1,720,964 research outputs found
Silent synapses in the developing hippocampus: lack of functional AMPA receptors or low probability of glutamate release?
No full textAt early developmental stages, silent synapses have been commonty found in different brain areas. These synapses are called silent because they do not respond at rest but are functional at positive membrane potentials. A widely accepted interpretation is that N-methyl-D-aspartate (NMDA) but not alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors are functionally expressed on the subsynaptic membrane. Here we show that, in both CA3 and CA1 hippocampal regions, AMPA-mediated synaptic responses can be detected already at early stages of postnatal development. However, some synapses appear silent because of a very low probability of glutamate release. They can be converted into functional ones by factors that enhance release probability such as paired-pulse stimulation, increasing the temperature or cyclothiazide (CTZ), a drug that blocks AMPA receptor desensitization and increases transmitter release. Conversely, conducting synapses can be switched off by increasing the frequency of stimulation. Although we cannot exclude that "latent AMPA receptors" can become functional after activity-dependent processes, our results clearly indicate that, in the neonatal hippocampus, a proportion of glutamatergic synaptic connections are presynaptically rather than postsynaptically silent
An ID-like current down-regulated by calcium modulates information coding at CA3-CA3 synapses in the rat hippocampus
No full textGenetic tests: between risks and opportunities
No full textCommercial genetic testing challenges traditional medical practice and the doctor–patient relationship. Neurodegenerative diseases may serve as the practical and ethical testing ground for the application of genomics to medicine
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
Frequency-dependent shift from paired-pulse facilitation to paired-pulse depression at unitary CA3-CA3 synapses in the rat hippocampus
No full textPaired recordings between CA3 interconnected pyramidal neurons were used to study the properties of short-term depression occurring in these synapses under different frequencies of presynaptic firing (n = 22). In stationary conditions (0.05-0.067 Hz) pairs of presynaptic action potentials (50 ms apart) evoked EPSCs whose amplitude fluctuated from trial to trial with occasional response failures. In 15/20 cells, paired-pulse ratio (PPR) was characterized by facilitation (PPF) while in the remaining five by depression (PPD). Increasing stimulation frequency from 0.05-0.067 Hz to 0.1-1 Hz induced low frequency depression (LFD) of EPSC amplitude with a gradual increase in the failure rate. Overall, 9/12 cells at 1 Hz became almost 'silent'. In six cells in which the firing rate was sequentially shifted from 0.05 to 0.1 and 1 Hz, changes in synaptic efficacy were so strong that PPR shifted from PPF to PPD. The time course of depression of EPSC1 could be fitted with single exponentials with time constants of 98 and 36 s at 0.1 and 1 Hz, respectively. In line with the inversion of PPR at I Hz, the time course of depression of EPSC2 was faster than EPSC1 (7 s). Recovery from depression could be obtained by lowering the frequency of stimulation to 0.025 Hz. These results could be explained by a model that takes into account two distinct release processes, one dependent on the residual calcium and the other on the size of the readily releasable pool of vesicle
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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