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排序方式: 共有644条查询结果,搜索用时 28 毫秒
101.
J. Falk-Vairant P. Corrèges L. Eder-Colli N. Salem F. M. Meunier B. Lesbats F. Loctin †M. Synguelakis M. Israël Y. Dunant 《Journal of neurochemistry》1996,66(3):1322-1325
Abstract: Transmitter release was elicited in two ways from cultured cells filled with acetylcholine: (a) in a biochemical assay by successive addition of a calcium ionophore and calcium and (b) electrophysiologically, by electrical stimulation of individual cells and real-time recording with an embryonic Xenopus myocyte. Glioma C6-Bu-1 cells were found to be competent for Ca2+ -dependent and quantal release. In contrast, no release could be elicited from mouse neuroblastoma N18TG-2 cells. However, acetylcholine release could be restored when N18TG-2 cells were transfected with a plasmid coding for mediatophore. Mediatophore is a protein of nerve terminal membranes purified from the Torpedo electric organ on the basis of its acetylcholine-releasing capacity. The transfected N18TG-2 cells expressed Torpedo mediatophore in their plasma membrane. In response to an electrical stimulus, they generated in the myocyte evoked currents that were curare sensitive and calcium dependent and displayed discrete amplitude levels, like in naturally occurring synapses. 相似文献
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105.
The major histocompatibility complex (MHC) presents a unique system to explore links between genetic diversity and pathogens, as diversity within MHC is maintained in part by pathogen driven selection. While the majority of wildlife MHC studies have investigated species that are of conservation concern, here we characterize MHC variation in a common and broadly distributed species, the North American raccoon (Procyon lotor). Raccoons host an array of broadly distributed wildlife diseases (e.g., canine distemper, parvovirus and raccoon rabies virus) and present important human health risks as they persist in high densities and in close proximity to humans and livestock. To further explore how genetic variation influences the spread and maintenance of disease in raccoons we characterized a fragment of MHC class II DRA exon 3 (250bp) and DRB exon 2 (228 bp). MHC DRA was found to be functionally monomorphic in the 32 individuals screened; whereas DRB exon 2 revealed 66 unique alleles among the 246 individuals screened. Between two and four alleles were observed in each individual suggesting we were amplifying a duplicated DRB locus. Nucleotide differences between DRB alleles ranged from 1 to 36 bp (0.4–15.8% divergence) and translated into 1 to 21 (1.3–27.6% divergence) amino acid differences. We detected a significant excess of nonsynonymous substitutions at the peptide binding region (P = 0.005), indicating that DRB exon 2 in raccoons has been influenced by positive selection. These data will form the basis of continued analyses into the spatial and temporal relationship of the raccoon rabies virus and the immunogenetic response in its primary host. 相似文献
106.
Although rabbit ear vessels are readily accessible, the veins can collapse and thrombose after multiple venipunctures, and the artery may undergo vasospasm when repeatedly catheterized. Twenty-two male and female New Zealand White rabbits were cannulated with the catheter tip located in the jugular vein. The mean life of the port was noted to be approximately 3.5 months, with ranges of 3 days to 10 months. With proper maintenance and care, vascular access ports are a useful alternative to multiple venipuncture for long-term studies, thereby sparing marginal and central vessels and minimizing stress to both animals and investigators. 相似文献
107.
Claude Meunier 《Biological cybernetics》1992,67(5):461-468
We study two different two-dimensional reductions of the Hodgkin-Huxley equations. We show that they display the same qualitative bifurcation scheme as the original equations but overestimate the current range where periodic emission occurs. This is essentially due to the assumption that the evolution of the sodium activation variable m is instantaneous with respect to the dynamics of the variables h and n, an hypothesis that breaks down at high values of the injected current. To prove this point we compare the current-amplitude relation, the current-frequency relation, and the shapes of individual spikes for the two reduced models to the results obtained for the original Hodgkin-Huxley model and for a three dimensional model with instantaneous sodium activation. We show that a more satisfying agreement with the original Hodgkin-Huxley equations is obtained if we modify the evolution equation for the potential by incorporating the prominent features of the dynamics of m. 相似文献
108.
