802 research outputs found
Identification of Nicotinic Acetylcholine Receptor Recycling and Its Role inn Maintaining Receptor Density at the Neuromuscular Junction \u3cem\u3eIn Vivo\u3c/em\u3e
In the CNS, receptor recycling is critical for synaptic plasticity; however, the recycling of receptors has never been observed at peripheral synapses. Using a novel imaging technique, we show here that nicotinic acetylcholine receptors (AChRs) recycle into the postsynaptic membrane of the neuromuscular junction. By sequentially labeling AChRs with biotin-bungarotoxin and streptavidin-fluorophore conjugates, we were able to distinguish recycled, preexisting, and new receptor pools at synapses in living mice. Time-lapse imaging revealed that recycled AChRs were incorporated into the synapse within hours of initial labeling, and their numbers increased with time. At fully functional synapses, AChR recycling was robust and comparable in magnitude with the insertion of newly synthesized receptors, whereas chronic synaptic activity blockade nearly abolished receptor recycling. Finally, using the same sequential labeling method, we found that acetylcholinesterase, another synaptic component, does not recycle. These results identify an activity-dependent AChR-recycling mechanism that enables the regulation of receptor density, which could lead to rapid alterations in synaptic efficacy
Second-generation antihistamines: a study of poisoning in children
The toxicity of second-generation antihistamines after an overdose by a child is still unknown. The objective of this study is to use data from Poisons Centres in France to describe the toxicity profile of second-generation antihistamines for children and to compare the severity of poisoning observed from these with a first-generation antihistamine. This was a retrospective, multi-centre and observational study focusing on human cases of single-substance exposure to a second-generation antihistamine and to mequitazine, reported between 1 January 2001 and 31 December 2016 in Poisons Centres in France. From a total of 9403 children included, 5980 were exposed to a second-generation antihistamine and 3423 were exposed to mequitazine. The severity of exposure to second-generation antihistamines in children is low: among the children followed until a known outcome, 9% of children were symptomatic and in 97% of cases, the symptoms shown were of a minor-level severity (primarily drowsiness or restlessness). Depending on the substance, children who ingested doses 16 to 69 times the maximum recommended therapeutic dose remained asymptomatic. No deaths or severe symptoms were observed. No cases of lengthening of the QT interval or arrhythmias were identified. Mequitazine led to more symptoms than other substances (14.8% symptomatic children vs. 7.5%, Odd ratio (OR): 2.3 (2.0-2.6), pâ<â0.0001), more symptoms of moderate intensity (1.4 vs. 0.2%, OR: 8.3 (4.1-18.5), pâ<â0.0001) and more hospitalisation (19.1 vs. 8.7%, OR: 2.5, 95% CI: (2.2-2.8), pâ<â0.0001). The severity of poisoning from second-generation antihistamines appears to be low among children and considerably lower than poisoning caused by mequitazine
Social Functioning and Self-Esteem in Young People with Disabilities Participating in Adapted Competitive Sport
Aims: The aim of this study was to investigate social functioning quality of life and self-esteem in young people with disabilities taking part in adapted competitive sport.Method: A sample of 496 athletes (mean age 16 years 4 months, range: 9 years to 20 years 9 months) was obtained from the 540 participants (91.8%) involved in a French national championship. The main outcome measurements were a social functioning inventory (PedsQL 4.0 social functioning) and a self-esteem inventory in physical areas (physical self inventory 6 PSI-6). Results: The mean PedsQL SF score was 74.6 (SD: 17.7). Comparisons of PedsQL SF according to gender, age, self mobility and training revealed no significant differences between the groups. PedsQL SF was weakly but significantly correlated with all subscales of the PSI-6 in the total population. PSI-6 scores were significantly different between boys and girls, with better self-esteem for boys on general self-esteem (7.7 vs. 6.9, p=0.018), physical condition (6.8 vs. 6.0, p=0.023) and attractive body subscores (6.5 vs. 5.1, p<0.001). Conclusion: Social functioning scores were significantly higher in this population than in the samples of young people with disabilities available in the literature. Interactions between self-concept, social functioning quality of life and participation in adapted sport activities require further studies
Eigenvalue estimates for non-selfadjoint Dirac operators on the real line
We show that the non-embedded eigenvalues of the Dirac operator on the real
line with non-Hermitian potential lie in the disjoint union of two disks in
the right and left half plane, respectively, provided that the of
is bounded from above by the speed of light times the reduced Planck
constant. An analogous result for the Schr\"odinger operator, originally proved
by Abramov, Aslanyan and Davies, emerges in the nonrelativistic limit. For
massless Dirac operators, the condition on implies the absence of nonreal
eigenvalues. Our results are further generalized to potentials with slower
decay at infinity. As an application, we determine bounds on resonances and
embedded eigenvalues of Dirac operators with Hermitian dilation-analytic
potentials
Scattering Theory Approach to Random Schroedinger Operators in One Dimension
Methods from scattering theory are introduced to analyze random Schroedinger
operators in one dimension by applying a volume cutoff to the potential. The
key ingredient is the Lifshitz-Krein spectral shift function, which is related
to the scattering phase by the theorem of Birman and Krein. The spectral shift
density is defined as the "thermodynamic limit" of the spectral shift function
per unit length of the interaction region. This density is shown to be equal to
the difference of the densities of states for the free and the interacting
Hamiltonians. Based on this construction, we give a new proof of the Thouless
formula. We provide a prescription how to obtain the Lyapunov exponent from the
scattering matrix, which suggest a way how to extend this notion to the higher
dimensional case. This prescription also allows a characterization of those
energies which have vanishing Lyapunov exponent.Comment: 1 figur
Does enhanced nitrogen deposition represent a threat to Sphagnum and thus the sustainability of Scottish peatlands?
