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Search Results: 1 - 10 of 216513 matches for " Manon W. H. Schaap "
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Predictability of Painful Stimulation Modulates the Somatosensory-Evoked Potential in the Rat
Manon W. H. Schaap, Hugo van Oostrom, Arie Doornenbal, Annemarie M. Baars, Saskia S. Arndt, Ludo J. Hellebrekers
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0061487
Abstract: Somatosensory-evoked potentials (SEPs) are used in humans and animals to increase knowledge about nociception and pain. Since the SEP in humans increases when noxious stimuli are administered unpredictably, predictability potentially influences the SEP in animals as well. To assess the effect of predictability on the SEP in animals, classical fear conditioning was applied to compare SEPs between rats receiving SEP-evoking electrical stimuli either predictably or unpredictably. As in humans, the rat’s SEP increased when SEP-evoking stimuli were administered unpredictably. These data support the hypothesis that the predictability of noxious stimuli plays a distinctive role in the processing of these stimuli in animals. The influence of predictability should be considered when studying nociception and pain in animals. Additionally, this finding suggests that animals confronted with (un)predictable noxious stimuli can be used to investigate the mechanisms underlying the influence of predictability on central processing of noxious stimuli.
Nociception and Conditioned Fear in Rats: Strains Matter
Manon W. H. Schaap, Hugo van Oostrom, Arie Doornenbal, José van 't Klooster, Annemarie M. Baars, Saskia S. Arndt, Ludo J. Hellebrekers
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0083339
Abstract: When using rats in pain research, strain-related differences in outcomes of tests for pain and nociception are acknowledged. However, very little is known about the specific characteristics of these strain differences. In this study four phylogenetically distant inbred rat strains, i.e. Wistar Kyoto (WKY), Fawn Hooded (FH), Brown Norway (BN) and Lewis (LE), were investigated in different tests related to pain and nociception. During Pavlovian fear conditioning, the LE and WKY showed a significantly longer duration of freezing behaviour than the FH and BN. Additionally, differences in c-Fos expression in subregions of the prefrontal cortex and amygdala between rat strains during retrieval and expression of conditioned fear were found. For example, the BN did not show recruitment of the basolateral amygdala, whereas the WKY, FH and LE did. During the hot plate test, the WKY and LE showed a lower thermal threshold compared to the BN and FH. In a follow-up experiment, the two most contrasting strains regarding behaviour during the hot plate test and Pavlovian fear conditioning (i.e. FH and WKY) were selected and the hot plate test, Von Frey test and somatosensory-evoked potential (SEP) were investigated. During the Von Frey test, the WKY showed a lower mechanical threshold compared to the FH. When measuring the SEP, the FH appeared to be less reactive to increasing stimulus intensities when considering both peak amplitudes and latencies. Altogether, the combined results indicate various differences between rat strains in Pavlovian fear conditioning, nociception related behaviours and nociceptive processing. These findings demonstrate the necessity of using multiple rat strains when using tests including noxious stimuli and suggest that the choice of rat strains should be considered. When selecting a strain for a particular study it should be considered how this strain behaves during the tests used in that study.
Proteomic Analysis of the Secretory Response of Aspergillus niger to D-Maltose and D-Xylose
José Miguel P. Ferreira de Oliveira, Mark W. J. van Passel, Peter J. Schaap, Leo H. de Graaff
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0020865
Abstract: Fungi utilize polysaccharide substrates through extracellular digestion catalyzed by secreted enzymes. Thus far, protein secretion by the filamentous fungus Aspergillus niger has mainly been studied at the level of individual proteins and by genome and transcriptome analyses. To extend these studies, a complementary proteomics approach was applied with the aim to investigate the changes in secretome and microsomal protein composition resulting from a shift to a high level secretion condition. During growth of A. niger on d-sorbitol, small amounts of d-maltose or d-xylose were used as inducers of the extracellular amylolytic and xylanolytic enzymes. Upon induction, protein compositions in the extracellular broth as well as in enriched secretory organelle (microsomal) fractions were analyzed using a shotgun proteomics approach. In total 102 secreted proteins and 1,126 microsomal proteins were identified in this study. Induction by d-maltose or d-xylose resulted in the increase in specific extracellular enzymes, such as glucoamylase A on d-maltose and β-xylosidase D on d-xylose, as well as of microsomal proteins. This reflects the differential expression of selected genes coding for dedicated extracellular enzymes. As expected, the addition of extra d-sorbitol had no effect on the expression of carbohydrate-active enzymes, compared to addition of d-xylose or d-maltose. Furthermore, d-maltose induction caused an increase in microsomal proteins related to translation (e.g., Rpl15) and vesicular transport (e.g., the endosomal-cargo receptor Erv14). Millimolar amounts of the inducers d-maltose and d-xylose are sufficient to cause a direct response in specific protein expression levels. Also, after induction by d-maltose or d-xylose, the induced enzymes were found in microsomes and extracellular. In agreement with our previous findings for d-xylose induction, d-maltose induction leads to recruitment of proteins involved in proteasome-mediated degradation.
