1,720,968 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)
EPSP-spike potentiation during primed burst-induced long-term potentiation in the CA1 region of rat hippocampal slices.
No full textLong-term potentiation induced by high-frequency stimulation in the CA1 region of the hippocampus exhibits EPSP-spike potentiation. This consists of an increase in population spike amplitude exceeding that predicted by EPSP potentiation alone. This phenomenon is apparently due to an increase in pyramidal cell excitability. Patterns of afferent stimuli which activate pyramidal cells to reproduce the theta rhythm observed in the hippocampus under physiological conditions, have been shown to induce LTP-like enhancement of synaptic responses in vitro. The aim of this study was to investigate the presence of EPSP-spike potentiation and/or changes in pyramidal cell excitability during the long-term potentiation induced in the CA1 region of rat hippocampal slices by theta-like patterns of stimuli: the primed burst and the patterned stimulation. Using extracellular recording, a significant leftward shift in the EPSP-spike relationship was found 30 min after primed burst or patterned stimulation. The magnitude of EPSP-spike potentiation induced by patterned stimulation was similar to that produced by high-frequency stimulation. Both were significantly greater than that induced by a primed burst, indicating that only a subset of pyramidal cells were potentiated by this kind of afferent activation. Modifications in synaptic efficacy and cell excitability brought about by a primed burst were investigated in 25 intracellularly recorded pyramidal cells. Consistent with extracellular results, it was found that only 11 out of 25 neurons receiving a primed burst were potentiated. In these cells the increase in probability of firing action potentials elicited by synaptic activation with test shocks was accompanied by enhanced cell excitability, but not by an increase in EPSP slope. High-frequency stimulation delivered 40 min after a primed burst invariably increased the EPSP slope, the probability of firing upon synaptic stimulation, and the excitability of cells. The presence of EPSP-spike potentiation and of increased excitability of potentiated cells during the primed burst-induced long-term potentiation strengthen the suggestion that theta pattern-induced synaptic potentiation can be considered similar to high-frequency stimulation and long-term potentiation and supports the notion that the EPSP-spike potentiation is a constitutive characteristic of long-term potentiation
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
Adenosine in the central nervous system: Effects on neurotransmission and neuroprotection.
No full textAdenosine is one of the principal neuromodulators in the brain and acts on four specific receptor subtypes: the A1, A2A, A2B and A3 receptors. Adenosine concentrations normally reached in the extracellular space are in the nanomolar range and may stimulate the high affinity A1 and A2A receptors. Inhibitory effects on neurotransmission are mediated mainly by A1 receptors while excitatory effects are mediated by A2A receptors. Adenosine has an overall net inhibitory effect on neurotransmission. Under normoxic conditions, A3 receptors do not exert a significant effect on neurotransmission and no data are available concerning the effect of A2B receptors. Given its ability to modulate neurotransmission, adenosine plays several physiological roles in the brain. It controls motility, acts as an endogenous anticonvulsant, and affects pain control, sleep, cognition and memory. It is also likely to be involved in the tonic modulation of affective states and consequently in social interaction and aggressive behaviour.
Under pathological conditions, adenosine plays an important role in neuroprotective mechanisms interacting with A1 and A2A receptors and more recently there is evidence that A3 receptors are also involved. It has been demonstrated that A2A antagonists may be useful for control of symptoms and potentially for neuroprotection in Parkinson's disease. One possible approach in cerebral ischaemia is that of agents increasing locally the extracellular concentration of adenosine and of using A2A antagonists. Recent data support the putative utility of A2A receptor ligands in Huntington's disease
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
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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