are gaining new insight into the basic mechanisms underlying this dual control of LHRH secretion and, hence, the initiation of mammalian puberty. Our results suggest that the initiation of puberty requires reciprocal neurone-glia communication involving excitatory amino acids and growth factors, and the coordinated actions of a group of transcriptional regulators that appear to represent a higher level of control governing the pubertal process.