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Long-term Decrease (long-term + decrease)

Distribution by Scientific Domains

Life Sciences	42%

Selected Abstracts

The induction of HIF-1 reduces astrocyte activation by amyloid beta peptide

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 7 2009
David Schubert
Abstract Reduced glucose metabolism and astrocyte activation in selective areas of the brain are pathological features of Alzheimer's disease (AD). The underlying mechanisms of low energy metabolism and a molecular basis for preventing astrocyte activation are not, however, known. Here we show that amyloid beta peptide (A,)-dependent astrocyte activation leads to a long-term decrease in hypoxia-inducible factor (HIF)-1, expression and a reduction in the rate of glycolysis. Glial activation and the glycolytic changes are reversed by the maintenance of HIF-1, levels with conditions that prevent the proteolysis of HIF-1,. A, increases the long-term production of reactive oxygen species (ROS) through the activation of nicotinamide adenine dinucleotide phosphate oxidase and reduces the amount of HIF-1, via the activation of the proteasome. ROS are not required for glial activation, but are required for the reduction in glycolysis. These data suggest a significant role for HIF-1,-mediated transcription in maintaining the metabolic integrity of the AD brain and identify the probable cause of the observed lower energy metabolism in afflicted areas. They may also explain the therapeutic success of metal chelators in animal models of AD. [source]

High-resolution regional climate simulations of the long-term decrease in September rainfall over Indochina

ATMOSPHERIC SCIENCE LETTERS, Issue 1 2009
Hiroshi G. Takahashi
Abstract We address the long-term decrease in September rainfall over the Indochina Peninsula. Distinct long-term decreases in rainfall along the monsoon trough across the Indochina Peninsula have been observed. We performed long-term simulations and discuss the effects of long-term changes in both the local surface conditions and large-scale circulation. Using a 30-year simulation for September for the period from 1966 to 1995 with land-use conditions fixed at present-day values and neglecting the recorded deforestation, we successfully simulated the observed long-term decrease in rainfall. We therefore conclude that the weakening tropical-cyclone activity over the Indochina Peninsula region is probably responsible for the decrease in rainfall. Copyright © 2008 Royal Meteorological Society [source]

Serotonin may stimulate granule cell proliferation in the adult hippocampus, as observed in rats grafted with foetal raphe neurons

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2000
Jean Michel Brezun
Abstract The long-term effects of hippocampal serotonergic denervation and reinnervation by foetal raphe tissue were examined in the dentate gyrus where neurons are continously born in the adult. Complete lesion of serotonin neurons following injections of 5,7-dihydroxytryptamine in the dorsal and medial raphe nuclei produced long-term decreases in the number of newly generated granule cells identified with 5-Bromo-2,-deoxyuridine (BrdU) and the polysialylated form of neural cell adhesion molecule (PSA-NCAM) immunostaining, as observed in 2-month-survival rats. The raphe grafts, but not the control grafts of embryonic spinal tissue, reversed the postlesion-induced decreases in the density of BrdU- and PSA-NCAM-labelled cells detected in the granule layer. Inhibition of serotonin synthesis in animals with raphe grafts reversed back to lesion-induced changes in granule cell proliferation. Furthermore, extensive serotonergic reinnervation of the dentate gyrus in the area proximal to the raphe graft could be associated with supranormal density of BrdU-labelled cells. These results indicate that serotonin may be considered a positive regulatory factor of adult granule cell proliferation. Finally, the lack of effect of embryonic nonserotonergic tissue grafted to serotonin-deprived rats suggests that neurotrophic factors may not be involved in the effects of serotonin on adult neurogenesis. [source]

Effects of altered water regimes on forest root systems

NEW PHYTOLOGIST, Issue 1 2000
J. D. JOSLIN
How ecosystems adapt to climate changes depends in part on how individual trees allocate resources to their components. A review of research using tree seedlings provides some support for the hypothesis that some tree species respond to exposure to drought with increases in root,shoot ratios but little change in total root biomass. Limited research on mature trees over moderately long time periods (2,10 yr), has given mixed results with some studies also providing evidence for increases in root: shoot ratios. The Throughfall Displacement Experiment (TDE) was designed to simulate both an increase and a decrease of 33% in water inputs to a mature deciduous forest over a number of years. Belowground research on TDE was designed to examine four hypothesized responses to long-term decreases in water availability; (1) increases in fine-root biomass, (2) increases in fine root,foliage ratio, (3) altered rates of fine-root turnover (FRT), and (4) depth of rooting. Minirhizotron root elongation data from 1994 to 1998 were examined to evaluate the first three hypotheses. Differences across treatments in net fine-root production (using minirhizotron root elongation observations as indices of biomass production) were small and not significant. Periods of lower root production in the dry treatment were compensated for by higher growth during favorable periods. Although not statistically significant, both the highest production (20 to 60% higher) and mortality (18 to 34% higher) rates were found in the wet treatment, resulting in the highest index of FRT. After 5 yr, a clear picture of stand fine-root-system response to drought exposure has yet to emerge in this forest ecosystem. Our results provide little support for either an increase in net fine-root production or a shift towards an increasing root,shoot ratio with long-term drought exposure. One possible explanation for higher FRT rates in the wet treatment could be a positive relationship between FRT and nitrogen and other nutrient availability, as treatments have apparently resulted in increased immobilization of nutrients in the forest floor litter under drier conditions. Such hypotheses point to the continued need to study the interactions of water stress, nutrient availability and carbon-fixation efficiency in future long-term studies. [source]