| 1. |
- Bravo, L, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
- Tabiri, S, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 3. |
- Wendisch, M., et al.
(författare)
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Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)(3) Project
- 2023
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Ingår i: Bulletin of the American Meteorological Society. - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)(3) project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric-ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.
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| 4. |
- Fransén, Erik, 1962-, et al.
(författare)
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Computational modeling of activity dependent velocity changes in peripheral C-fibers
- 2011
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Konferensbidrag (refereegranskat)abstract
- Initiation and propagation of action potentials along unmyelinated C-fibers are the first steps of the pain pathway. Propagation velocity and its fiber class-specific activity-dependent slowing (ADS) is intimately linked to fibre excitability. In chronic pain patients, ADS alterations have been suggested to reflect increased excitability, possibly underlying clinical pain. Due to their small diameter, peripheral axons of nociceptors in patients are not accessible for intraaxonal recordings of their ion channel properties. We have therefore constructed a model of a C-fibre to study the relationship between ion channel composition and velocity changes as well as excitability. Ion channels are modeled from data of DRG somata using a Hodgkin-Huxley formalism (Na currents: TTX-sensitive, Nav1.8, Nav1.9, K currents: Kdr, A-type, Kv7.3, non-specific cationic: HCN). Moreover, ion pumps (Na/K-ATPase) and concentrations of intra and extraaxonal sodium and potassium are also included. The geometry and temperature of the fibre represents a section of the superficial branch and the deeper parent and is represented by a multicompartmental structure where each compartment contains passive as well as ion channel and pump elements. Using parameter estimation techniques, we optimized ion channel and pump expression pattern such that basic electrophysiological characteristics of the action potential and its velocity matched the experimental data. Moreover, we have also replicated activity dependent slowing. In ongoing work, we extend optimization to also include recovery cycles. The model will be used to study hypothesis of the relationship between individual ion channel subtypes and axonal excitability related to pain, generating independent information on impact of selective neuronal targets.
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| 5. |
- Fransén, Erik, 1962-, et al.
(författare)
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Differences in action potential propagation in mechanosensitive and insensitive C-nociceptors - a modeling approach
- 2012
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Konferensbidrag (refereegranskat)abstract
- C-fibers, unmyelinated afferent axons, convey information from the periphery of the nervous system to the spinal cord. They transmit signals originating from noxious stimulation evoking the sensations of itch and pain in the central nervous system. Different classes of C-fibers are characterized by functional, morphological and biochemical characteristics. In pain studies, a classification into mechano-insensitive (CMi) and mechano responsive fibers (CM) has proven useful as changes in proportions and response characteristics of these fibers have been observed in neuropathy patients (Weidner et al. 1999, 2000; Orstavik 2003, 2010). In this study, using computational modeling of a C-fiber, we have studied the possible contribution of different ion channel subtypes (Na-TTXs, Nav1.8, Nav1.9, Kdr, KA, KM, K(Na), h) as well as the Na/K-ATPase pump to conductive properties of C-fibers. In particular we investigated mechanisms that could generate the fiber-specific differences between CM and CMi fibers with regard to activity dependent slowing (ADS) and recovery cycles (RC). In our study we represent the axon by three cylindrical sections, one representing the peripheral thin end (branch, 2.5 cm), one the central part (parent, 10 cm) and a conical section between these (0.5 cm). In total 730 compartments are used. Temperature is set to 32 degrees C in branch and 37 degrees in parent sections. We represent variable ion concentrations of Na and K intra axonally, periaxonally and extracellularly, from which reversal potentials are calculated. We use ion channel models based on Hodgkin Huxley formalism. An ion pump (Na/K-ATPase) is included. We find that TTX-sensitive Na and Nav1.8 have the strongest influence on action potential conduction velocity as is expected since these are the major components of the rising phase of the action potential. Preliminary observations indicate that a small subset of Na and K currents play a key role in determining differences in activity dependent velocity changes (ADS) in the two fiber classes. We plan to also study contributions from morphological characteristics (superficial branch lengths) to activity dependent differences between the fiber classes (Schmidt et al. 2002). We further intend to investigate candidate ion channels which could play a role in changing the functional characteristics of a CMi fiber to that of a CM fiber. Our studies may provide insights into ionic changes underlying changes in the excitability of C-fibers associated with pain.
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| 6. |
- Legradi, J. B., et al.
