Hormone Neurons Research Articles

Diminished M Currents Contribute to Hyperactivity of Corticotrophin‐Releasing Hormone Neurons in Acute Stress

AbstractCorticosterone‐releasing hormone (CRH) neuron in the paraventricular nucleus (PVN) of hypothalamus is the essential component of hypothalamic‐pituitary‐adrenal (HPA) axis in regulating endocrine responses to stress. M‐current, generated through KCNQ2/3 channel, plays a key role in controlling neuronal excitability. In this study, we test a hypothesis that acute stress diminishes M currents to stimulate CRH neurons. The adeno‐associated viral (AAV) vector was microinjected into the PVN prior to acute stress, which carries sequence of green fluorescent protein (GFP) driven by CRH promoter. GFP‐tagged CRH neurons displayed positive immunoreactivity with a specific antibody against CRH. Compared to unstressed rats, acute restraint stress significantly elevated serum corticosterone levels; and the basal firing rate of GFP‐tagged CRH neurons was significantly higher in acute restraint rats. Meanwhile blocking KCNQ2/3 with XE991 induced greater depolarization and firing frequency in GFP‐tagged CRH neurons of unstressed rats, but not stressed rats. Furthermore, M‐currents were markedly decreased in PVN‐CRH neurons in acute restraint rats. Acute restraint stress significantly decreased protein and mRNA expression of KCNQ3, but not KCN2 in PVN. Collectively, our data suggest that diminished M current results in hyperactivity of CRH neuron in acute stress.This study was supported by NIMH grants MH096086.

Tumor necrosis factor αlpha impairs kisspeptin signaling in human fetal hypothalamic neurons

Previous studies in both human and animal models have linked overnutrition-related metabolic dysfunctions to hypothalamic inflammation (1, 2). Moreover, metabolic disorders are often associated with male hypogonadotropic hypogonadism, suggesting that inflammatory pathways may impair central regulatory networks involving gonadotropin releasing hormone (GnRH) neuron activity. However, studies in humans are strongly hampered by the anatomical distribution of these neurons, scattered within the preoptic area of the hypothalamus. This study was aimed at investigating the effects of inflammatory stimuli in human fetal hypothalamic (hfHypo) primary cell cultures. These cells have shown evident GnRH neuron features, as demonstrated by quantitative gene expression profile, immunohistochemistry, flow cytometry and ELISA detection of GnRH peptide in the culture medium. Moreover, hfHypo cells express KISS1R and accordingly respond to kisspeptin, the main central regulator of GnRH neuron function. Exposing hfHypo cells to TNFα (10ng/ml, 5h) determined nuclear translocation of NFkB, as well as a significant increase of COX2 mRNA expression, thus demonstrating the induction of inflammatory signaling. Prolonged exposure (24 h) to TNFα strongly down-regulated KISS1R mRNA without changing GnRH expression. Moreover, we know that kisspeptin is able to depolarize GnRH neurons through the activation of a canonical transient receptor potential (TRPC)-like cationic channel. Electrophisiological studies demonstrated that kisspeptin (1 μM) induced a clear TRPC-mediated depolarizing response in hfHypo cells. Pretreating cells with TNFα (10 ng/ml, 24h) significantly inhibited kisspeptin-sensitive TRPC currents. Our results indicate that inflammatory pathways may impair GnRH neuron function by interfering with the ability of these neurons in responding to kisspeptin.

The Ventral Ascending Noradrenergic Bundles Are Involved in the Stress Response to Immobilization in Rats

Stressful stimuli induced by immobilization are perceived as acute stress in rats. This acute stress activates corticotropin-releasing hormone (CRH) neurons in the hypothalamic paraventricular nucleus (PVN), resulting in stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. The ventral ascending noradrenergic bundles (V-NAB) from the brainstem innervate the PVN. To investigate the relationship between the response of the HPA axis and the V-NAB, we examined changes in plasma corticosterone, the final output of the HPA axis, and extracellular noradrenaline (NA) in the PVN following immobilization stress in rats that received bilateral 6-hydroxydopamine (6-OHDA) lesions of the V-NAB. 6-OHDA microinjection into the V-NAB reduced the magnitude of the responses of plasma corticosterone and extracellular NA in the PVN following immobilization stress. Our results suggest that V-NAB innervation of the PVN is involved in immobilization stress-induced activation of the HPA axis.

