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排序方式: 共有220条查询结果,搜索用时 93 毫秒
101.
Maximilian Schultheiss Sven Schnichels Thoralf Hermann Jose Hurst Marita Feldkaemper Blanca Arango-Gonzalez Marius Ueffing Karl U. Bartz-Schmidt Guenther Zeck Martin S. Spitzer 《PloS one》2016,11(2)
Purpose
Hypothermia has been shown to be neuroprotective in the therapy of ischemic stroke in the brain. To date no studies exist on the level of the inner retina and it is unclear if hypothermia would prolong the ischemic tolerance time of retinal ganglion cells, which are decisive in many ischemic retinopathies.Methods
Bovine eyes were enucleated and stored either at 21°C or 37°C for 100 or 340 minutes, respectively. Afterwards the globes were dissected, the retina was prepared and either the spontaneous ganglion cell responses were measured or the retina was incubated as an organotypic culture for additional 24 hours. After incubation the retina was either processed for histology (H&E and DAPI staining) or real-time PCR (Thy-1 expression) was performed.Results
Hypothermia prolonged ganglion cell survival up to 340 minutes under ischemic conditions. In contrast to eyes kept at 37°C the eyes stored at 21°C still showed spontaneous ganglion cell spiking (56.8% versus 0%), a 5.8 fold higher Thy-1 mRNA expression (not significant, but a trend) and a preserved retinal structure after 340 minutes of ischemia.Conclusion
Hypothermia protects retinal ganglion cells against ischemia and prolongs their ischemic tolerance time. 相似文献102.
Thoralf Christoffersen Trond Berg 《Biochimica et Biophysica Acta (BBA)/General Subjects》1975,381(1):72-77
The hormone control of cyclic AMP-formation in isolated parenchymal liver cells from rats fed the carcinogen 2-acetylaminofluorene (0.025% for 4–8 weeks) was studied. The cells from the carcinogen-treated animals responded much more strongly to adrenergic agents than cells from control animals, while no significant difference was found for the glucagon effect. Of the adrenergic substances studied, the order of potency was isoprenalin ⩾ adrenalin > phenylephrine; stimulation was blocked by propranolol, but not by phentolamine. The effects of supramaximal concentrations of isoprenalin and glucagon were not additive. 相似文献
103.
104.
Hila Gingold Disa Tehler Nanna R. Christoffersen Morten M. Nielsen Fazila Asmar Susanne M. Kooistra Nicolaj S. Christophersen Lise Lotte Christensen Michael Borre Karina D. Sørensen Lars D. Andersen Claus L. Andersen Esther Hulleman Tom Wurdinger Elisabeth Ralfkiær Kristian Helin Kirsten Grønbæk Torben Ørntoft Sebastian M. Waszak Orna Dahan Jakob Skou Pedersen Anders H. Lund Yitzhak Pilpel 《Cell》2014
105.
Lars O. Mortensen Erik Jeppesen Niels Martin Schmidt Kirsten S. Christoffersen Mikkel P. Tamstorf Mads C. Forchhammer 《Polar Biology》2014,37(8):1073-1082
The high arctic is undergoing a faster change in climate than most other regions of the planet, with already observed ecological consequences. Combined with the characteristics of high-arctic ecosystems, such as low species redundancy, high seasonality and weather extremes, shifts in individual species performance and phenology may lead to altered interaction dynamics through trophic mismatch and cascades. An ecosystem approach is therefore desirable in the attempt to understand the multidimensional impacts of climate. Here, we present ecosystem-wide trend analyses of a long-term dataset on terrestrial and limnic biota with focus on the distribution of observed trends and associated variation across the ecosystem. We used 114 time series drawn from 11 abiotic variables, 19 terrestrial and 7 limnic biotic species/taxa and compared temporal trends, changes and abrupt shifts in the variation within and across the two biota. A total of 36 % of the time series analysed showed a significant trend during the study period with a higher frequency of trends occurring within performance variables. Overall, the changes tended to be negative, indicating advances in phenology but reduced species performance. General system variance was also higher in the limnic biota than in the terrestrial biota, both exhibiting increasing variance up through the trophic system. Overall, our results suggest that multiple biotic responses to the climatic changes in this high-arctic ecosystem are not synchronised across trophic levels and may differ qualitatively and quantitatively between terrestrial and limnic biota. 相似文献
106.
107.
Modeling of Cell-to-Cell Communication Processes with Petri Nets Using the Example of Quorum Sensing
Janowski S Kormeier B Töpel T Hippe K Hofestädt R Willassen N Friesen R Rubert S Borck D Haugen P Chen M 《In silico biology》2010,10(1):27-48
The understanding of the molecular mechanism of cell-to-cell communication is fundamental for system biology. Up to now, the main objectives of bioinformatics have been reconstruction, modeling and analysis of metabolic, regulatory and signaling processes, based on data generated from high-throughput technologies. Cell-to-cell communication or quorum sensing (QS), the use of small molecule signals to coordinate complex patterns of behavior in bacteria, has been the focus of many reports over the past decade. Based on the quorum sensing process of the organism Aliivibrio salmonicida, we aim at developing a functional Petri net, which will allow modeling and simulating cell-to-cell communication processes. Using a new editor-controlled information system called VANESA (http://vanesa.sf.net), we present how to combine different fields of studies such as life-science, database consulting, modeling, visualization and simulation for a semi-automatic reconstruction of the complex signaling quorum sensing network. We show how cell-to-cell communication processes and information-flow within a cell and across cell colonies can be modeled using VANESA and how those models can be simulated with Petri net network structures in a sophisticated way. 相似文献
108.
