| 1. |
- Björklund, Jesper, 1979, et al.
(författare)
-
Scientific Merits and Analytical Challenges ofTree-Ring Densitometry
- 2019
-
Ingår i: Reviews of Geophysics. - : American Geophysical Union (AGU). - 8755-1209 .- 1944-9208. ; 57:4, s. 1224-1264
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray microdensitometry on annually resolved tree-ring samples has gained an exceptional position in last-millennium paleoclimatology through the maximum latewood density (MXD) parameter, but also increasingly through other density parameters. For 50 years, X-ray based measurement techniques have been the de facto standard. However, studies report offsets in the mean levels for MXD measurements derived from different laboratories, indicating challenges of accuracy and precision. Moreover, reflected visible light-based techniques are becoming increasingly popular, and wood anatomical techniques are emerging as a potentially powerful pathway to extract density information at the highest resolution. Here we review the current understanding and merits of wood density for tree-ring research, associated microdensitometric techniques, and analytical measurement challenges. The review is further complemented with a careful comparison of new measurements derived at 17 laboratories, using several different techniques. The new experiment allowed us to corroborate and refresh "long-standing wisdom" but also provide new insights. Key outcomes include (i) a demonstration of the need for mass/volume-based recalibration to accurately estimate average ring density; (ii) a substantiation of systematic differences in MXD measurements that cautions for great care when combining density data sets for climate reconstructions; and (iii) insights into the relevance of analytical measurement resolution in signals derived from tree-ring density data. Finally, we provide recommendations expected to facilitate futureinter-comparability and interpretations for global change research.
|
|
| 2. |
- Buntgen, U., et al.
(författare)
-
Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE
- 2018
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.
|
|
| 3. |
- Cook, ER, et al.
(författare)
-
Old World megadroughts and pluvials during the Common Era
- 2015
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 1:10
-
Tidskriftsartikel (refereegranskat)abstract
- Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other “Old World” climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the “Old World Drought Atlas” (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. TheOWDAmatches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.
|
|
| 4. |
- Björklund, J., et al.
(författare)
-
Scientific Merits and Analytical Challenges of Tree-Ring Densitometry
- 2019
-
Ingår i: Reviews of geophysics. - 8755-1209 .- 1944-9208. ; 57:4, s. 1224-1264
-
Forskningsöversikt (refereegranskat)abstract
- X-ray microdensitometry on annually resolved tree-ring samples has gained an exceptional position in last-millennium paleoclimatology through the maximum latewood density (MXD) parameter, but also increasingly through other density parameters. For 50 years, X-ray based measurement techniques have been the de facto standard. However, studies report offsets in the mean levels for MXD measurements derived from different laboratories, indicating challenges of accuracy and precision. Moreover, reflected visible light-based techniques are becoming increasingly popular, and wood anatomical techniques are emerging as a potentially powerful pathway to extract density information at the highest resolution. Here we review the current understanding and merits of wood density for tree-ring research, associated microdensitometric techniques, and analytical measurement challenges. The review is further complemented with a careful comparison of new measurements derived at 17 laboratories, using several different techniques. The new experiment allowed us to corroborate and refresh long-standing wisdom but also provide new insights. Key outcomes include (i) a demonstration of the need for mass/volume-based recalibration to accurately estimate average ring density; (ii) a substantiation of systematic differences in MXD measurements that cautions for great care when combining density data sets for climate reconstructions; and (iii) insights into the relevance of analytical measurement resolution in signals derived from tree-ring density data. Finally, we provide recommendations expected to facilitate futureinter-comparability and interpretations for global change research.
|
|
| 5. |
- Bottger, P, et al.
(författare)
-
Glutamate-system defects behind psychiatric manifestations in a familial hemiplegic migraine type 2 disease-mutation mouse model
- 2016
-
Ingår i: Scientific reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6, s. 22047-
-
Tidskriftsartikel (refereegranskat)abstract
- Migraine is a complex brain disorder, and understanding the complexity of this prevalent disease could improve quality of life for millions of people. Familial Hemiplegic Migraine type 2 (FHM2) is a subtype of migraine with aura and co-morbidities like epilepsy/seizures, cognitive impairments and psychiatric manifestations, such as obsessive-compulsive disorder (OCD). FHM2 disease-mutations locate to the ATP1A2 gene encoding the astrocyte-located α2-isoform of the sodium-potassium pump (α2Na+/K+-ATPase). We show that knock-in mice heterozygous for the FHM2-associated G301R-mutation (α2+/G301R) phenocopy several FHM2-relevant disease traits e.g., by mimicking mood depression and OCD. In vitro studies showed impaired glutamate uptake in hippocampal mixed astrocyte-neuron cultures from α2G301R/G301R E17 embryonic mice, and moreover, induction of cortical spreading depression (CSD) resulted in reduced recovery in α2+/G301R male mice. Moreover, NMDA-type glutamate receptor antagonists or progestin-only treatment reverted specific α2+/G301R behavioral phenotypes. Our findings demonstrate that studies of an in vivo relevant FHM2 disease knock-in mouse model provide a link between the female sex hormone cycle and the glutamate system and a link to co-morbid psychiatric manifestations of FHM2.
|
|
| 6. |
|
|
| 7. |
- Illarionava, Nina B., et al.