Identification of neuropeptide receptors expressed by melanin-concentrating hormone neurons.

Melanin-concentrating hormone (MCH) is a 19-amino-acid cyclic neuropeptide that acts in rodents via the MCH receptor 1 (MCHR1) to regulate a wide variety of physiological functions. MCH is produced by a distinct population of neurons located in the lateral hypothalamus (LH) and zona incerta (ZI), but MCHR1 mRNA is widely expressed throughout the brain. The physiological responses and behaviors regulated by the MCH system have been investigated, but less is known about how MCH neurons are regulated. The effects of most classical neurotransmitters on MCH neurons have been studied, but those of most neuropeptides are poorly understood. To gain insight into how neuropeptides regulate the MCH system, we investigated which neuropeptide receptors are expressed by MCH neurons by using double in situ hybridization. In all, 20 receptors, selected based on either a suspected interaction with the MCH system or demonstrated high expression levels in the LH and ZI, were tested to determine whether they are expressed by MCH neurons. Overall, 11 neuropeptide receptors were found to exhibit significant colocalization with MCH neurons: nociceptin/orphanin FQ opioid receptor (NOP), MCHR1, both orexin receptors (ORX), somatostatin receptors 1 and 2 (SSTR1, SSTR2), kisspeptin recepotor (KissR1), neurotensin receptor 1 (NTSR1), neuropeptide S receptor (NPSR), cholecystokinin receptor A (CCKAR), and the κ-opioid receptor (KOR). Among these receptors, six have never before been linked to the MCH system. Surprisingly, several receptors thought to regulate MCH neurons displayed minimal colocalization with MCH, suggesting that they may not directly regulate the MCH system.

Identification of corticotropin‐releasing hormone neurons in paraventricular nucleus in rats (876.6)

Corticotropin‐releasing factor (CRH) neurons in the paraventricular nucleus (PVN) are the essential component of the hypothalamus‐pituitary‐adrenal axis play a critical role in the regulation of autonomic, endocrine and behavioral responses to stress. Assessment of the CRH neurons provides valuable information on cellular mechanisms during physiological and disease process. However, CRH neurons in the rats cannot be reliably identified in live tissues since the identification of CRH neurons requires neuronal labeling and post‐mortem immunohistochemistry. To efficiently identifying CRH neurons in live tissue, we constructed a CRH promoter‐GFP plasmid and integrated this sequence into an adeno‐associated virus (AAV) vector. This AAV‐CRH promoter‐GFP vector was delivered into the rat PVN through microinjection (100 nl). The hypothalamic slices containing GFP‐tagged neurons was immunostained with a specific antibody against CRH. We found that 76.4% CRH immunoreactivity positive PVN neurons colocalized with GFP and 92.8% GFP‐tagged PVN neurons expressed CRH immunoreactivity. Whole‐cell recordings were performed on these GFP‐tagged CRH neurons in hypothalamic slice to assess their electrophysiological properties. Therefore, this AAV‐CRH‐GFP reliably targets CRH neurons in rat brain for in vitro assessment.Grant Funding Source: NIH: MH096086

