1,720,959 research outputs found
THE EFFECTS OF EARLY LIFE UNDERNUTRITION ON LONGEVITY AND ASPECTS OF AGEING OF THE RODENT BRAIN
No full textDiet restriction has been widely acknowledged among gerontologists as a method to delay or retard ageing, and extend the lifespan of many organisms. A considerable and growing number of studies have been dedicated to reveal the effects of diet restriction on factors that may be involved in the ageing of a given organism. Despite this, a comprehensive explanation of the exact mechanisms that may be involved remain largely uncertain. The hypothesis that has gained the most support is the reduced oxidative damage hypothesis although even this hypothesis needs further research to confirm or deny its validity. The present project aimed to examine (1) the effects of relatively short periods of undernutrition at differing stages of early life (i.e. pre- and post-weaning) on the lifespan of mice, (2) the effects of these periods of undernutrition on the oxidative stress status of the brain of rodents, and (3) to investigate whether any alterations in this status correlate with changes at the cellular and behavioural levels in the animals. The oxidative stress parameters investigated included the levels of mRNA and activities of major anti-oxidant enzymes (i.e. manganese superoxide dismutase [MnSOD], copper/ zinc superoxide dismutase [Cu/ZnSOD], catalase, and glutathione peroxidase 1 [GPx 1]), as well as measures of reduced glutathione (GSH), and lipid peroxidation. Further studies estimated the effects of undernutrition during different stages of early life on the cell numbers in the hippocampal formation and on spatial and motor coordination behaviours. The present study found that there were no differences in the maximum, mean, and median lifespan between mice undernourished during either the pre- or postweaning periods and well-fed controls. However, some long-term changes in body weight and the reduced incidence of pathological disorders were observed in some of the undernourished groups of animals. There were some long-term alterations in the levels of mRNA of Cu/ZnSOD in both the forebrain and cerebellum of the mice and rats that had been undernourished during the pre-weaning period. In addition, there were some transient increases in the levels of mRNA of MnSOD in the cerebellum of the mice and catalase in the forebrain of the undernourished rats. These alterations in gene expression, however, did not correlate with the activity levels of the enzymes in most instances. This finding suggests that pre-weaning undernutrition may regulate the anti-oxidant enzymes at the transcriptional level differently from the posttranscriptional, translational, or post-translational levels. Another observation in this set of experiments was the long-lasting increase in the levels of GSH in the forebrain of mice following pre-weaning undernutrition. The exact significance of this change on the ageing process of an animal remains uncertain at present. Pre-weaning undernutrition did not affect the total number of CA2-CA3 pyramidal neurons of the hippocampus of the rats. However, such undernutrition did cause significant long-term alterations in the behavioural performance of the mice in the learning tasks used in this study. These effects on behaviour were not observed in mice undernourished during the post-weaning period. The significance of these results to the various hypotheses on the effects of diet restriction on an animals ageing is discussed in detail
The number, size, and type of axons in rat subcortical white matter on left and right sides: A stereological, ultrastructural study
No full textAbundant evidence indicates important functional differences between the two cerebral hemispheres of humans, although the cellular basis of these differences is unknown. A recent hypothesis proposes that these functional differences depend on differences between sides in the "repertoire" of axonal conduction delays for cortico-cortical axons. In morphological terms this corresponds to differences in caliber, or proportion, of myelinated versus unmyelinated axons. Several behavioural studies have indicated that cerebral asymmetry occurs in rodents, in which rigorous morphological analysis is possible. The hypothesis was therefore tested for the first time in adult male Wistar rats, using transmission electron microscopy and stereological methods. Subcortical white matter was compared between left and right sides in three regions (frontal, parietal, and occipital). The average caliber and numerical density of unmyelinated and myelinated axons was compared between sides and between regions. All data were corrected for shrinkage. No significant differences between sides were found in the average caliber of either type of axon in any region. The numerical density of either type of axon also yielded no significant differences between sides in any region. Significant differences were evident between regions in both caliber and numerical density of the two axonal types, and these quantitative data are reported. The proportion of unmyelinated axons in the lateral white matter was also higher than in previous studies of hemispheric white matter that studied the corpus callosum. The present study provides no evidence supporting the hypothesis that functional hemispheric specialization is due to differences in axonal number, caliber or type
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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