1,720,958 research outputs found
Glial toxin effect on protein synthesis in an insect connective
No full textAnalysis of electron autoradiographs from the nerve cord of the insect, Periplaneta americana (L.) shows a significant incorporation of 3H-labelled protein in the axons. The axonal activity is greatly reduced after treatment of the cord with the glial toxin ethidium bromide. This is interpreted as substantiating the possibility that adaxonal glia can transfer proteins to the axons
Regenerating adult cockroach dorsal unpaired median neurones in vitro retain their in vivo membrane characteristics
No full textThe ability of differentiated neurones to recover from disease or injury depends upon both intrinsic and extrinsic factors. Whereas most mammalian neurones have a limited capacity for regeneration, regulated, in part, by physical and chemical cues in the brain microenvironment (Bray et al. 1987; Caroni and Schwab, 1988, 1989), invertebrates, and in particular insects, exhibit a far greater capacity for repair of central neurones and circuits (Treherne et al. 1988). Studies of the cues that regulate the regenerative process are made easier by the use of individual, identified neurones, cultured under controlled conditions. Invertebrates are particularly useful in this regard; neurones from mature nervous systems of both annelids and molluscs have been grown successfully in culture and their growth can be influenced by changes in the culture conditions (Acklin and Nicholls, 1990; Dagan and Levitan, 1981; Ready and Nicholls, 1979; Syed et al. 1990). Routine and long-term culture of identified neurones from the insect central nervous system (CNS) has proved more elusive, preventing the use of neurones from these well-studied systems. Recently, however, cultures of cockroach (Howes et al. 1991), locust (Kirchoff and Bicker, 1992) and moth (Hayashi and Levine, 1992) adult neurones have been described. <br/
Mechanisms of glial regeneration in an insect central nervous system
No full textAs in other repairing systems, glial regeneration in insect central nervous connectives, following selective chemical lesioning, involves both exogenous and endogenous elements. Our current evidence, including that obtained with monoclonal antibodies, indicates that the reactive, granule-containing cells are derived from a sub-population of circulating haemocytes which, within 24 h, invade, and are restricted to, the lesion zone. The granule-containing cells are involved in the initial repair of the perineurial region. They also contribute to the first stage in the restoration of the blood-brain barrier and are responsible for recruiting reactive endogenous glia, apparently from the vicinity of the anterior abdominal ganglion. The granule-containing cells transform into or are replaced by functional glia between 3 and 5 days after selective glial disruption, coincident with the appearance in the lesion zone of dividing reactive cells
Long-term growth in vitro of isolated, fully differentiated neurones from the central nervous system of an adult insect
No full textA method is described for the isolation and growth in vitro of fully differentiated neurones from the thoracic ganglia of adult cockroaches. The presence of insect blood in the culture system is shown to promote growth. The morphology of the growing neurones and the plasticity of the branching processes are described and growth rates are measured. Using a fluorescent Ca2+ indicator dye, changes of intracellular calcium levels in the growing neurones in response to K+ depolarization have been measured. The results, indicating the presence of voltage-dependent Ca2+ channels on neuronal processes in vitro, show that neurones can be maintained in a functional state for several weeks by this technique. Such preparations could prove useful for studying a variety of physiological and pharmacological properties of neurones, including the mechanisms controlling growth, synapse formation and neuronal interactions with other cell types. <br/
Cell proliferation in the repairing adult insect central nervous system: incorporation of the thymidine analogue 5-bromo-2-deoxyuridine in vivo
No full textUptake of the thymidine analogue 5-bromo-2-deoxyuridine into non-neuronal cells of the insect central nervous system has been examined following a controlled lesioning of the glial elements. The pattern of BUdR labelling along the penultimate abdominal connective was examined over a period of 17 days. Cell proliferation occurred in and immediately around the site of damage in both perineurial and subperineurial glial cells but at different times post-lesion for the two regions. Proliferation in the perineurial zone was maximal at 6-8 days post-lesion but continued for at least 17 days. Subperineurial proliferation was less dramatic and peaked between days 8-11 post-lesion. In both areas division appears to be confined to the reactive glial cells. These results are discussed in the context of past research on this system, particularly with regard to the restoration of the blood-brain barrier
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
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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