1,720,973 research outputs found
The role of semaphorin signaling in the etiology of hypogonadotropic hypogonadism
No full textIn mammals fertility depends on timely onset and cyclic secretion of gonadotropin-releasing hormone (GnRH), secreted by scattered hypothalamic neurons (GnRH neurons). These cells originate in the nasal placode and migrate first in the nasal compartment, then through the cribriform plate and finally across the basal forebrain, before they set in their final position in the hypothalamus. This long journey is regulated by many different factors that could be mutated in neuroendocrine syndromes such as congenital hypogonadotropic hypogonadism (CHH), Kallmann Syndrome (KS) and CHARGE syndrome. Recently, semaphorins, a large family of molecules, previously discovered as axon guidance cues, are emerging as key regulators of the neuroendocrine control of GnRH neurons and are acquiring an increasing role in the etiopathogenesis of CHH and KS. Specifically, semaphorins play a multifaceted action in GnRH neuron biology: on one hand regulating their migration and survival during embryonic development and, on the other, controlling the plasticity of the median eminence (ME) in terms of its response to varying sex steroid hormone levels. In this review we will focus our attention on recent studies describing the roles of different semaphorins in the normal and pathological biology of the GnRH neuronal system
Semaphorin signalling in GnRH neurons: from development to disease
No full textIn mammals, fertility critically depends on the pulsatile secretion of gonadotropin-releasing hormone (GnRH) by scattered hypothalamic neurons (GnRH neurons). During development, GnRH neurons originate in the nasal placode and migrate first in the nasal compartment and then through the nasal/forebrain junction, before reaching their final positions in the hypothalamus. This neurodevelopmental process, which has been extensively studied in mouse models, is regulated by a plethora of factors that might control GnRH neuron migration or survival as well as the fasciculation/targeting of the olfactory/vomeronasal axons along which the GnRH neurons migrate. Defects in GnRH neuron development or release can lead to Isolated GnRH Deficiency (IGD), whose underlying genetic causes are still partially unknown. Recently, semaphorins and their receptors neuropilins and plexins, a large family of molecules implicated in neuronal developmental and plasticity processes, are emerging as key regulators of GnRH neuron biology and deficiency. Specifically, semaphorins have been shown to play different roles in GnRH neuron biology, by regulating migration and survival during embryonic development as well as secretion in adulthood
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
From trascriptomic analysis to in vivo functional experiments: zebrafish as a model for studying GnRH system
No full textGnRH neurons are a small group of hypothalamic neurons that controls reproductive functions and fertility in mammals. During embryonic life, GnRH neurons arise from the olfacory placode and migrate towards the hypothalamus throughout the nasal mesenchyme and the forebrain. Once they have established in their final location, they extend their axons to the median eminence where GnRH is secreted. Defects in the development of the this neuroendocrine system could lead to rare genetic disorders such as Kallmann Syndrome (KS) and Hypogonadotropic Hypogonadism (HH). To date, the genetic basis of such syndromes is largely still unknown and only few mutated genes have been identified. The study of GnRH neuron develpoment is difficult because GnRH neurons are small in numbers and scattered along the migratory route, making complex their isolation. Here, we have taken advantage from a transgenic rat carrying GFP-labelled GnRH neurons and FACS to isolate GnRH neurons and perform a gene expression analysis to generate a trascriptome profile of GnRH neurons. Specifically, GnRH neurons at three different embryonic stages that represent the beginning, the transition from nose to forebrain and the cease of migration have been isolated. GFP-positive cells have been separated from GFP-negative cells by FACS and gene expression analysis performed using the Affymetrix GeneChip. All arrays have been normalized and data filtered by removing the probes with the smallest variances across the arrays. We have classified the differentially expressed genes into gene ontology pathways by using bioinformatic tools and selected a small number of genes associated to migration and neurite extension pathways. To study the functional relevance of these novel genes we first performed in situ hybridization experiments in zebrafish embryos to study their expression pattern during GnRH neuron development and started gene knock-down xperiments with morfolinos
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