1,720,958 research outputs found
Sustained oscillatory noise in the light responses of a retinal neuron
No full textIn the retina of the turtle, prolonged illumination of the receptive field surrond can lead to the appearance of sustained oscillatory responses in horizontal cells. In most cells the oscillations consist of a main component of 40–50 Hz frequency modulated by slower waves. The
experimental evidence suggests that these responses are due to the activation of the feeback circuit linking cone photoreceptors and horizontal cells in the vertebrate retina
Effects of transretinal currents on the synaptic transmission block from photoreceptors (PHs) to horizontal cells (HCs) induced by divalent cations in the turtle retina
No full textEFFECTS OF TRANSRETINAL CURRENTS ON THE SYNAPTIC TRANSMISSION BLOCK FROM PHOTORECEPTORS (PHS) TO HORIZONTAL CELLS (HCS) INDUCED BY DIVALENT-CATION
Low calcium relives synaptic transmission block from photoreceptors (PHs) to horizontal cells (HC) induced by antagonist divalent cations in the turtle retina
No full textLow calcium relives synaptic transmission block from photoreceptors (PHs) to horizontal cells (HC) induced by antagonist divalent cations in the turtle retina
Low-calcium-induced enhancement of chemical synaptic transmission from photoreceptors to horizontal cells in the vertebrate retina
No full textAccording to the classical calcium hypothesis of synaptic transmission, the release of neurotransmitter from presynaptic terminals occurs through an exocytotic process triggered by depolarization-induced presynaptic calcium influx. However, evidence has been accumulating in the last two decades indicating that, in many preparations, synaptic transmitter release can persist or even increase when calcium is omitted from the perfusing saline, leading to the notion of a "calcium-independent release" mechanism. Our study shows that the enhancement of synaptic transmission between photoreceptors and horizontal cells of the vertebrate retina induced by low-calcium media is caused by an increase of calcium influx into presynaptic terminals. This paradoxical effect is accounted for by modifications of surface potential on the photoreceptor membrane. Since lowering extracellular calcium concentration may likewise enhance calcium influx into other nerve cells, other experimental observations of "calcium-independent" release may be reaccommodated within the framework of the classical calcium hypothesis without invoking unconventional processes
Common beliefs and bias in retinoblastoma
No full textThe ''two hit'' hypothesis, formulated by Knudson in 1971, has represented the first attempt of unitary explanation of the differences usually found in the clinical expression of the disease. The theory, by highlighting the role and distribution in time of two mutational events, has not only given a substantial contribution to the comprehension of the clinical differences between unilateral and bilateral, familial and sporadic disease, but it has also allowed the discovery of an entirely new category of genes (tumour suppressor genes) normally involved in the control of cell proliferation. However, after 16 years from its formulation, a more accurate analysis of epidemiological, biological and molecular data concerning retinoblastoma reveals a number of discrepancies between the theory, its clinical consequences, and the different aspects of the disease. Common beliefs, biases and misinterpretations have largely contributed to this substantially incorrect approach to the unitary explanation of the disease. The aim of the present paper is to contribute to a new and methodologically correct approach to the interpretation of clinical, biological and molecular aspects of tile disease, by demonstrating inconsistencies, drawbacks and pitfalls contained in the ''two hit'' hypothesis formulation
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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