Showing papers by "University of Amsterdam published in 1997"

Heart rate variability: Origins, methods, and interpretive caveats

Abstract: Components of heart rate variability have attracted considerable attention in psychology and medicine and have become important dependent measures in psychophysiology and behavioral medicine. Quantification and interpretation of heart rate variability, however, remain complex issues and are fraught with pitfalls. The present report (a) examines the physiological origins and mechanisms of heart rate variability, (b) considers quantitative approaches to measurement, and (c) highlights important caveats in the interpretation of heart rate variability. Summary guidelines for research in this area are outlined, and suggestions and prospects for future developments are considered.

A short-term study of chimeric monoclonal antibody cA2 to tumor necrosis factor alpha for Crohn's disease. Crohn's Disease cA2 Study Group.

Abstract: Background Studies in animals and an open-label trial have suggested a role for antibodies to tumor necrosis factor alpha, specifically chimeric monoclonal antibody cA2, in the treatment of Crohn's disease. Methods We conducted a 12-week multicenter, double-blind, placebo-controlled trial of cA2 in 108 patients with moderate-to-severe Crohn's disease that was resistant to treatment. All had scores on the Crohn's Disease Activity Index between 220 and 400 (scores can range from 0 to about 600, with higher scores indicating more severe illness). Patients were randomly assigned to receive a single two-hour intravenous infusion of either placebo or cA2 in a dose of 5 mg per kilogram of body weight, 10 mg per kilogram, or 20 mg per kilogram. Clinical response, the primary end point, was defined as a reduction of 70 or more points in the score on the Crohn's Disease Activity Index at four weeks that was not accompanied by a change in any concomitant medications. Results At four weeks, 81 percent of the patients given 5 mg of cA2 per kilogram (22 of 27 patients), 50 percent of those given 10 mg of cA2 per kilogram (14 of 28), and 64 percent of those given 20 mg of cA2 per kilogram (18 of 28) had had a clinical response, as compared with 17 percent of patients in the placebo group (4 of 24) (p Conclusions A single infusion of cA2 was an effective short-term treatment in many patients with moderate-to-severe, treatment-resistant Crohn's disease.

Phenotypic and Functional Separation of Memory and Effector Human CD8+ T Cells

Abstract: Human CD8+ memory- and effector-type T cells are poorly defined. We show here that, next to a naive compartment, two discrete primed subpopulations can be found within the circulating human CD8+ T cell subset. First, CD45RA−CD45R0+ cells are reminiscent of memory-type T cells in that they express elevated levels of CD95 (Fas) and the integrin family members CD11a, CD18, CD29, CD49d, and CD49e, compared to naive CD8+ T cells, and are able to secrete not only interleukin (IL) 2 but also interferon γ, tumor necrosis factor α, and IL-4. This subset does not exert cytolytic activity without prior in vitro stimulation but does contain virus-specific cytotoxic T lymphocyte (CTL) precursors. A second primed population is characterized by CD45RA expression with concomitant absence of expression of the costimulatory molecules CD27 and CD28. The CD8+CD45RA+CD27− population contains T cells expressing high levels of CD11a, CD11b, CD18, and CD49d, whereas CD62L (L-selectin) is not expressed. These T cells do not secrete IL-2 or -4 but can produce IFN-γ and TNF-α. In accordance with this finding, cells contained within this subpopulation depend for proliferation on exogenous growth factors such as IL-2 and -15. Interestingly, CD8+CD45RA+CD27− cells parallel effector CTLs, as they abundantly express Fas-ligand mRNA, contain perforin and granzyme B, and have high cytolytic activity without in vitro prestimulation. Based on both phenotypic and functional properties, we conclude that memory- and effector-type T cells can be separated as distinct entities within the human CD8+ T cell subset.