(författare)
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An ecotoxicological view on neurotoxicity assessment
- 2018
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Ingår i: Environmental Sciences Europe. - : Springer. - 2190-4707 .- 2190-4715. ; 30
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Forskningsöversikt (refereegranskat)abstract
- The numbers of potential neurotoxicants in the environment are raising and pose a great risk for humans and the environment. Currently neurotoxicity assessment is mostly performed to predict and prevent harm to human populations. Despite all the efforts invested in the last years in developing novel in vitro or in silico test systems, in vivo tests with rodents are still the only accepted test for neurotoxicity risk assessment in Europe. Despite an increasing number of reports of species showing altered behaviour, neurotoxicity assessment for species in the environment is not required and therefore mostly not performed. Considering the increasing numbers of environmental contaminants with potential neurotoxic potential, eco-neurotoxicity should be also considered in risk assessment. In order to do so novel test systems are needed that can cope with species differences within ecosystems. In the field, online-biomonitoring systems using behavioural information could be used to detect neurotoxic effects and effect-directed analyses could be applied to identify the neurotoxicants causing the effect. Additionally, toxic pressure calculations in combination with mixture modelling could use environmental chemical monitoring data to predict adverse effects and prioritize pollutants for laboratory testing. Cheminformatics based on computational toxicological data from in vitro and in vivo studies could help to identify potential neurotoxicants. An array of in vitro assays covering different modes of action could be applied to screen compounds for neurotoxicity. The selection of in vitro assays could be guided by AOPs relevant for eco-neurotoxicity. In order to be able to perform risk assessment for eco-neurotoxicity, methods need to focus on the most sensitive species in an ecosystem. A test battery using species from different trophic levels might be the best approach. To implement eco-neurotoxicity assessment into European risk assessment, cheminformatics and in vitro screening tests could be used as first approach to identify eco-neurotoxic pollutants. In a second step, a small species test battery could be applied to assess the risks of ecosystems.
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| 7. |
- Olsen, Paul E., et al.
(författare)
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Empirical record, geochronology and theoretical determinates of Mesozoic climate in the Junggar Basin, northwest China in relation to other basins in northeast China
- 2024
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Ingår i: Geological Society Special Publication. - 0305-8719 .- 2041-4927. ; 538:1
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Tidskriftsartikel (refereegranskat)abstract
- Mesozoic continental basins of northern China, including the Junggar Basin, provide some of the most spectacular and important fossil assemblages in the world, but their climatic and environmental contexts have been shrouded in uncertainty. Here we examine the main factors that determine those contexts: palaeolatitude; the effects of changing atmospheric gases on the radiative balance; and orbitally paced variations in insolation. Empirical evidence on these factors is accumulating rapidly and promises to upend many long standing paradigms. We focus primarily on the Junggar Basin in Xinjiang northwest China with the renowned Shishugou Biota and the basins in Liaoning, Hebei, and Inner Mongolia with their famous Jehol and Yanliao Biotas. Accurate geochronology is necessary for disentangling these various factors and we review the Late Triassic to Early Cretaceous U-Pb ages for these areas and supply one new LA-ICP-MS age for the otherwise un-dated Sangonghe Formation of Early Jurassic age. We review climatic-sensitive facies patterns in North China and show that the climatic context changed synchronously in northwestern and northeastern China consistent with a previously proposed huge Late Jurassic-earliest Cretaceous True Polar Wander (TPW) event with all the major plates of East Asia docked with Siberia and moving together since at least the Triassic, when the north China Basins were at Arctic latitudes. We conclude that this TPW shift is was responsible for the coals and ice rafted debris being produced at high latitudes and the red beds and eolian strata being deposited at low latitudes, within the same basin. The climatic and taphonomic context in which the famous Shishugou, Yanlaio and Jehol biotas preserved was thus a function of TPW as opposed to local tectonics or climate change.
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| 8. |
- Petersson, Marcus E., et al.
