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

Modelling KNDy neurons and gonadotropin-releasing hormone pulse generation

This is the final version. Available on open access from Elsevier via the DOI in this record The pulsatile release of gonadotropin-releasing hormone (GnRH) and its frequency are crucial for healthy reproductive function. To understand what drives GnRH pulses a combination of experimental and mathematical modelling approaches have been used. Early work focussed on the possibility that GnRH pulse generation is an intrinsic feature of GnRH neurons, with autocrine feedback generating pulsatility. However, there is now ample evidence suggesting that a network of upstream KNDy (kisspeptin, neurokinin-B and dynorphin) neurons are the source of this GnRH pulse generator. The interplay of slow positive and negative feedback via neurokinin-B and dynorphin respectively allow the network to act as a relaxation oscillator, driving pulsatile secretion of kisspeptin, and consequently, of GnRH and LH. Here we review the mathematical modelling approaches exploring both scenarios and suggest that with pulsatile GnRH secretion driven by the KNDy pulse generator, autocrine feedback still has the potential to modulate GnRH output.Engineering and Physical Sciences Research Council (EPSRC)Biotechnology & Biological Sciences Research Council (BBSRC

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

Mathematical Modelling of Endocrine Systems

This is the final (in press) version. Available from Elsevier via the DOI in this recordHormone rhythms are ubiquitous and essential to sustain normal physiological functions. Combined mathematical modelling and experimental approaches have shown that these rhythms result from regulatory processes occurring at multiple levels of organisation and require continuous dynamic equilibration, particularly in response to stimuli. We review how such an interdisciplinary approach has been successfully applied to unravel complex regulatory mechanisms in the metabolic, stress, and reproductive axes. We discuss how this strategy is likely to be instrumental for making progress in emerging areas such as chronobiology and network physiology. Ultimately, we envisage that the insight provided by mathematical models could lead to novel experimental tools able to continuously adapt parameters to gradual physiological changes and the design of clinical interventions to restore normal endocrine function.Medical Research Council (MRC)Engineering and Physical Sciences Research Council (EPSRC)Wellcome Trus

Mathematical models in GnRH research

This is the final version. Available on open access from Wiley via the DOI in this recordMathematical modelling is an indispensable tool in modern biosciences, enabling quantitative analysis and integration of biological data, transparent formulation of our understanding of complex biological systems, and efficient experimental design based on model predictions. This review article provides an overview of the impact that mathematical models had on GnRH research. Indeed, over the last 20 years mathematical modelling has been used to describe and explore the physiology of the GnRH neuron, the mechanisms underlying GnRH pulsatile secretion, and GnRH signalling to the pituitary. Importantly, these models have contributed to GnRH research via novel hypotheses and predictions regarding the bursting behaviour of the GnRH neuron, the role of kisspeptin neurons in the emergence of pulsatile GnRH dynamics, and the decoding of GnRH signals by biochemical signalling networks. We envisage that with the advent of novel experimental technologies, mathematical modelling will have an even greater role to play in our endeavour to understand the complex spatiotemporal dynamics underlying the reproductive neuroendocrine system.Biotechnology & Biological Sciences Research Council (BBSRC)Kings College Londo

The Role Hypothalamic Kisspeptin Neurons Play in Estradiol Negative and Positive Feedback Regulation of Reproduction

