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Rochefort C Arabo A André M Poucet B Save E Rondi-Reig L 《Science (New York, N.Y.)》2011,334(6054):385-389
Spatial representation is an active process that requires complex multimodal integration from a large interacting network of cortical and subcortical structures. We sought to determine the role of cerebellar protein kinase C (PKC)-dependent plasticity in spatial navigation by recording the activity of hippocampal place cells in transgenic L7PKCI mice with selective disruption of PKC-dependent plasticity at parallel fiber-Purkinje cell synapses. Place cell properties were exclusively impaired when L7PKCI mice had to rely on self-motion cues. The behavioral consequence of such a deficit is evidenced here by selectively impaired navigation capabilities during a path integration task. Together, these results suggest that cerebellar PKC-dependent mechanisms are involved in processing self-motion signals essential to the shaping of hippocampal spatial representation. 相似文献
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International food aid has long been known to be motivated by domestic and foreign policy objectives as well as humanitarian concerns. The policy objectives sometimes complicate delivery of emergency food, and lead to situations that result in adverse effects on the economic and agricultural systems of recipient countries. Despite the long history and extensive documentation of such effects, they were observed to occur once again during the 1992 Somalia intervention. This intervention encountered many frequently described barriers to effective use of emergency food aid. It also set a new precedent; for the first time, troops were deployed to enforce the safe delivery of food. This action led to the creation of an army of occupation engaged in military conflict with the very people it had come to serve and, eventually, to further deterioration of the country's food economy. The Somalia intervention provided further evidence for the need to uncouple humanitarian food aid from other policy objectives, and to design and manage emergency and long-term food aid programs to maximize benefits, minimize adverse consequences, and strengthen local agricultural production and marketing systems. 相似文献
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Marion Valeix Hervé Fritz Rodolphe Sabatier Felix Murindagomo David Cumming Patrick Duncan 《Biological conservation》2011,(2):902-912
African elephants can affect the quality of the habitat of other species by breaking or uprooting trees and shrubs in savannas. Their effect on vegetation has been widely studied but less is known about the effects of such vegetation changes on other animals. We studied how changes in the vegetation caused by elephants influence the selection of microhabitats by five African herbivore species (giraffe, kudu, steenbok, impala, and zebra) in Hwange National Park, Zimbabwe. There was no clear significant effect of overall elephant-induced vegetation changes on microhabitat selection except for the small species (steenbok and impala) that used vegetation modified by elephants preferentially. This is consistent with a medium-term browsing facilitation hypothesis. More subtle possible effects were detected for larger browsers (giraffe and kudu). They selected areas with broken and uprooted plants and avoided coppiced areas. All of the browsers selected sites characterized by plants uprooted and broken by elephants, which were associated with a higher visibility, and ultimately a better probability of detecting an approaching predator, suggesting that perceived predation risk plays an important role in microhabitat selection. These results illustrate how elephants can initiate indirect effects that influence microhabitat selection by other herbivores. Understanding the indirect effects of elephants through changes in food availability and predation risk thus needs further investigation. The results of this study do not provide support for the hypothesis that elephant-induced changes in the structure of habitats have caused the declines in the populations of the other herbivores in the study area. 相似文献
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This study evaluated the effect of extreme HCl deposition on soil acid neutralization following simulated shuttle rocket launches. Four soils along a soil chronosequence from Vandenberg Air Force Base were selected and evaluated as a function of pH spike addition (pH=1.0, 2.5, 4.0, and 5.6) and time (0 to 4 mo) in a leaching-incubation experiment. The pH=1.0 treatment led to a rapid soil extract pH decrease to 2.5 in poorly buffered soils and increased leaching of basic cations (Ca, Mg, K, and Na), Al, and Si. In general, there were no significant differences among the pH= 2.5, 4.0, and 5.6 treatments. Acid neutralization capacity increased with increasing soil age. The acid neutralization process involved two steps. In Step 1, acid is neutralized by direct or indirect exchange with exchangeable basic cations. The most likely mechanisms for this step are: (1) the direct exchange of H′ for basic cations followed by an interchange reaction between surface H′ and structural Al, and (2) the indirect exchange through H+ neutralization by polyhydroxyl-Al complexes with concurrent base displacement. Acid neutralization by a gibbsite-like mineral is an unlikely mechanism controlling the initial acid neutralization step. Eventually a pure acidic (H-A l) complex develops. In Step 2, further acid neutralization is governed by mineral dissolution via the acidic cations (H′, All'). 相似文献
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Marion A. Sonnleitner Madeleine S. Günthardt-Goerg Inga K. Bucher-Wallin Werner Attinger Sybille Reis Rainer Schulin 《Water, air, and soil pollution》2001,126(3-4):271-290
Sixteen open-top chambers, each equipped with two non-weighablegravity-drained lysimeter compartments, were used to investigate the impacts of elevated atmospheric carbon dioxide (CO2) concentration and nitrogen (N) deposition on the water relations and growth of young model forest ecosystems on two different types of soils. The same vegetation of a mixed spruce and beech overstorey and various herbs in the understorey was planted in all treatments on both soils. The soils were repacked on top of a drainage layer. Four combinations of treatments were applied in four replicates each: ambient (370 cm3 m-3) CO2 + low (7 kg N ha-1 a-1) N deposition, ambient CO2 + high(70 kg N ha-1 a-1) N deposition, elevated (590 cm3 m-3) CO2 + low N deposition, and elevated CO2 + high N deposition. After canopy closure, treatment effects on evapotranspiration and growth during the third year of study were very different for the two soils.On the acidic sandy loam, elevated CO2 enhanced growth(leaf biomass +21%, roots +27%) at reduced evapotranspiration (–9%). High N deposition increased aboveground growth even more strongly (+50%), but also increased evapotranspiration (+16%). Together, elevated CO2 and high N had a more than additive fertilizer effect on growth, while their effects on evapotranspirationcompensated. On the calcareous loamy sand, elevated CO2not only tended to enhance growth (leaf biomass +17%, roots +20%), but also increased evapotranspiration (+5%).On this soil, aboveground growth was stimulated by N only incombination with elevated CO2, but less than on the acidic soil, while evapotranspiration (–6.5%) and root growth into the subsoil (–54%) were decreased by increased N deposition at both CO2 concentrations, in contrast to the N treatments on the acidic sandy loam. The influence of the soil on the observed ecosystem responses canbe interpreted in terms of the concept of optimal resource allocation. 相似文献
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Alexis Duhamelle Isabelle Langlois Marion Desmarchelier 《The Canadian veterinary journal. La revue veterinaire canadienne》2015,56(7):737-740
A 3.5-year-old spayed female ferret, fed a diet high in refined sugar, was referred for lethargy, polyuria, polydipsia, and polyphagia. Diabetic ketoacidosis was diagnosed. Treatment included insulin therapy and a low carbohydrate diet. Diabetes mellitus resolved 54 d later, and insulin therapy was discontinued. There has been no recurrence of the diabetes mellitus. 相似文献