CO-ELABORATION OF MEANING IN PEER-LED LITERATURE CIRCLES IN SECONDARY SCHOOL The interplay between reading modes, quality of talk and collaboration modes
L1 Educational Studies in Language and Literature , 2008,
Abstract: This study investigated the interplay between reading and social variables in peer-led literature circles at seventh grade school level, wherein students read a novel by themselves and discuss it without any teacher assistance. Specifically, this in-depth study of one classroom activity sought to answer the five following questions: 1) In what proportions do students use and vary the different reading modes in this type of peer-led literature circle? 2) To what extent do they elaborate their talk? 3) To what relative de-gree do they use different modes of collaboration and types of interaction? 4) Are there any linkages among these several variables? 5) Are there differences between the two regular and two “fast track” groups? The 20 participants (4 peer-led groups) belonged to a multiethnic school in a middle-class, urban environment in Canada. Quantitative and qualitative content analysis methods have been used to analyze transcripts of the discussions. Results show that in this type of peer-led group: 1) The literal reading mode is dominant; 2) by contrast, when students adopt an aesthetic or a textual mode of reading, the quality of their talk tends to be superior; 3) modes of collaboration centred on feedback and management greatly support this type of shared interpretation; 4) a microanalysis of excellent episodes would seem to demonstrate that fast-track groups adopt a more divergent means of co-elaborating meaning. Future research should better examine the many intellectual tools that are required to support peer scaffolding in this specific mode of peer-led discussion.
Modelling the partitioning of ammonium nitrate in the convective boundary layer
J. M. J. Aan de Brugh, J. S. Henzing, M. Schaap, W. T. Morgan, C. C. van Heerwaarden, E. P. Weijers, H. Coe,M. C. Krol
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: An explanatory model study is presented on semi-volatile secondary inorganic aerosols on three clear days in May 2008 during the IMPACT campaign at the Cabauw tower in the Netherlands. A single column model in combination with the equilibrium aerosol model ISORROPIA is used. This model uses surface observations from IMPACT and calculates the gas-aerosol partitioning of ammonium nitrate. The calculated gas-aerosol equilibrium overestimates the gas phase fraction during daytime, and overestimates the aerosol phase fraction during night-time. This discrepancy can partly be solved when the approach of the gas-aerosol equilibrium is forced to proceed with a delay timescale of up to two hours. Although it is shown that the delay itself has a small effect, the most important effect is caused by the mixing of air from higher altitudes at which the equilibrium is shifted to the aerosol phase. Thus, vertical mixing is shown to have a significant influence on the calculated partitioning at the surface. On some occasions, the correspondence to the observed partitioning improves dramatically. Even though gas-aerosol partitioning of ammonium nitrate is not instantaneous, observations show that a different equilibrium in the upper boundary layer causes aerosol ammonium nitrate concentrations to increase with altitude. Our model calculates similar vertical gradients depending on the assumed speed of gas-aerosol equilibrium. The calculated optical properties of the aerosol show a similar behaviour. The aerosol optical properties depend on the aerosol size distribution both directly, because light scattering depends on particle size, and indirectly, because the equilibration timescale depends on the aerosol sizes. Future studies should therefore focus on a fully size-resolved treatment of the gas-aerosol partitioning. Finally, coarser-resolution models may treat the gas-aerosol equilibrium of ammonium nitrate by calculating the equilibrium with a temperature and humidity sampled at a different altitude. We found that the equilibrium at an altitude of 200 m (night) up to 600 m (day) is representative for the partitioning of ammonium nitrate at the surface in the beginning of May 2008.
