1,720,958 research outputs found
PLOIDY AND NUCLEARITY OF RAT HEPATOCYTES AFTER COMPENSATORY REGENERATION OR MITOGEN-INDUCED LIVER GROWTH
No full textThe distribution pattern of rat liver parenchymal cells of different ploidy classes was investigated in Wistar rats following cell proliferation induced by surgical partial hepatectomy (compensatory regeneration) or primary mitogens (direct hyperplasia). Animals were killed at 1, 2, 3, 4 and 15 days after the proliferative stimulus, and ploidy and nuclearity were measured using a computer-assisted imaging system in hepatocytes isolated by collagenase perfusion. Analysis of hepatocytes from animals undergoing regeneration after partial hepatectomy revealed a large increase in tetraploid and octoploid mononucleate cells. The most striking feature was the almost complete disappearance of binucleate cells (from 20% to < 1%) at 3 days after partial hepatectomy. On the contrary, when hepatocytes were analyzed after treatment with the mitogen lead nitrate, a high number of binucleate cells (40%) was observed. The increase that was maximal at 3 days after treatment occurred mainly in 4x2c and in 8x2c compartments. This resulted in an overall increase in the ratio of binucleate/mononucleate cells as well as in the ratio (8c + 16c) : (2c + 4c). The cytological changes induced by lead nitrate were not reversible 2 weeks after treatment. Because a massive elimination of excess liver cells occurred by apoptosis during this time period, it appears that polyploid cells are not preferentially eliminated. The hepatic content of DNA at the end of the regression phase was similar to control values. However, because of the higher ploidy state, the number of cells present in the liver 2 weeks after treatment appears to be lower than that of controls (approximately - 16%). When liver growth was induced by a single treatment with another mitogen, the peroxisome proliferator nafenopin, a slight increase in the ploidy state of the liver was observed; because of the shift towards higher ploidy classes (8c), the increase in DNA content observed 3 days after a single treatment with nafenopin (+ 21%) appears to be almost entirely justified by polyploidy rather than by a hyperplastic event
Possible roles of nonparenchymal cells in hepatocyte proliferation induced by lead nitrate and by tumor necrosis factor alpha
No full textA single intravenous injection of lead nitrate (LN) to rats induces liver cell proliferation without causing cell necrosis (direct hyperplasia), We suggested that liver cell proliferation in this model may be triggered by the induction of liver tumor necrosis factor alpha (TNF-alpha), Because administration of TNF-alpha in vivo has been shown to induce proliferation of both parenchymal and nonparenchymal cells of the Liver, we analyzed the temporal sequences of DNA synthesis in both cell populations following LN and recombinant TNF-alpha treatment by 5-bromo-2-deoxyuridine (BrdU) immunohistochemistry. The patterns of cell proliferation induced by these agents were further compared with those induced by a single dose of nafenopin (NAF), a direct mitogen which does not induce liver TNF-alpha messenger RNA (mRNA), In male Wistar rats given a single dose of LN (100 mu mol/kg), BrdU incorporation of hepatocytes and nonparenchymal cells (Kupffer cells, endothelial cells and periportal nondescript cells) became evident 12 hours after the treatment; The labeling of all cell types reached a peak. after 38 hours and declined thereafter, Rats given a single intravenous injection of human recombinant TNF-alpha (46 mu g/rat) showed an increase of BrdU labeling in nonparenchymal cells after 24 hours, whereas the labeling of hepatocytes became evident at 36 hours, A single intragastric administration of NAF resulted in a rapid increase in the number of labeled hepatocytes with no substantial labeling of nonparenchymal cells, These results add further support to the notion that LN-induced liver cell proliferation is mediated by TNF-alpha, and suggest that different cell populations are involved in the initial proliferative response of the liver to mitogens, depending on the capacity of the mitogens to stimulate TNF-alpha production
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
Effects of cell proliferation and cell death (apoptosis and necrosis) on the early stages of rat hepatocarcinogenesis
No full textAn experiment was performed to investigate whether, during regression of the liver hyperplasia induced by a direct mitogen, apoptosis differentially affects replicated and non-replicated hepatocytes, After a single dose of the direct mitogen lead nitrate (LN), male Wistar rats were given repeated injections of tritiated thymidine, and were killed either 3 days (time of maximal hepatic DNA increase) or 15 days (complete regression of the hyperplasia) after mitogen treatment, Determination of liver DNA radioactivities and labelling indices (LIs) at the two time points revealed an similar to 40% loss in total liver DNA radioactivity, a 20% decrease in the specific activity of DNA, and a 20% reduction in the cell LI, Three days after LN administration 64% of the apoptotic bodies contained thymidine grains in their nuclear fragments, The results indicated that apoptosis affects both hepatocytes that replicated, and those that did not replicate, the former being slightly more sensitive, A second experiment was then performed to investigate whether and to what extent different types of cell death (apoptosis versus necrosis) influence the growth of hepatocytes initiated by a chemical carcinogen, Male Wistar rats were given a single dose of diethylnitrosamine, and 2 weeks thereafter either a single dose of LN, or a necrogenic dose of carbon tetrachloride (CCl4). Bromodeoxyuridine was next infused for 5 days, and some of the animals were killed at this time point, and others after an additional 3 weeks, Administration of CCl4 resulted in an increase in both the average size and the percentage area occupied by placental glutathione S-transferase-positive lesions, In contrast, administration of lead nitrate resulted in a strong reduction (50%) in the number of positive lesions with no remarkable change in the percentage area occupied by them, These differential effects occurred even though comparable LIs were observed in rats treated with the two agents, The results suggest that lead nitrate leads to a loss of initiated hepatocytes, due to the apoptosis that occurs during regression of the LN-induced hyperplasia
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
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