1,721,001 research outputs found
Protein homeostasis in neurons and its pathological alterations
No full textIn neuronal cells, proteins are synthesized on ribosomes from the genetic information encoded in DNA. In some instances translation takes place at the neuronal cell soma but in other it occurs at distal location, such as in a dendritic spine. Folding is usually initiated before the completion of protein synthesis and its outcome strictly depends on the local environment in which the nascent protein is submerged. Incompletely folded proteins and, more importantly, misfolded proteins are under the surveillance of several quality control systems that re-establish the correct conformation or initiate protein degradation. Regulation and maintenance of these systems is a vital issue for neuronal and glial cells, and impairments at different levels leads to neurodegenerative diseases
Mechanisms of spontaneous miniature activity at CA3-CA1 synapses: evidence for a divergence from a random Poisson process
No full textIndependent regulation of Rap1 and mitogen-activated protein kinase by the alpha chain of Go
No full textReceptors coupled to G(i/o) proteins stimulate the mitogen-activated protein kinase (MAPK) cascade. The intracellular pathways linking the alpha chains of these G proteins to MAPK activation are not completely understood. One of the signaling molecules which has been suggested to act downstream of Galpha(i/o) is the small G protein Rap1. We investigated the role of Rap1 in MAPK stimulation by Galpha(o) in Chinese hamster ovary (CHO) cells. Our previous results have shown that in this cell system activated Galpha(o) strongly potentiates the MAPK response to the epidermal growth factor (EGF) receptor. Rap1 regulation was examined in cells transfected with Rap1 and wild-type Galpha(o) or the activated mutant Galpha(o)-Q205L. Immunocytochemical analysis detected both Rap1 and the Galpha(o) subunit at the plasma membrane as well as on perinuclear cytoplasmic vesicles. Expression of wild-type Galpha(o) had no significant effect on the levels of activated Rap1. In contrast, Galpha(o)-Q205L virtually abolished the activation of Rap1 induced by EGF. Further experiments showed that MAPK stimulation by EGF was greatly inhibited by expression of activated Rap1, suggesting that Rap1 inhibition could mediate the effect of Galpha(o) on the MAPK cascade. However, Galpha(o)-Q205L efficiently inhibited the activation of Rap1 induced by fibroblast growth factor (FGF). We have previously found that the ability of FGF to activate MAPK is not modified by Galpha(o). In addition, expression of the GAP protein RAP1GAPII blocked Rap1 activation without affecting EGF- or FGF-dependent MAPK stimulation. These findings provide evidence for independent regulation of Rap1 and MAPK by the G(o )alpha chain
EGF raises cytosolic Ca2+ in A431 and Swiss 3T3 cells by a dual mechanism. Redistribution from intracellular stores and stimulated influx
No full textThe changes in Ca2+ homeostasis and phosphoinositide hydrolysis induced by EGF were studied in human epidermoid carcinoma A431 cells both when attached to a substratum and after detachment and suspension. The cytosolic Ca2+ concentration was measured by the conventional fluorimetric technique, using the specific probe, quin2, as well as by a new microscopic technique in which single cells are investigated after loading with another probe, fura-2. EGF applied in the complete, Ca2+-containing medium caused a rapid rise in the cytosolic Ca2+ concentration, that remained elevated for several minutes. In Ca2+-free, EGTA-containing medium, part of this response persisted, as revealed by quin2 results in suspended cells and microscopic results with fura-2. The lack of Ca2+ rise seen in attached cells loaded with quin2 and treated with EGF in Ca2+-free medium was probably the result of a Ca2+ buffer artifact. Concomitantly to the Ca2+ signal, EGF induced phosphoinositide hydrolysis, with stimulated accumulation of inositol 1,3,4,trisphosphate and -1,3,4,5-tetrakisphosphate. These results, as well as additional microscopic fura-2 results in Swiss 3T3 fibroblasts, demonstrate that the Ca2+ signal elicited by EGF is due to two components: redistribution from an intracellular store (possibly mediated by generation of inositol trisphosphate) and stimulated influx across the plasmalemma. This latter process was not detected in 3T3 cells treated with either PDGF or bombesin (growth factors that cause much greater phosphoinositide hydrolysis and Ca2+ redistribution responses than EGF). It is therefore suggested that the Ca2+ influx effect of EGF is under the control of a separate, as yet unidentified mechanism
Detection of Fractal Behavior in Temporal Series of Synaptic Quantal Release Events: A Feasibility Study
Full text linkSince the pioneering work of Fatt & Katz at the neuromuscular junction (NMJ), spontaneous synaptic release, i.e. the quantal discharge of neurotransmitter molecules which occurs in the absence of action potentials (minis), has been unanimously considered a memoryless random Poisson process where each quantum is discharged with a very low release probability independently from neighboring quanta. When this model was thoroughly tested, for both population and single-synapse recordings, some clear evidence in favor of a more complex scenario emerged. This included short and long-range correlation in mini occurrences and divergence from mono-exponential inter-mini interval distributions, both unexpected for a homogeneous Poisson process, i.e. with a rate parameter that does not change over time. Since we are interested in accurately quantifying the fractal exponent α of the spontaneous neurotransmitter release process at central synaptic sites, this work is aimed at evaluating the sensitivity of the most established methods available, such as the periodogram, the Allan factor and the detrended fluctuation analysis. For this analysis we used spontaneous release series recorded at individual hippocampal synapses (single-synapse recordings). Based on these data, we generated large collections of simulated quantal events by means of a custom algorithm combining Monte Carlo sampling methods with spectral methods for the generation of 1/f series. These tests were performed by separately varying the fractal exponent α of the rate driving the release process; ii) the distribution of intervals between successive releases, mimicking those encountered in single-synapse experimental series; iii) the number of samples. Our results aim at providing a methodological framework for approaching the fractal analysis of single-unit spontaneous release series recorded at central synapses
Characterization of persistent pre-synaptic enhancement in S-LTP and L-LTP: evidence for recruitment of silent terminals.
No full textCalcium : the common theme in vesicular cycling
No full textSynaptic vesicle release is known to depend on calcium. A new technique for separating endocytosis from exocytosis now shows that calcium regulates both processes
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
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