Self-Organized Criticality in Developing Neuronal Networks

Recently evidence has accumulated that many neural networks exhibit self-organized criticality. In this state, activity is similar across temporal scales and this is beneficial with respect to information flow. If subcritical, activity can die out, if supercritical epileptiform patterns may occur. Little is known about how developing networks will reach and stabilize criticality. Here we monitor the development between 13 and 95 days in vitro (DIV) of cortical cell cultures (n = 20) and find four different phases, related to their morphological maturation: An initial low-activity state (≈19 DIV) is followed by a supercritical (≈20 DIV) and then a subcritical one (≈36 DIV) until the network finally reaches stable criticality (≈58 DIV). Using network modeling and mathematical analysis we describe the dynamics of the emergent connectivity in such developing systems. Based on physiological observations, the synaptic development in the model is determined by the drive of the neurons to adjust their connectivity for reaching on average firing rate homeostasis. We predict a specific time course for the maturation of inhibition, with strong onset and delayed pruning, and that total synaptic connectivity should be strongly linked to the relative levels of excitation and inhibition. These results demonstrate that the interplay between activity and connectivity guides developing networks into criticality suggesting that this may be a generic and stable state of many networks in vivo and in vitro

Allopregnanolone-induced rise in intracellular calcium in embryonic hippocampal neurons parallels their proliferative potential

<p>Abstract</p> <p>Background</p> <p>Factors that regulate intracellular calcium concentration are known to play a critical role in brain function and neural development, including neural plasticity and neurogenesis. We previously demonstrated that the neurosteroid allopregnanolone (APα; 5α-pregnan-3α-ol-20-one) promotes neural progenitor proliferation <it>in vitro </it>in cultures of rodent hippocampal and human cortical neural progenitors, and <it>in vivo </it>in triple transgenic Alzheimer's disease mice dentate gyrus. We also found that APα-induced proliferation of neural progenitors is abolished by a calcium channel blocker, nifedipine, indicating a calcium dependent mechanism for the proliferation.</p> <p>Methods</p> <p>In the present study, we investigated the effect of APα on the regulation of intracellular calcium concentration in E18 rat hippocampal neurons using ratiometric Fura2-AM imaging.</p> <p>Results</p> <p>Results indicate that APα rapidly increased intracellular calcium concentration in a dose-dependent and developmentally regulated manner, with an EC₅₀of 110 ± 15 nM and a maximal response occurring at three days <it>in vitro</it>. The stereoisomers 3β-hydroxy-5α-hydroxy-pregnan-20-one, and 3β-hydroxy-5β-hydroxy-pregnan-20-one, as well as progesterone, were without significant effect. APα-induced intracellular calcium concentration increase was not observed in calcium depleted medium and was blocked in the presence of the broad spectrum calcium channel blocker La³⁺, or the L-type calcium channel blocker nifedipine. Furthermore, the GABA_Areceptor blockers bicuculline and picrotoxin abolished APα-induced intracellular calcium concentration rise.</p> <p>Conclusion</p> <p>Collectively, these data indicate that APα promotes a rapid, dose-dependent, stereo-specific, and developmentally regulated increase of intracellular calcium concentration in rat embryonic hippocampal neurons via a mechanism that requires both the GABA_Areceptor and L-type calcium channel. These data suggest that APα-induced intracellular calcium concentration increase serves as the initiation mechanism whereby APα promotes neurogenesis.</p

Potential Benefits of Sequential Inhibitor-Mutagen Treatments of RNA Virus Infections