Roles for Primary Cilia in Gonadotrophin‐Releasing Hormone Neurones in the Mouse

During embryonic development, gonadotrophin-releasing hormone (GnRH) neurones make an extraordinary migration out of the nose and into the brain where, in adulthood, they drive the pituitary regulation of gonadal function and fertility. Primary cilia are antennae-like, immotile organelles that project from the surface of nearly all cells, including GnRH neurones. Links between defects in primary cilia and a variety of human pathologies have been discovered that suggest a role for primary cilia in embryogenesis and reproductive function. The present study aimed to investigate whether GnRH neurone primary cilia are critical for their embryonic migration and the adult control of fertility. To achieve this, we used a Cre-loxP strategy to selectively disrupt primary cilia by deleting Kif3a, an intraflagellar transport protein family member essential for primary cilia assembly and function, specifically in GnRH neurones. Confocal analysis revealed that, in Kif3a(fl/fl) (WT-Kif3a) controls, all GnRH neurones possessed primary cilia, whereas, in GnRH-Cre(+/-) ;Kif3a(fl/fl) (GnRH-Kif3aKO) mice, 60% of GnRH neurones lacked any evidence of primary cilia and the remaining 40% possessed only stunted primary cilia (< 2 μm). Despite abolishing normal primary cilia assembly in GnRH neurones from embryogenesis, adult GnRH neurone distribution and reproductive function was remarkably normal. The total number of GnRH neurones was the same in GnRH-Kif3aKO and WT-Kif3a controls; however, a significant increase (25%) was identified in the number of GnRH neurones sampled through the midpoint of the rostral pre-optic area in GnRH-Kif3aKO mice (P < 0.05). The time to vaginal opening was not different in GnRH-Kif3aKO mice, although they displayed significantly advanced first oestrus (P < 0.05), and oestrous cycle length was increased (P < 0.05). However, females displayed normal basal levels of luteinising hormone, responded normally to oestrogen-induced negative- and positive-feedback, and displayed normal fecundity. Taken together, these data suggest that primary cilia and associated signal transduction pathways play a role in the topographical distribution and specific functions of GnRH neurones; however, they are not essential for fertility.

Gender-specific DNA methylome analysis of a Han Chinese longevity population.

Human longevity is always a biological hotspot and so much effort has been devoted to identifying genes and genetic variations associated with longer lives. Most of the demographic studies have highlighted that females have a longer life span than males. The reasons for this are not entirely clear. In this study, we carried out a pool-based, epigenome-wide investigation of DNA methylation profiles in male and female nonagenarians/centenarians using the Illumina 450 K Methylation Beadchip assays. Although no significant difference was detected for the average methylation levels of examined CpGs (or probes) between male and female samples, a significant number of differentially methylated probes (DMPs) were identified, which appeared to be enriched in certain chromosome regions and certain parts of genes. Further analysis of DMP-containing genes (named DMGs) revealed that almost all of them are solely hypermethylated or hypomethylated. Functional enrichment analysis of these DMGs indicated that DNA hypermethylation and hypomethylation may regulate genes involved in different biological processes, such as hormone regulation, neuron projection, and disease-related pathways. This is the first effort to explore the gender-based methylome difference in nonagenarians/centenarians, which may provide new insights into the complex mechanism of longevity gender gap of human beings.

Kallmann’s Syndrome: A Rare Cause of Primary Amenorrhoea

Kallmann syndrome is a very rare hereditary disease. It is characterized by hypogonadotropic hypogonadism in association with anosmia ot hyposmia, both of which occur as a result of impairment of olfactory axon development and failure of migration of gonadotropin-releasing hormone (GnRH) neurons. Mode of inheritance can be autosomal dominant, autosomal recessive, or X-linked. We report a case of Kallmann syndrome in an 18 year old girl who presented with primary amenorrhoea, poor sexual development with poor sense of smell and colour blindness. Plasma levels of LH, FSH and oestradiol were very low. The patient’s other pituitary hormone levels were normal. Chromosome analysis showed 46, XX karyotype. USG of lower abdomen confirmed presence of uterus and ovaries. MRI of brain showed olfactory bulbs to be present and there was no pituitary or hypothalamic lesion. We present this case for its very rare occurrence in the eastern part of the world and the typical feature being normal MRI brain with functional defect of the olfactory pathway. Treatment was started with cyclic conjugated oestrogen and progestin. Our patient is now on regular follow-up to monitor response to treatment.

