1,721,059 research outputs found
Differentiation−dependent changes of the nicotinic acetylcholine receptor and other synapse−associated proteins
No full textDevelopmentally regulated changes were followed by analyzing the appearance of synapse−associated proteins of the electric organ of Torpedo marmorata. At early stages of development acetylcholine receptor and acetylcholine esterase are distributed diffusely over the myotube surface. With differentiation they become increasingly restricted to the central cell surface. This process occurs before axons contact the electrocytes. As soon as axons begin to contact electrocytes one finds a rapid increase in acetylcholine receptor concentration, which is shortly followed by an increased synthesis of 17 S AChE. The final stages of the synapse formation coincide with increasing amounts of a hydrophobic 6 S AChE and increasing amounts of Mr43000 polypeptides, suggesting that the appearance of these components is linked to the maturation of receptor and synapse functio
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Development of the neuromuscular junction
No full textThe differentiation of the neuromuscular junction is a multistep process requiring coordinated interactions between nerve terminals and muscle. Although innervation is not needed for muscle production, the formation of nerve−muscle contacts, intramuscular nerve branching, and neuronal survival require reciprocal signals from nerve and muscle to regulate the formation of synapses. Following the production of muscle fibers, clusters of acetylcholine receptors (AChRs) are concentrated in the central regions of the myofibers via a process termed "prepatterning". The postsynaptic protein MuSK is essential for this process activating possibly its own expression, in addition to the expression of AChR. AChR complexes (aggregated and stabilized by rapsyn) are thus prepatterned independently of neuronal signals in developing myofibers. ACh released by branching motor nerves causes AChR−induced postsynaptic potentials and positively regulates the localization and stabilization of developing synaptic contacts. These "active" contact sites may prevent AChRs clustering in non−contacted regions and counteract the establishment of additional contacts. ACh−induced signals also cause the dispersion of non−synaptic AChR clusters and possibly the removal of excess AChR. A further neuronal factor, agrin, stabilizes the accumulation of AChR at synaptic sites. Agrin released from the branching motor nerve may form a structural link specifically to the ACh−activated endplates, thereby enhancing MuSK kinase activity and AChR accumulation and preventing dispersion of postsynaptic specializations. The successful stabilization of prepatterned AChR clusters by agrin and the generation of singly innervated myofibers appear to require AChR−mediated postsynaptic potentials indicating that the differentiation of the nerve terminal proceeds only after postsynaptic specializations have formed
Characterization of Multiple Forms of Acetylcholinesterase in Electric Organ of Torpedo Marmorata
No full textThree molecular forms of acetylcholinesterase can be isolated by velocity sedimentation from extracts of electric organ from Torpedo marmorata. Their apparent sedimentation coefficients are 6 S, 13 S and 17 S. Characteristic differences are found with regard to their solubilization properties. The 13 S and 17 S forms are extracted only in the presence of high salt concentrations. At low ionic conditions only a fraction of the 6 S form is solubilized. Quantitative recovery of this form can be achieved in the presence of Triton X−100 at concentrations of 0.5−1%. The relative ratio of the various forms changes during the development of the fis
Distribution of Acetylcholinesterase Molecular Formas in Brain, Nerve and Muscle Tissue of Torpedo Marmorata
No full textThe distribution of multiple molecular esterase forms in brain, electromotor nerve, back muscle and a subcellular synaptosomal fraction from the electric organ of Torpedo marmorata was investigated. Each tissue was characterized by a specific pattern of distribution of esterase forms. Electric lobe exhibited a marked difference to the other brain tissues and electric organ, in that it contained predominantly fast sedimenting 17 S acetylcholinesterase. The solubilization properties indicated that the 17 S form is not exclusively associated with basal lamina. The results support the view that location and function of the various molecular esterase forms can vary from tissue to tissue and depend on the physiological demands of each syste
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