Elodie Claverie Félicien Meunier Mathieu Javaux Walid Sadok 《Physiologia plantarum》2018,162(3):290-300
Increasing evidence suggests that in crops, nocturnal water use could represent 30% of daytime water consumption, particularly in semi‐arid and arid areas. This raises the questions of whether nocturnal transpiration rates (TRN) are (1) less influenced by drought than daytime TR (TRD), (2) increased by higher nocturnal vapor pressure deficit (VPDN), which prevails in such environments and (3) involved in crop drought tolerance. In this investigation, we addressed those questions by subjecting two wheat genotypes differing in drought tolerance to progressive soil drying under two long‐term VPDN regimes imposed under naturally fluctuating conditions. A first goal was to characterize the response curves of whole‐plant TRN and TRN/TRD ratios to progressive soil drying. A second goal was to examine the effect of VPDN increase on TRN response to soil drying and on 13 other developmental traits. The study revealed that under drought, TRN was not responsive to progressive soil drying and – intriguingly – that TRN seemingly increased with drought under high VPDN consistently for the drought‐sensitive genotype. Because TRD was concomitantly decreasing with progressive drought, this resulted in TRN representing up to 70% of TRD at the end of the drydown. In addition, under drought, VPDN increase was found not to influence traits such as leaf area or stomata density. Overall, those findings indicate that TRN contribution to daily water use under drought might be much higher than previously thought, that it is controlled by specific mechanisms and that decreasing TRN under drought might be a valuable trait for improving drought tolerance. 相似文献
109.
pH as a proxy for estimating plant-available Si? A case study in rice fields in Karnataka (South India) 总被引:1,自引:0,他引:1
Jean-Dominique Meunier Kollalu Sandhya Nagabovanalli B. Prakash Daniel Borschneck Philippe Dussouillez 《Plant and Soil》2018,431(1-2):143-157
Background and aims
Soil nutrient dynamics are affected by root-microbe interactions and plant development. We investigated the influence of plant growth stage and arbuscular mycorrhiza fungi (AMF) on carbon (C) and nitrogen (N) rhizodeposition and the transfer into the microbial biomass (MB).Methods
Pea varieties (Pisum sativum L.) with (Frisson) and without mycorrhiza (P2) were 13C-15N-labelled and harvested at 45, 63, 71, and 95 days after sowing. Mycorrhization, MB, total C, N, 13C, 15N were determined in plant and soil compartments to calculate C and N derived from rhizodeposition (CdfR, NdfR).Results
Total CdfR increased until pea maturity, NdfR until end of flowering. Their relative contribution steadily decreased over time, accounting for 4–10% of total plant C and N at harvest. Rhizodeposition contributed between 1 and 6% to MB C and N, although 20% of the rhizodeposits were discovered in the MB. Frisson released more NdfR than P2 but it was not possible to accurately estimate AMF effects on C and N due to differences in biomass partitioning.Conclusions
CdfR followed an even flow from early growth until senescence. NdfR flow ceased after flowering possibly due to N relocation within the plant. Rhizodeposits contribute very little to MB in our study.110.
Temporal Changes in State Transitions and Photosystem Organization in the Unicellular,Diazotrophic Cyanobacterium Cyanothece sp. ATCC 51142 总被引:2,自引:1,他引:1
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The unicellular Cyanobacterium Cyanothece sp. ATCC 51142, grown under alternating 12-h light/12-h dark conditions, temporally separated N2 fixation from photosynthesis. The regulation of photosynthesis was studied using fluorescence spectra and kinetics to determine changes in state transitions and photosystem organization. The redox poise of the plastoquinone (PQ) pool appeared to be central to this regulation. Respiration supported N2 fixation by oxidizing carbohydrate granules, but reduced the PQ pool. This induced state 2 photosystem II monomers and lowered the capacity for O2 evolution. State 2 favored photosystem I trimers and cyclic electron transport, which could stimulate N2 fixation; the stimulation suggested an ATP limitation to N2 and CO2 fixation. The exhaustion of carbohydrate granules at around 6 h in the dark resulted in reduced respiratory electron flow, which led to a more oxidized PQ pool and produced a sharp transition from state 2 to state 1. This transient state 1 returned to state 2 in the remaining hours of darkness. In the light phase, photosystem II dimerization correlated with increased phycobilisome coupling to photosystem II (state 1) and increased rates of O2 evolution. However, dark adaptation did not guarantee state 2 and left photosystem I centers in a mostly monomeric state at certain times. 相似文献