Neural and Behavioral Developmental Toxicity of the Plasticizer DEHP

Di-(2-ethylhexyl) phthalate (DEHP) is an environmental endocrine disruptor that possesses weak estrogenic and anti-androgenic activity. Humans and wildlife exposed to DEHP lifetime through different channels. Maternal DEHP can be transferred either to the fetus across the placenta during pregnancy, or to the nursing infant through breast milk during lactation. Perinatal DEHP exposure can interfere with the effect of estrogen on brain development through sex-specifically changing the activities of aromatase enzyme and estrogen receptor in hypothalamic preoptic area of rat offspring. DEHP and its metabolites affect the proliferation and differentiation of neurons, synapse formation, and the regulatory effects of amino acid neurotransmitters system on gonadotropin releasing hormone (GnRH) neurons which are modulated by sexual hormones. DEHP affects the development of dopamine neurotransmitter system of the midbrain and induces motor hyperactivity. These effects of DEHP ultimately lead to abnormal development of behaviors such as early behavior, learning and memory, and emotional behavior of animal.

Genistein Excitation of Gonadotrophin‐Releasing Hormone Neurones in Juvenile Female Mice

We investigated the effects of the phytoestrogen genistein on gonadotrophin-releasing hormone (GnRH) neurones using single-cell electrophysiology on GnRH-green fluorescent protein (GFP) transgenic juvenile female mice. Perforated patch-clamp recordings from GnRH-GFP neurones showed that approximately 83% of GnRH neurones responded to 30 μm genistein with a markedly prolonged membrane depolarisation. This effect not only persisted in the presence of tetrodotoxin, but also in the presence of amino acid receptor antagonists, indicating the direct site of action on postsynaptic GnRH neurones. Using a voltage clamp technique, we found that 30 μm genistein increased the frequency of synaptic current of GnRH neurones clamped at -60 mV in the presence of glutamate receptor blocker but not GABAA receptor blocker. Pre-incubation of GnRH neurones with 30 μm genistein enhanced kisspeptin-induced membrane depolarisation and firing. GnRH neurones of juvenile mice injected with genistein in vivo showed an enhanced kisspeptin response compared to vehicle-injected controls. The transient receptor potential channel (TRPC) blocker 2-aminoethoxydiphenyl borate (75 μm) blocked the genistein-mediated response on GnRH neurones. These results demonstrate that genistein acts on GnRH neurones in juvenile female mice to induce excitation via GABA neurotransmission and TRPCs to enhance kisspeptin-induced activation.

A Network Model of the Periodic Synchronization Process in the Dynamics of Calcium Concentration in GnRH Neurons

Mathematical neuroendocrinology is a branch of mathematical neurosciences that is specifically interested in endocrine neurons, which have the uncommon ability of secreting neurohormones into the blood. One of the most striking features of neuroendocrine networks is their ability to exhibit very slow rhythms of neurosecretion, on the order of one or several hours. A prototypical instance is that of the pulsatile secretion pattern of GnRH (gonadotropin releasing hormone), the master hormone controlling the reproductive function, whose origin remains a puzzle issue since its discovery in the seventies. In this paper, we investigate the question of GnRH neuron synchronization on a mesoscopic scale, and study how synchronized events in calcium dynamics can arise from the average electric activity of individual neurons. We use as reference seminal experiments performed on embryonic GnRH neurons from rhesus monkeys, where calcium imaging series were recorded simultaneously in tens of neurons, and which have clearly shown the occurrence of synchronized calcium peaks associated with GnRH pulses, superposed on asynchronous, yet oscillatory individual background dynamics. We design a network model by coupling 3D individual dynamics of FitzHugh–Nagumo type. Using phase-plane analysis, we constrain the model behavior so that it meets qualitative and quantitative specifications derived from the experiments, including the precise control of the frequency of the synchronization episodes. In particular, we show how the time scales of the model can be tuned to fit the individual and synchronized time scales of the experiments. Finally, we illustrate the ability of the model to reproduce additional experimental observations, such as partial recruitment of cells within the synchronization process or the occurrence of doublets of synchronization.

