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排序方式: 共有1351条查询结果,搜索用时 265 毫秒
81.
Dietrich D Kirschstein T Kukley M Pereverzev A von der Brelie C Schneider T Beck H 《Neuron》2003,39(3):483-496
Ca2+ influx into presynaptic terminals via voltage-dependent Ca2+ channels triggers fast neurotransmitter release as well as different forms of synaptic plasticity. Using electrophysiological and genetic techniques we demonstrate that presynaptic Ca2+ entry through Cav2.3 subunits contributes to the induction of mossy fiber LTP and posttetanic potentiation by brief trains of presynaptic action potentials while they do not play a role in fast synaptic transmission, paired-pulse facilitation, or frequency facilitation. This functional specialization is most likely achieved by a localization remote from the release machinery and by a Cav2.3 channel-dependent facilitation of presynaptic Ca2+ influx. Thus, the presence of Cav2.3 channels boosts the accumulation of presynaptic Ca2+ triggering presynaptic LTP and posttetanic potentiation without affecting the low release probability that is a prerequisite for the enormous plasticity displayed by mossy fiber synapses. 相似文献
82.
Fibroblast growth factors (Fgfs) and their receptors have been implicated in embryonic pancreas development. Recently it was shown that Fgf10, a major ligand for the IIIb isoform of fibroblast growth factor receptor 2 (Fgfr2b), has an important regulatory role in early pancreas development. The aim of our study was to define the role of Fgfr2b in pancreas development by analyzing the phenotype of Fgfr2b (-/-) mice. Pancreases of Fgfr2b (-/-) embryos were noticeably smaller than the wild type littermates during embryogenesis, and pancreatic ductal branching as well as duct cell proliferation was significantly reduced. However, both exocrine and endocrine pancreatic differentiation occurred relatively normally. Exogenous addition of Fgfr2b ligands (Fgf7 and Fgf10) stimulated duct cell proliferation and inhibited endocrine cell differentiation in the ex vivo embryonic organ cultures of wild type pancreas. Our results thus suggest that Fgfr2b-mediated signaling plays a major role in pancreatic ductal proliferation and branching morphogenesis, but has little effect on endocrine and exocrine differentiation. 相似文献
83.
Imbach T Grünewald S Schenk B Burda P Schollen E Wevers RA Jaeken J de Klerk JB Berger EG Matthijs G Aebi M Hennet T 《Human genetics》2000,106(5):538-545
Congenital disorders of glycosylation (CDG), formerly known as carbohydrate-deficient glycoprotein syndrome, represent a family of genetic diseases with variable clinical presentations. Common to all types of CDG characterized to date is a defective Asn-linked glycosylation caused by enzymatic defects of N-glycan synthesis. Previously, we have identified a mutation in the ALG6 alpha1,3 glucosyltransferase gene as the cause of CDG-Ic in four related patients. Here, we present the identification of seven additional cases of CDG-Ic among a group of 35 untyped CDG patients. Analysis of lipid-linked oligosaccharides in fibroblasts confirmed the accumulation of dolichyl pyrophosphate-Man9GlcNAc2 in the CDG-Ic patients. The genomic organization of the human ALG6 gene was determined, revealing 14 exons spread over 55 kb. By polymerase chain reaction amplification and sequencing of ALG6 exons, three mutations, in addition to the previously described A333 V substitution, were detected in CDG-Ic patients. The detrimental effect of these mutations on ALG6 activity was confirmed by complementation of alg6 yeast mutants. Haplotype analysis of CDG-Ic patients revealed a founder effect for the ALG6 allele bearing the A333 V mutation. Although more than 80% of CDG are type Ia, CDG-Ic may be the second most common form of the disease. 相似文献
84.
85.
Biomanipulation as an Application of Food-Chain Theory: Constraints, Synthesis, and Recommendations for Temperate Lakes 总被引:25,自引:2,他引:23
Lars-Anders Hansson Helene Annadotter Eva Bergman Stellan F. Hamrin Erik Jeppesen Timo Kairesalo Eira Luokkanen Per-Åke Nilsson Martin Søndergaard John Strand 《Ecosystems》1998,1(6):558-574
The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation.
An important conclusion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation.
Instead, this process should be viewed as the “trigger” for secondary processes, such as establishment of submerged macrophytes,
reduced internal loading of nutrients, and reduced resuspension of particles from the sediment. However, fish reduction also
leads to a high recruitment of young-of-the-year (YOY) fish, which feed extensively on zooplankton. This expansion of YOY
the first years after fish reduction is probably a major reason for less successful biomanipulations. Recent, large-scale
biomanipulations have made it possible to update earlier recommendations regarding when, where, and how biomanipulation should
be performed. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75%
or more; (2) the fish reduction should be performed efficiently and rapidly (within 1–3 years); (3) efforts should be made
to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment
of submerged macrophytes should be improved; and (6) the external input of nutrients (phosphorus and nitrogen) should be reduced
as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly performed, the method also
achieves results in large, relatively deep and eutrophic lakes, at least in a 5-year perspective. Although repeated measures
may be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and
attractive method for management of eutrophic lakes, and in particular as a follow-up measure to reduced nutrient load.
