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ω-Conotoxin inhibition of excitatory synaptic transmission evoked by dorsal root stimulation in rat superficial dorsal horn
No full textA number of ω-conotoxins are potent and selective antagonists of N-type voltage-gated calcium channels (VGCCs) and are potentially effective as analgesic agents. ω-Conotoxins CVID and CVIB, venom peptides from Conus catus, inhibit N-type and N/P/Q-type VGCCs, respectively, in rat dorsal root ganglion sensory neurons. In the present study, we tested the effects of five different ω-conotoxins, CVID, CVIB, MVIIA, MVIIC and GVIA, on excitatory synaptic transmission between primary afferents and dorsal horn superficial lamina neurons of rat spinal cord. The N-type VGCC antagonists CVID (200 nM) and MVIIA (500 nM) completely and irreversibly inhibited excitatory postsynaptic currents (EPSCs) in the dorsal horn superficial lamina. The N- and P/Q-type VGCC antagonist CVIB (200 nM) reversibly reduced evoked EPSC amplitude an average of 34 ± 8%, whereas MVIIC (200 nM) had no effect on excitatory synaptic transmission. In neurons receiving polysynaptic input, CVIB reduced both the EPSC amplitude and the "success rate" calculated as the relative number of primary afferent stimulations that resulted in postsynaptic responses. These results indicate that (i) the analgesic action of ω-conotoxins that antagonise N-type VGCCs may be attributed to inhibition of neurotransmission between primary afferents and superficial dorsal horn neurons, (ii) nociceptive synaptic transmission between primary afferents and superficial lamina neurons is mediated predominantly by N-type VGCCs, and (iii) in contrast to the irreversible inhibition by CVID, MVIIA and GVIA, the inhibition of excitatory monosynaptic transmission by CVIB is reversible
Dihydropyridine inhibition of the glycine receptor: Subunit selectivity and a molecular determinant of inhibition
No full textThe dihydropyridines (DHPs), nifedipine and nicardipine, modulate native glycine receptors (GlyRs) at micromolar concentrations. Nicardipine has a biphasic potentiating and inhibitory effect, whereas nifedipine causes inhibition only. The present study sought to investigate (1) the molecular mechanism by which these compounds inhibit recombinant GlyRs, and (2) their potential utility as subunit-selective inhibitors of α1, α1β, α3 and α3β GlyRs. The rate of onset of inhibition in the open state was accelerated by pre-application of DHP in the closed state, with the degree of acceleration proportional to the concentration of pre-applied DHP. This implies a non-inhibitory binding site close to the DHP inhibitory site. DHP inhibition was use-dependent and independent of glycine concentration, consistent with a pore-blocking mode of action. DHP sensitivity was abolished by the G2′A mutation, providing a strong case for a DHP binding site in the pore. Nifedipine exhibited an approximately 10-fold higher inhibitory potency at α1-containing relative to α3-containing receptors, whereas nicardipine was only weakly selective for α1-containing GlyRs. The differential sensitivities of nifedipine and nicardipine for different GlyR isoforms suggest that DHPs may be a useful resource to screen as pharmacological tools for selectively inhibiting different synaptic GlyR isoforms
쥐 해마 CA1 세포의 시냅스 가소성 연구: LTP와 depotentiation
Get PDF학위논문 (석사)-- 서울대학교 대학원 : 뇌인지과학과, 2013. 8. Graham L. Collingridge.In 1949, Donald Hebb introduced the hypothesis that memory formation in the brain is based on activity- dependent synaptic change, where synapses between two cells could be strengthened if both cells are active simultaneously. The first identification of the Hebbian synapse in the mammalian brain was from entorhinal perforant pathway to dentate granule cells in the hippocampus (Bliss and Lomo, 1973). Brief high-frequency tetanus of this excitatory pathway elicited a long-lasting enhancement of synaptic transmission, which is now termed as long-term potentiation (LTP). Since then, LTP has been known to possess a number of properties that make it an attractive model for memory storage, which include input specificity, associativity, and cooperativity (Bliss and Collingridge, 1993Collingridge et al., 2004Neves et al., 2008). In the 40 years that have passed by from its first identification, LTP has been considered to be the best cellular correlate of learning and memory, and provided motivation to understand the detailed mechanism of synaptic plasticity.