Lateral hypothalamic GAD65 neurons are spontaneously firing and distinct from orexin‐ and melanin‐concentrating hormone neurons

GABAergic neurons are vital for brain function. Their neurochemical and electrical features have been classically characterized in the cortex, but in the lateral hypothalamic area (LHA), such knowledge is lacking, despite the emerging roles of LHA GABAergic cells in feeding and sleep. We used GAD65-GFP transgenic mice, developed for studies of cortical GABAergic cells, to determine fundamental properties of LHA GAD65 neurons, and compare them to 'classical' GABAergic cell types of the cortex, and to previously described classes of LHA cells. Whole-cell patch-clamp recordings in acute brain slices revealed that, unlike cortical GABAergic interneurons, LHA GAD65 neurons were intrinsically depolarized and fired action potentials spontaneously. Similar to cortical GABAergic cells, LHA GAD65 cells fell into four major subtypes based on evoked firing: fast spiking, late spiking, low threshold spiking and regular spiking. Three-dimensional reconstructions of biocytin-filled neurons, performed after the patch-clamp analysis, did not reveal striking morphological differences between these electrophysiological subtypes. Peptide transmitters expressed in known classes of LHA projection neurons, namely melanin-concentrating hormone (MCH) and hypocretin/orexin (hcrt/orx), were not detected in LHA GAD65 cells. Approximately 40% of LHA GAD65 cells were directly inhibited by physiological increases in extracellular glucose concentration. Glucose inhibition was most prevalent in the fast spiking subpopulation, although some glucose-responsive neurons were found in each electrophysiological subpopulation. These results suggest that LHA GAD65 neurons are electrically different from 'classical' GABAergic neurons of the cortex, are neurochemically distinct from LHA hcrt/orx and MCH cells, but partly resemble hcrt/orx cells in their glucose responses.

From Precocious Puberty to Infertility: Metabolic Control of the Reproductive Function

From Precocious Puberty to Infertility: Metabolic Control of the Reproductive Function

Effects of Nourishing “Yin”-Removing “Fire” Chinese Herb Mixture on the Differential Expression of GABA&amp;lt;sub&amp;gt;A&amp;lt;/sub&amp;gt; Receptor &amp;lt;i&amp;gt;α&amp;lt;/i&amp;gt; Subunits in Hypothalamus of Precocious Puberty Female Rats

GABAergic input to Gonadotropin-releasing hormone (GnRH) neurons is necessary to initiate the onset of puberty and its action mainly depends on GABAA receptor of which the subunit composition, properties and consequently function varies during this period. Nourishing “Yin”-Removing “Fire” Chinese herb mixture, a Chinese herb-based formulation, has been proved that it may retard the initiation of pubertal development in female precocious puberty rats. Our objective is to investigate the effects of Nourishing “Yin”-Removing “Fire” Chinese herb mixture on the expression of GABAA receptor α subunits in hypothalamus. Female Sprague-Dawley rats were divided into normal (N), precocious puberty model (M) induced by danazol, model exposed to saline (MS) and model exposed to Chinese herb mixture (CHM) groups. All rats were administered by the Chinese herb mixture from P15 on. Coefficients of reproductive organs and serum gonadotropins and estradiol levels in M were significantly enhanced while they were significantly decreased in CHM. The hypothalamic GnRH mRNA was also significantly increased in M and in CHM, as well as ERα mRNA. At the mean time, the hypothalamic GABAA receptor α1 and α3 subunits mRNA were more significantly decreased in M than those of N, while they were more significantly enhanced in CHM than those in M (p 0.01), the protein expression of which in hypothalamus had the same trend as the mRNA expression. The evidence suggests that Nourishing “Yin”-Removing “Fire” Chinese herb mixture could significantly retard the sexual development of the precocious rats, and up-regulate the expressions of hypothalamic GABAA receptor α1 and α3 subunits. Our result indicated that GABAA receptor α1 and α3 subunits might involve in the effective treatment of herb mixture on idiopathic precocious puberty.

Aromatase Knockout Mice Show Normal Steroid‐Induced Activation of Gonadotrophin‐Releasing Hormone Neurones and Luteinising Hormone Surges With a Reduced Population of Kisspeptin Neurones in the Rostral Hypothalamus