The use of opioids at the end of life: the knowledge level of Dutch physicians as a potential barrier to effective pain management
Mette L Rurup, Christiaan A Rhodius, Sander D Borgsteede, Manon SA Boddaert, Astrid GM Keijser, H Roeline W Pasman, Bregje D Onwuteaka-Philipsen
BMC Palliative Care , 2010, DOI: 10.1186/1472-684x-9-23
Abstract: The research question of this study is: what is the level of knowledge of Dutch physicians concerning pain management and the use of opioids at the end of life?A written questionnaire was sent to a random sample of physicians of specialties most often involved in end of life care in the Netherlands. The questionnaire was completed by 406 physicians, response rate 41%.Almost all physicians were aware of the most basal knowledge about opioids, e.g. that it is important for treatment purposes to distinguish nociceptive from neuropathic pain (97%). Approximately half of the physicians (46%) did not know that decreased renal function raises plasma concentration of morphine(-metabolites) and 34% of the clinical specialists erroneously thought opioids are the favoured drug for palliative sedation.Although 91% knew that opioids titrated against pain do not shorten life, 10% sometimes or often gave higher dosages than needed with the explicit aim to hasten death. About half felt sometimes or often pressured by relatives to hasten death by increasing opioiddosage.The large majority (83%) of physicians was interested in additional education about subjects related to the end of life, the most popular subject was opioid rotation (46%).Although the basic knowledge of physicians was adequate, there seemed to be a lack of knowledge in several areas, which can be a barrier for good pain management at the end of life. From this study four areas emerge, in which it seems likely that an improvement can improve the quality of pain management at the end of life for many patients in the Netherlands: 1)palliative sedation; 2)expected effect of opioids on survival; and 3) opioid rotation.Many factors may hamper optimal pain management such as patient nonadherence to drug therapy, underreporting of pain or miscommunication between patient and caregivers; from a healthcare provider perspective, inadequate assessment of pain, poor documentation and miscommunication may limit optimal pain manag
Continuous Fields and Discrete Samples: Reconstruction through Delaunay Tessellations
W. E. Schaap,R. van de Weygaert
Physics , 2000,
Abstract: Here we introduce the Delaunay Density Estimator Method. Its purpose is rendering a fully volume-covering reconstruction of a density field from a set of discrete data points sampling this field. Reconstructing density or intensity fields from a set of irregularly sampled data is a recurring key issue in operations on astronomical data sets, both in an observational context as well as in the context of numerical simulations. Our technique is based upon the stochastic geometric concept of the Delaunay tessellation generated by the point set. We shortly describe the method, and illustrate its virtues by means of an application to an N-body simulation of cosmic structure formation. The presented technique is a fully adaptive method: automatically it probes high density regions at maximum possible resolution, while low density regions are recovered as moderately varying regions devoid of the often irritating shot-noise effects. Of equal importance is its capability to sharply and undilutedly recover anisotropic density features like filaments and walls. The prominence of such features at a range of resolution levels within a hierarchical clustering scenario as the example of the standard CDM scenario is shown to be impressively recovered by our scheme.
Reconstructing cosmological fields using tessellation methods
W. E. Schaap,R. van de Weygaert
Physics , 2001,
Abstract: Astronomical observations, physical experiments as well as computer simulations often involve discrete data sets supposed to represent a fair sample of an underlying smooth and continuous field. Reconstructing the underlying fields from a set of irregularly sampled data is therefore a recurring key issue in operations on astronomical data sets. Conventional methods involve artificial filtering through a grid or a smoothing kernel and fail to achieve an optimal result. Here we describe a fully self-adaptive geometric method which does not make use of artificial filtering, and which makes optimal use of the available information.
Delaunay recovery of cosmic density and velocity probes
W. E. Schaap,R. van de Weygaert
Physics , 2001,
Abstract: Optimally resolved one-dimensional density and velocity profiles through cosmological N-body simulations are constructed by means of the Voronoi-Delaunay tessellation reconstruction technique. In a fully self-adaptive fashion a strikingly detailed view of the density features and the corresponding cosmic motions is recovered.
HPTN 071 (PopART): A Cluster-Randomized Trial of the Population Impact of an HIV Combination Prevention Intervention Including Universal Testing and Treatment: Mathematical Model
Anne Cori, Helen Ayles, Nulda Beyers, Ab Schaap, Sian Floyd, Kalpana Sabapathy, Jeffrey W. Eaton, Katharina Hauck, Peter Smith, Sam Griffith, Ayana Moore, Deborah Donnell, Sten H. Vermund, Sarah Fidler, Richard Hayes, Christophe Fraser, HPTN 071 (PopART) study team
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0084511
Abstract: Background The HPTN 052 trial confirmed that antiretroviral therapy (ART) can nearly eliminate HIV transmission from successfully treated HIV-infected individuals within couples. Here, we present the mathematical modeling used to inform the design and monitoring of a new trial aiming to test whether widespread provision of ART is feasible and can substantially reduce population-level HIV incidence. Methods and Findings The HPTN 071 (PopART) trial is a three-arm cluster-randomized trial of 21 large population clusters in Zambia and South Africa, starting in 2013. A combination prevention package including home-based voluntary testing and counseling, and ART for HIV positive individuals, will be delivered in arms A and B, with ART offered universally in arm A and according to national guidelines in arm B. Arm C will be the control arm. The primary endpoint is the cumulative three-year HIV incidence. We developed a mathematical model of heterosexual HIV transmission, informed by recent data on HIV-1 natural history. We focused on realistically modeling the intervention package. Parameters were calibrated to data previously collected in these communities and national surveillance data. We predict that, if targets are reached, HIV incidence over three years will drop by >60% in arm A and >25% in arm B, relative to arm C. The considerable uncertainty in the predicted reduction in incidence justifies the need for a trial. The main drivers of this uncertainty are possible community-level behavioral changes associated with the intervention, uptake of testing and treatment, as well as ART retention and adherence. Conclusions The HPTN 071 (PopART) trial intervention could reduce HIV population-level incidence by >60% over three years. This intervention could serve as a paradigm for national or supra-national implementation. Our analysis highlights the role mathematical modeling can play in trial development and monitoring, and more widely in evaluating the impact of treatment as prevention.
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