Showing papers by "University of Fribourg published in 2003"
TL;DR: Using distinct stimuli to indicate the probability of reward, it was found that the phasic activation of dopamine neurons varied monotonically across the full range of probabilities, supporting past claims that this response codes the discrepancy between predicted and actual reward.
Abstract: Uncertainty is critical in the measure of information and in assessing the accuracy of predictions. It is determined by probability P, being maximal at P = 0.5 and decreasing at higher and lower probabilities. Using distinct stimuli to indicate the probability of reward, we found that the phasic activation of dopamine neurons varied monotonically across the full range of probabilities, supporting past claims that this response codes the discrepancy between predicted and actual reward. In contrast, a previously unobserved response covaried with uncertainty and consisted of a gradual increase in activity until the potential time of reward. The coding of uncertainty suggests a possible role for dopamine signals in attention-based learning and risk-taking behavior.
1,950 citations
TL;DR: In this paper, the authors present a review of hydrogen storage on materials with high specific surface area, hydrogen intercalation in metals and complex hydrides, and storage of hydrogen based on metals and water.
1,486 citations
TL;DR: In this article, the International Year of the Mountains (IYM) 2002 has been used as a basis for a review of issues related to current and future climatic change and its impacts on mountain environments and economies.
Abstract: This paper addresses a number of issues related to current and future climatic change and its impacts on mountain environments and economies, focusing on the `Mountain Regions' Chapter 13 of Agenda 21, a basis document presented at the 1992 United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro, and the International Year of the Mountains (IYM) 2002. The awareness that mountain regions are an important component of the earth's ecosystems, in terms of the resources and services that they provide to both mountain communities and lowland residents, has risen in the intervening decade. Based upon the themes outlined in the supporting documents for IYM, this paper will provide a succinct review of a number of sectors that warrant particular attention, according to IYM. These sectors include water resources, ecosystems and biological diversity, natural hazards, health issues, and tourism. A portfolio of research and policy options are discussed in the concluding section, as a summary of what the IYM and other concerned international networks consider to be the priority for mountain environmental protection, capacity building, and response strategies in the face of climatic change in the short to medium term future.
1,234 citations
TL;DR: Analysis of the Arabidopsis mutant npr1 revealed that the antagonistic effect of SA on JA signaling requires the regulatory protein NPR1, indicating that cross-talk between SA and JA is modulated through a novel function of NPR1 in the cytosol.
Abstract: Plant defenses against pathogens and insects are regulated differentially by cross-communicating signal transduction pathways in which salicylic acid (SA) and jasmonic acid (JA) play key roles. In this study, we investigated the molecular mechanism of the antagonistic effect of SA on JA signaling. Arabidopsis plants unable to accumulate SA produced 25-fold higher levels of JA and showed enhanced expression of the JA-responsive genes LOX2, PDF1.2, and VSP in response to infection by Pseudomonas syringae pv tomato DC3000, indicating that in wild-type plants, pathogen-induced SA accumulation is associated with the suppression of JA signaling. Analysis of the Arabidopsis mutant npr1, which is impaired in SA signal transduction, revealed that the antagonistic effect of SA on JA signaling requires the regulatory protein NPR1. Nuclear localization of NPR1, which is essential for SA-mediated defense gene expression, is not required for the suppression of JA signaling, indicating that cross-talk between SA and JA is modulated through a novel function of NPR1 in the cytosol.
1,088 citations
TL;DR: It is shown that TOR deficiency in the nematode Caenorhabditis elegans more than doubles its natural lifespan, suggesting a new function for TOR signalling in ageing control may represent a link between nutrition, metabolism and longevity.
Abstract: The group of enzymes known as TOR (for 'target of rapamycin') kinases regulates cell growth and proliferation in response to nutrients and hormone-dependent mitogenic signals1,2. Here we show that TOR deficiency in the nematode Caenorhabditis elegans more than doubles its natural lifespan. This new function for TOR signalling in ageing control may represent a link between nutrition, metabolism and longevity.
