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Reverberation of chloride-dependent synaptic potentials in the rat entorhinal cortex in vitro
No full textParticipation of GABA<sub>A</sub>-Mediated Inhibition in Ictallike Discharges in the Rat Entorhinal Cortex
No full textLopantsev, Valeri and Massimo Avoli. Participation of GABAA-mediated inhibition in ictallike discharges in the rat entorhinal cortex. J. Neurophysiol. 79: 352–360, 1998. The spontaneous, synchronous activity induced by 4-aminopyridine (4AP, 50 μM) in the adult rat entorhinal cortex was analyzed with simultaneous field potential and intracellular recordings in an in vitro slice preparation. Four-AP induced isolated negative-going field potentials (interval of occurrence = 27.6 ± 9.9 (SD) s; n = 27 slices) that corresponded to intracellular long-lasting depolarizations (LLDs), and ictallike epileptiform discharges (interval of occurrence = 10.4 ± 5.7 min; n = 27 slices) that were initiated by the negative field potentials. LLDs recorded with K-acetate–filled microelectrodes triggered few action potentials of variable amplitude and had a duration of 1.7 ± 0.8 s ( n = 26 neurons), a peak amplitude of 11.8 ± 5.0 mV ( n = 26 neurons) and a reversal potential of −66.2 ± 3.9 mV ( n = 17 neurons). The ictal discharges studied with K-acetate microelectrodes consisted of prolonged depolarizations (duration = 72.9 ± 44.3 s; peak amplitude = 29.2 ± 11.4 mV; n = 25 neurons) with action-potential firing during both the tonic and the clonic phase. These depolarizations had a reversal potential of −45.3 ± 3.8 mV ( n = 4 neurons). Intracellular Cl−diffusion from KCl-filled microelectrodes made both LLDs and ictal depolarizations increase in amplitude (30.5 ± 8.2 mV, n = 8 and 41.8 ± 9.8 mV, n = 6 neurons, respectively). LLDs recorded with KCl and 2-(trimethyl-amino) N-(2,6-dimethylphenyl)-acetamide (QX-314) microelectrodesreached an amplitude of 36.3 ± 5.2 mV, lasted 12.5 ± 6.5 s, and had a reversal potential of −31.3 ± 2.5 mV ( n = 4 neurons); under these recording procedures the ictal discharge amplitude was 41.5 ± 5.0 mV and the reversal potential −24.0 ± 7.0 mV ( n = 4 neurons). The N-methyl-d-aspartate (NMDA) receptor antagonist 3,3-(2-carboxy-piperazine-4-yl)-pro-pyl-l-phosphonate (10 μM, n = 5 neurons) alone or concomitant with the nonNMDA receptor antagonist 6-cyano-7-nitro-quinoxaline-2,3-dione (10 μM, n = 4 neurons) abolished ictal discharges, without influencing LLDs. LLDs were blocked by the γ-aminobutyric acid-A (GABAA) receptor antagonist bicuculline methiodide (BMI, 10 μM, n = 6 neurons) or the μ-opioid receptor agonist (d-Ala2-N-Me-Phe, Gly-ol) enkephalin (DAGO, 10 μM, n = 2 neurons). Application of BMI ( n = 4 neurons) or DAGO ( n = 2 neurons) to control the medium abolished LLDs and ictal discharges but disclosed a novel type of epileptiform depolarization that lasted 3.5 ± 1.2 s and occurred every 5.2 ± 2.6 s ( n = 6 neurons). Our data indicate that 4AP induces in the rat entorhinal cortex a synchronous, GABA-mediated potential that is instrumental in initiating NMDA-dependent, ictal discharges. Moreover we present evidence for an active role played by GABAA-mediated potentials in the maintenance and termination of these prolonged epileptiform events.</jats:p
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
GABA<sub>A</sub>-Dependent Chloride Influx Modulates Reversal Potential of GABA<sub>B</sub>-Mediated IPSPs in Hippocampal Pyramidal Cells
No full text Changes in intracellular chloride concentration, mediated by chloride influx through GABAA receptor–gated channels, may modulate GABAB receptor–mediated inhibitory postsynaptic potentials (GABAB IPSPs) via unknown mechanisms. Recording from CA3 pyramidal cells in hippocampal slices, we investigated the impact of chloride influx during GABAA receptor–mediated IPSPs (GABAA IPSPs) on the properties of GABAB IPSPs. At relatively positive membrane potentials (near −55 mV), mossy fiber–evoked GABAB IPSPs were reduced (compared with their magnitude at −60 mV) when preceded by GABAAreceptor–mediated chloride influx. This effect was not associated with a correlated reduction in membrane permeability during the GABAB IPSP. The mossy fiber–evoked GABAB IPSP showed a positive shift in reversal potential (from −99 to −93 mV) when it was preceded by a GABAA IPSP evoked at cell membrane potential of −55 mV as compared with −60 mV. Similarly, when intracellular chloride concentration was raised via chloride diffusion from an intracellular microelectrode, there was a reduction of the pharmacologically isolated monosynaptic GABABIPSP and a concurrent shift of GABAB IPSP reversal potential from −98 to −90 mV. We conclude that in hippocampal pyramidal cells, in which “resting” membrane potential is near action potential threshold, chloride influx via GABAA IPSPs shifts the reversal potential of subsequent GABAB receptor–mediated postsynaptic responses in a positive direction and reduces their magnitude. </jats:p
GABA<sub>A</sub>-Dependent Chloride Influx Modulates GABA<sub>B</sub>-Mediated IPSPs in Hippocampal Pyramidal Cells
No full text The relationship between postsynaptic inhibitory responses [the fast GABAA-mediated inhibitory postsynaptic potential (IPSP) and the slow GABAB-mediated IPSP] were investigated in hippocampal CA3 pyramidal cells. Mossy fiber-evoked GABAB-mediated IPSPs were, paradoxically, of greater amplitude in cells with resting membrane potential of −62 mV (13.6 ± 0.5 mV; mean ± SE) as compared with cells with resting membrane potential of −54 mV (7.0 ± 0.8 mV). In addition, when a cell’s membrane potential was artificially manipulated, GABAB-mediated IPSPs were reduced at relatively depolarized levels (−55 mV) and enhanced at relatively hyperpolarized potentials (at least −60 mV). In contrast, the preceding GABAA-mediated IPSPs were larger at the more positive membrane potentials and smaller as the cell was hyperpolarized. Similar voltage dependency was obtained when monosynaptic GABAA- and GABAB-mediated IPSPs were isolated in the presence of glutamatergic receptor antagonists. However, monosynaptic GABAB-mediated IPSPs isolated in the presence of glutamatergic and GABAA receptor antagonists were not reduced at the more positive membrane potentials, and were significantly larger in amplitude than GABAB-mediated IPSPs preceded by a monosynaptic GABAA-mediated IPSP. The amplitude of the isolated monosynaptic GABAB-mediated IPSPs recorded with potassium chloride-containing microelectrodes was significantly smaller than the comparable potential recorded with potassium acetate microelectrodes without chloride. We conclude that voltage-dependent chloride influx, via GABAA receptor-gated channels, modulates postsynaptic GABAB-mediated inhibition in hippocampal CA3 pyramidal cells. </jats:p
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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