Induction of Anti-Hebbian LTP in CA1 Stratum Oriens Interneurons: Interactions between Group I Metabotropic Glutamate Receptors and M1 Muscarinic Receptors

An anti-Hebbian form of LTP is observed at excitatory synapses made with some hippocampal interneurons. LTP induction is facilitated when postsynaptic interneurons are hyperpolarized, presumably because Ca(2+) entry through Ca(2+)-permeable glutamate receptors is enhanced. The contribution of modulatory transmitters to anti-Hebbian LTP induction remains to be established. Activation of group I metabotropic receptors (mGluRs) is required for anti-Hebbian LTP induction in interneurons with cell bodies in the CA1 stratum oriens. This region receives a strong cholinergic innervation from the septum, and muscarinic acetylcholine receptors (mAChRs) share some signaling pathways and cooperate with mGluRs in the control of neuronal excitability.We therefore examined possible interactions between group I mGluRs and mAChRs in anti-Hebbian LTP at synapses which excite oriens interneurons in rat brain slices. We found that blockade of either group I mGluRs or M1 mAChRs prevented the induction of anti-Hebbian LTP by pairing presynaptic activity with postsynaptic hyperpolarization. Blocking either receptor also suppressed long-term effects of activation of the other G-protein coupled receptor on interneuron membrane potential. However, no crossed blockade was detected for mGluR or mAchR effects on interneuron after-burst potentials or on the frequency of miniature EPSPs. Paired recordings between pyramidal neurons and oriens interneurons were obtained to determine whether LTP could be induced without concurrent stimulation of cholinergic axons. Exogenous activation of mAChRs led to LTP, with changes in EPSP amplitude distributions consistent with a presynaptic locus of expression. LTP, however, required noninvasive presynaptic and postsynaptic recordings

Formation des ions bromate dans une colonne à bulles: Effets du peroxyde d'hydrogène lors de l'ozonation