Visuomotor integration is associated with zero time-lag synchronization among cortical areas

Abstract: INFORMATION processing in the cerebral cortex invariably involves the activation of millions of neurons that are widely distributed over its various areas. These distributed activity patterns need to be integrated into coherent representational states. A candidate mechanism for the integration and coordination of neuronal activity between different brain regions is synchronization on a fine temporal scale1–3. In the visual cortex, synchronization occurs selectively between the responses of neurons that represent related features2–5 and that need to be integrated for the generation of coherent percepts; neurons in other areas of the cerebral cortex also synchronize their discharges6–10. However, little is known about the patterns and the behavioural correlates of synchrony among widely separated cortical regions. Here we report that synchronization occurs between areas of the visual and parietal cortex, and between areas of the parietal and motor cortex, in the awake cat. When cats responded to a sudden change of a visual pattern, neuronal activity in cortical areas exhibited synchrony without time lags; this synchrony was particularly strong between areas subserving related functions. During reward and inter-trial episodes, zero-time-lag synchrony was lost and replaced by interactions exhibiting large and unsystematic time lags.

Development of prosocial, individualistic, and competitive orientations : Theory and preliminary evidence

Abstract: The authors adopt an interdependen ce analysis of social value orientation, proposing that prosocial, individualistic, and competitive orientations are (a) partially rooted in different patterns of social interaction as experienced during the periods spanning early childhood to young adulthood and (b) further shaped by different patterns of social interaction as experienced during early adulthood, middle adulthood, and old age. Congruent with this analysis, results revealed that relative to individualists and competitors, prosocial individuals exhibited greater levels of secure attachment (Studies 1 and 2) and reported having more siblings, especially sisters (Study 3). Finally, the prevalence of prosocials increased—and the prevalence of individualist s and competitors decreased—from early adulthood to middle adulthood and old age (Study 4). Traditional theories and insights assume that the principle of rational self-interest or economic man reflects the prevailing motivation among humankind (Luce & Raiffa, 1957; Von Neuman & Morgenstern, 1947; cf. Roth, 1988). However, more recent theoretical developments have indicated that individuals systematically differ in the manner in which they approach interdependent others. Some people are inclined to give interdependent others the benefit of the doubt and approach them cooperatively, whereas other people are inclined to approach interdependent others in a less cooperative manner. Such individual differences are related to social value orientation, defined as stable preferences for certain patterns of outcomes for oneself and others (McClintock, 1978; Messick & McClintock, 1968). Although a variety of different social value orientations can be distinguished from a theoretical point of view (e.g., Knight & Dubro, 1984), in this article we address a three-category typology of social value orientation, examining differences between prosocial, individualistic, and competitive orientations. Prosocials tend to maximize outcomes for both themselves and others (i.e., cooperation) and to minimize differences between outcomes for

Criterion validity of the Center for Epidemiologic Studies Depression scale (CES-D): results from a community-based sample of older subjects in The Netherlands.

Abstract: The Center for Epidemiologic Studies Depression scale (CES-D) has been widely used in studies of late-life depression. Psychometric properties are generally favourable, but data on the criterion validity of the CES-D in elderly community-based samples are lacking. In a sample of older (55-85 years) inhabitants of the Netherlands, 487 subjects were selected to study criterion validity of the CES-D. Using the 1-month prevalence of major depression derived from the Diagnostic Interview Schedule (DIS) as criterion, the weighted sensitivity of the CES-D was 100%; specificity 88%; and positive predictive value 13.2%. False positives were not more likely among elderly with physical illness, cognitive decline or anxiety. We conclude that the criterion validity of the CES-D for major depression was very satisfactory in this sample of older adults.

