1,721,041 research outputs found
Visual stimuli-induced LTD of GABAergic synapses mediated by presynaptic NMDA receptors
No full textLocal GABA (gamma-aminobutyric acid) circuits contribute to sensory experience-dependent refinement of neuronal connections in the developing nervous system, but whether GABAergic synapses themselves can be rapidly modified by sensory stimuli is largely unknown. Here we report that repetitive light stimuli or theta burst stimulation (TBS) of the optic nerve in the developing Xenopus retinotectal system induces long-term potentiation (LTP) of glutamatergic inputs but long-term depression (LTD) of GABAergic inputs to the same tectal neuron. The LTD is due to a reduction in presynaptic GABA release and requires activation of presynaptic NMDA (N-methyl-D-aspartate) receptors (NMDARs) and coincident high-level GABAergic activity. Thus, the presynaptic NMDAR may function as a coincidence detector for adjacent glutamatergic and GABAergic activities, leading to coordinated synaptic modification by sensory experience
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Cocaine-induced Modification of Synaptic Plasticity in Rat Medial Prefrontal Cortex
Full text linkMedial prefrontal cortex (mPFC) is involved in relapse after withdrawal for cocaine exposure, but changes in synaptic function and plasticity in the mPFC during the period of withdrawal remain largely unknown. After the termination of repeated cocaine treatments in rats, I observed a gradual enhancement in the susceptibility of excitatory synapses on layer V mPFC pyramidal neurons to activity-induced long-term potentiation (LTP). This enhanced synaptic plasticity could be attributed to a gradual increase in the expression of brain-derived neurotrophic factor (BDNF) and its suppression of GABAergic inhibition in the mPFC via reducing the surface expression of GABAA receptors. The BDNF effect is mediated by TrkB activation in these neurons and accompanied by elevated protein phosphatase 2A activity and increased de-phosphorylation of GABAA receptor beta3 subunit in the mPFC. Thus, elevated BDNF expression during cocaine withdrawal sensitizes the excitatory inputs in the mPFC for activity-induced persistent synaptic potentiation that may contribute to cue-induced drug craving and seeking.Prenatal cocaine-exposed new-born babies could be considered as undergoing withdrawal from cocaine exposure in utero. Previous studies have shown that prenatal cocaine exposure results in abnormal brain development and cognitive dysfunction, but the underlying cellular mechanism remains largely unclear. I proposed the hypothesis that prenatal cocaine exposure may cause similar modification of synaptic plasticity in the mPFC as that found in above cocaine withdrawal studies in juvenile rats. Thus, in the second part of my study, I examined synaptic functions in the mPFC of postnatal rats which were exposed to cocaine in utero, using whole-cell recording from mPFC layer V pyramidal neurons in acute brain slices. I found that cocaine exposure in utero also resulted in a facilitated LTP of excitatory synapses on these pyramidal neurons and an elevated neuronal excitability in postnatal rat pups after P15. This facilitated LTP could be largely attributed to the reduction of GABAergic inhibition. Biochemical assays of isolated mPFC tissue from postnatal rats further showed that cocaine exposure in utero caused a marked reduction in the surface expression of GABAA receptor subunits alpha1, beta2, and beta3, but had no effect on glutamate receptor subunit GluR1. Both facilitated LTP and reduced surface expression of GABAA receptors persisted in rats up to at least P42. Finally, the behavioral consequence of cocaine exposure in utero was reflected by the reduction in the sensitivity of locomotor activity in postnatal rats to cocaine and the dopamine receptor agonist apomorphine. Since the mPFC plays important roles in cognitive functions, these findings offer new insights into the cellular mechanism underlying the adverse effects of cocaine exposure in utero on brain development and cognitive functions.In summary, this thesis work showed that excitatory inputs to mPFC layer V pyramidal neurons are sensitized for activity-induced persistent synaptic potentiation due to the reduction of GABAergic inhibition after withdrawal from repeated cocaine exposure either in utero or after birth. These findings have increased our understanding of the neurobiological basis of cocaine addiction and may help to establish more thorough pharmacological treatments for cocaine addiction
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
Spike Timing-Dependent Plasticity of Neural Circuits
No full textAbstractRecent findings of spike timing-dependent plasticity (STDP) have stimulated much interest among experimentalists and theorists. Beyond the traditional correlation-based Hebbian plasticity, STDP opens up new avenues for understanding information coding and circuit plasticity that depend on the precise timing of neuronal spikes. Here we summarize experimental characterization of STDP at various synapses, the underlying cellular mechanisms, and the associated changes in neuronal excitability and dendritic integration. We also describe STDP in the context of complex spike patterns and its dependence on the dendritic location of the synapse. Finally, we discuss timing-dependent modification of neuronal receptive fields and human visual perception and the computational significance of STDP as a synaptic learning rule
Spike Timing-Dependent LTP/LTD Mediates Visual Experience-Dependent Plasticity in a Developing Retinotectal System
No full textSummarySensory experience plays an instructive role in the development of the nervous system. Here we showed that visual experience can induce persistent modification of developing retinotectal circuits via spike timing-dependent plasticity (STDP). Pairing light stimuli with spiking of the tectal cell induced persistent enhancement or reduction of light-evoked responses, with a dependence on the relative timing between light stimulus and postsynaptic spiking similar to that for STDP. Using precisely timed sequential three-bar stimulation to mimic a moving bar, we showed that spike timing-dependent LTP/LTD can account for the asymmetric modification of the tectal cell receptive field induced by moving bar. Furthermore, selective inhibition of signaling mediated by brain-derived neurotrophic factor and nitric oxide, which are respectively required for light-induced LTP and LTD, interfered with moving bar-induced temporally specific changes in the tectal cell responses. Together, these findings suggest that STDP can mediate sensory experience-dependent circuit refinement in the developing nervous system
Spike Train Timing-Dependent Associative Modification of Hippocampal CA3 Recurrent Synapses by Mossy Fibers
No full textAbstractIn the CA3 region of the hippocampus, extensive recurrent associational/commissural (A/C) connections made by pyramidal cells may function as a network for associative memory storage and recall. We here report that long-term potentiation (LTP) at the A/C synapses can be induced by association of brief spike trains in mossy fibers (MFs) from the dentate gyrus and A/C fibers. This LTP not only required substantial overlap between spike trains in MFs and A/C fibers, but also depended on the temporal order of these spike trains in a manner not predicted by the well-known rule of spike timing-dependent plasticity and requiring activation of type 1 metabotropic glutamate receptors. Importantly, spike trains in a putative single MF input provided effective postsynaptic activity for the induction of LTP at A/C synapses. Thus, the timing of spike trains in individual MFs may code information that is crucial for the associative modification of CA3 recurrent synapses
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
Activity-Dependent Neural Plasticity from Bench to Bedside
No full textMuch progress has been made in understanding how behavioral experience and neural activity can modify the structure and function of neural circuits during development and in the adult brain. Studies of physiological and molecular mechanisms underlying activity-dependent plasticity in animal models have suggested potential therapeutic approaches for a wide range of brain disorders in humans. Physiological and electrical stimulations as well as plasticity-modifying molecular agents may facilitate functional recovery by selectively enhancing existing neural circuits or promoting the formation of new functional circuits. Here, we review the advances in basic studies of neural plasticity mechanisms in developing and adult nervous systems and current clinical treatments that harness neural plasticity, and we offer perspectives on future development of plasticity-based therapy
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