We recently reported that female aromatase knockout (ArKO) mice show deficits in sexual behaviour and a decreased population of kisspeptin-immunoreactive neurones in the rostral periventricular area of the third ventricle (RP3V), resurrecting the question of whether oestradiol actively contributes to female-typical sexual differentiation. To further address this question, we assessed the capacity of ArKO mice to generate a steroid-induced luteinising hormone (LH) surge. Adult, gonadectomised wild-type (WT) and ArKO mice were given silastic oestradiol implants s.c. and, 1 week later, received s.c. injections of either oestradiol benzoate (EB) followed by progesterone, EB alone, or no additional steroids to activate gonadotrophin-releasing hormone (GnRH) neurones and generate an LH surge. Treatment with EB and progesterone induced significant Fos/GnRH double-labelling and, consequently, an LH surge in female WT and in ArKO mice of both sexes but not in male WT mice. ArKO mice of both sexes had fewer cells expressing Kiss-1 mRNA in the RP3V compared to female WT mice but had more Kiss-1 mRNA-expressing cells compared to WT males, reflecting an incomplete sexual differentiation of this system. To determine the number of cells expressing kisspeptin, the same experimental design was repeated in Experiment 2 with the addition of groups of WT and ArKO mice that were given EB + progesterone and sacrificed 2 h before the expected LH surge. No differences were observed in the number of kisspeptin-immunoreactive cells 2 h before and at the time of the LH surge. The finding that ArKO mice of both sexes have a competent LH surge system suggests that oestradiol has predominantly defeminising actions on the GnRH/LH surge system in males and that the steroid-induced LH surge can occur in females even with a greatly reduced population of kisspeptin neurones in the RP3V.

Two Types of Burst Firing in Gonadotrophin‐Releasing Hormone Neurones

Gonadotrophin-releasing hormone (GnRH) neurones fire spontaneous bursts of action potentials, although little is understood about the underlying mechanisms. In the present study, we report evidence for two types of bursting/oscillation driven by different mechanisms. Properties of these different types are clarified using mathematical modelling and a recently developed active-phase/silent-phase correlation technique. The first type of GnRH neurone (1-2%) exhibits slow (∼0.05 Hz) spontaneous oscillations in membrane potential. Action potential bursts are often observed during oscillation depolarisation, although some oscillations were entirely subthreshold. Oscillations persist after blockade of fast sodium channels with tetrodotoxin (TTX) and blocking receptors for ionotropic fast synaptic transmission, indicating that they are intrinsically generated. In the second type of GnRH neurone, bursts were irregular and TTX caused a stable membrane potential. The two types of bursting cells exhibited distinct active-phase/silent-phase correlation patterns, which is suggestive of distinct mechanisms underlying the rhythms. Further studies of type 1 oscillating cells revealed that the oscillation period was not affected by current or voltage steps, although amplitude was sometimes damped. Oestradiol, an important feedback regulator of GnRH neuronal activity, acutely and markedly altered oscillations, specifically depolarising the oscillation nadir and initiating or increasing firing. Blocking calcium-activated potassium channels, which are rapidly reduced by oestradiol, had a similar effect on oscillations. Kisspeptin, a potent activator of GnRH neurones, translated the oscillation to more depolarised potentials, without altering period or amplitude. These data show that there are at least two distinct types of GnRH neurone bursting patterns with different underlying mechanisms.

Immunofluorescent histochemical and ultrastructural studies on the innervation of kisspeptin/neurokinin B neurons to tuberoinfundibular dopaminergic neurons in the arcuate nucleus of rats

Kisspeptin is a pivotal regulator of the onset of puberty and the estrus cycle, but may also take part in pregnancy and lactation. Kisspeptin neurons and their fibers are distributed abundantly throughout the arcuate nucleus (ARC) of the hypothalamus, but the targets of the fiber projections in the ARC have not been fully investigated. The present study followed the projection of kisspeptin fibers to tuberoinfundibular dopaminergic (TIDA) neurons in the ARC, pivotal endocrine neurons that control prolactin secretion. Immunoreactive fibers of kisspeptin or neurokinin B, a peptide coexpressed in kisspeptin neurons, were abundantly found adjacent to TIDA neurons in female rats, but few were observed in male rats. The immunoreactivities of both peptides adjacent to TIDA neurons were significantly reduced in estradiol-primed ovariectomized rats. Precise 3D analysis of the attachment of kisspeptin-immunoreactive fibers to TIDA neurons was achieved using a synaptic marker that indicated synaptic connection. Finally, double-labeling immunoelectron microscopy confirmed the synaptic connections of kisspeptin-immunoreactive fibers to the cell body and fibers of TIDA neurons. These findings indicate that in female rats, kisspeptin/NKB fibers may directly affect TIDA neurons that regulate prolactin secretion, and that they are more likely to be activated during low estradiol status.