Nutrient limited ombrotrophic bogs and peatlands support high conservation valued ecosystems, potentially susceptible to current elevated levels of reactive nitrogen (N) deposition. Here, we present the effects and consequences of different N forms, wet, dry, reduced and oxidised N on the functioning of a bog moss, Sphagnum capillifolium. Sphagnum mosses maintain the acid, low nutrient conditions, crucial for the sustainability of peat lands, where productivity must exceed decomposition. Dry deposited ammonia substantially elevated shoot N status, which led to tissue breakdown loss of function and death in S. capillifolium. Wet deposited nitrate and ammonium also negatively affected S. capillifolium, significantly reducing shoot extension and cover and significantly elevating N status. These effects occurred over 5 years and were significant even at the lowest reduced N dose, 8 kg N ha-1 y1 (background = 8-10 kg N ha-1 y-1), highlighting the threat N poses for the effective functioning of bog ecosystems
Zitterbewegung and semiclassical observables for the Dirac equation
In a semiclassical context we investigate the Zitterbewegung of relativistic
particles with spin 1/2 moving in external fields. It is shown that the
analogue of Zitterbewegung for general observables can be removed to arbitrary
order in \hbar by projecting to dynamically almost invariant subspaces of the
quantum mechanical Hilbert space which are associated with particles and
anti-particles. This not only allows to identify observables with a
semiclassical meaning, but also to recover combined classical dynamics for the
translational and spin degrees of freedom. Finally, we discuss properties of
eigenspinors of a Dirac-Hamiltonian when these are projected to the almost
invariant subspaces, including the phenomenon of quantum ergodicity
Tailored voltage waveform capacitively coupled plasmas in electronegative gases : frequency dependence of asymmetry effects
Capacitively coupled radio frequency plasmas operated in an electronegative gas (CF4) and driven by voltage waveforms composed of four consecutive harmonics are investigated for different fundamental driving frequencies using PIC/MCC simulations and an analytical model. As has been observed previously for electropositive gases, the application of peak-shaped waveforms (that are characterized by a strong amplitude asymmetry) results in the development of a DC self-bias due to the electrical asymmetry effect (EAE), which increases the energy of ions arriving at the powered electrode. In contrast to the electropositive case (Korolov et al 2012 J. Phys. D: Appl. Phys. 45 465202) the absolute value of the DC self-bias is found to increase as the fundamental frequency is reduced in this electronegative discharge, providing an increased range over which the DC self-bias can be controlled. The analytical model reveals that this increased DC self-bias is caused by changes in the spatial profile and the mean value of the net charge density in the grounded electrode sheath. The spatio-temporally resolved simulation data show that as the frequency is reduced the grounded electrode sheath region becomes electronegative. The presence of negative ions in this sheath leads to very different dynamics of the power absorption of electrons, which in turn enhances the local electronegativity and plasma density via ionization and attachment processes. The ion flux to the grounded electrode (where the ion energy is lowest) can be up to twice that to the powered electrode. At the same time, while the mean ion energies at both electrodes are quite different, their ratio remains approximately constant for all base frequencies studied here
Random repeated quantum interactions and random invariant states
We consider a generalized model of repeated quantum interactions, where a
system is interacting in a random way with a sequence of
independent quantum systems . Two types of randomness
are studied in detail. One is provided by considering Haar-distributed
unitaries to describe each interaction between and
. The other involves random quantum states describing each copy
. In the limit of a large number of interactions, we present
convergence results for the asymptotic state of . This is achieved
by studying spectral properties of (random) quantum channels which guarantee
the existence of unique invariant states. Finally this allows to introduce a
new physically motivated ensemble of random density matrices called the
\emph{asymptotic induced ensemble}
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