Transient optical emission from the error box of the gamma-ray burst of 28 February 1997

Abstract: For almost a quarter of a century1, the origin of γ-ray bursts— brief, energetic bursts of high-energy photons—has remained unknown. The detection of a counterpart at another wavelength has long been thought to be a key to understanding the nature of these bursts (see, for example, ref. 2), but intensive searches have not revealed such a counterpart. The distribution and properties of the bursts3 are explained naturally if they lie at cosmological distances (a few Gpc)4, but there is a countervailing view that they are relatively local objects5, perhaps distributed in a very large halo around our Galaxy. Here we report the detection of a transient and fading optical source in the error box associated with the burst GRB970228, less than 21 hours after the burst6,7. The optical transient appears to be associated with a faint galaxy7,8, suggesting that the burst occurred in that galaxy and thus that γ-ray bursts in general lie at cosmological distance.

The phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 inhibit autophagy in isolated rat hepatocytes

Abstract: Recent studies indicate that phosphatidylinositol 3-kinase is essential in the regulation of many processes dependent on membrane flow. Autophagy is a complex pathway in which cell material, including proteins, can be degraded. Membrane flow plays a pivotal role in this process. To find out whether phosphatidylinositol 3-kinase is also required for autophagy, we tested the effects on autophagy of two structurally unrelated phosphatidylinositol 3-kinase inhibitors, wortmannin and 2-(4-morpholinyl)-8-phenylchromone (LY294002). The addition of low concentrations of each of these inhibitors to incubations of hepatocytes in the absence of amino acids resulted in a strong inhibition of proteolysis. The antiproteolytic effect of wortmannin (IC50 30 nM) and LY294002 (IC50 10 mu M) was accompanied by inhibition of autophagic sequestration and not by an increase in lysosomal pH or a decrease in intracellular ATP. No further inhibition of proteolysis by the two compounds was observed when autophagy was already maximally inhibited by high concentrations of amino acids. 3-Methyladenine, which is commonly used as a specific inhibitor of autophagic sequestration, was an inhibitor of phosphatidylinositol 3-kinase, thus providing a target for its action. It is proposed that phosphatidylinositol 3-kinase activity is required for autophagy. 3-Methyladenine inhibits autophagy by inhibition of this enzyme.

Using explicit ontologies in KBS development

Abstract: This article presents a number of ways in which ontologies-schematic descriptions of the contents of domain knowledge-can be constructed and can be used to improve the knowledge engineering process. The main message is that early in the knowledge engineering process an application-specific ontology should be constructed. To facilitate this, the article presents some principles for organizing a library of reusable ontological theories which can be configured into an application ontology. This application ontology is then exploited to organize the knowledge acquisition process and to support computational design. The process is illustrated with a knowledge engineering scenario in the domain of treating acute radiation syndrome.

Convention for the Protection of Human Rights and Dignity of the Human Being with Regard to the Application of Biology and Medicine: Convention on Human Rights and Biomedicine

Abstract: I. This Explanatory Report to the Convention on human rights and biomedicine was drawn up under the responsibility of the Secretary General of the Council of Europe, on the basis of a draft prepared, at the request of the Steering Committee on Bioethics (CDBI), by Mr Jean MICHAUD (France), Chairman of the CDBI. It takes into account the discussions held in the CDBI and its Working Group entrusted with the drafting of the Convention; it also takes into account the remarks and proposals made by Delegations.

Clinical activity score as a guide in the management of patients with Graves' ophthalmopathy