In hippocampal Schaffer collateral to CA1 (SC-CA1) synapses, it has been reported there are two forms of LTP following distinct underlying mechanisms (in addition to an initial short-term potentiation, which is not considered further in this thesis), which are known as early LTP (E-LTP) and late LTP (L-LTP). E-LTP is induced by a single tetanus, which in some laboratories only lasts for 1 - 2 hron the other hand, L-LTP is induced by multiple tetani and is maintained as long as experiments are continued (Huang et al., 1996Reymann and Frey, 2007Mayford et al., 2012). The major mechanistic difference between two types of LTP is protein kinase A (PKA)- and protein synthesis- dependency, indicating E-LTP does not require the process of PKA and protein synthesis (Frey et al., 1993Huang and Kandel, 1994Huang et al., 1996Mayford et al., 2012). However, the concept of early- and late- LTP has been highly controversial because of its vague criteria. For example, it was suggested that a single tetanus can generate long-lasting LTP, which is not influenced by the PKA inhibitor, Rp-cAMPS (Bortolotto and Collingridge, 2000). Moreover, LTP induced by multiple tetani at condensed time interval was not affected by PKA inhibition in both genetic and pharmacological studies, though prolonged for many hours (Nguyen and Woo, 2003Woo et al., 2003Kim et al., 2010Zhang et al., 2011). Similarly, compressed- multiple tetani produced stable LTP that was less sensitive to the protein synthesis inhibitor, anisomycin (Scharf et al., 2002).
Here, we suggest a new model to explain the mechanism of LTP that encompasses the previous controversial results together with new findings (Fig. 12). According to this model, long-lasting LTP exists as two distinct forms in the criteria of PKA- and protein synthesis- dependencywhich we refer to here as LTP1 and LTP2. LTP1 is induced by a single tetanus or compressed- multiple tetani, and does not require the process of PKA and protein synthesis. On the other hand, LTP2 is induced by spaced- multiple tetani, and mediated by the mechanism which involves both PKA and protein synthesis. In turn, as a potential mediator between LTP1 and LTP2, we tested calcium-permeable AMPA receptors (CP-AMPARs) since they are transiently expressed after LTP induction as well as have a powerful capability to change the intra-synaptic microcosm (Cull-Candy et al., 2006Plant et al., 2006Liu and Zukin, 2007Guire et al., 2008Man, 2011). We found CP-AMPARs are required for the induction of LTP2, but not LTP1. Thus we propose that CP-AMPARs are positioned into synaptic site through LTP1 initiation, and that LTP2 is mediated by the synergistic Ca2+ influx via CP-AMPARs and NMDARs, which may be strong enough to promote protein synthesis.
To test this hypothesis, we utilized slice field recording at SC-CA1 synapses in the adult rat hippocampus (Fig. 1). Various drug combinations were used to specifically antagonize the molecules we are interested inand the results supported our hypothetical model, indicating stimulus parameters determine the role of PKA, protein synthesis, and CP-AMPARs in LTP.
Additionally, we investigated the reversible property of long-term potentiation (LTP), the phenomenon is often termed depotentiation (DP). Despite LTP is remarkable for its stability, it has been reported that low-frequency stimulation (LFS, such as 2 Hz) can disrupt LTP within brief time-periods of its induction. However, has no single paper been published to systematically compare the amount of DP depending on the time-delay after LTP induction. Furthermore, the cellular mechanism of this type of synaptic plasticity remained largely unknown.
