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Adaptation in chemoreception cells II: The effects of cross-adapting backgrounds depend on spectral tuning.
No full text1. The cross-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using NH4 receptor cells, of known spectral tuning, from the lobster (Homarus americanus). 2. Spectrum experiments: The spectral tuning of NH4 receptor cells was investigated using NH4Cl and 7 other compounds selected as the most stimulatory non-best compounds for NH4 cells from a longer list of compounds tested in previous studies. Based on their responses to the compounds tested, 3 spectral subpopulations of NH4 cells were revealed: NH4-Glu cells which responded second-best to Glutamate (Glu); NH4- Bet cells which responded second-best to Betaine (Bet); and 'pure' NH4 cells, which responded to NH4C1 only (Fig. 1). 3. Cross-adaptation experiments: Overall, cross-adaptation with Glu and Bet backgrounds caused suppression of response of NH4 receptor cells to various concentrations of NH4Cl. However, the different subpopulations of NH4 cells were affected differently: (a) The stimulus-response functions of NH4-Glu cells were significantly suppressed by both a 3 μM (G3) and 300 μM (G300) Glu backgrounds, (b) The stimulus-response functions of NH4-Bet cells was not affected by a 3 μM (B3), but significantly suppressed by a 300 μM (B300) Bet background. (c) The stimulus-response functions of pure NH4 cells were not affected by any of the Glu or Bet backgrounds (Figs. 3, 4). 4. The stimulus-response functions of 5 cells from all different subpopulations were enhanced by cross-adaptation with the G300 and B300 backgrounds (Fig. 4, Table 1). 5. Whereas self-adaptation caused parallel shifts in stimulus-response functions (Borroni and Atema 1988), cross-adaptation caused a decrease in slope of stimulus-response functions. Implications of the results from cross- and self-adaptation experiments on NH4 receptor cells, for a receptor cell model are discussed
Adaptation in chemoreception cells I: Self-adapting backgrounds determine threshold and cause parallel shift of response function.
No full text1. The self-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using lobster (Homarus americanus) NH4 receptor cells. 2. These receptors responded for several seconds to the onset of the backgrounds, and then returned to their initial level of spontaneous activity (usually zero). The strongest response always occurred only during the steepest concentration change; the response then decayed back to zero or to the earlier spontaneous firing level, while the background concentration was still rising, and remained silent during the entire time that the background was maintained constant (20-30 min) (Fig. 2). 3. Exposure to constant self-adapting backgrounds eliminated the responses of NH4 receptor cells to stimuli of concentration lower than the background, and reduced the responses to all higher stimulus concentrations tested by a nearly equal amount. This resulted in a parallel shift of the stimulus-response function to the right along the abscissa (Figs. 3 and 4). 4. Since the response threshold was completely re-set by adaptation to backgrounds, NH4 receptors seem to function mostly as detectors of relative rather than absolute stimulus intensity across their entire dynamic range: the response to a given stimulus-to-background ratio remained the same over 3 log step increases of background concentration (Fig. 6). 5. As in other sensory modalities, a parallel shift of response functions appears to be an important property of chemoreceptor cells, allowing for this sensory system to function over a wider stimulus intensity range than the instantaneous dynamic range of individual receptor cells
Response properties of lobster chemoreceptors : tuning of primary taste neurons in walking legs
No full text1. We determined the tuning properties of 66 single chemoreceptor cells from the legs of the lobsterHomarus americanus. The specificity of these (taste) cells was tested electrophysiologically in the upper range of biologically relevant stimulus concentrations (3×10–4 mol/l) with 15 compounds listed in Table 1.
2. Most of the chemoreceptors surveyed were narrowly tuned to specific test chemicals (Fig. 3). The best stimuli for these chemoreceptors were glutamate (Glu), ammonium chloride (NH4), betaine (Bet) and hydroxyproline (OH-Pro) (Fig. 4). Cell populations were defined by their best stimulus. Populations of cells responding best to Glu and NH4 were extremely narrowly tuned; populations responding best to Bet and OH-Pro were less narrowly tuned (Fig. 5, Table 2).
3. Each cell population showed a range of response specificities, from cells responding to only one compound to cells responding more broadly to other compounds. Within each population cells were arranged by their tuning breadth (H). Cells that shared a best stimulus but responded also to other compounds showed no consistency for the next best stimulus (Fig. 6). This suggests that even cells responding to the same stimulus do not share the same receptor complement.
4. The response patterns to Glu, NH4 and Bet elicited across all the chemoreceptor cells surveyed can be distinguished statistically as different from each other and from all others tested. Similarly, OH-Pro can be distinguished from all other stimuli except glycine and taurine (Figs. 8 and 9).
5. Systematic prior exposure to all 15 test compounds (corresponding to 21 stimulus exposures) at our stimulus concentrations reduced the absolute sensitivity of Glu best cells but did not change the slope of their dose-response functions (Fig. 10) with respect to earlier results (Derby and Atema 1982a).
6. We suggest that extremely narrowly tuned cells in lobster legs may function to detect key compounds as feeding stimuli over a large dynamic range of mixture concentrations such as found in nature. These cells may not be affected as much as broadly tuned cells by ambient backgrounds of cross-adapting compounds. In addition, both narrowly tuned and broadly tuned cells may participate in across fiber patterns to encode the quality of naturally occurring stimulus mixtures
Adaptation and mixture interactions in chemoreceptor cells: mechanisms for diversity and contrast enhancement.
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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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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