(författare)
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Differential Axonal Conduction Patterns of Mechano-Sensitive and Mechano-Insensitive Nociceptors - A Combined Experimental and Modelling Study
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:8, s. e103556-
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Tidskriftsartikel (refereegranskat)abstract
- Cutaneous pain sensations are mediated largely by C-nociceptors consisting of both mechano-sensitive (CM) and mechano-insensitive (CMi) fibres that can be distinguished from one another according to their characteristic axonal properties. In healthy skin and relative to CMi fibres, CM fibres show a higher initial conduction velocity, less activity-dependent conduction velocity slowing, and less prominent post-spike supernormality. However, after sensitization with nerve growth factor, the electrical signature of CMi fibres changes towards a profile similar to that of CM fibres. Here we take a combined experimental and modelling approach to examine the molecular basis of such alterations to the excitation thresholds. Changes in electrical activation thresholds and activity-dependent slowing were examined in vivo using single-fibre recordings of CM and CMi fibres in domestic pigs following NGF application. Using computational modelling, we investigated which axonal mechanisms contribute most to the electrophysiological differences between the fibre classes. Simulations of axonal conduction suggest that the differences between CMi and CM fibres are strongly influenced by the densities of the delayed rectifier potassium channel (Kdr), the voltage-gated sodium channels Na(V)1.7 and Na(V)1.8, and the Na+/K+-ATPase. Specifically, the CM fibre profile required less K-dr and Na(V)1.8 in combination with more Na(V)1.7 and Na+/ K(+)AT-Pase. The difference between CM and CMi fibres is thus likely to reflect a relative rather than an absolute difference in protein expression. In support of this, it was possible to replicate the experimental reduction of the ADS pattern of CMi nociceptors towards a CM-like pattern following intradermal injection of nerve growth factor by decreasing the contribution of Kdr (by 50%), increasing the Na+/K+-ATPase (by 10%), and reducing the branch length from 2 cm to 1 cm. The findings highlight key molecules that potentially contribute to the NGF-induced switch in nociceptors phenotype, in particular NaV1.7 which has already been identified clinically as a principal contributor to chronic pain states such as inherited erythromelalgia.
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| 9. |
- Petäjä, Tuukka, et al.
(författare)
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Overview : Integrative and Comprehensive Understanding on Polar Environments (iCUPE) - concept and initial results
- 2020
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:14, s. 8551-8592
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Tidskriftsartikel (refereegranskat)abstract
- The role of polar regions is increasing in terms of megatrends such as globalization, new transport routes, demography, and the use of natural resources with consequent effects on regional and transported pollutant concentrations. We set up the ERA-PLANET Strand 4 project iCUPE - integrative and Comprehensive Understanding on Polar Environments to provide novel insights and observational data on global grand challenges with an Arctic focus. We utilize an integrated approach combining in situ observations, satellite remote sensing Earth observations (EOs), and multi-scale modeling to synthesize data from comprehensive long-term measurements, intensive campaigns, and satellites to deliver data products, metrics, and indicators to stakeholders concerning the environmental status, availability, and extraction of natural resources in the polar areas. The iCUPE work consists of thematic state-of-the-art research and the provision of novel data in atmospheric pollution, local sources and transboundary transport, the characterization of arctic surfaces and their changes, an assessment of the concentrations and impacts of heavy metals and persistent organic pollutants and their cycling, the quantification of emissions from natural resource extraction, and the validation and optimization of satellite Earth observation (EO) data streams. In this paper we introduce the iCUPE project and summarize initial results arising out of the integration of comprehensive in situ observations, satellite remote sensing, and multi-scale modeling in the Arctic context.
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| 10. |
- Ponsot, Elodie, 1973-, et al.
(författare)
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Mitochondrial tissue specificity of substrates utilization in rat cardiac and skeletal muscles
- 2005
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Ingår i: Journal of Cellular Physiology. - Hoboken, USA : John Wiley & Sons. - 0021-9541 .- 1097-4652. ; 203:3, s. 479-86
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Tidskriftsartikel (refereegranskat)abstract
- As energetic metabolism is crucial for muscles, they develop different adaptations to respond to fluctuating demand among muscle types. Whereas quantitative characteristics are known, no study described simultaneously quantitative and qualitative differences among muscle types in terms of substrates utilization patterns. This study thus defined the pattern of substrates preferential utilization by mitochondria from glycolytic gastrocnemius (GAS) and oxidative soleus (SOL) skeletal muscles and from heart left ventrical (LV) in rats. We measured in situ, ADP (2 mM)-stimulated, mitochondrial respiration rates from skinned fibers in presence of increasing concentrations of pyruvate (Pyr) + malate (Mal), palmitoyl-carnitine (Palm-C) + Mal, glutamate (Glut) + Mal, glycerol-3-phosphate (G3-P), lactate (Lact) + Mal. Because the fibers oxygen uptake (Vs) followed Michaelis-Menten kinetics in function of substrates level we determined the Vs and Km, representing maximal oxidative capacity and the mitochondrial sensibility for each substrate, respectively. Vs were in the order GAS < SOL < LV for Pyr, Glu, and Palm-C substrates, whereas in the order SOL = LV < GAS with G3-P. Moreover, the relative capacity to oxidize Palm-C is extremely higher in LV than in SOL. Vs was not stimulated by the Lact substrate. The Km was equal for Pyr among muscles, but much lower for G3-P in GAS and lower for Palm-C in LV. These results demonstrate qualitative mitochondrial tissue specificity for metabolic pathways. Mitochondria of glycolytic muscle fibers are well adapted to play a central role for maintaining a satisfactory cytosolic redox state in these fibers, whereas mitochondria of LV developed important capacities to use fatty acids.
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