Lethal mutagenesis is an antiviral strategy consisting of virus extinction associated with enhanced mutagenesis. The use of non-mutagenic antiviral inhibitors has faced the problem of selection of inhibitor-resistant virus mutants. Quasispecies dynamics predicts, and clinical results have confirmed, that combination therapy has an advantage over monotherapy to delay or prevent selection of inhibitor-escape mutants. Using ribavirin-mediated mutagenesis of foot-and-mouth disease virus (FMDV), here we show that, contrary to expectations, sequential administration of the antiviral inhibitor guanidine (GU) first, followed by ribavirin, is more effective than combination therapy with the two drugs, or than either drug used individually. Coelectroporation experiments suggest that limited inhibition of replication of interfering mutants by GU may contribute to the benefits of the sequential treatment. In lethal mutagenesis, a sequential inhibitor-mutagen treatment can be more effective than the corresponding combination treatment to drive a virus towards extinction. Such an advantage is also supported by a theoretical model for the evolution of a viral population under the action of increased mutagenesis in the presence of an inhibitor of viral replication. The model suggests that benefits of the sequential treatment are due to the involvement of a mutagenic agent, and to competition for susceptible cells exerted by the mutant spectrum. The results may impact lethal mutagenesis-based protocols, as well as current antiviral therapies involving ribavirin

The combined EURL-Salmonella interlaboratory comparison study for Food and Primary production (2017) . Detection of Salmonella in hygiene swabs

In October 2017, a combined EURL-Salmonella interlaboratory comparison study on the detection of Salmonella in food samples and animal primary production stage was organised. In this study, hygiene swabs were chosen to be the matrix. All the laboratories involved were able to detect Salmonella in all the contaminated hygiene swab samples; they were all successful in analysing both the blank control sample and the positive control sample correctly. One laboratory made a mistake reporting the positive control negative for Salmonella and was, therefore, scored as having a 'moderate performance'. Blank hygiene swab samples, not contaminated with Salmonella, were correctly analysed as negative by almost all the laboratories. One laboratory found Salmonella present in two of the six blank samples and this was scored as a 'poor performance'. In a follow-up study this laboratory obtained good results for all samples. Participation was obligatory for all EU Member State National Reference Laboratories (NRLs) responsible for the detection of Salmonella in food samples, and voluntary for NRLs responsible for the detection of Salmonella in primary production stage samples. These latter laboratories had already participated in the compulsory EURL study for the detection of Salmonella in primary production samples which was organised in March 2017. A total of 56 NRLs participated in this study: 33 NRLs for Salmonella in Food matrices and 23 NRLs for Salmonella in Primary Production Stage matrices (PPS). The participants came from all 28 EU Member States (MS), four of the NRLs were based in third European countries and one was based in a non-European country. The EURL-Salmonella is situated at the Dutch National Institute for Public Health and the Environment (RIVM). An important task of the EURL-Salmonella is to monitor and to improve the performance of the National Reference Laboratories in Europe

EURL-Salmonella Proficiency Test Primary Production, 2018 : Detection of Salmonella in boot socks with chicken faeces

In oktober 2018 organiseerde het EURL-Salmonella een ringonderzoek om Salmonella aan te tonen in kippenmest die op overschoentjes zit. Alle deelnemers op één na waren hiertoe in staat. Eén laboratorium heeft problemen gehad met de analyse van de monsters en kon in het grootste gedeelte van de monsters geen Salmonella aantonen. Dit kwam hoogst waarschijnlijk doordat de bacteriën niet meer in leven waren na de lange transporttijd en de hoge temperaturen waaraan het pakje met monsters is blootgesteld tijdens het transport naar dit laboratorium. Deze jaarlijkse kwaliteitstoets is verplicht voor alle Nationale Referentie Laboratoria (NRL's) van de Europese lidstaten die ervoor verantwoordelijk zijn Salmonella aan te tonen in de leefomgeving van dieren die voor de voedselproductie worden gehouden. In totaal hebben 36 NRL's deelgenomen: 29 NRL's afkomstig uit alle 28 EU-lidstaten, zes NRL's uit andere Europese landen en één NRL uit een niet-Europees land. Het Europese Referentielaboratorium (EURL) Salmonella is gevestigd bij het Nederlandse Rijksinstituut voor Volksgezondheid en Milieu (RIVM). Een belangrijke taak van het EURL-Salmonella is toezien op de kwaliteit van de nationale referentielaboratoria voor deze bacterie in Europa

