1,721,018 research outputs found
Studio dell'espressione di SNAP-25 e SNAP-23 nella corteccia cerebellare
Full text linkIl sistema nervoso elabora le informazioni inviando segnali attraverso le sinapsi, giunzioni intercellulari specializzate. Tramite le sinapsi, i neuroni formano una rete di cellule in grado di comunicare tra di loro. Le sinapsi, costituite da un elemento pre- ed uno post-sinaptico, trasmettono gli impulsi nervosi molto velocemente e sono altamente plastiche. Le loro diverse proprietà funzionali sono determinate dalla presenza, all’interno dei due compartimenti, di molecole specifiche, dalla loro diversa combinazione nonché dal microcircuito nel quale sono immerse. Di recente è stato osservato che diverse isoforme delle proteine appartenenti al complesso SNARE, coinvolto nel rilascio vescicolare sinaptico, sono preferenzialmente espresse in specifiche sinapsi piuttosto che in altre. Ad esempio in neuroni ippocampali GABAergici sembra che la SNAP-25 sia assente mentre sia presente la usa isoforma SNAP-23. Tale differenza si riflette in una diversa entrata di calcio in seguito a stimolazione, infatti in seguito a espressione esogena di SNAP-25 l’entrata di calcio risulta minore rispetto alla sola presenza di SNAP-23. Da questo studio e succesivi è emerso un fatto molto interessante, che la SNAP-25 oltre ad essere coinvolta meccanicamente nel rilascio vescicolare ha anche un ruolo regolatorio a livello delle sinapsi tramite un’interazione con i canali voltaggio dipendenti. Interessante è che differenze nei livelli di espressione di SNAP-25 sono state riscontarte di recente anche in sottopopolazioni di terminazione glutamatergiche. Poiché nel cervelletto non è stata condotta un’analisi approfondiata riguardo la distribuzione dello SNARE complex ed in particolare delle isoforme SNAP, scopo della tesi è stato quello di caratterizzare la distribuzione della SNAP-25 e della SNAP-23 nelle sinapsi glutamatergiche e gabaergiche della corteccia cerebellare tramite tecniche di immunofluorescenza e microscopia confocale. L’analisi quantitativa dei dati sperimentali, supportati dalla microscopia elettronica, ha rilevato un’espressione variabile della SNAP-25 nei diversi terminali sinaptici della corteccia cerebellare. I livelli di espressione estremamente bassi della SNAP-25 nelle terminazioni GABAergiche, e in una sottopopolazione glutamatergica, ci hanno suggerito che livelli molto bassi di tale proteina ed in particolare nella fibra rampicante, non possono essere responsabili del rilascio vescicolare che avviene in tali sinapsi. A conferma di tale ipotesi abbiamo eseguito degli esperimenti con la BoNT-A per verificare in vivo il rilascio vescicolare a livello della rampicante. I livelli di espressione estremamente bassi della SNAP-25 in una sottopopolazione glutamatergica, ci ha indotto inoltre a ricercare il possibile sostituto di tale proteina. Poichè l’isoforma SNAP-23, sembra essere in grado di sostituire funzionalmente la SNAP-25 nella secrezione neuroendocrina ne abbiamo analizzato la distribuzione nella corteccia cerebellare. Livelli di espressione non elevati della SNAP-23 nei terminali che non esprimono la SNAP-25 suggeriscono che anche tale isoforma non sembra essere coinvolta nel rilascio sinaptico evocato. Tali risultati hanno aperto una nuove linee di ricerca che potrebbero aiutare a capire i meccanismi molecolari alla base della trasmissione sinaptica e della plasticità neuronale. Un obiettivo sarà quello di identificare l’isoforma o la proteina non nota che sostituisce la SNAP-25 nel rilascio vescicolare evocato in questi particolari terminazioni. Un altro progetto indagherà in maniera più approfondita il nuovo ruolo regolatorio della SNAP-25 esprimendo in vivo tale isoforma nel terminale glutamatergico in cui risulta assente (la fibra rampicante) e studiarne quindi gli effetti a livello elettrofisiologico.The brain processes information by transmitting signal at synapses, specialized intercellular junctions. The synapses connect neurons into vast networks of communicating cells. They are composed by a pre and a post-synaptic compartment, transmit information by an extremely fast mechanism, and are highly plastic. The functional properties of the synapses are specified by the presence, inside both compartments, of specific molecules, by their different arrangement and by the microcircuitry around them. Recently it has been observed that different isoform of proteins belonging to the SNARE complex, involved in the synaptic vesicular release, are differentially expressed in different subtypes of neuronal populations. For example it has been reported that in hippocampal gabaergic neurons SNAP-25 is absent and that they are characterized by a higher calcium responsiveness compared with excitatory neurons. Exogenous expression of SNAP-25 in interneurons significantly reduces calcium responses to depolarizing stimuli. Interestingly, from this study and others it is emerging the notion that SNAP-25 is a multifunctional protein that participates in exocytotic function both at the mechanistic and at regulatory level by promoting inhibition of VGCCs. Interestingly, very recently it has been observed a difference in the expression levels of SNAP-25 in different subpopulations of glutamatergic neurons. Since in the cerebellum, the SNARE complex distribution has not been well characterized, the aim of the PhD thesis was to investigate the expression of SNAP-25 and SNAP-23 in the gabaergic and glutamatergic neurons of the cerebellar cortex by means of immunofluorescence experiments and confocal imaging. The quantitative analysis, supported by electron microscopy studies, showed a differential expression of SNAP-25 in the different synaptic terminals of the cerebellar cortex. Very low levels of SNAP-25 were detected in the gabaergic terminals and in a specific population of glutamatergic terminals represented by the climbing fiber. The low levels of SNAP-25 can not be responsible of the synaptic vesicular release. This hypothesis was supported by an in vivo test by using the botulinum toxin A that cleaves specifically the SNAP-25. We therefore investigated the presence of SNAP-23, a potential isoform that could replace SNAP-25 in the regulated exocitosis. Also SNAP-23 resulted expressed at very low levels in the terminals SNAP-25 negative. The possible involvement of other homolog should be also taken into account. These results have open different lines of research that could contribute in understanding the molecular mechanisms involved in synaptic transmission and plastic events. One goal will be to identify the potential substitute of SNAP-25 in such terminals. A second line of research aims at investigating the regulatory role of SNAP-25 by in vivo expression of this isoform in the glutamatergic terminals where is virtually absent, the climbing fiber, and by performing electrophysiological experiments
The South American mammals collection at the Museo Geologico Giovanni Capellini (Bologna, Italy)
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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
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