Afferent Neuronal Control of Type-I Gonadotropin Releasing Hormone Neurons in the Human.

Understanding the regulation of the human menstrual cycle represents an important ultimate challenge of reproductive neuroendocrine research. However, direct translation of information from laboratory animal experiments to the human is often complicated by strikingly different and unique reproductive strategies and central regulatory mechanisms that can be present in even closely related animal species. In all mammals studied so far, type-I gonadotropin releasing hormone (GnRH) synthesizing neurons form the final common output way from the hypothalamus in the neuroendocrine control of the adenohypophysis. Under various physiological and pathological conditions, hormonal and metabolic signals either regulate GnRH neurons directly or act on upstream neuronal circuitries to influence the pattern of pulsatile GnRH secretion into the hypophysial portal circulation. Neuronal afferents to GnRH cells convey important metabolic-, stress-, sex steroid-, lactational-, and circadian signals to the reproductive axis, among other effects. This article gives an overview of the available neuroanatomical literature that described the afferent regulation of human GnRH neurons by peptidergic, monoaminergic, and amino acidergic neuronal systems. Recent studies of human genetics provided evidence that central peptidergic signaling by kisspeptins and neurokinin B (NKB) play particularly important roles in puberty onset and later, in the sex steroid-dependent feedback regulation of GnRH neurons. This review article places special emphasis on the topographic distribution, sexual dimorphism, aging-dependent neuroanatomical changes, and plastic connectivity to GnRH neurons of the critically important human hypothalamic kisspeptin and NKB systems

Neuroanatomy of the human hypothalamic kisspeptin system.

Hypothalamic kisspeptin (KP) neurons are key players in the neuronal network that regulates the onset of puberty and the pulsatile secretion of gonadotropin-releasing hormone (GnRH). In various mammalian species, the majority of KP-synthesizing neurons are concentrated in two distinct cell populations in the preoptic region and the arcuate nucleus (ARC). While studies of female rodents have provided evidence that preoptic KP neurons play a critical sex-specific role in positive estrogen feedback, KP neurons of the ARC have been implicated in negative sex steroid feedback and they have also been hypothesized to contribute to the pulse generator network which regulates episodic GnRH secretion in both females and males. Except for relatively few morphological studies available in monkeys and humans, our neuroanatomical knowledge of the hypothalamic KP systems is predominantly based on observations of laboratory species which are phylogenetically distant from the human. This review article discusses the currently available literature on the topographic distribution, network connectivity, neurochemistry, sexual dimorphism, and aging-dependent morphological plasticity of the human hypothalamic KP neuronal system

A beta-típusú ösztrogén receptor szerepe LHRH sejtek működésének szabályozásában = The role of beta estrogen receptor in the regulation of LHRH cells

A pályázatban meghatározott célok az 1996-ban felfedezett, béta ösztrogén receptor altípus (ER-) emlős reprodukcióban játszott szerepének megértését célozták. A pályázat támogatásával végzett in situ hibridizációs és immuncitokémiai vizsgálatok felfedték a receptor regionális eloszlását és előfordulását a patkány és a humán hipotalamusz több fontos neuroszekretoros rendszerében, köztük a luteinizing-hormone-releasing hormon (LHRH), oxitocin és vazopresszin tartalmú neuronrendszerekben. Egyik fő eredményként, igazoltuk, hogy az ER- szelektíven fordul elő az emberi LHRH neuronokban is, hasonlóan a korábban általunk patkányban megfigyeltekkel. A pályázat támogatásával megkezdett, és jelenleg is folyó in vivo vizsgálatsorozat egyik fő célja az ER- által közvetített specifikus genomikus hatások azonosítása, különös tekintettel az ER- LHRH idegsejteken érvényesülő, pozitív és negatív ösztrogén-visszacsatolás jelenségeiben játszott szerepére. | The long-term goal of the proposed research was to gain a better understanding of the role of the beta estrogen receptor isoform (ER-), discovered in 1996, in mammalian reproduction. In situ hybridization and immunocytochemical studies supported by this grant revealed the regional distribution of this receptor both in the rodent and human hypothalami, including its occurrence in several important neurosecretory systems, such as oxytocin and vasopressin neurons of the paraventricular and supraoptic nuclei and luteinizing hormone-releasing hormone (LHRH) neurons of the preoptic area. One of the main achievements was to prove the selective occurrence of the ER- estrogen receptor isoform in human LHRH neurons, a finding reminiscent to previous data we obtained in the rodent brain. A series of ongoing in vivo experiments, which had been started with this grant support, is aimed at identifying the specific genomic effects exerted through ER-, with a particular emphasis on its contribution to the phenomena of positive and negative estrogen feedback upon LHRH neurons