L'utilisation de l'ozone, aujourd'hui très répandue dans les filières de potabilisation, n'est pas sans effet secondaire. De nombreux sous-produits peuvent se former comme notamment les ions bromates, sous produits finaux d'oxydation des bromures contenus dans les eaux. Malheureusement, le mécanisme de production de cette espèce est complexe et dépend de nombreux paramètres difficiles à appréhender.Sur une installation pilote de type colonne à bulles fonctionnant à contre-courant, nous avons étudié l'influence de différents paramètres, comme le pH, le temps de contact, la dose d'ozone et la dose de peroxyde d'hydrogène, sur la formation des bromates et la dégradation des pesticides, représentée par l'atrazine.Les résultats de la littérature ont été confirmés lors de l'emploi unique de l'ozone. La formation des ions bromate est influencée par la présence du peroxyde d'hydrogène. Cet oxydant intervient de manière non négligeable sur la consommation des entités intermédiaires. Le couple HOBr/OBr- peut être oxydé par l'ozone moléculaire et le radical OH° mais peut également être réduit par l'ozone et par le peroxyde sous sa forme acide ou sa base conjuguée. En ce qui concerne la dégradation des pesticides, l'utilisation de peroxyde d'hydrogène couplé à l'ozone favorise l'oxydation de la molécule d'atrazine grâce à la présence plus importante de radicaux hydroxyles.Une pollution accidentelle en pesticides pourra être traitée par l'ajout ponctuel de peroxyde d'hydrogène avec une augmentation de pH, la formation des bromates sera, dans ce cas, faible. La désinfection sera alors assurée par l'étape de chloration.In drinking water treatment plants, ozonation is often used to disinfect, to remove micropollutants and to improve water taste and odour. Ozonation increases organic matter biodegradability before filtration through granular active carbon and reduces the concentration of haloform precursors that react in the final chlorination step. However, by-products that could be detrimental to human health could be formed. For example, bromates, which are classified as carcinogenic compounds by the I.A.R.C, are produced during the ozonation of bromide-containing water. The mechanism of bromate formation is complex, due to the participation of molecular ozone and radical (hydroxyl and carbonate) reactions. The optimisation of the process should allow for a good disinfection and a reduction in the levels of micropollutants, together with low by-product formation.Using a pilot-scale counter-current bubble column, we have measured the bromate concentration in relation to pesticide removal. Water spiked with bromide and atrazine was stored in a completely stirred-tank (2 m3) before being pumped to the top of the column. The inlet gaseous ozone was measured by an analyser using UV detection, the outlet gaseous ozone was monitored by the potassium iodide method, and the dissolved ozone concentration was determined by the indigo trisulfonate method. Bromides and bromates were quantified by ion chromatography with a conductimetric detector, with a sodium carbonate solution as the eluant. Samples for bromate analysis were pretreated by OnGuard-Ag and OnGuard-H cartridges in series before injection. Atrazine degradation was measured by high performance liquid chromatography with a diode array detector, with a CH3CN/H2O mixture as the eluant. The linearisation of atrazine removal allowed us to calculate the hydroxyl radical concentration in a series of a completely-stirred tank reactors and in a plug-flow reactor.We have studied the influence of several parameters on bromate formation, including pH, bromide concentration and hydrogen peroxide concentration. As bromate production is a function of bromide concentration, we have chosen to calculate the ratio between the real bromate concentration and the theoretical bromate concentration if all bromide were oxidised to bromate. The pH affects bromate formation: an increase in pH in the absence of hydrogen peroxide increases bromate production, but when this oxidant is applied bromate production decreases when the pH increases. If reaction progress is represented as a function of [O3]*TC, we note that the presence of hydrogen peroxide increases bromate formation because of the increase in hydroxyl radical concentration, which favours radical formation. Nevertheless, if we represent reaction progress as a function of [OH∘]*TC, hydrogen peroxide seems to be an initiator and a scavenger in the mechanism of bromate formation. If we calculate the rates of all the oxidation and reduction reactions for HOBr/OBr- species, the contribution to the reduction of HOBr/OBr- species by peroxide is very important in comparison to the oxidation reactions, which inhibits bromate production. Without the hydrogen peroxide, the contribution of oxidation is equal to that of the reduction reaction, and in this case bromate formation is effective. When, under the same initial operational conditions, we apply hydrogen peroxide with an increase in pH, we observe a decrease in bromate formation with a decrease of the dissolved ozone concentration, which hinders the desired disinfection. The main contribution to atrazine oxidation is from the free-radical reactions, which explains why removal is better when we apply hydrogen peroxide than when we use ozone alone. However, if we want to respect a low bromate level in drinking water, atrazine degradation should not be greater than 90% for the operational conditions on our pilot-scale.If an accidental high pesticide concentration is observed, an addition of hydrogen peroxide with a concurrent increase of pH, could treat the pollution. In this case, a subsequent chlorination step would then have to be used to assure the disinfection alone

The LHC Dipole Geometry as Built in Industry

The LHC dipoles magnets are produced in 5 industrial production sites in Europe. The production is well underway and more than half of the total quantity has been delivered to CERN. One of the important characteristics of the dipole magnets is their geometry. To achieve the requested mechanical tolerances on the magnets, which are 15 m long and have a 28 t mass, the final assembly operations includes precise optical measurements. To ensure the good quality and high production rate, the final assembly procedure has been automated as much as possible. The authors report here about the assembly procedure, the features of the software that guides the optical measurements (and consequently the assembly operations) and the results obtained on the geometry in the different sites

Measurement and Analysis of Axial End Forces in a Full-Length Prototype of LHC Main Dipole Magnets

A full-length, twin aperture prototype (MBP2N1) dipole magnet for the LHC project was assembled at CERN with collared coils delivered by industry. The design of this prototype is close to that foreseen for the dipole series manufacture as far the coil geometry and that of the yoke components are concerned. The bolts that transfer the axial magnetic forces from the coil ends to the cold mass end plates were instrumented to verify the axial coil support. These axial forces were initially measured after partial assembly, during a standard and an accelerated cool down Introduction to 1.9 K, and during magnet excitation up to 9.2 T. High force levels were observed, triggering a comparison with analytical models and measurements routinely made on 1-m single aperture dipole models. The prototype magnet was re-assembled with lower initial axial force settings and with additional instrumentation, to monitor these forces during the entire assembly process, and re-tested, to possibly correlate axial forces with training behaviour. This paper reports about the experimental observations and provides models towards their understandin

Genetic variation and evolutionary history of a mycorrhizal fungus regulate the currency of exchange in symbiosis with the food security crop cassava.

