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Response of a neuronal membrane to applied sinusoidal currents
No full textThe membrane model of Connor and Stevens was used to calculate the response of a neuron to an injected sinusoidal current. This stimulating current simulates the effects of cell exposure to incident time-harmonic electromagnetic fields. The theoretical results obtained with this model were compared with intracellular recordings carried out during the injection of a sinusoidal transmembrane current through a single microelectrode. Experimental and theoretical data were substantially in agreement for current amplitudes that can be induced by actual exposure condition
Glycosylation is required for maintenance of functional voltage-activated channels in growing neocortical neurons of the rat
No full textVoltage-activated currents were studied in whole-cell patch-clamped rat neocortical neurons growing in culture and treated with tunicamycin (TU), an inhibitor of protein N-glycosylation. The size of the Na+ current decreased progressively in the presence of TU (1-2 microM). This decrease was faster in growing 5-14 day-old neurons (to ca. 40% of control after 24 hours of treatment) than in fully grown 20-40-day-old neurons (to ca. 40% of control after 68 hours of treatment). The fast transient K+ current (A-current) was abolished, and the delayed rectifier K+ current was markedly reduced by a 24 hour treatment with TU (1-2 microM) in growing neurons. In contrast, in fully grown neurons these currents were unaffected by the same TU treatment. The size of the Ca2+ current was significantly reduced following a 24 hour treatment with TU (1-2 microM) in neurons at early stages of differentiation, but remained stable in 20-40-day-old neurons. It is concluded that protein glycosylation, presumably of the channel proteins themselves, is important for the functional expression of voltage-activated channels in embryonic cortical neurons during the early stages of cell growth in culture; the channels become less dependent on glycosylation in mature neurons
Acetylcholine-elicited responses in primary and secondary mammalian oocytes disappear after fertilisation.
No full textCell-to-cell electrical coupling in seminiferous cords of mouse fetal testis
No full textExperiments performed on mouse fetal testes in vitro using electrophysiological techniques and intracellular injections of the fluorescent tracer disodium fluorescein showed that junctional transfer occurs between cells inside the seminiferous cords. This suggests a possible metabolic cooperation between testis cells at an early stage of gonad development
Development of membrane sensitivity to the parthenogenetic agent calcium ionophore A23187 during meiotic maturation in the hamster oocyte
No full textThe response to the parthenogenetic agent Ca-ionophore A23187 was studied in hamster oocytes undergoing meiotic maturation, by using electrophysiological techniques. Following germinal vesicle breakdown, the activating agent induces a long-lasting hyperpolarization accompanied by an increased membrane conductance. The duration of the response progressively shortens during the long metaphase I stage. Terminal metaphase I oocytes respond to A23187 by a hyperpolarization that is very similar to that seen in metaphase II oocytes. The ionic mechanism of the change in the membrane sensitivity to A23187 during meiotic maturation is discussed
Modulation of voltage-activated channels by calcitonin gene-related peptide in cultured rat neurones
No full text1. Whole-cell currents were recorded from cultures of dissociated neocortical neurones of the rat. Rat alpha-calcitonin gene-related peptide (CGRP; 1 nM-1 microM) caused significant dose-dependent decreases in the voltage-activated transient (A-current) and delayed rectifier K+ currents. Forskolin (10 nM-20 microM) mimicked this effect. Peak K+ currents were gradually decreased after loading neurones with cyclic AMP (100 microM) through patch pipettes. CGRP was ineffective in neurones loaded with cyclic AMP. 2. CGRP (0.5-2 microM) increased cytosolic cyclic AMP concentration and this effect was mimicked by forskolin (5-40 microM). 3. CGRP (0.1-1 microM) reduced high-threshold Ca2+ currents; as did forskolin (5-20 microM) and cyclic AMP loaded into the neurones. In contrast, low-threshold Ca2+ currents were not affected by any of these agents. 4. Voltage-activated Na+ currents were significantly reduced by both CGRP (0.1-1 microM) and forskolin (5-20 microM). A similar effect was observed when cells were loaded with cyclic AMP. 5. We conclude that, in neocortical neurones, CGRP attenuates voltage-activated currents by stimulating the intracellular cyclic AMP signalling system
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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