Experimental cortical spreading depression induces NMDA receptor dependent potassium currents in microglia

Cortical spreading depression (CSD) is a propagating event of neuronal depolarization, which is considered as the cellular correlate of the migraine aura. It is characterized by a change in the intrinsic optical signal and by a negative DC potential shift. Microglia are the resident macrophages of the CNS and act as sensors for pathological changes. In the present study, we analyzed whether microglial cells might sense CSD by recording membrane currents from microglia in acutely isolated cortical mouse brain slices during an experimentally induced CSD. Coincident with the change in the intrinsic optical signal and the negative DC potential shift we recorded an increase in potassium conductance predominantly mediated by K(+) inward rectifier (Kir)2.1, which was blocked by the NMDA receptor antagonist D-AP5. Application of NMDA and an increase in extracellular K(+) mimics the CSD-induced Kir activation. Application of D-AP5, but not the purinergic receptor antagonist RB2, blocks the NMDA-induced Kir activation. The K(+) channel blocker Ba(2+) blocks both the CSD- and the NMDA-triggered increase in Kir channel activity. In addition, we could confirm previous findings that microglia in the adult brain do not express functional NMDA receptors by recording from microglia cultured from adult brain. From these observations we conclude that CSD activates neuronal NMDA receptors, which lead to an increase in extracellular [K(+)] resulting in the activation of Kir channel activity in microglia

Auswirkungen der Pflanzenschutzmittel-Belastung auf Lebensgemeinschaften in Fließgewässern des landwirtschaftlich geprägten Raumes

In die ökologische Risikoabschätzung von Pflanzenschutzmitteln (PSM) sollten zukünftig Erfassungen von toxischen Effekten im Freiland einbezogen werden. Ziel des Projektes war, Dosis-Wirkungs-Beziehungen zwischen der PSM-Belastung und aquatischen Lebensgemeinschaften in kleinen Fließgewässern durch Freilanduntersuchungen zu beschreiben. An 14 Gewässern in Niedersachsen und Brandenburg wurden neben anderen Faktoren die PSM-Belastung und die Makroinvertebratenbesiedelung aufgenommen. In Wasserproben aus 11 der 14 Gewässer wurden Belastungen mit PSM verschiedener Wirkstoffe nachgewiesen. Stichlinge (Gasterosteus aculeatus L.) aus mit Parathion belasteten Gewässern zeigten eine erniedrigte Aktivität von Butyryl-Cholinesterase (BChE) im Muskelgewebe. Im Laborversuch wurde gezeigt, daß bereits geringe Parathion-Konzentrationen bei sehr kurzzeitiger Exposition die BChE-Aktivität in Stichlingen partiell zu hemmen vermögen. Eine Literaturauswertung ergab, daß sich Makroinvertebraten-Ordnungen nach ihrer relativen Empfindlichkeit gegenüber organischen Toxinen unterscheiden und in ein entsprechendes Rangordnungssystem einordnen lassen. Zur Datenauswertung wurde ein Index zur Beschreibung von Zönosenveränderungen durch Toxine gebildet (Sensitivity-Recovery-Index, SR-Index). In den PSM-belasteten Gewässern wurde eine geringere Artenzahl physiologisch empfindlicher Invertebraten sowie ein geringerer Abundanzanteil von Arten mit einem mehrjährigen Entwicklungszyklus gefunden. Zwischen der Gesamttoxizität (TUsum) der in den Gewässern nachgewiesenen PSM und dem Abundanzanteil der empfindlichen Arten sowie dem SR-Index bestanden lineare Zusammenhänge. Die Ergebnisse zeigten, daß bereits Parathion-Konzentrationen von weniger als 1 µg/l bei kurzzeitiger Kontamination eine hohe Bioverfügbarkeit aufweisen. Weiterhin wurde gezeigt, daß auch gering konzentrierte PSM-Belastungen Lebensgemeinschaften in Fließgewässern chronisch verändern können, sofern die Belastung regelmäßig wiederkehrt.Evaluations on toxic effects of pesticides in the field are to be included in future ecological risk assessments. Aim of this project was to determine the dose-response relationships between pesticide contamination and aquatic communities in small streams through fieldwork research. Fourteen streams in Niedersachsen and Brandenburg were investigated to record pesticide contamination, the macroinvertebrate community structure and other factors. Water samples from 11 of the 14 streams showed pesticide contamination. Sticklebacks (Gasterosteus aculeatus L.) present in parathion-contaminated streams revealed reduced Butyryl-Cholinesterase (BChE) activity in their muscle tissue. Laboratory experiments indicated that already low parathion concentrations during short-term contamination inhibited BChE activity. A literature evaluation revealed that macroinvertebrate orders can be distinguished by their relative sensitivity to organic toxins using a ranking system. A Sensitivity-Recovery-Index (SR-Index) evaluated data by describing the community changes resulting from toxin contamination. At pesticide contaminated sites lower numbers of sensitive species and lower relative abundance of species with a long reproduction cycle were found. There was a linear correlation between total toxicity (TUsum) of pesticides detected, between relative abundance of sensitive species and the SR-Index. Results showed that even parathion concentrations lower than 1µg/L exhibited strong bioavailability following short-term contamination. Moreover, pesticide contamination in low concentrations can affect and alter the stream community on a long term scale providing contamination occurs regularly. The observed dose-response relationship verifies that results from field investigations can be used to derive quality measures and objectives to control agricultural pesticide application