Most land plants form symbioses with arbuscular mycorrhizal fungi (AMF). Diversity of AMF increases plant community productivity and plant diversity. For decades, it was known that plants trade carbohydrates for phosphate with their fungal symbionts. However, recent studies show that plant-derived lipids probably represent the most essential currency of exchange. Understanding the regulation of plant genes involved in the currency of exchange is crucial to understanding stability of this mutualism. Plants encounter many different AMF genotypes that vary greatly in the benefit they confer to plants. Yet the role that fungal genetic variation plays in the regulation of this currency has not received much attention. We used a high-resolution phylogeny of one AMF species (Rhizophagus irregularis) to show that fungal genetic variation drives the regulation of the plant fatty acid pathway in cassava (Manihot esculenta); a pathway regulating one of the essential currencies of trade in the symbiosis. The regulation of this pathway was explained by clearly defined patterns of fungal genome-wide variation representing the precise fungal evolutionary history. This represents the first demonstrated link between the genetics of AMF and reprogramming of an essential plant pathway regulating the currency of exchange in the symbiosis. The transcription factor RAM1 was also revealed as the dominant gene in the fatty acid plant gene co-expression network. Our study highlights the crucial role of variation in fungal genomes in the trade of resources in this important symbiosis and also opens the door to discovering characteristics of AMF genomes responsible for interactions between AMF and cassava that will lead to optimal cassava growth

Stocking activities for the Arctic charr in Lake Geneva: Genetic effects in space and time

Artificial stocking practices are widely used by resource managers worldwide, in order to sustain fish populations exploited by both recreational and commercial activities, but their benefits are controversial. Former practices involved exotic strains, although current programs rather consider artificial breeding of local fishes (supportive breeding). Understanding the complex genetic effects of these management strategies is an importan t challenge with economic and conservation implications, especially in the context of population declines. In this study, we focus on the declining Arctic charr (Salvelinus alpinus) population from Lake Geneva (Switzerland and France), which has initially been restocked with allochtonous fishes in the early eighties, followed by supportive breeding. In this context, we conducted a genetic survey to document the evolution of the genetic diversity and structure throughout the last 50 years, before and after the initiation of hatchery supplementation, using contemporary and historical samples. We show that the introduction of exotic fishes was associated with a genetic bottleneck in the 1980–1990s, a break of Hardy–Weinberg Equilibrium (HWE), a reduction in genetic diversity, an increase in genetic structure among spawning sites, and a change in their genetic composition. Together with better environmental conditions, three decades of subsequent supportive breeding using local fishes allowed to re-establish HWE and the initial levels of genetic variation. However, current spawning sites have not fully recovered their original genetic composition and were extensively h omogenized across the lake. Our study demonstrates the drastic genetic consequ e nces of different restocking tactics in a comprehensive spatiotemporal framewo rk and suggests that genetic alteration by nonlocal stocking may be partly reversible through supportive breeding. We recommend that conservation-based programs consider local diversity and implement adequate protocols to limit the genetic homogenization of this Arctic charr population

Coexistence of genetically different Rhizophagus irregularis isolates induces genes involved in a putative fungal mating response.