1,007 citations
TL;DR: In this article, a complex hydride called LiBH 4, which consists of 18.5% of hydrogen, was successfully catalyzed with SiO 2 and 13.5 % of hydrogen was liberated starting already at 200°C.
854 citations
TL;DR: LiBH 4 was first synthesized by Schlesinger and Brown [ J. Inorg. Chem. Soc. 62 (1940) 3429] in an organic solvent.
615 citations
TL;DR: Global expression phenotype similarities among mutants suggested, and experiments confirmed, that EDS3 affects SA signaling while EDS8 and PAD1 affect JA signaling, and modeling of network topology, definition of co-regulated genes, and placement of previously uncharacterized regulatory genes in the network.
Abstract: The signal transduction network controlling plant responses to pathogens includes pathways requiring the signal molecules salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). The network topology was explored using global expression phenotyping of wild-type and signaling-defective mutant plants, including eds3, eds4, eds5, eds8, pad1, pad2, pad4, NahG, npr1, sid2, ein2, and coi1. Hierarchical clustering was used to define groups of mutations with similar effects on gene expression and groups of similarly regulated genes. Mutations affecting SA signaling formed two groups: one comprised of eds4, eds5, sid2, and npr1-3 affecting only SA signaling; and the other comprised of pad2, eds3, npr1-1, pad4, and NahG affecting SA signaling as well as another unknown process. Major differences between the expression patterns in NahG and the SA biosynthetic mutant sid2 suggest that NahG has pleiotropic effects beyond elimination of SA. A third group of mutants comprised of eds8, pad1, ein2, and coi1 affected ethylene and jasmonate signaling. Expression patterns of some genes revealed mutual inhibition between SA- and JA-dependent signaling, while other genes required JA and ET signaling as well as the unknown signaling process for full expression. Global expression phenotype similarities among mutants suggested, and experiments confirmed, that EDS3 affects SA signaling while EDS8 and PAD1 affect JA signaling. This work allowed modeling of network topology, definition of co-regulated genes, and placement of previously uncharacterized regulatory genes in the network.
503 citations
TL;DR: Concepts about host–parasite interactions are classified into these two families and discussed with the help of a defence component model and two-dimensional classification scheme of the individual components to clarify some of the confusing terminology.
Abstract: Evolutionary ecology has developed along two major conceptual avenues, starting from the observation that hosts vary in their immune defence against parasites The first avenue, rooted in life-history theory, assumes fitness costs of immune defence and tradeoffs in the face of limited resources, rather than specific host–parasite interactions. The second avenue focuses on specific responses, especially those generated by genotype–genotype interaction between and within host and parasite species. Specificity in the interactions between hosts and parasites play a crucial role in the field but analysis is difficult. Here, we classify concepts about host–parasite interactions into these two families and discuss their reconciliation with the help of a defence component model and two-dimensional classification scheme of the individual components. This helps to clarify some of the confusing terminology and might guide further research in the field.
461 citations
TL;DR: Mechanistic data and mouse phenotypic analyses are summarised, and the possible success of therapeutic inhibition of distinct PI3K isoforms is discussed.
431 citations
TL;DR: The requirements for ISR observed in this study in Peronospora parasitica induced by Pseudomonas fluorescens CHA0r only partially overlap with those published so far for Per onospora Parasitica, indicating a great degree of flexibility in the molecular processes leading to ISR.