EU-ringonderzoek primaire productie XVIII (2015) : Detectie van Salmonella in varkensmest

alleen digitaal verschenenIn maart 2015 vond het achttiende EURL-ringonderzoek naar detectie van Salmonella plaats. Deelname aan deze kwaliteitstoets is verplicht voor alle Nationale Referentie Laboratoria (NRL's) van de Europese lidstaten die verantwoordelijk zijn voor het aantonen van Salmonella in dierlijke mest. Voor dit ringonderzoek is een ander type mest gebruikt, dat dit keer geen geschikt alternatief bleek. Daardoor waren de resultaten van de deelnemers niet onderling te vergelijken. In totaal hebben 36 NRL's deelgenomen aan dit ringonderzoek: 29 NRL's afkomstig van 28 lidstaten in de EU, 6 NRL's afkomstig uit kandidaatlanden voor het EU-lidmaatschap of lidstaten van de European Free Trade Association (EFTA) status en 1 niet-Europees NRL op verzoek van de Europese Unie. Werkwijze Er is varkensmest gebruikt omdat het vanwege de vogelgriep in de herfst van 2014 niet was toegestaan om kippenmest te transporteren. Varkensmest staat bekend als een geschikt alternatief. Wel moeten de monsters bij een lagere temperatuur (-20 °C in plaats van 5 of 10 °C) worden bewaard om te voorkomen dat er gisten en schimmels in gaan groeien. In de testfase bleek onder deze omstandigheden een gedeelte van de toegevoegde Salmonella dood te gaan. Door extra veel Salmonella toe te voegen, zouden er genoeg bacteriën in leven moeten blijven. Tijdens de analyses van de varkensmestmonsters door de laboratoria bleek echter dat Salmonella het invriezen niet goed had overleefd. De hoeveelheid Salmonella in de aangeleverde monsters verschilde daardoor per laboratorium, zodat de resultaten niet met elkaar konden worden vergeleken. De laboratoria hebben de monsters geanalyseerd met behulp van de internationaal voorgeschreven analysemethode (MSRV). Het overkoepelend referentielaboratorium van de Europese Unie voor Salmonella (EURL-Salmonella) is gevestigd bij het RIVM.In March 2015, the EURL-Salmonella organised the 18th interlaboratory comparison study on the detection of Salmonella in samples from the primary production stage. Participation was obligatory for all EU Member State NRLs that are responsible for the detection of Salmonella in samples from primary production. In total, 36 NRLs participated in this study: 29 NRLs from the 28 EU-Member States (MS), 6 NRLs from other countries in Europe (EU candidate MS or potential EU candidate MS and members of the European Free Trade Association (EFTA)) and, at the request of DG-Santé, one NRL from a non-European country. EURL-Salmonella is part of the Dutch National Institute for Public Health and the Environment (RIVM). Due to the avian influenza outbreak in the Netherlands, it was not possible to transport chicken faeces. Therefore, the EURL chose pig faeces as an alternative matrix for this detection study. Pre-studies showed that pig faeces were susceptible to the growth of yeast and moulds during storage at 5 °C or 10 °C. Therefore, storage at -20 °C was tested as an alternative. Salmonella was found to be sensitive to freezing, but by using a higher starting inoculation levels, it was expected that Salmonella would still be found after freezing of the pig faeces. Unfortunately, Salmonella survival in the frozen pig faeces samples was not stable. The results varied tremendously amongst the participants. Therefore, the performance of the participants could not be evaluated in this study.European CommissionDirectorate General for Health and Consumer Protection (DG-Sante

Het EURL-Salmonella ringonderzoek productiedieren (2018) : Detectie van Salmonella in overschoentjes met kippenmest

