| 1. |
- Saltó, C, et al.
(författare)
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Ablation of TRalpha2 and a concomitant overexpression of alpha1 yields a mixed hypo- and hyperthyroid phenotype in mice.
- 2001
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Ingår i: Molecular endocrinology (Baltimore, Md.). - : The Endocrine Society. - 0888-8809. ; 15:12, s. 2115-28
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Tidskriftsartikel (refereegranskat)abstract
- Thyroid hormone governs a diverse repertoire of physiological functions through receptors encoded in the receptor genes alpha and beta, which each generate variant proteins. In mammals, the alpha gene generates, in addition to the normal receptor TRalpha1, a non-hormone-binding variant TRalpha2 whose exact function is unclear. Here, we present the phenotype associated with the targeted ablation of TRalpha2 expression. Selective ablation of TRalpha2 resulted in an inevitable, concomitant overexpression of TRalpha1. Both TRalpha2 +/- and -/- mice show a complex phenotype with low levels of free T3 and free T4, and have inappropriately normal levels of TSH. The thyroid glands exhibit mild morphological signs of dysfunction and respond poorly to TSH, suggesting that the genetic changes affect the ability of the gland to release thyroid hormones. However, the phenotype of the mutant mice also has features of hyperthyroidism, including decreased body weight, elevated heart rate, and a raised body temperature. Furthermore, TRalpha2-/- and TRalpha2+/- mice are obese and exhibit skeletal alterations, associated with a late-onset growth retardation. The results thus suggest that the overexpression of TRalpha1 and the concomitant decrease in TRalpha2 expression lead to a mixed hyper- and hypothyroid phenotype, dependent on the tissue studied. The phenotypes suggest that the balance of TRalpha1:TRalpha2 expressed from the TRalpha gene provides an additional level of tuning the control of growth and homeostasis in mammalian species.
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| 2. |
- Sögaard, H, et al.
(författare)
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Trace gas exchange in a high-arctic valley 3. Integrating and scaling CO2 fluxes from canopy to landscape using flux data, footprint modeling, and remote sensing
- 2000
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 14:3, s. 725-744
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Tidskriftsartikel (refereegranskat)abstract
- Within the framework of the European Land Arctic Physical Processes project and as part of the Danish Research Council's Polar Program, a study on trace gas exchange in a high-arctic ecosystem was conducted in NE Greenland, May-August 1997. On the basis of carbon dioxide flux measurements from three dominant surface types, this paper reports on the upscaling of such measurements from canopy to landscape level. Over a three-week period starting in mid-July, the different surfaces revealed large differences in the CO2 flux with uptake rates ranging from 0.7 g C m(-2) d(-1) over the dwarf shrub heath to 3.0 g C m(2) d(-1) over denser parts of the fen, while willow snowbed revealed intermediate uptake rates. The carbon dioxide exchange could be simulated by a CO2 model, combining photosynthesis and soil respiration routines, for which the parametrization depended on the vegetation type. Results from the simulation were supported by a sensitivity analysis based on a three-dimensional footprint model where it was shown that the CO2 uptake was strongly related to the measured leaf area index. The CO2 model was used to calculate the spatial distribution in Net Ecosystem Exchange (NEE) on the basis of Landsat satellite data acquired at the peak of the growing season and stratified according to vegetation type. It was found that there was a reasonable agreement between the satellite-based flux estimate (-0.77 g C m(-2) d(-1)) and the CO2 flux found by areal weighting of the eddy correlation measurements (-0.88 g C m(-2) d(-1)) for Me specific study day. Finally, the summer season NEE was calculated for the whole Zackenberg Valley bottom. In June, there was a valley-wide carbon loss of 8.4+/-2.6 g C m(-2) month(-1), whereas the valley system accumulated 18.8+/-6.7 g C m(-2) season(-1) during the growing season (July-August).
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| 3. |
- Christensen, Torben, et al.
(författare)
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Trace gas exchange in a high-arctic valley 1. Variations in CO2 and CH4 flux between tundra vegetation types
- 2000
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Ingår i: Global Biogeochemical Cycles. - 0886-6236. ; 14:3, s. 701-714
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystem exchanges of CO2 and CH4 were studied by chamber techniques in five different vegetation types in a high arctic valley at Zackenberg, NE Greenland. The vegetation types were categorized as Cassiope heath, hummocky fen, continuous fen, grass land and Salix arctica snowbed. Integrated daytime fluxes for the different vegetation types of the valley showed that the fen areas and the grassland, were significant sources of CH4 with a mean efflux of 6.3 mg CH4 m(-2) h(-1) and sinks for CO2, with almost -170 mg CO2 m(-2) hr(-1). The heath and snowbed areas had much lower carbon sequestration rates of about -25 mg CO2 m(-2) hr(-1) and were also sinks for CH4. Methane emissions from the valley dominated in the hummocky fens. Computation of area integrated mean daytime flux values across all vegetation types of the entire valley bottom revealed that it was a sink of CO2 in the order of -96+/-33 mg CO2 m-2 hr-1 and a source of 1.9+/-0.7 m(-2) CH4 m(-2) hr(-1). These values were in accordance with eddy correlation measurements reported elsewhere in this issue and reflect a high-carbon exchange despite the high arctic location. In the fens, where the water table was at or above the soil surface, methane emissions increased with net ecosystem CO2 flux. In places with the water table below the soil surface, such as particularly in the hummocky parts of the fen, oxidation tended to become the dominant controlling factor on methane efflux.
