1,720,976 research outputs found
Antagonism by (1,2,5,6-tetrahydropyridine-4-yl) methylphosphinic acid of synaptic transmission in the neonatal rat spinal cord in vitro: an electrophysiological study
No full textThe effect of the novel GABAc receptor antagonist (1,2,5,6-tetrahydropyridine-4-yl)methyl-phosphinic acid (TPMPA) on synaptic transmission and GABA-mediated responses was investigated with electrophysiological recordings from the in vitro spinal cord preparation of the neonatal rat. Bath-applied TPMPA (10 microM) had no effect on spinal reflexes evoked by dorsal root stimulation, on ventral root polarization level or amplitude of ventral root depolarizations induced by exogenously applied GABA (0.5 mM). TPMPA significantly attenuated the depressant action of GABA on spinal reflexes without changing responses induced by the GABA(A) receptor agonist isoguvacine (50 microM) or the GABA(B) receptor agonist baclofen (0.5-2 microM). Following block of GABA(A) receptors by bicuculline (20 microM) and of glycine receptors by strychnine (1 microM), regular bursting activity recorded from ventral roots developed spontaneously and persisted unchanged for many hours. This bursting pattern, which is generated at the level of the interneuronal network, was significantly slowed down by TPMPA, which also increased the duration of individual bursts and the number of intraburst oscillations. These results suggest that in the neonatal rat spinal cord some functional GABAc receptors exist: their role was clearly unmasked following pharmacological block of GABA(A) (and glycine) receptors. Under these conditions GABAc receptors appeared to contribute to the excitation of spinal interneurons supporting rhythmic bursting activity
In vivo and in vitro development of mouse pancreatic beta-cells in organotypic slices
No full textTaking tissue slices of the embryonic and newborn pancreas is a novel approach for the study of the perinatal development of this gland. The aim of this study was to describe the morphology and physiology of in vivo and in vitro developing beta-cells. In addition, we wanted to lay a foundation for the functional analysis of other pancreatic cells, either alone or as part of an integrative pancreatic physiology approach. We used cytochemistry and light microscopy to detect specific markers and the whole-cell patch-clamp to assess the function of single beta-cells. The insulin signal in the embryonic beta-cells was condensed to a subcellular compartment and redistributed throughout the cytosol during the first 2 days after birth. The hormone distribution correlated well with the development of membrane excitability and hormone release competence in beta-cells. Endocrine cells survived in the organotypic tissue culture and maintained their physiological properties for weeks. We conclude that our preparation fulfills the criteria for a method of choice to characterize the function of developing pancreas in wild-type and genetically modified mice that die at birth. We suggest organotypic culture for in vitro studies of the development and regeneration of beta-cells
Experimental and modeling studies of novel bursts induced by blocking na(+) pump and synaptic inhibition in the rat spinal cord
No full textThis study addressed some electrophysiological mechanisms enabling neonatal rat spinal networks in vitro to generate spontaneous rhythmicity. Networks, made up by excitatory connections only after block of GABAergic and glycinergic transmission, develop regular bursting (disinhibited bursts) suppressed by the Na(+) pump blocker strophanthidin. Thus the Na(+) pump is considered important to control bursts. This study, however, shows that, after about 1 h in strophanthidin solution, networks of the rat isolated spinal cord surprisingly resumed spontaneous bursting ("strophanthidin bursting"), which consisted of slow depolarizations with repeated oscillations. This pattern, recorded from lumbar ventral roots, was synchronous on both sides, of irregular periodicity, and lasted for > or =12 h. Assays of (86)Rb(+) uptake by spinal tissue confirmed Na(+) pump block by strophanthidin. The strophanthidin rhythm was abolished by glutamate receptor antagonists or tetrodotoxin, indicating its network origin. N-methyl-D-aspartate (NMDA), serotonin, or high K(+) could not accelerate it. The size of each burst was linearly related to the length of the preceding pause. Bursts could also be generated by dorsal root electrical stimulation and possessed similar dependence on the preceding pause. Conversely, disinhibited bursts could be evoked at short intervals from the preceding one unless repeated pulses were applied in close sequence. These data suggest that rhythmicity expressed by excitatory spinal networks could be controlled by Na(+) pump activity or slow synaptic depression. A model based on the differential time course of pump operation and synaptic depression could simulate disinhibited and strophanthidin bursting, indicating two fundamental, activity-dependent processes for regulating network discharge
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
Experimental and modeling studies of novel bursts induced by blocking na(+) pump and synaptic inhibition in the rat spinal cord
No full textThis study addressed some electrophysiological mechanisms enabling neonatal rat spinal networks in vitro to generate spontaneous rhythmicity. Networks, made up by excitatory connections only after block of GABAergic and glycinergic transmission, develop regular bursting (disinhibited bursts) suppressed by the Na(+) pump blocker strophanthidin. Thus the Na(+) pump is considered important to control bursts. This study, however, shows that, after about 1 h in strophanthidin solution, networks of the rat isolated spinal cord surprisingly resumed spontaneous bursting ("strophanthidin bursting"), which consisted of slow depolarizations with repeated oscillations. This pattern, recorded from lumbar ventral roots, was synchronous on both sides, of irregular periodicity, and lasted for > or =12 h. Assays of (86)Rb(+) uptake by spinal tissue confirmed Na(+) pump block by strophanthidin. The strophanthidin rhythm was abolished by glutamate receptor antagonists or tetrodotoxin, indicating its network origin. N-methyl-D-aspartate (NMDA), serotonin, or high K(+) could not accelerate it. The size of each burst was linearly related to the length of the preceding pause. Bursts could also be generated by dorsal root electrical stimulation and possessed similar dependence on the preceding pause. Conversely, disinhibited bursts could be evoked at short intervals from the preceding one unless repeated pulses were applied in close sequence. These data suggest that rhythmicity expressed by excitatory spinal networks could be controlled by Na(+) pump activity or slow synaptic depression. A model based on the differential time course of pump operation and synaptic depression could simulate disinhibited and strophanthidin bursting, indicating two fundamental, activity-dependent processes for regulating network discharge
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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