(författare)
-
Role of Na,K-ATPase alpha 1 and alpha 2 Isoforms in the Support of Astrocyte Glutamate Uptake
- 2014
-
Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:6, s. e98469-
-
Tidskriftsartikel (refereegranskat)abstract
- Glutamate released during neuronal activity is cleared from the synaptic space via the astrocytic glutamate/Na+ co-transporters. This transport is driven by the transmembrane Na+ gradient mediated by Na,K-ATPase. Astrocytes express two isoforms of the catalytic Na, K-ATPase alpha subunits; the ubiquitously expressed alpha 1 subunit and the alpha 2 subunit that has a more specific expression profile. In the brain alpha 2 is predominantly expressed in astrocytes. The isoforms differ with regard to Na+ affinity, which is lower for alpha 2. The relative roles of the alpha 1 and alpha 2 isoforms in astrocytes are not well understood. Here we present evidence that the presence of the alpha 2 isoform may contribute to a more efficient restoration of glutamate triggered increases in intracellular sodium concentration [Na+](i). Studies were performed on primary astrocytes derived from E17 rat striatum expressing Na, K-ATPase alpha 1 and alpha 2 and the glutamate/Na+ co-transporter GLAST. Selective inhibition of alpha 2 resulted in a modest increase of [Na+](i) accompanied by a disproportionately large decrease in uptake of aspartate, an indicator of glutamate uptake. To compare the capacity of alpha 1 and alpha 2 to handle increases in [Na+](i) triggered by glutamate, primary astrocytes overexpressing either alpha 1 or alpha 2 were used. Exposure to glutamate 200 mM caused a significantly larger increase in [Na+](i) in alpha 1 than in alpha 2 overexpressing cells, and as a consequence restoration of [Na+](i), after glutamate exposure was discontinued, took longer time in alpha 1 than in alpha 2 overexpressing cells. Both alpha 1 and alpha 2 interacted with astrocyte glutamate/Na+ co-transporters via the 1st intracellular loop.
|
|
| 8. |
- Illarionova, N. B., et al.
(författare)
-
FUNCTIONAL AND MOLECULAR INTERACTIONS BETWEEN AQUAPORINS AND Na,K-ATPase
- 2010
-
Ingår i: Neuroscience. - : Elsevier BV. - 0306-4522 .- 1873-7544. ; 168:4, s. 915-925
-
Tidskriftsartikel (refereegranskat)abstract
- The water channel aquaporin 4 (AQP4) is abundantly expressed in astrocytes and provides a mechanism by which water permeability of the plasma membrane can be regulated. Astrocytes play a key role in the clearance of both potassium (K+) and glutamate released during neuronal activity. Emerging evidence suggests that AQP4 facilitates K+ clearance by astrocytes and contributes to recovery of neuronal excitability. Here we report that AQP4 can assemble with its regulator metabotropic glutamate receptor 5 (mGluR5) and with Na,K-ATPase; the enzyme responsible for active K+ transport and for establishing the electrochemical gradient across the cell plasma membrane. We have, by use of pull down assays in rat brain tissue, identified the segment in the AQP4 NH2-terminus containing the amino acid residues 23-32 as the site for interaction with Na,K-ATPase catalytic subunit and with mGluR5. Mutagenesis studies revealed that the AQP4 amino acids K27 and W30 are of key importance for interaction with both Na,K-ATPase and mGluR5. To confirm that interaction also occurs within intact cells, we have performed fluorescence resonance energy transfer (FRET) studies in primary astrocytes derived from rat striatum. The results indicate close proximity of wild type AQP4 and Na,K-ATPase in the plasma membrane of rat astrocytes. FRET efficiencies observed with the mutants AQP4 K27A and AQP4 W30A were significantly lower, highlighting the importance of these residues for the interaction between AQP4 and Na,K-ATPase. We conclude that AQP4/Na,K-ATPase/mGluR5 can form a macromolecular complex/transporting microdomain in astrocytes. This complex may be of functional importance for the regulation of water and K+ homeostasis in the brain, as well as for neuron-astrocyte metabolic crosstalk. (C) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.
|
|
| 9. |
|
|
| 10. |
|
|
