1,720,985 research outputs found
Acute and chronic changes in K(+)-induced depolarization alter NMDA and nNOS gene expression in cultured cerebellar granule cells
Full text linkThe influence of low or high (10 or 25 mM) K(+)-induced membrane depolarization on the mRNA levels for NMDA receptor subunits was investigated by RNase protection assay in cultured rat cerebellar granule cells. Cells, maintained for 7 days in K25+, a condition that promotes their survival and maturation, express the highest levels of NR-1 and NR-2A mRNA, whereas NR-2B is maximally expressed in cells grown in K10+. Acute changes in medium K+ concentration had a significant effect on the mRNA levels for NMDA receptor subunits. A concomitant reduction of NR-2A mRNA and induction of NR-2B was observed following a 24-h shift of the culture medium from K25+ to K10+. Under these circumstances NR-2C, not detected in basal conditions, became expressed. Neuronal nitric oxide synthase, an enzyme linked to NMDA receptor activation, was also influenced by growth conditions. Its expression, higher under low excitation (K10+), is induced in the shift from K25+ to K10+ and is markedly decreased in the opposite situation. These data indicate that several factors may influence the expression of NMDA receptor subunits and consequently may modulate the function of this receptor complex and its adaptation to acute and chronic changes in neuronal activity
SHORT-TERM AND LONG-TERM INDUCTION OF BASIC FIBROBLAST GROWTH-FACTOR GENE-EXPRESSION IN RAT CENTRAL-NERVOUS-SYSTEM FOLLOWING KAINATE INJECTION
No full textBoth RNase protection assay and in situ hybridization were used to investigate the effect of intraperitoneal injection of kainate on the messenger RNA levels for basic fibroblast growth factor in the rat central nervous system. Limbic motor seizures were produced by kainate injection and this event was followed by a significant elevation of basic fibroblast growth factor gene expression in rat hippocampus and striatum 6 h after the convulsant injection. The increase in hippocampus was maximal at 24 h and it was delayed with respect to nerve growth factor induction, which peaked 3 h after kainate injection. Animals that suffered prolonged seizure activity also showed a significant elevation of basic fibroblast growth factor gene expression four and 14 days after kainate, when no changes in nerve growth factor gene expression were observed. We show that, within the hippocampus, the increase of basic fibroblast growth factor messenger RNA was localized in dentate gyrus and the CA1 layer 6 and 24 h after kainate injection. Long-term effects on its gene expression were measurable only in the CA1 hippocampal subfield, where major cell damage and astrocytosis have been reported to occur following kainate-induced seizure activity [Ben-Ari Y. et al. (1981) Neuroscience 7, 1361-1391; Lothman E.W. and Collins R.C. (1981) Blain Res. 218, 299-318; Schwob J.E. et al. (1980) Neuroscience 5, 991-1014]. Indeed, the animals which displayed elevated messenger RNA levels for basic fibroblast growth factor four and 14 days after kainate injection showed a marked induction of messenger RNA expression for the astroglial marker glial fibrillary acidic protein. These results indicate that the glutamate analogue kainate produces short- and long-term increases of basic fibroblast growth factor messenger RNA expression with a specific anatomical pattern. Therefore, the gene expression for this neurotrophic factor is probably regulated by neuronal activity at early points in time, whereas the induction observed at later time points is related to adaptive mechanisms taking place following kainate-induced neuronal degeneration
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
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