Arbuscular mycorrhizal fungi (AMF) are of great ecological importance because of their effects on plant growth. Closely related genotypes of the same AMF species coexist in plant roots. However, almost nothing is known about the molecular interactions occurring during such coexistence. We compared in planta AMF gene transcription in single and coinoculation treatments with two genetically different isolates of Rhizophagus irregularis in symbiosis independently on three genetically different cassava genotypes. Remarkably few genes were specifically upregulated when the two fungi coexisted. Strikingly, almost all of the genes with an identifiable putative function were known to be involved in mating in other fungal species. Several genes were consistent across host plant genotypes but more upregulated genes involved in putative mating were observed in host genotype (COL2215) compared with the two other host genotypes. The AMF genes that we observed to be specifically upregulated during coexistence were either involved in the mating pheromone response, in meiosis, sexual sporulation or were homologs of MAT-locus genes known in other fungal species. We did not observe the upregulation of the expected homeodomain genes contained in a putative AMF MAT-locus, but observed upregulation of HMG-box genes similar to those known to be involved in mating in Mucoromycotina species. Finally, we demonstrated that coexistence between the two fungal genotypes in the coinoculation treatments explained the number of putative mating response genes activated in the different plant host genotypes. This study demonstrates experimentally the activation of genes involved in a putative mating response and represents an important step towards the understanding of coexistence and sexual reproduction in these important plant symbionts

Within-species phylogenetic relatedness of a common mycorrhizal fungus affects evenness in plant communities through effects on dominant species.

Arbuscular mycorrhizal fungi (AMF) have been shown to influence plant community structure and diversity. Studies based on single plant-single AMF isolate experiments show that within AMF species variation leads to large differential growth responses of different plant species. Because of these differential effects, genetic differences among isolates of an AMF species could potentially have strong effects on the structure of plant communities. We tested the hypothesis that within species variation in the AMF Rhizophagus irregularis significantly affects plant community structure and plant co-existence. We took advantage of a recent genetic characterization of several isolates using double-digest restriction-site associated DNA sequencing (ddRADseq). This allowed us to test not only for the impact of within AMF species variation on plant community structure but also for the role of the R. irregularis phylogeny on plant community metrics. Nine isolates of R. irregularis, belonging to three different genetic groups (Gp1, Gp3 and Gp4), were used as either single inoculum or as mixed diversity inoculum. Plants in a mesocosm representing common species that naturally co-exist in European grasslands were inoculated with the different AMF treatments. We found that within-species differences in R. irregularis did not strongly influence the performance of individual plants or the structure of the overall plant community. However, the evenness of the plant community was affected by the phylogeny of the fungal isolates, where more closely-related AMF isolates were more likely to affect plant community evenness in a similar way compared to more genetically distant isolates. This study underlines the effect of within AMF species variability on plant community structure. While differential effects of the AMF isolates were not strong, a single AMF species had enough functional variability to change the equilibrium of a plant community in a way that is associated with the evolutionary history of the fungus

Hydrological responses of a watershed to historical land use evolution and future land use scenarios under climate change conditions

Watershed runoff is closely related to land use but this influence is difficult to quantify. This study focused on the Chaudière River watershed (Québec, Canada) and had two objectives: (i) to quantify the influence of historical agricultural land use evolution on watershed runoff; and (ii) to assess the effect of future land use evolution scenarios under climate change conditions (CC). To achieve this, we used the integrated modeling system GIBSI. Past land use evolution was constructed using satellite images that were integrated into GIBSI. The general trend was an increase of agricultural land in the 80's, a slight decrease in the beginning of the 90's and a steady state over the last ten years. Simulations showed strong correlations between land use evolution and water discharge at the watershed outlet. For the prospective approach, we first assessed the effect of CC and then defined two opposite land use evolution scenarios for the horizon 2025 based on two different trends: agriculture intensification and sustainable development. Simulations led to a wide range of results depending on the climatologic models and gas emission scenarios considered, varying from a decrease to an increase of annual and monthly water discharge. In this context, the two land use scenarios induced opposite effects on water discharge and low flow sequences, especially during the growing season. However, due to the large uncertainty linked to CC simulations, it is difficult to conclude that one land use scenario provides a better adaptation to CC than another. Nevertheless, this study shows that land use is a key factor that has to be taken into account when predicting potential future hydrological responses of a watershed