Endogén glutamát jelentősége neuroendokrin rendszerek szabályozásában = Role of endogenous glutamate in the regulation of neurosecretory systems

A kutatási támogatás segítségével a kutatócsoport tanulmányozta és feltérképezte az átvivőanyagként glutamátot használó (vezikuláris glutamát transzportereket tartalmazó) idegsejtek pontos anatómiai megoszlását rágcsálók hipotalamuszában. Leírta ezen glutamáterg idegsejtek részvételét az emberi hipotalamusz, és ezen belül, az emberi szaporodást irányító GnRH idegsejtek beidegzésében. Igazolta glutamáterg idegi fenotípus jegyeinek meglétét a szuprakiazmatikus mag egy elszórt neuron populációjában, továbbá korábban peptidergként megismert olyan neuronrendszerekben, melyek az agyalapi mirigy mellső és hátsó lebenyének működését szabályozzák. Tanulmányozta és endokrin fenotípus szerint azonosította a mellső hipofízis hámsejtjeiben is a glutamáterg neuronokra jellemző VGLUT1 és VGLUT2 enzim izoformákat és vizsgálta azok termelődésének szabályozását endokrin állatmodelleken. Elektronmikroszkópos vizsgálatokkal megállapította, hogy míg a neuroendokrin rendszerekben a VGLUT2 marker enzim mikrovezikulákhoz asszociált, addig az agyalapi mirigy mellső lebenyének hámsejtjeiben szekretoros granulumokban fordul elő. In situ hibridizáció használatával részletesen feltérképezte az egér hipotalamuszában az endokannabinoid érzékeny glutamáterg és GABAerg idegsejtek megoszlását. A projekthez kapcsolódó egyéb tanulmányokban új eredményeket szolgáltatott a reprodukció és az ösztrogén szignalizáció hipotalamikus és agykérgi mechanizmusainak jobb megértéséhez is. | Using this grant support, the research group described the topographic distribution of neurons that use glutamate (and contain one of the two major isoforms of vesicular glutamate transporter enzymes, VGLUT1 and VGLUT2) as synaptic transmitter in the rodent hypothalamus. They described the contribution of glutamatergic neurons to the innervation of the human hypothalamus and specifically, its GnRH neurons. They provided evidence for the occurrence of scattered glutamatergic neurons in the suprachiasmatic nucleus and in parvi- and magnocellular neurons known to regulate the anterior and posterior pituitary lobes solely via peptidergic mechanisms. They characterized epithelial cells in the anterior pituitary that express the VGLUT1 and VGLUT2 enzyme isoforms and studied the regulation of these enzymes under different endocrine challenges. They used electron microscopy and established that the glutamatergic marker enzyme VGLUT2 is associated with small-clear synaptic vesicles in neuroendocrine neuronal cells of the hypothalamus and with dense-core vesicles in glutamatergic endothelial cells of the adenohypophysis. They provided a detalied in situ hybridization map on the distribution of endocannabinoid-sensitive (CB1 mRNA expressing) hypothalamic neurons that exhibit glutamatergic and GABAergic phenotypes. In other studies linked to the project they provided new data about the regulation of reproduction and about estrogen signaling in the hypothalamus and the cerebral cortex

A simple integrative electrophysiological model of bursting GnRH neurons

In this paper a modular model of the GnRH neuron is presented. For the aim of simplicity, the currents corresponding to fast time scales and action potential generation are described by an impulsive system, while the slower currents and calcium dynamics are described by usual ordinary differential equations (ODEs). The model is able to reproduce the depolarizing afterpotentials, afterhyperpolarization, periodic bursting behavior and the corresponding calcium transients observed in the case of GnRH neurons

New perspectives for anatomical and molecular studies of kisspeptin neurons in the aging human brain

