1,721,016 research outputs found
A3 Adenosine receptor antagonistsdelay irreversible synaptic failure caused by oxygen and glucose deprivation in the rat CA1 hippocampus in vitro
No full textThe role of adenosine A3 receptor activation during ischaemia-like conditions produced byoxy gen and glucose deprivation (OGD) was evaluated with extracellular recordings from the CA1 region of rat hippocampal slices. In all, 7 min of OGD evoked tissue anoxic depolarisation (AD, peak atB7 min from OGD start, n1⁄420) and were invariablyfollowed byirreversible loss of electrically evoked field epsps (fepsps, n1⁄442)
Changes in synaptosomal high affinity choline uptake following electrical stimulation of guinea-pig cortical slices: effect of atropine and physostigmine.
No full textSuperfused guinea-pig cortical slices were electrically stimulated at different frequencies and the changes in acetylcholine (ACh) content measured. Synaptosomes were prepared at the end of the stimulation period and high affinity choline uptake (HACU) rate was measured. 2 The effect of increasing KC1 concentrations was compared on ACh content of the slices and on synaptosomal HACU. 3 Electrical stimulation (2, 5, 10, 20 Hz) elicited a frequency-dependent linear increase in synaptosomal HACU rate and a decrease in ACh content of the slices. 4 The addition of atropine (1.5 x 10(-8) M) to the slices enhanced and that of physostigmine (3 x 10(-5) M) reduced the frequency-dependent increase in HACU rate. Atropine (1.5 x 10(-6) M) not only antagonized the effect of physostigmine, but the HACU rate measured after treatment with both drugs was larger than that found after atropine alone. 5 These results indicate that in the cortical cholinergic nerve endings, depolarization caused by electrical stimulation is coupled with an increase in choline transport which can be modulated by the addition of atropine or physostigmine. Furthermore, within given experimental conditions a linear relationship exists between the reciprocal of ACh content in the slices and synaptosomal HACU
Effect of adenosine, adenosine triphosphate, adenosine deaminase, dipyridamole and aminophylline on acetylcholine release from electrically-stimulated brain slices
No full textThe effect of adenosine on release of acetylcholine (ACh) was investigated in slices of rat cortex perfused with Krebs solution, at rest and during electrical stimulation at frequencies between 0.2 and 20 Hz. Electrical stimulation brought about a linear increase in release of ACh. Adenosine, in concentrations ranging from 1 to 100 microM, reduced in a dose-dependent manner the release of ACh and was more active on the stimulated than on the resting release. However, the fractional reduction by adenosine of stimulated release of ACh did not vary with increasing stimulation rate. Adenosine triphosphate was less active than adenosine in reducing release of ACh. The inhibitory effect of adenosine was antagonized by aminophylline (0.5 mM) and did not occur when the stimulated release of ACh was enhanced by blocking muscarinic autoreceptors with atropine (15 nM). Aminophylline (0.1 and 0.5 mM) itself exerted a biphasic effect on release of ACh, increasing it at rest and during stimulation at low frequencies, and decreasing it at higher stimulation rates. The manipulation of endogenous adenosine concentrations by adding adenosine deaminase or diphyridamole, an inhibitor of adenosine uptake, had little effect on release of ACh. Dipyridamole, (4 microM), only significantly decreased release of ACh at the 20 Hz stimulation rate
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
Modification of adenosine extracellular levels and adenosine A(2A) receptor mRNA by dopamine denervation
No full textAdenosine A2A receptor antagonists have been proposed as an effective therapy in the treatment of Parkinson's disease. To explore the possibility that dopamine denervation may produce modifications in adenosine A2A transmission, we measured the extracellular concentration of adenosine and adenosine A2A receptor mRNA in the striatum of rats infused unilaterally with 6-hydroxydopamine in the medial forebrain bundle. Fifteen days after 6-hydroxydopamine infusion, extracellular adenosine levels, measured by in vivo microdialysis, were significantly lower (−35%) in the dopamine-denervated striatum. At the time of the decrease in adenosine levels, an increase in striatal adenosine A2A receptor mRNA levels (+20%), measured by in situ hybridization, was observed. Modifications in adenosine A2A transmission, following nigrostriatal dopamine neuron degeneration, establish a potential neural basis for the effectiveness of adenosine A2A receptor antagonists in the treatment of Parkinson's diseas
Role of adenosine A(3) receptors on CA1 hippocampal neurotransmission during oxygen-glucose deprivation episodes of different duration
No full textThe role of adenosine A3 receptors in synaptic transmission under severe (7 min) and shorter (2–5 min) ischemic conditions, obtained by oxygen and glucose deprivation (OGD), was investigated in rat hippocampal slices. The effects of selective A3 agonists or antagonists were examined on field excitatory postsynaptic potentials (fEPSPs) extracellularly recorded at the dendritic level of the CA1 pyramidal region. The novel, selective A3 antagonist LJ1251 ((2R,3R,4S)-2-(2-chloro-6-(3-iodobenzylamino)-9H-purin-9-yl)tetrahydrothiophene-
3,4-diol, 0.1–10 nM) protected hippocampal slices from irreversible fEPSP depression induced by severe OGD and prevented or delayed the appearance of anoxic depolarization. Similar results were obtained when severe OGD was carried out with a long, receptor-desensitizing exposure to various selective A3 agonists: 5-N-methylcarboxamidoadenosine
derivatives Cl-IB-MECA (N6-(3-iodobenzyl)-2-chloro), VT72 (N6-methoxy-2-phenylethynyl), VT158 (N6-methoxy-2-phenylethynyl), VT160 (N6-methoxy-2-(2-pyridinyl)-ethynyl), and VT163 (N6-methoxy-2-p-acetylphenylethynyl) and AR132 (N6-methyl-2-
phenylethynyladenosine).
The selective A3 antagonist MRS1523 (3-propyl-6-ethyl-5-[(ethylthio)carbonyl]-2-phenyl-4-propyl-3-pyridine carboxylate, 100 nM) reduced fEPSP depression evoked by 2-min OGD and induced a faster recovery of fEPSP amplitude after 5-min OGD. Similar results were obtained for 2- or 5-min OGD applied in the presence of each of the A3 agonists tested
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