The brain regulates fertility through gonadotropin-releasing hormone (GnRH) neurons. Estradiol induces negative feedback on pulsatile GnRH/luteinizing hormone (LH) release and positive feedback generating GnRH/LH surges. Negative and positive feedback are postulated to be mediated by kisspeptin neurons in arcuate and anteroventral periventricular (AVPV) kisspeptin neurons, respectively. The work in this dissertation first demonstrated AVPV kisspeptin neurons were more excitable during positive feedback by performing electrophysiological recordings on cells from cycling and hormonal manipulated adult female mice. To test if the estradiol mediated excitability is due to estradiol action on estrogen receptor alpha (ERα) in kisspeptin neurons, kisspeptin specific ERα knockout mice (KERKO) and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 based AAV vectors that target Esr1 gene injected mice were used. The estradiol-induced increase in excitability of AVPV kisspeptin neurons was lost in cells from KERKO or AAV ERα knockdown mice. The comparable intrinsic excitability between two models suggests activational effects of estradiol can regulate firing activity. Besides intrinsic excitability, glutamatergic transmission to AVPV and arcuate kisspeptin neurons was characterized in cycling and hormonal manipulated adult female mice, as well as KERKO mice. This revealed that glutamatergic transmission to AVPV kisspeptin neurons is decreased during estradiol negative feedback whereas transmission to arcuate kisspeptin neurons is increased during negative feedback; frequency of glutamatergic transmission during positive feedback has the opposite pattern, being increased to AVPV and decreased to arcuate cells. Deletion of ERα in kisspeptin cells decreases glutamate transmission to AVPV neurons and markedly increases it to arcuate kisspeptin neurons, which also exhibits increased spontaneous firing rate. KERKO mice exhibit increased LH pulse frequency, indicating loss of negative feedback. The CRISPR/Cas9 based AAV approach enables spatial- and temporal-specific gene editing in mice. This allows us to test the role of estradiol and ERα in AVPV and arcuate kisspeptin neurons plays to sense estradiol and orchestrate pulsatile and surge release of GnRH/LH and thus reproductive output.PHDMolecular and Integrative PhysiologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146091/1/wanglh_1.pd

Endokannabinoid szignalizáció szerepe a reprodukció hypothalamikus szintű szabályozásában = Endocannabinoid signaling in hypothalamic regulation of reproduction

A szaporodás idegrendszeri szabályozásában kulcs szerepet tölt be a gonadotropin-releasing hormone (GnRH) neuronrendszer. A rendszer működését perifériás hormonhatások és más agyi neuronhálózatok szabályozzák. Multidiszciplináris megközelítés alkalmazásával tanulmányoztuk a GnRH neuronrendszer kapcsolatait és szignál transzdukciós mechanizmusait, különös tekintettel a retrográd endokannabinoid szignalizáció szabályozó szerepére. Kísérleti eredményeinkről 24 tudományos közleményben adtunk számot, 96 összesített impakt értékkel. Feltártuk a hypothalamus kannabinoid receptor 1 (CB1) hírvivő RNS-t termelő idegsejtjeinek lokalizációját, valamint azok glutamáterg és GABA-erg fenotípusait. Igazoltuk, hogy a GnRH sejteken végződő GABA tartalmú idegvégződések CB1-t tartalmaznak, valamint bebizonyítottuk, hogy a GnRH idegsejtekből felszabaduló endokannabinoidok befolyásolják a GABA közvetítette információ átadást a GnRH neuronok felé. Feltártuk a ghrelin és endokannabinoid szignalizációs útvonalak kapcsolt jellegét a hypothalamusban. Igazoltuk a humán GnRH idegsejtek glutamát- és GABA-erg beidegzését. A GnRH neuronrendszer kisspeptinerg afferensei vonatkozásában új regulációs adatokat szolgáltattunk. Vizsgáltuk az ösztrogén szignalizáció szerepét a GnRH idegsejtek működésében, valamint az agykéregben. A GnRH idegsejtek működésének elmélyültebb tanulmányozására matematikai modellt alkottunk. Összegezve, eredményeink a reprodukció szabályozásának új mechanizmusait tárták fel. | Gonadotropin-releasing hormone (GnRH)-synthesizing neurons play a pivotal role in the central regulation of reproduction. Their operation depends on signaling by peripheral hormones and interactions with other neuronal circuits. By means of a multidisciplinary approach, the networking and signal transduction mechanisms of GnRH neurons were studied, with special reference to a putative retrograde endogenous cannabinoid signaling mechanism. The research results were published in 24 original papers representing a cumulative impact value of 96. Specifically, we mapped the hypothalamic distribution of cannabinoid receptor 1 (CB1) mRNA-expressing neurons and their GABA- and glutamatergic phenotypes, proved the presence of CB1 in neuronal afferents of GnRH neurons and characterized the impact of endocannabinoids liberated from GnRH neurons on the GABA-ergic signal transduction to GnRH cells. We provided evidence for the coupled nature of the ghrelin and the endocannabinoid signaling mechanisms. New GABA- and glutamatergic afferents of human GnRH neurons were also identified. In addition, novel regulatory mechanisms executed by kisspeptinergic circuits upon GnRH cells were revealed. We elucidated further characteristics of estradiol feedback effects to GnRH and cortical neurons. We established a mathematical model for the better understanding of GnRH cell performance. Collectively, our results shed light on novel mechanisms regulating reproduction at the hypothalamic level