Due to its capability for producing various microcystins, Microcystis aeruginosa is recognized as one of the most toxic, bloom-forming cyanobacteria. In this study, the fates of intra- and extracellular
microcystin-LR (MC-LR) were investigated when the mixotrophic golden alga Poterioochromonas sp. (ZX1) was grazing on M. aeruginosa cells. In the control groups, the total MC-LR concentration increased with the growth of M. aeruginosa with an MC-LR content per cell of 0.5–1.5 × 10−8 μg cell−1. In the treatment with ZX1, the total MC-LR decreased linearly throughout the incubation period. In particular, intracellular
MC-LR disappeared with a loss of M. aeruginosa cells in the first few days. Part of the intracellular MC-LR was released to the medium under the grazing stress, resulting
in an increase of extracellular MC-LR. The degradation rate of MC-LR was positively related to the initial abundance of ZX1
and negatively related to that of M. aeruginosa. The inhibition ratio of MC-LR production dropped sharply from 98 to 67% when the initial abundance of M. aeruginosa increased from 106 to 107 cells ml−1. However, it increased from 84 to 99% when the initial ZX1 abundance increased from 104 to 105 cells ml−1. The effective removal of both M. aeruginosa cells and MC-LR was observed under lower M. aeruginosa abundance (<106 cells ml−1) and higher ZX1 abundance (>1% of M. aeruginosa abundance). Light had little impact on MC-LR degradation, but MC-LR degradation decreased due to the loss of ZX1 after 10 days
of darkness. This study showed that the interactions between M. aeruginosa and ZX1 were strongly influenced by their initial abundances. 相似文献
109.
Kirsten Christoffersen Nethe Andersen Morten Søndergaard Lone Liboriussen Erik Jeppesen 《Hydrobiologia》2006,560(1):259-266
Global warming scenarios foresee increases in air temperatures of 3–5 °C in Northern European regions within the next 70 years.
To evaluate the potential effects of global warming on shallow eutrophic lakes, a flow-through experiment combining three
temperature scenarios and two nutrient levels was conducted in 24 outdoor mesocosms. Eight mesocosms were unheated and acted
as controls, while sixteen were heated – eight according to the Intergovernmental Panel on Climate Change’s (IPCC) climate
scenario A2 down-scaled to regional level (2.5–4.4 °C, depending on season) and eight according to scenario A2+ with an additional
50% temperature increase. Half of the mesocosms were enriched with nitrogen and phosphorus to simulate increased runoff from
terrestrial sources due to the increased precipitation predicted by the A2 scenario. The other half were un-enriched and received
only natural nutrient input from the groundwater that fed all the mesocosms. The abundance and development pattern of the
microbial communities within the mesocosms were tracked during a 16-month period. Generally, the results showed that the abundances
of picoalgae, bacteria and heterotrophic nanoflagellates changed in a similar manner over time; abundances being lower in
winter than in summer. Warming in itself had no effect on abundance, albeit it significantly modified the positive effect
of the nutrients. Only at ambient temperatures did the whole microbial assemblage respond positively to nutrients. In the
A2 scenario, only picoalgae responded to nutrients, while in the A2+ scenario all but the heterotrophic nanoflagellates showed
a response. Elevated winter temperatures seemed not to be more important for the microbial assemblage than elevated summer
temperatures. Our results demonstrate that the direct effects of warming were far less important than the nutrient effect.
The results furthermore reveal that warming and nutrients in combination set off complex interactions. In consequence, global
warming may possibly have pronounced effects on aquatic ecosystems if accompanied by increased nutrient loading. 相似文献
110.
Stig Christoffersen Anders Kadziola Michael Rasmussen Martin Willemoës 《Journal of molecular biology》2009,393(2):464-477
Uracil phosphoribosyltransferase catalyzes the conversion of 5-phosphoribosyl-α-1-diphosphate (PRPP) and uracil to uridine monophosphate (UMP) and diphosphate (PPi). The tetrameric enzyme from Sulfolobus solfataricus has a unique type of allosteric regulation by cytidine triphosphate (CTP) and guanosine triphosphate (GTP). Here we report two structures of the activated state in complex with GTP. One structure (refined at 2.8-Å resolution) contains PRPP in all active sites, while the other structure (refined at 2.9-Å resolution) has PRPP in two sites and the hydrolysis products, ribose-5-phosphate and PPi, in the other sites. Combined with three existing structures of uracil phosphoribosyltransferase in complex with UMP and the allosteric inhibitor cytidine triphosphate (CTP), these structures provide valuable insight into the mechanism of allosteric transition from inhibited to active enzyme. The regulatory triphosphates bind at a site in the center of the tetramer in a different manner and change the quaternary arrangement. Both effectors contact Pro94 at the beginning of a long β-strand in the dimer interface, which extends into a flexible loop over the active site. In the GTP-bound state, two flexible loop residues, Tyr123 and Lys125, bind the PPi moiety of PRPP in the neighboring subunit and contribute to catalysis, while in the inhibited state, they contribute to the configuration of the active site for UMP rather than PRPP binding. The C-terminal Gly216 participates in a hydrogen-bond network in the dimer interface that stabilizes the inhibited, but not the activated, state. Tagging the C-terminus with additional amino acids generates an endogenously activated enzyme that binds GTP without effects on activity. 相似文献