Received 14 April 1998; accepted 31 August 1998 相似文献
86.
87.
Jari Ilmonen Lauri Paasivirta Risto Virtanen Timo Muotka 《Journal of Biogeography》2009,36(5):822-834
Aim To identify the most important environmental drivers of benthic macroinvertebrate assemblages in boreal springs at different spatial scales, and to assess how well benthic assemblages correspond to terrestrially derived ecoregions. Location Finland. Methods Benthic invertebrates were sampled from 153 springs across four boreal ecoregions of Finland, and these data were used to analyse patterns in assemblage variation in relation to environmental factors. Species data were classified using hierarchical divisive clustering (twinspan ) and ordinated using non‐metric multidimensional scaling. The prediction success of the species and environmental data into a priori (ecoregions) and a posteriori (twinspan ) groups was compared using discriminant function analysis. Indicator species analysis was used to identify indicator taxa for both a priori and a posteriori assemblage types. Results The main patterns in assemblage clusters were related to large‐scale geographical variation in temperature. A secondary gradient in species data reflected variation in local habitat structure, particularly abundance of minerogenic spring brooks. Water chemistry variables were only weakly related to assemblage variation. Several indicator species representing southern faunistic elements in boreal springs were identified. Discriminant function analysis showed poorer success in classifying sites into ecoregions based on environmental than on species data. Similarly, when classifying springs into the twinspan groups, classification based on species data vastly outperformed that based on environmental data. Main conclusions A latitudinal zonation pattern of spring assemblages driven by regional thermal conditions is documented, closely paralleling corresponding latitudinal patterns in both terrestrial and freshwater assemblages in Fennoscandia. The importance of local‐scale environmental variables increased with decreasing spatial extent. Ecoregions provide an initial stratification scheme for the bioassessment of benthic macroinvertebrates of North European springs. Our results imply that climate warming, landscape disturbance and degradation of spring habitat pose serious threats to spring biodiversity in northern Europe, especially to its already threatened southern faunistic elements. 相似文献
88.
89.
Johanna H?stbacka Filip Fredén Maarit Hult Maria Bergquist Erika Wilkman Jyrki Vuola Timo Sorsa Taina Tervahartiala Fredrik Huss 《PloS one》2015,10(5)
IntroductionMatrix metalloproteinases (MMPs) -8 and -9 are released from neutrophils in acute inflammation and may contribute to permeability changes in burn injury. In retrospective studies on sepsis, levels of MMP-8, MMP-9, and tissue inhibitor of metalloproteinase-1 (TIMP-1) differed from those of healthy controls, and TIMP-1 showed an association with outcome. Our objective was to investigate the relationship between these proteins and disease severity and outcome in burn patients.MethodsIn this prospective, observational, two-center study, we collected plasma samples from admission to day 21 post-burn, and burn blister fluid samples on admission. We compared MMP-8, -9, and TIMP-1 levels between TBSA<20% (N = 19) and TBSA>20% (N = 30) injured patients and healthy controls, and between 90-day survivors and non-survivors. MMP-8, -9, and TIMP-1 levels at 24-48 hours from injury, their maximal levels, and their time-adjusted means were compared between groups. Correlations with clinical parameters and the extent of burn were analyzed. MMP-8, -9, and TIMP-1 levels in burn blister fluids were also studied.ResultsPlasma MMP-8 and -9 were higher in patients than in healthy controls (P<0.001 and P = 0.016), but only MMP-8 differed between the TBSA<20% and TBSA>20% groups. MMP-8 and -9 were not associated with clinical severity or outcome measures. TIMP-1 differed significantly between patients and controls (P<0.001) and between TBSA<20% and TBSA>20% groups (P<0.002). TIMP-1 was associated with 90-day mortality and correlated with the extent of injury and clinical measures of disease severity. TIMP-1 may serve as a new biomarker in outcome prognostication of burn patients. 相似文献
90.
Miikka Tarkia Antti Saraste Christoffer Stark Tommi V?h?silta Timo Savunen Marjatta Strandberg Virva Saunavaara Tuula Tolvanen Jarmo Teuho Mika Ter?s Olli Mets?l? Petteri Rinne Ilkka Heinonen Nina Savisto Mikko Pietil? Pekka Saukko Anne Roivainen Juhani Knuuti 《PloS one》2015,10(6)