In oktober 2018 organiseerde het EURL-Salmonella een ringonderzoek om Salmonella aan te tonen in kippenmest die op overschoentjes zit. Alle deelnemers op één na waren hiertoe in staat. Eén laboratorium heeft problemen gehad met de analyse van de monsters en kon in het grootste gedeelte van de monsters geen Salmonella aantonen. Dit kwam hoogst waarschijnlijk doordat de bacteriën niet meer in leven waren na de lange transporttijd en de hoge temperaturen waaraan het pakje met monsters is blootgesteld tijdens het transport naar dit laboratorium. Deze jaarlijkse kwaliteitstoets is verplicht voor alle Nationale Referentie Laboratoria (NRL's) van de Europese lidstaten die ervoor verantwoordelijk zijn Salmonella aan te tonen in de leefomgeving van dieren die voor de voedselproductie worden gehouden. In totaal hebben 36 NRL's deelgenomen: 29 NRL's afkomstig uit alle 28 EU-lidstaten, zes NRL's uit andere Europese landen en één NRL uit een niet-Europees land. Het Europese Referentielaboratorium (EURL) Salmonella is gevestigd bij het Nederlandse Rijksinstituut voor Volksgezondheid en Milieu (RIVM). Een belangrijke taak van het EURL-Salmonella is toezien op de kwaliteit van de nationale referentielaboratoria voor deze bacterie in Europa.In October 2018, the EURL-Salmonella organised a Proficiency Test on the detection of Salmonella in animal production samples. Boot sock samples with chicken faeces were selected as matrix. All but one laboratory were successful in finding Salmonella in the contaminated boot sock samples. One laboratory had some problems with the contaminated boot sock samples, scoring the majority of the samples negative for Salmonella. This was most likely caused by the inactivation of the Salmonella bacteria due to the long transport period and the high temperatures the samples experienced during transport to this laboratory. Participation was obligatory for all EU Member State National Reference Laboratories (NRLs) responsible for analysing Salmonella in animal production samples. In total, 36 NRLs participated in this study: 29 participants originated from 28 EU Member States (MS), six were based in third European countries, and one was based in a non-European country. The EURL-Salmonella is located at the Dutch National Institute for Public Health and the Environment (RIVM). An important task of the EURL-Salmonella is to monitor and improve the performance of the National Reference Laboratories in Europe.European Commission, Directorat e-General for Health and Food Safety (DG-SANTE

Combined EURL-Salmonella Proficiency Test Primary Production and Food, 2020. Detection of Salmonella in hygiene swab samples

The National Reference Laboratories (NRLs) of the European Union were able to detect Salmonella in hygiene swab samples in the annual EURLSalmonella Proficiency Test. All laboratories were successful in finding Salmonella in high and low concentrations in the contaminated hygiene swab samples. All but two laboratories scored good results. These two laboratories reported the positive control sample as having a negative result. One laboratory made an administrative error in reporting their positive result accidently as a negative one and scored a moderate performance. The other laboratory proved with their raw data that they misinterpreted the purpose of this sample. They considered this sample as a normal sample and added an extra sample as their positive control. This laboratory also scored a moderate performance. This was the outcome of the Proficiency Test for detection of Salmonella in hygiene swab samples organised by the coordinating EURL-Salmonella in October 2020. Since 1992, all NRLs from EU members states are obliged to participate in the annual quality control proficiency tests for Salmonella. Every Member State has to appoint a National Reference Laboratory, which is responsible for analysing Salmonella in samples taken from the animal primary production stage (PPS). Because of the nature of the samples, the participation of NRLs that are responsible for analysing Salmonella in food samples was allowed on voluntary basis. In total, 65 NRLs participated in this study: 37 NRLs PPS and 28 NRLs Food originating from 28 EU Member States (MS), five NRLs were based in third countries in Europe (non-EU members), and one was based in a non-European country. The EURL-Salmonella is located at the Dutch National Institute for Public Health and the Environment (RIVM). An important task of the EURLSalmonella is to monitor and improve the performance of the National Reference Laboratories for Salmonella in Europe