Satellite microglia display spontaneous electrical activity uncorrelated with activity of the attached neuron

Microglia are innate immune cells of the brain. We have studied a subpopulation of microglia, called satellite microglia. This cell type is defined by a close morphological soma-to-soma association with a neuron, indicative of a direct functional interaction. Indeed, ultrastructural analysis revealed closely attached plasma membranes of satellite microglia and neurons. However, we found no apparent morphological specializations of the contact and biocytin injection into satellite microglia showed no dye-coupling with the apposed neuron or any other cell. Likewise, evoked local field potentials or action potentials and postsynaptic potentials of the associated neuron did not lead to any transmembrane currents or non-capacitive changes in the membrane potential of the satellite microglia in the cortex and hippocampus. Both satellite and non-satellite microglia, however, showed spontaneous transient membrane depolarizations which were not correlated with neuronal activity. These events could be divided into fast and slow rising depolarisations, which exhibited different characteristics in satellite and non-satellite microglia. Fast and slow rising potentials differed with regard to voltage dependence. The frequency of these events was not affected by application of TTX, but fast rising event frequency decreased after application of GABA. We conclude that microglial cells show spontaneous electrical activity uncorrelated with the activity of adjacent neurons

In vivo cholinesterase sensitivity of gilthead seabream (Sparus aurata) exposed to organophosphate compounds: Influence of biological factors

Two cholinesterases have been found in vertebrates, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). These enzymes are present in the gilthead seabream, AChE in the brain and muscle and BChE in the muscle. Cholinesterases have been used as biomarker of effect in environmental monitoring studies. However, there are few studies about the influence of biometric parameters on ChE. This paper studies the possible influence of biological factors on brain and muscle cholinesterase (ChE) in Sparus aurata. Our results show that ChE activity in brain and muscle tissues changes depending on several biological variables. ChE activity in these tissues decreased when the age (48-152 week), body length (14.15-28.95 cm) and body weight (42.73-380.74 g) of the fishes studied increased. The relationships between brain and muscle ChE activity and several biometric factors were curvilinear

Traits and stress: keys to identify community effects of low levels of toxicants in test systems