In the second chapter, we studied on the properties and mechanisms of DP, using the slice field recording under pharmacological manipulations (Fig. 13). As a result, here we established the vulnerable time-points of LTP in the CA1 region of hippocampus, and that this LFS- induced DP is mediated by NMDAR (containing GluN2A and GluN2B) and protein phosphatases.1949년, Donald Hebb은 뇌의 기억 형성 메커니즘에 대한 하나의 가설을 발표하였다. 기억은 서로 다른 두 신경세포가 동시에 활성화 되었을 경우, 세포 간의 신호 전달이 강하게 유지됨으로써 형성된다는 것이다. 그 후 1973년, 쥐의 해마를 연구하던 중 Hebb의 가설에 부합되는 현상이 처음으로 발견되었다 (Bliss and Lomo, 1973). Bliss와 Lomo는 고주파 전기 자극 (high frequency stimulation, HFS)을 주었을 경우, 해마 시냅스의 신경 전달이 지속적으로 강하게 유지되는 것을 확인하였으며, 이후 이 현상은 long-term potentiation (LTP)이라고 명명되었다. 지속적인 연구를 통해, LTP에는 특이성, 결합성, 협동성이라는 다양한 특성이 존재하는 것으로 밝혀졌으며, 기억 저장의 훌륭한 세포학적 모델로 각광을 받았다 (Bliss and Collingridge, 1993Neves et al., 2008). 발견 이후 40년이 지난 현재까지도, LTP는 가장 적합한 학습과 기억의 분자적 메커니즘으로 받아들여지고 있으며, 시냅스 가소성 연구의 중추적인 역할을 담당해 왔다.
해마 CA1 세포에는 early LTP (E-LTP)와 late LTP (L-LTP)라는 두 가지 형태의 LTP가 존재한다고 알려져 있다. E-LTP는 한 번의 HFS로 유도되고 1 - 2시간 정도 유지되는 반면, L-LTP는 여러 번의 HFS에 의해 형성되며 수십 시간에서 며칠, 심지어 몇 주까지 지속된다고 알려져 있다 (Huang et al., 1996Mayford et al., 2012). 이런 두 형태의 LTP에 있어서, 가장 큰 메커니즘적 차이는 protein kinase A (PKA)와 protein synthesis 과정이 수반되는 지에 대한 유무이다L-LTP와 달리, E-LTP는 PKA와 protein synthesis 과정이 필요하지 않다고 알려져 있다 (Frey et al., 1993Mayford et al., 2012). 하지만, early 또는 late LTP라는 개념은 그 모호한 기준으로 인해 많은 논란이 야기되었다. 몇몇 연구 결과에 따르면, 한 번의 HFS만으로도 지속적으로 유지되는 LTP를 형성시킬 수 있으며, 심지어 이 LTP는 PKA 억제제에 의해서도 영향을 받지 않는 것을 확인할 수 있었다 (Bortolotto and Collingridge, 2000). 또한 LTP를 유도하는 여러 번의 HFS를 짧은 시간 간격으로 주었을 경우에는, PKA 및 protein synthesis에 의존성이 없음을 유전적 또는 약리학적 방법에 의해 확인된 바 있다 (Scharf et al., 2002Nguyen and Woo, 2003Zhang et al., 2011).
본 논문에서는 기존의 연구 결과와 새로이 발견한 내용을 토대로, LTP의 메커니즘을 설명하는 새로운 모델을 제시하였다 (fig. 12). 이 모델에 따르면, LTP는 PKA와 protein synthesis에 대한 의존성이라는 기준에 따라 크게 두 가지로 나뉜다여기서는 LTP1과 LTP2로 명명하여 구별하였다. LTP1은 한 번의 전기 자극 또는 여러 번의 전기 자극을 압축해서 주었을 때 유도되며, PKA와 protein synthesis의 과정을 필요로 하지 않는다. 반면, LTP2는 몇 분의 시간 간격을 둔 여러 번의 전기 자극에 의해서 유도되며, PKA와 protein synthesis 과정이 수반된다. 나아가, LTP1과 LTP2를 구별짓는 매개자로서, calcium-permeable AMPAR receptors (CP-AMPARs)를 시험해 보았다. CP-AMPARs는 LTP가 유도된 후 일시적으로 발현되며, 시냅스 내부의 분자적 매커니즘에 강한 영향을 줄 수 있는 것으로 알려져 있기 때문이다 (Cull-Candy et al., 2006Man, 2011). 이 논문에서는 LTP1에 의해서 CP-AMPARs가 발현되기 시작하며, LTP2가 유도되기 위해서는 CP-AMPARs가 필요하다는 것을 확인하였다. 이에 대한 설명으로, CP-AMPARs와 NMDA receptors를 통한 시냅스 내 강한 Ca2+ 유입이 LTP2 형성 조건을 만족시킬 수 있다고 판단하였다.