Abstract: Root inoculation of Arabidopsis thaliana ecotype Columbia with Pseudomonas fluorescens CHA0r partially protected leaves from the oomycete Peronospora parasitica. The molecular determinants of Pseudomonas fluorescens CHA0r for this induced systemic resistance (ISR) were investigated, using mutants derived from strain CHA0: CHA400 (pyoverdine deficient), CHA805 (exoprotease deficient), CHA77 (HCN deficient), CHA660 (pyoluteorin deficient), CHA631 (2,4-diacetylphloroglucinol [DAPG] deficient), and CHA89 (HCN, DAPG- and pyoluteorin deficient). Only mutations interfering with DAPG production led to a significant decrease in ISR to Peronospora parasitica. Thus, DAPG production in Pseudomonas fluorescens is required for the induction of ISR to Peronospora parasitica. DAPG is known for its antibiotic activity; however, our data indicate that one action of DAPG could be due to an effect on the physiology of the plant. DAPG at 10 to 100 µM applied to roots of Arabidopsis mimicked the ISR effect. CHA0r-mediated ISR was also tested in various Arabidopsis mutants and transgenic plants: NahG (transgenic line degrading salicylic acid [SA]), sid2-1 (nonproducing SA), npr1-1 (nonexpressing NPR1 protein), jar1-1 (insensitive to jasmonic acid and methyl jasmonic acid), ein2-1 (insensitive to ethylene), etr1-1 (insensitive to ethylene), eir1-1 (insensitive to ethylene in roots), and pad2-1 (phytoalexin deficient). Only jar1-1, eir1-1, and npr1-1 mutants were unable to undergo ISR. Sensitivity to jasmonic acid and functional NPR1 and EIR1 proteins were required for full expression of CHA0rmediated ISR. The requirements for ISR observed in this study in Peronospora parasitica induced by Pseudomonas fluorescens CHA0r only partially overlap with those published so far for Peronospora parasitica, indicating a great degree of flexibility in the molecular processes leading to ISR.
TL;DR: The European Variscan and Alpine mountain chains are collisional orogens, and are built up of pre-Variscan "building blocks" which, in most cases, originated at the Gondwana margin this article.
TL;DR: Reliable preferences in reward choice trials and differences in anticipatory licks, performance errors, and reaction times indicated that animals differentially expected the various reward amounts predicted by the instruction cues.
Abstract: In behavioral science, it is well known that humans and nonhuman animals are highly sensitive to differences in reward magnitude when choosing an outcome from a set of alternatives. We know that a realm of behavioral reactions is altered when animals begin to expect different levels of reward outcome. Our present aim was to investigate how the expectation for different magnitudes of reward influences behavior-related neurophysiology in the anterior striatum. In a spatial delayed response task, different instruction pictures are presented to the monkey. Each image represents a different magnitude of juice. By reaching to the spatial location where an instruction picture was presented, animals could receive the particular liquid amount designated by the stimulus. Reliable preferences in reward choice trials and differences in anticipatory licks, performance errors, and reaction times indicated that animals differentially expected the various reward amounts predicted by the instruction cues. A total of 374 of 2,000 neurons in the anterior parts of the caudate nucleus, putamen, and ventral striatum showed five forms of task-related activation during the preparation or execution of movement and activations preceding or following the liquid drop delivery. Approximately one-half of these striatal neurons showed differing response levels dependent on the magnitude of liquid to be received. Results of a linear regression analysis showed that reward magnitude and single cell discharge rate were related in a subset of neurons by a monotonic positive or negative relationship. Overall, these data support the idea that the striatum utilizes expectancies that contain precise information concerning the predicted, forthcoming level of reward in directing general behavioral reactions.
TL;DR: The results strongly suggest that the AMPAR-PI3K complex may constitute a critical molecular signal responsible for AMPAR insertion at activated CA1 synapses during LTP, and consequently, this lipid kinase may serve to determine the polarity of NMDA receptor-dependent synaptic plasticity.
TL;DR: The COOH-terminal region of Bcl-2 can be converted into a targeting signal for the MOM by increasing the basicity surrounding its TM, and it is proposed that B cl-2 acts on several intracellular membranes whereas BCl-xL specifically functions on the Mom.