Kisspeptins and the control of gonadotrophin secretion

Kisspeptins, the peptide products of the KiSS-1 gene, bind to the G protein coupled receptor 54 (GPR54). Since 2003, research has revealed the important role of kisspeptins in initiating puberty, timing puberty and regulating fertility in adulthood. Specific mutations in GPR54 gene cause either delayed/absent puberty or precocious puberty. The KiSS-1/GPR54 system stimulates the gonadotrophin releasing hormone (GnRH) neurons and is involved in the feedback regulation of the HPG axis by gonadal steroids. Different hypothalamic nuclei are involved in negative (arcuate nucleus; ARC) and positive (anteroventral periventricular nucleus; AVPV) feedback in mice. Continuous administration of kisspeptins down-regulates the HPG axis. During pregnancy, kisspeptins are secreted from the placenta in large amounts and are responsible for the physiological invasion of primary human trophoblast. Kisspeptins have been administered to normal male and female individuals as well as to women with hypothalamic secondary amenorrhoea. In all cases, gonadotrophin secretion was potently stimulated. Kisspeptin antagonists have been synthesized to successfully suppress GnRH and gonadotrophin release. These agonists and antagonists appear as valuable new tools for manipulating the HPG axis and are promising drugs for future treatment. The scope of this review highlights the role of kisspeptins in regulating gonadotrophin secretion and explores their possible therapeutic use.

Differential involvement of noradrenaline and nitric oxide in the regulation of vasopressin and oxytocin expression in rat supraoptic nucleus

The hydroosmotic balance of the body is controlled by supraoptic nuclei and paraventricular nuclei of the hypothalamo-posthypophyseal complex. In response to a physiological stimulation such as an osmotic stress, the supraoptic nuclei (SON) and the paraventricular nuclei undergo remarkable neurochemical and morphological changes. Therefore, the neuroendocrine hypothalamus is a particularly relevant model for studying the molecular and cellular mechanisms that govern these plasticity phenomena. Slices of rat hypothalamus maintained ex vivo by perfusion were used to study the short-term involvement of noradrenaline (NA) and nitric oxide (NO) in the mechanisms of chemical plasticity of the SON. NA is involved early in the regulation of the expression of neuropeptides, including vasopressin (AVP) and oxytocin (OT). NO appears to be a key molecule in noradrenergic control of the chemical plasticity of the endocrine neurons: in the SON, NO is involved in the signaling pathway regulating the expression of AVP but not that of OT.

The intimate relationship of gonadotropin‐releasing hormone neurons with the polysialylated neural cell adhesion molecule revisited across development and adult plasticity

The neurohormone gonadotropin-releasing hormone (GnRH) is critical for all the aspects of reproductive life in vertebrates. GnRH is secreted by a small number of neurons dispersed within the preoptic-hypothalamic region. These neurons are derived from the embryonic olfactory pit. They then migrate along olfactory, vomeronasal and terminal nerves to their final destination. Classical approaches to study the regulation of GnRH secretion during the reproductive cycle have focused on the various neuronal inputs on GnRH neurons and their regulation by ovarian steroids. However, it is well known that steroids will change the microenvironment of neuronal networks and can induce plasticity and functional changes. In this review, we will focus on the intimate relationship of developing and adult GnRH neurons with the polysialylated form of neural cell adhesion molecule (PSA-NCAM), a major molecular actor in the morphogenesis and adult plasticity of the nervous system. We will first recapitulate the spatiotemporal relationship between PSA-NCAM and migrating GnRH neurons during embryogenesis of various vertebrate species and discuss its importance for GnRH neuron development as shown by various loss of function studies. In the adult, we will review the relationships between PSA-NCAM and GnRH neurons across various physiological states, and open the discussion to the use of new model systems that can help to unravel the function and mechanism of action of PSA-NCAM on GnRH neuronal network activity and GnRH release.