The human infundibular nucleus (corresponding to the rodent arcuate nucleus) serves as an important integration center for neuronal signals and hormones released by peripheral endocrine organs. Kisspeptin (KP) producing neurons of this anatomical site many of which also synthesize neurokinin B (NKB) are critically involved in sex hormone signaling to gonadotropin-releasing homone (GnRH) neurons. In recent years, the basic topography, morphology, neuropeptide content and connectivity of human KP neurons have been investigated with in situ hybridization and immunohistochemistry on post mortem tissues. These studies revealed that human KP neurons differ neurochemically from their rodent counterparts and show robust aging-related plasticity. Earlier immunohistochemical experiments also provided evidence for temporal changes in the hypothalamus of aging men whose NKB and KP neurons undergo hypertrophy, increase in number, exhibit increased neuropeptide mRNA expression and immunoreactivity and give rise to higher numbers of immunoreactive fibers and afferent contacts onto GnRH neurons. Increasing percentages of KP-expressing NKB perikarya, NKB axons and NKB inputs to GnRH neurons raise the intriguing possibility that a significant subset of NKB neurons begins to co-synthesize KP as aging proceeds. Although use of post mortem tissues is technically challenging, recently-available single-cell anatomical and molecular approaches discussed in this review article provide promising new tools to investigate the aging-related anatomical and functional plasticity of the human KP neuronal system.

Ovariectomy and Subsequent Treatment with Estrogen Receptor Agonists Tune the Innate Immune System of the Hippocampus in Middle-Aged Female Rats

The innate immune system including microglia has a major contribution to maintenance of the physiological functions of the hippocampus by permanent monitoring of the neural milieu and elimination of tissue-damaging threats. The hippocampus is vulnerable to age-related changes ranging from gene expression to network connectivity. The risk of hippocampal deterioration increases with the decline of gonadal hormone supply. To explore the impact of hormone milieu on the function of the innate immune system in middle-aged female rats, we compared mRNA expression in the hippocampus after gonadal hormone withdrawal, with or without subsequent estrogen replacement using estradiol and isotype-selective estrogen receptor (ER) agonists. Targeted profiling assessed the status of the innate immune system (macrophage-associated receptors, complement, inhibitory neuronal ligands), local estradiol synthesis (P450 aromatase) and estrogen reception (ER). Results established upregulation of macrophage-associated (Cd45, Iba1, Cd68, Cd11b, Cd18, Fcgr1a, Fcgr2b) and complement (C3, factor B, properdin) genes in response to ovariectomy. Ovariectomy upregulated Cd22 and downregulated semaphorin3A (Sema3a) expression, indicating altered neuronal regulation of microglia. Ovariectomy also led to downregulation of aromatase and upregulation of ERa gene. Of note, analogous changes were observed in the hippocampus of postmenopausal women. In ovariectomized rats, estradiol replacement attenuated Iba1, Cd11b, Fcgr1a, C3, increased mannose receptor Mrc1, Cd163 and reversed Sema3a expression. In contrast, reduced expression of aromatase was not reversed by estradiol. While the effects of ERa agonist closely resembled those of estradiol, ERb agonist was also capable of attenuating the expression of several macrophage-associated and complement genes. These data together indicate that the innate immune system of the aging hippocampus is highly responsive to the gonadal hormone milieu. In ovariectomized female rats, estradiol replacement exerts potent immunomodulatory effects including attenuation of microglia sensitization, initiation of M2-like activation and modulation of complement expression by targeting hippocampal neurons and glial cells through ERa and ERb

Ovariectomy Alters Gene Expression of the Hippocampal Formation in Middle-Aged Rats

Ovarian hormones regulate the transcriptome of the hippocampus and modulate its functions. During 29 menopause, this complex signaling declines, leading to impaired learning and memory. This study was 30 undertaken to clarify the effects of long-term, surgical ovariectomy (OVX) on the rat hippocampal 31 transcriptome. At age of 13 months, intact control and ovariectomized groups were formed. All animals 32 were sacrificed 5 weeks after gonadectomy, hippocampal formations were dissected and processed for 33 transcriptome analysis. Microarray and PCR studies identified 252 and 61 genes, respectively, whose 34 expression was altered in the lack of ovarian hormones. Pathway analysis revealed impact on 35 neuroactive ligand-receptor interaction, endocannabinoid and estrogen signaling, among others. 36 Network and interaction analyses of proteins encoded by OVX-regulated genes revealed upregulation 37 of growth/ troph/transcription factor signaling assembly (Mdk, Fgf1, Igf2, Ngf, Ngfr, Ntf3, Ntrk1, Otx2, 38 Hif1a, Esr1, Nr4a3), peptides/peptide receptors (Cartp, Kl, Ttr, Gnrhr), neurotransmission (Grm1, 39 Gria4, Gls, Slc18a2, Kcj6) and genes serving immune functions (C3, Ccl2, Itgam, Il1b). Downregulated 40 clusters included neuropeptides and their receptors (Adcyap1, Cbln2, Cck, Cckbr, Crhr1 and 2, Oprd1, 41 Nts, Penk, Sstr1, Vip), neurotransmitter signaling (Htr2c, hrna3, Chrm4, Grm8, Hrh3, Slc17a6) and 42 potassium channels (Kcnk9, Kcnj9, Kcnma1, Kcnc2). Several transcription factors (Rxra, Thrb), solute 43 carriers and defense molecules (Apitd1, Bcl2, Clql3, Ilr3a, Sod1, Sncb) also underwent downregulation. 44 The findings indicate that surgical gonadectomy carried out at middle-age robustly changes the 45 hippocampal transcriptome that alters neurogenesis, synaptic plasticity, immune modulation causing 46 cognitive dysfunctions

Menopause leads to elevated expression of macrophage-associated genes in the aging frontal cortex: rat and human studies identify strikingly similar changes.