Abstract: It is assumed that the survival factors Bcl-2 and Bcl-xL are mainly functional on mitochondria and therefore must contain mitochondrial targeting sequences. Here we show, however, that only Bcl-xL is specifically targeted to the mitochondrial outer membrane (MOM) whereas Bcl-2 distributes on several intracellular membranes. Mitochondrial targeting of Bcl-xL requires the COOH-terminal transmembrane (TM) domain flanked at both ends by at least two basic amino acids. This sequence is a bona fide targeting signal for the MOM as it confers specific mitochondrial localization to soluble EGFP. The signal is present in numerous proteins known to be directed to the MOM. Bcl-2 lacks the signal and therefore localizes to several intracellular membranes. The COOH-terminal region of Bcl-2 can be converted into a targeting signal for the MOM by increasing the basicity surrounding its TM. These data define a new targeting sequence for the MOM and propose that Bcl-2 acts on several intracellular membranes whereas Bcl-xL specifically functions on the MOM.
TL;DR: It is argued that there is little theoretical justification and no empirical evidence for the plan that social interventions that lower pathogen transmission will indirectly select lower virulence because of a trade-off between transmission and virulence, and direct selection against virulence itself might be a more rewarding approach.
TL;DR: In this article, the electrochemical double-layer (ECDL) capacitors have been made using various types of CNT and activated carbon (a-C) as electrode material.
TL;DR: In this article, the structural uniformity of carbon nanotubes/nanofibres (CNs) produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications.
Abstract: The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.
TL;DR: It is shown that the evolution of an improved learning ability in replicated experimental fly populations has been consistently associated with a decline of larval competitive ability, compared with replicated control populations, providing evidence for a constitutive fitness cost of learning ability.
Abstract: Maintenance of substantial genetic variation for learning ability in many animal populations suggests that learning ability has fitness costs, but there is little empirical evidence for them. In this paper, we demonstrate an evolutionary trade-off between learning ability and competitive ability in Drosophila melanogaster. We show that the evolution of an improved learning ability in replicated experimental fly populations has been consistently associated with a decline of larval competitive ability, compared with replicated control populations. The competitive ability was not affected by crossing of the replicate populations within each selection regime, excluding differential inbreeding as a potential confounding factor. Our results provide evidence for a constitutive fitness cost of learning ability, i.e. one that is paid irrespective of whether or not the learning ability is actually used.
TL;DR: In this paper, the authors discuss resonance and threshold phenomena in low-energy electron collisions with molecules and clusters, and the theoretical description of electron-molecule collisions generally requires an adequate description of electronic, vibrational and rotational degrees of freedom.
Abstract: Publisher Summary This chapter discusses resonance and threshold phenomena in low-energy electron collisions with molecules and clusters. Low-energy collisions of electrons with atoms and molecules are among the most important elementary processes in gaseous environments such as discharges, arcs, gas lasers, gaseous dielectrics and the earth's atmosphere. The dynamics behavior of low-energy electron-molecule collisions is discussed. The dynamical behavior of slow electrons traversing gases is to a large extent determined by two effects: the energy dependent evolution of the scattering phases for the relevant partial waves and the influence of temporary negative ion states (resonances). Some aspects of resonance and threshold phenomena are discussed. The theoretical description of electron-molecule collisions generally requires an adequate description of electronic, vibrational and rotational degrees of freedom. However, if the typical collision time is short compared to the rotational period, the molecule can be treated as having a fixed orientation during the collision process, and the result for the cross-section can be averaged over orientations. Treatment of vibrational dynamics is usually more important and more challenging to the theory. In the electron energy region important for applications, many inelastic processes such as vibrational excitation and dissociative electron attachment are driven by negative-ion resonances. The theoretical description of vibrational dynamics in these cases is usually based on the nonlocal complex potential describing the nuclear motion in the intermediate negative-ion state.
TL;DR: It is argued that this conception of CST is neither theoretically sound nor conducive to reflective practice, and to a new view of reflective professional practice in general, as critically systemic discourse.
