1,720,957 research outputs found
Adenosine down-regulates giant depolarizing potentials in the developing rat hippocampus by exerting a negative control on glutamatergic inputs
No full textAdenosine is a widespread neuromodulator that can be directly released in the extracellular space during sustained network activity or can be generated as the breakdown product of adenosine triphosphate ( ATP). Whole cell patch- clamp recordings were performed from CA3 principal cells and interneurons in hippocampal slices obtained from P2 - P7 neonatal rats to study the modulatory effects of adenosine on giant depolarizing potentials ( GDPs) that constitute the hallmark of developmental networks. We found that GDPs were extremely sensitive to the inhibitory action of adenosine ( IC50 = 0.52 mu M). Adenosine also contributed to the depressant effect of ATP as indicated by DPCPX- sensitive changes of ATP- induced reduction of GDP frequency. Similarly, adenosine exerted a strong inhibitory action on spontaneous glutamatergic synaptic events recorded from GABAergic interneurons and on interictal bursts that developed in CA3 principal cells after blockade of gamma- aminobutyric acid type A ( GABA(A)) receptors with bicuculline. All these effects were prevented by DPCPX, indicating the involvement of inhibitory A1 receptors. In contrast, GABAergic synaptic events were not changed by adenosine. Consistent with the endogenous role of adenosine on network activity, DPCPX per se increased the frequency of GDPs, interictal bursts, and spontaneous glutamatergic synaptic events recorded from GABAergic interneurons. Moreover, the adenosine transport inhibitor NBTI and the adenosine deaminase blocker EHNA decreased the frequency of GDPs, thus providing further evidence that endogenous adenosine exerts a powerful control on GDP generation. We conclude that, in the neonatal rat hippocampus, the inhibitory action of adenosine on GDPs arises from the negative control of glutamatergic, but not GABAergic, inputs
GABA-mediated giant depolarizing potentials as coincidence detectors for enhancing synaptic efficacy in the developing hippocampus
No full textATP contributes to the generation of network-driven giant depolarizing potentials in the neonatal rat hippocampus
No full textIn the immature hippocampus, the so-called 'giant depolarizing potentials' (GDPs) are network-driven synaptic events generated by the synergistic action of glutamate and GABA. Here we tested the hypothesis that ATP, a widely distributed neurotransmitter, directly contributes to the network activity during the first postnatal week. We found that in CA3 pyramidal cells, in the presence of the adenosine antagonist 8-cyclopentyl- 1,3-dipropylxanthine (DPCPX), ATP produced a transient facilitation of GDPs; followed by a depressant effect. A similar biphasic effect was produced by blockade of the ectoATPase activity with 6-N,N-diethyl-D-beta,gamma-dibromomethylene ATP (ARL-67156). The effects of exogenous and endogenous ATP on GDPs; were prevented by the P2X receptor antagonist pyridoxal phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). On pyramidal cells, ATP upregulated spontaneous action-potential-dependent GABA(A)-mediated synaptic events (GABA-SPSPs), suggesting a network-driven effect. Recordings from interneurones allowed comparison of ATP effects on GABAergic and glutamatergic synaptic activity. While ATP depressed GABA-SPSPs via metabotropic P2Y(1) receptors, it up- and downregulated glutamatergic SPSPs via PPADS-sensitive receptors. Thus, ATP exerts an excitatory action on CA3 pyramidal cells via facilitation of GDPs; and SPSPs. This excitatory drive is propagated to pyramidal cells by interneurons that represent the 'common pathway' for generation of GDPs; and SPSPs. Our results show that ATP operating via distinct P2X and P2Y receptors directly contributes to modulate network activity at the early stages of postnatal development
Associative mossy fibre LTP induced by pairing presynaptic stimulation with postsynaptic hyperpolarisation of CA3 neurones in rat hippocampal slice
No full textPresynaptic R-type calcium channels contribute to fast excitatory synaptic transmission in the rat hippocampus
No full textThe possibility that R-type calcium channels contribute to fast glutamatergic transmission in the hippocampus has been assessed using low concentrations of NiCl2 and the peptide toxin SNX 482, a selective antagonist of the pore-forming alpha (1E) subunit of R-type calcium channel. EPSPs or EPSCs were recorded in the whole-cell configuration of the patch-clamp technique mainly from CA3 hippocampal neurons. Effects of both NiCl2 and SNX 482 were tested on large (composite) EPSCs evoked by mossy and associative-commissural fiber stimulation. NiCl2 effects were also tested on minimal EPSPs-EPSCs. Both substances reduced the amplitude of EPSPs-EPSCs. This effect was associated with an increase in the number of response failures of minimal EPSPs-EPSCs, an enhancement of the paired-pulse facilitation ratios of both minimal and composite EPSCs, and a reduction of the inverse squared coefficient of variation (CV-2). The reduction of CV-2 was positively correlated with the decrease in EPSC amplitude. The inhibitory effect of NiCl2 was occluded by SNX 482 but not by omega -conotoxin-MVIIC, a broad-spectrum antagonist thought to interact with Nand P/Q-type calcium channels, supporting a specific action of low concentrations of NiCl2 on R-type calcium channels. Together, these observations indicate that both NiCl2 and SNX 482 act at presynaptic sites and block R-type calcium channels with pharmacological properties similar to those encoded by the alpha (1E) gene. These channels are involved in fast glutamatergic transmission at hippocampal synapses
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
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