이 가설을 검증하기 위해, 쥐의 해마 CA1 세포에서 전기생리학 실험을 수행하였다. 약리학적 방법으로 접근하여 LTP 실험을 진행한 결과, 우리의 LTP 모델과 일치하는 데이터를 얻을 수 있었다. 결론적으로, 본 논문의 첫 번째 장에서는 LTP를 조절하는 분자적 메커니즘을 연구하였으며, 전기 자극 조건에 따라 PKA, protein synthesis, 그리고 CP-AMPARs의 역할이 달라진 다는 것을 확인하였다.
또한, long-term potentiation (LTP)의 가역성에 대해서 연구하였다 – 이 현상은 종종 depotentiation (DP)으로 불린다. LTP가 유도된 지 짧은 시간내에는 2 Hz와 같은 저주파 전기 자극 (low frequency stimulation, LFS)에 의해서 LTP 발현이 억제된다고 보고된 바 있다. 그러나 아직까지, LTP 유도 이후의 시간과 DP의 정도에 대한 상관관계를 체계적으로 비교한 연구는 이루어진 바 없다. 더욱이, DP의 분자적 메커니즘에 대해서는 잘 알려져 있지 않다.
본 논문의 두 번째 장에서는, DP의 특성과 메커니즘에 중점을 두어 연구하였다. 결과적으로, CA1 세포에서 DP의 정도와 LTP 유도 시간에 대한 체계적인 관계를 구축하였고, LFS에 의해 유도된 DP은 NMDA receptors (GluN2A/GluN2B를 포함하는)와 protein phosphatases에 의해 매개된다는 것을 확인하였다.Contents
List of Figures - P. 1
Abstract - P. 3
Chapter I. Stimulus parameters determine the role of PKA, protein synthesis, and CP-AMPARs in LTP
Introduction - P. 8
Experimental Procedure - P. 14
Results - P. 16
Figures - P. 21
Discussion - P. 36
Chapter II. Mechanisms of depotentiation
Introduction - P. 40
Experimental Procedure - P. 42
Results - P. 44
Figures - P. 47
Discussion - P. 55
References - P. 57
국문초록 - P. 66Maste
The induction of long-term plasticity of non-synaptic, synchronized activity by the activation of group I mGluRs
No full textIt is well established that activation of group I metabotropic glutamate receptors (mGluRs) produces long-lasting alterations in synaptic efficacy. We now demonstrate that activation of mGluRs can also induce long-term alterations in synchronised network activity that are both induced and expressed in the absence of chemical synaptic transmission. Specifically, in hippocampal slices in which synaptic transmission was eliminated by perfusing with a Ca 2+-free medium, the selective group I mGluR agonist 3,5-dihydroxyphenylglycine (DHPG) induced a persistent (>3 h) enhancement (>2-fold) of the frequency of synchronised bursting activity. The underlying biochemical mechanism responsible for the induction of this form of plasticity was similar to that for DHPG-induced long-term depression (LTD) in that it required the activation of tyrosine phosphatases. Also, like DHPG-induced LTD, this form of neuronal plasticity could be reversed by application of the mGluR antagonist α-methyl-4-carboxyphenylglycine (MCPG). This unusual form of plasticity, which presumably also occurs when synaptic transmission is intact, could contribute to long-term alterations in synchronised activity in hippocampal neuronal networks. © 2008 Elsevier Ltd. All rights reserved
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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