Abstract: Professional competence in applied disciplines such as OR/MS requires both technical expertise and critically reflective skills. Yet, a widespread misconception has taken hold of the OR/MS communit...
TL;DR: Genetic, biochemical and genomic approaches have led to major advances in understanding the molecular and cellular basis of mammalian circadian clock components and mechanisms.
TL;DR: In this paper, carbon nanotubes were grown by the decomposition of C2H2 over a thin catalyst film in order to investigate the growth mechanism of CNTs by chemical vapour deposition (CVD).
TL;DR: It is suggested that PV deficiency, due to an increased short-term facilitation of GABA release, enhances inhibition by high-frequency burst-firing PV-expressing interneurons and may affect the higher cognitive functions associated with gamma oscillations.
Abstract: In the hippocampus, the calcium-binding protein parvalbumin (PV) is expressed in interneurons that innervate perisomatic regions. PV in GABAergic synaptic terminals was proposed to limit repetitive...
TL;DR: In this paper, the authors investigated the possible changes in snow volume and seasonality in the Swiss Alps and found that snow volume in the Alps may respond by reductions of at least 90% at altitudes close to 1000 m, by 50% at 2000 m, and by 35% at 3000 m.
Abstract: Summary Snow is a key feature of mountain environments in terms of the controls it exerts on hydrology, vegetation, and in terms of its economic significance (e.g. for the ski industry). Its quantification in a changing climate is thus important for various environmental and economic impact assessments. Based on observational analysis, surface energy balance modeling, and the latest data from high-resolution regional climate models, this paper investigates the possible changes in snow volume and seasonality in the Swiss Alps. An average warming of 4 � C as projected for the period 2071–2100 with respect to current climate suggests that snow volume in the Alps may respond by reductions of at least 90% at altitudes close to 1000 m, by 50% at 2000 m, and 35% at 3000 m. In addition, the duration of snow cover is sharply reduced in the warmer climate, with a termination of the season 50–60 days earlier at high elevations above 2000–2500 m and 110–130 days earlier at medium elevation sites close to the 1000 m altitude. The shortening of the snow season concerns more the end (spring) rather than the beginning (autumn), so that it should be expected that snow melt will intervene much earlier in the season than under current conditions. The results of this study are of relevance to the estimations of the impacts that the projected warming may have on the amount and timing of water in hydrological basins, on the start of the vegetation season, and on the financial status of many mountain resorts.
TL;DR: In this article, a review summarizes the principles and the results in a special field of metallosupramolecular architectures, namely chiral derivatives of pyridine and polypyridine ligands.
TL;DR: In this paper, an overview of density functional theory (DFT) based techniques for the calculation of the magnetic properties of molecular and supramolecular assemblies is presented, and three different approaches to compute the exchange coupling constant (Jex) are reviewed, i.e., broken symmetry (BS), single determinant (SD), and spin projection method.
TL;DR: A differential conditioning paradigm in which odorants are paired with positive or negative gustatory reinforcers is developed and it is shown that breaks improve performance, in accord with basic principles of associative learning.
Abstract: Insect and mammalian olfactory systems are strikingly similar. Therefore, Drosophila can be used as a simple model for olfaction and olfactory learning. The brain of adult Drosophila, however, is still complex. We therefore chose to work on the larva with its yet simpler but adult-like olfactory system and provide evidence for olfactory learning in individually assayed Drosophila larvae. We developed a differential conditioning paradigm in which odorants are paired with positive ("+" fructose) or negative ("-" quinine or sodium chloride) gustatory reinforcers. Test performance of individuals from two treatment conditions is compared-one received odorant A with the positive reinforcer and odorant B with a negative reinforcer (A+/B-); animals from the other treatment condition were trained reciprocally (A-/B+). During test, differences in choice between A and B of individuals having undergone either A+/B- or A-/B+ training therefore indicate associative learning. We provide such evidence for both combinations of reinforcers; this was replicable across repetitions, laboratories, and experimenters. We further show that breaks improve performance, in accord with basic principles of associative learning. The present individual assay will facilitate electrophysiological studies, which necessarily use individuals. As such approaches are established for the larval neuromuscular synapse, but not in adults, an individual larval learning paradigm will serve to link behavioral levels of analysis to synaptic physiology.