BACKGROUND The intricate interactions between the immune, endocrine and central nervous systems shape the innate immune response of the brain. We have previously shown that estradiol suppresses expression of immune genes in the frontal cortex of middle-aged ovariectomized rats, but not in young ones reflecting elevated expression of these genes in middle-aged, ovarian hormone deficient animals. Here, we explored the impact of menopause on the microglia phenotype capitalizing on the differential expression of macrophage-associated genes in quiescent and activated microglia. METHODS We selected twenty-three genes encoding phagocytic and recognition receptors expressed primarily in microglia, and eleven proinflammatory genes and followed their expression in the rat frontal cortex by real-time PCR. We used young, middle-aged and middle-aged ovariectomized rats to reveal age- and ovariectomy-related alterations. We analyzed the expression of the same set of genes in the postcentral and superior frontal gyrus of pre- and postmenopausal women using raw microarray data from our previous study. RESULTS Ovariectomy caused up-regulation of four classic microglia reactivity marker genes including Cd11b, Cd18, Cd45 and Cd86. The change was reversible since estradiol attenuated transcriptional activation of the four marker genes. Expression of genes encoding phagocytic and toll-like receptors such as Cd11b, Cd18, C3, Cd32, Msr2 and Tlr4 increased, whereas scavenger receptor Cd36 decreased following ovariectomy. Ovarian hormone deprivation altered the expression of major components of estrogen and neuronal inhibitory signaling which are involved in the control of microglia reactivity. Strikingly similar changes took place in the postcentral and superior frontal gyrus of postmenopausal women. CONCLUSIONS Based on the overlapping results of rat and human studies we propose that the microglia phenotype shifts from the resting toward the reactive state which can be characterized by up-regulation of CD11b, CD14, CD18, CD45, CD74, CD86, TLR4, down-regulation of CD36 and unchanged CD40 expression. As a result of this shift, microglial cells have lower threshold for subsequent activation in the forebrain of postmenopausal women

Distribution of type 1 cannabinoid receptor expressing neurons in the septal-hypothalamic region of the mouse. Colocalization with GABAergic and glutamatergic markers.

Type 1 cannabinoid receptor (CB1) is the principal mediator of retrograde endocannabinoid signaling in the brain. In this study, we addressed the topographic distribution and amino acid neurotransmitter phenotype of endocannabinoid-sensitive hypothalamic neurons in mice. The in situ hybridization detection of CB1 mRNA revealed high levels of expression in the medial septum (MS) and the diagonal band of Broca (DBB), moderate levels in the preoptic area and the hypothalamic lateroanterior (LA), paraventricular (Pa), ventromedial (VMH), lateral mammillary (LM) and ventral premammillary (PMV) nuclei, and low levels in many other hypothalamic regions including the suprachiasmatic (SCh) and arcuate (Arc) nuclei. This regional distribution pattern was compared to location of GABAergic and glutamatergic cell groups, as identified by the expression of glutamic acid decarboxylase 65 (GAD65) and type 2 vesicular glutamate transporter (VGLUT2) mRNAs, respectively. The MS, DBB and preoptic area showed overlaps between GABAergic and CB1-expressing neurons, whereas hypothalamic sites with moderate CB1 signals, including the LA, Pa, VMH, LM and PMV, were dominated by glutamatergic neurons. Low CB1 mRNA levels were also present in other glutamatergic and GABAergic regions. Dual-label in situ hybridization experiments confirmed the cellular co-expression of CB1 with both glutamatergic and GABAergic markers. In this report we provide a detailed anatomical map of hypothalamic glutamatergic and GABAergic systems whose neurotransmitter release is controlled by retrograde endocannabinoid signaling from hypothalamic and extrahypothalamic target neurons. This neuroanatomical information contributes to the understanding of the role that the endocannabinoid system plays in the regulation of endocrine and metabolic functions. J. Comp. Neurol., 2011. (c) 2011 Wiley-Liss, Inc