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| 4. |
- Dacke, Marie, et al.
(författare)
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A specialized dorsal rim area for polarized light detection in the compound eye of the scarab beetle Pachysoma striatum.
- 2002
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Ingår i: Journal of Comparative Physiology A. - : Springer Science and Business Media LLC. - 1432-1351. ; 188:3, s. 211-216
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Tidskriftsartikel (refereegranskat)abstract
- Many animals have been shown to use the pattern of polarized light in the sky as an optical compass. Specialised photoreceptors are used to analyse this pattern. We here present evidence for an eye design suitable for polarized skylight navigation in the flightless desert scarab Pachysoma striatum. Morphological and electrophysiological studies show that an extensive part of the dorsal eye is equivalent to the dorsal rim area used for polarized light navigation in other insects. A polarization-sensitivity of 12.8 (average) can be recorded from cells sensitive to the ultraviolet spectrum of light. Features commonly known to increase the visual fields of polarization-sensitive photoreceptors, or to decrease their spatial resolution, are not found in the eye of this beetle. We argue that in this insect an optically unspecialised area for polarized light detection allows it not be used exclusively for polarized light navigation.
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| 5. |
- Ederoth, Per, et al.
(författare)
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Local metabolic changes in subcutaneous adipose tissue during intravenous and epidural analgesia.
- 2002
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Ingår i: Acta Anaesthesiologica Scandinavica. - : Wiley. - 0001-5172. ; 46:5, s. 585-591
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: This clinical study aimed at investigating the impact of postoperative thoracic epidural analgesia on extracellular glycerol concentration and glucose metabolism in subcutaneous adipose tissue, using the microdialysis technique. The sympathetic nervous activity, which can be attenuated by epidural anesthesia, influences lipolysis and the release of glycerol. METHODS: Fourteen patients who underwent major abdominal or thoraco-abdominal surgery were studied postoperatively over 3 days. For postoperative analgesia the patients were prospectively randomized to receive either thoracic epidural analgesia with a bupivacaine/morphine infusion (EPI-group, n=6) or a continuous i.v. infusion of morphine (MO-group, n=8). The concentration of glycerol, glucose and lactate in the abdominal and deltoid subcutaneous adipose tissue were measured using a microdialysis technique. RESULTS: The abdominal glycerol levels were equal in both groups. In the deltoid region of the EPI-group, glycerol concentrations started to increase on Day 2, and reached significantly higher levels on Day 3 compared with the MO-group. The glucose and lactate levels showed no differences between groups in the two regions. CONCLUSION: The uniform glycerol levels in abdominal subcutaneous adipose tissue in conjunction with the difference in glycerol levels in the deltoid area indicate that the local lipolysis is different in the two study groups. This might be explained by a regional metabolic influence of thoracic epidural analgesia, possibly via the sympathetic nervous system.
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| 6. |
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| 7. |
- Åstot, C, et al.
(författare)
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An alternative cytokinin biosynthesis pathway
- 2000
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 97:26, s. 14778-14783
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Tidskriftsartikel (refereegranskat)abstract
- Studies of de novo cytokinin biosynthesis in isopentenyltransferase (ipt)-transformed Arabidopsis thaliana, involving in vivo deuterium labeling and mass spectrometry, showed that the biosynthetic rate of zeatinriboside-5'-monophosphate was around 66-fold higher than that of isopentenyladenosine-5'-monophosphate (iPMP), the proposed primary product of the Agrobacterium ipt. Double tracer analysis, using [(2)H(6)] isopentenyladenosine and deuterium oxide, provided evidence for an alternative, iPMP-independent, biosynthetic pathway for zeatin-type cytokinins, present in both ipt-expressing and wild-type Arabidopsis thaliana. Reduction of the biosynthetic flux in the alternative pathway by use of mevastatin, an inhibitor for 3-hydroxy-3-methylglutaryl CoA reductase, indicated a terpenoid origin for the side-chain precursor of the iPMP independent pathway.
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