TL;DR: In this article, the authors studied the behavior of snow in the Swiss Alps, in particular the duration of the seasonal snow-pack, on the basis of observational data from a number of Swiss climatological stations.
Abstract: ¶In many instances, snow cover and duration are a major controlling factor on a range of environmental systems in mountain regions. When assessing the impacts of climatic change on mountain ecosystems and river basins whose origin lie in the Alps, one of the key controls on such systems will reside in changes in snow amount and duration. At present, regional climate models or statistical downscaling techniques, which are the principal methods applied to the derivation of climatic variables in a future, changing climate, do not provide adequate information at the scales required for investigations in which snow is playing a major role. A study has thus been undertaken on the behavior of snow in the Swiss Alps, in particular the duration of the seasonal snow-pack, on the basis of observational data from a number of Swiss climatological stations. It is seen that there is a distinct link between snow-cover duration and height (i.e., temperature), and that this link has a specific “signature” according to the type of winter. Milder winters are associated with higher precipitation levels than colder winters, but with more solid precipitation at elevations exceeding 1,700–2,000 m above sea-level, and more liquid precipitation below. These results can be combined within a single diagram, linking winter minimum temperature, winter precipitation, and snow-cover duration. The resulting contour surfaces can then be used to assess the manner in which the length of the snow-season may change according to specified shifts in temperature and precipitation. While the technique is clearly empirical, it can be combined with regional climate model information to provide a useful estimate of the length of the snow season with snow cover, for various climate-impacts studies.
TL;DR: Numerical simulations imply that the effect of uncharacterised endogenous Ca2+ binding proteins is negligible, that buffered diffusion and dye saturation significantly affects spineous Ca2- transients but not those in the dendritic shafts, and that neither CB nor PV undergoes saturation in spines or dendrites during climbing fibre‐evoked Ca 2+ transients.
Abstract: The mechanisms governing the kinetics of climbing fibre-mediated Ca2+ transients in spiny dendrites of cerebellar Purkinje cells (PCs) were quantified with high-resolution confocal Ca2+ imaging. Ca2+ dynamics in parvalbumin (PV−/−) and parvalbumin/calbindin D28k null-mutant (PV/CB−/−) mice were compared with responses in wild-type (WT) animals. In the WT, Ca2+ transients in dendritic shafts were characterised by double exponential decay kinetics that were not due to buffered Ca2+ diffusion or saturation of the indicator dye. Ca2+ transients in PV−/− PCs reached the same peak amplitude as in the WT but the biphasic nature of the decay was less pronounced, an effect that could be attributed to PV's slow binding kinetics. In contrast, peak amplitudes in PV/CB−/− PCs were about two times higher than in the WT and the decay became nearly monophasic. Numerical simulations indicate that the residual deviation from a single exponential decay in PV/CB−/− is due to saturation of the Ca2+ indicator dye. Furthermore, the simulations imply that the effect of uncharacterised endogenous Ca2+ binding proteins is negligible, that buffered diffusion and dye saturation significantly affects spineous Ca2+ transients but not those in the dendritic shafts, and that neither CB nor PV undergoes saturation in spines or dendrites during climbing fibre-evoked Ca2+ transients. Calbindin's medium-affinity binding sites are fast enough to reduce the peak amplitude of the Ca2+ signal. However, similar to PV, delayed binding by CB leads to biphasic Ca2+ decay kinetics. Our results suggest that the distinct kinetics of PV and CB underlie the biphasic kinetics of synaptically evoked Ca2+ transients in dendritic shafts of PCs.