Community effects of low toxicant concentrations are obscured by a multitude of confounding factors. To resolve this issue for community test systems, we propose a trait-based approach to detect toxic effects. An experiment with outdoor stream mesocosms was established 2-years before contamination to allow the development of biotic interactions within the community. Following pulse contamination with the insecticide thiacloprid, communities were monitored for additional 2 years to observe long-term effects. Applying a priori ecotoxicological knowledge species were aggregated into trait-based groups that reflected stressor-specific vulnerability of populations to toxicant exposure. This reduces inter-replicate variation that is not related to toxicant effects and enables to better link exposure and effect. Species with low intrinsic sensitivity showed only transient effects at the highest thiacloprid concentration of 100 μg/l. Sensitive multivoltine species showed transient effects at 3.3 μg/l. Sensitive univoltine species were affected at 0.1 μg/l and did not recover during the year after contamination. Based on these results the new indicator SPEARmesocosm was calculated as the relative abundance of sensitive univoltine taxa. Long-term community effects of thiacloprid were detected at concentrations 1,000 times below those detected by the PRC (Principal Response Curve) approach. We also found that those species, characterised by the most vulnerable trait combination, that were stressed were affected more strongly by thiacloprid than non-stressed species. We conclude that the grouping of species according to toxicant-related traits enables identification and prediction of community response to low levels of toxicants and that additionally the environmental context determines species sensitivity to toxicants

Double trouble at high density::Cross-level test of ressource-related adaptive plasticity and crowding-related fitness.

Population size is often regulated by negative feedback between population density and individual fitness. At high population densities, animals run into double trouble: they might concurrently suffer from overexploitation of resources and also from negative interference among individuals regardless of resource availability, referred to as crowding. Animals are able to adapt to resource shortages by exhibiting a repertoire of life history and physiological plasticities. In addition to resource-related plasticity, crowding might lead to reduced fitness, with consequences for individual life history. We explored how different mechanisms behind resource-related plasticity and crowding-related fitness act independently or together, using the water flea Daphnia magna as a case study. For testing hypotheses related to mechanisms of plasticity and crowding stress across different biological levels, we used an individual-based population model that is based on dynamic energy budget theory. Each of the hypotheses, represented by a sub-model, is based on specific assumptions on how the uptake and allocation of energy are altered under conditions of resource shortage or crowding. For cross-level testing of different hypotheses, we explored how well the sub-models fit individual level data and also how well they predict population dynamics under different conditions of resource availability. Only operating resource-related and crowding-related hypotheses together enabled accurate model predictions of D. magna population dynamics and size structure. Whereas this study showed that various mechanisms might play a role in the negative feedback between population density and individual life history, it also indicated that different density levels might instigate the onset of the different mechanisms. This study provides an example of how the integration of dynamic energy budget theory and individual-based modelling can facilitate the exploration of mechanisms behind the regulation of population size. Such understanding is important for assessment, management and the conservation of populations and thereby biodiversity in ecosystems

5-Point programme for sustainable plant protection

Abstract This position paper intends to stimulate a profound rethinking of contemporary agricultural practice. We criticise the current intensity of chemical plant protection in Germany as ecologically unsustainable and thus threatening the achievement of key targets of environmental protection and nature conservation policies. In the first part of the paper, we provide background information on the use of plant protection products (PPP) in German agriculture, the role of agricultural policy, European pesticide legislation, the principles of and framework for environmental risk assessment and risk management of PPP, as well as environmental effects of PPP. The second part is presented against the backdrop of the European “Sustainable Use Directive” (2009/128/EC). This directive requires that “Member States shall adopt National Action Plans to set up their quantitative objectives, targets, measures, and timetables to reduce risks and impacts of pesticide use on human health and the environment and to encourage the development and introduction of integrated pest management and of alternative approaches or techniques to reduce dependency on the use of pesticides.” Reflecting on the corresponding debate in Germany, we suggest the following five key principles for a sustainable use of PPP and provide recommendations for their implementation: (1) minimising use; (2) identifying, quantifying, and communicating risks; (3) optimising risk management; (4) compensating for unavoidable effects; (5) internalising external costs