Abstract: OBJECTIVE Approximately 35% of patients with Graves' ophthalmopathy do not respond to immunosuppressive treatment. A possible explanation for this finding is that only patients with active ophthalmopathy respond to immunosuppressive treatment, whereas patients with fibrotic end stage disease do not. To distinguish between these two groups and to predict the outcome of immunosuppressive treatment, we developed a clinical activity score (CAS) based on four of the five classical signs of inflammation and tested its efficacy in a double-blind, prospective study. DESIGN, PATIENTS AND MEASUREMENTS The CAS was determined by an ophthalmologist before, on the day of, and after the start of either oral prednisone or retrobulbar irradiation in 43 patients with moderate to severe Graves' ophthalmopathy. The therapeutic outcome was determined by a second ophthalmologist unaware of the CAS stores given. Success of treatment was defined as an improvement in NOSPECS class or grade. RESULTS Responders (22) and non-responders (21) did not differ in age, sex, duration or severity of their Graves' ophthalmopathy. The pretreatment CAS, however, was significantly higher in responders than in non-responders. Twelve of 22 responders and three of 21 non-responders had a CAS ≥ 4 (80% vs 36%; P < 0.01). Using this CAS cut-off point, the accuracy of CAS in predicting the therapeutic outcome was: specificity 86%, sensitivity 55%, positive predictive value 80%, negative predictive value 64%. Patients with a CAS ≥ 4 had a similar duration of Graves' ophthalmopathy as patients with a CAS < 4. CONCLUSIONS The clinical activity score has a high predictive value for the outcome of immunosuppressive treatment in Graves' ophthalmopathy. Disease activity, and not disease duration, is the prime determinant of therapeutic outcome.

The concept of personal initiative : Operationalization, reliability and validity in two German samples

Abstract: Personal initiative is conceptualized as a behavioural syndrome made up of several factors. It is important for organizational effectiveness and is one aspect of ‘contextual performance’. The construct validity of a set of interview- and questionnaire-based scales for measuring initiative was ascertained in interrelated studies (two waves from a longitudinal study in East Germany [N = 543] and a cross-sectional study in West Germany [N = 160]). As hypothesized, initiative correlated with partners' assessments, need for achievement, action orientation, problem-focused and passive emotion-focused coping, career planning and executing plans, but not with job satisfaction. Higher initiative existed in small-scale entrepreneurs in the East and in those unemployed who got a job more quickly.

Activation of the complement system during and after cardiopulmonary bypass surgery: postsurgery activation involves C-reactive protein and is associated with postoperative arrhythmia.

Abstract: Background Complement activation during cardiopulmonary bypass (CPB) surgery is considered to result from interaction of blood with the extracorporeal circuit. We investigated whether additional mechanisms may contribute to complement activation during and after CPB and, in particular, focused on a possible role of the acute-phase protein C–reactive protein (CRP). Methods and Results In 19 patients enrolled for myocardial revascularization, perioperative and postoperative levels of complement activation products, interleukin-6 (IL-6), CRP, and complement-CRP complexes, reflecting CRP-mediated complement activation in vivo, were measured and related to clinical symptoms. A biphasic activation of complement was observed. The ratio between the areas under the curve of perioperative and postoperative C3b/c and C4b/c were 3:2 and 1:46, respectively. IL-6 levels reached a maximum at 6 hours post-surgery. CRP levels peaked on the second postoperative day. Each complement-CRP complex had peak levels on the second...

Fundamentals of Argumentation Theory : A Handbook of Historical Backgrounds and Contemporary Developments

Abstract: Contents: Preface. Introduction. Part I: Historical Backgrounds. Analytic, Dialectic and Rhetoric. Analysis of Fallacies, Controversy, and Discussion. Perelman and Olbrechts-Tyteca's New Rhetoric. Toulmin's Model of Argumentation. Part II: Contemporary Developments. Informal Logic and Critical Thinking. Communication and Rhetoric. Fallacies and Formal Logic. Dialogue Logic and Formal Dialectics. Pragma-Dialectics and Critical Discussion. Language-Oriented Approaches to Argumentation. Other Significant Developments.

Job Destruction and Propagation of Shocks

Abstract: We develop and quantitatively implement a dynamic general equilibrium model with labor" market matching and endogenous job destruction. The model produces a close match with data on" job creation and destruction. Cyclical fluctuations in the job destruction rate serve to magnify the" effects of productivity shock on output, as well as making the effects much more persistent. " Interactions between household savings decisions and separation decisions in employment" relationships play a key role in propagating shocks.

Argument-based extended logic programming with defeasible priorities

Abstract: Inspired by legal reasoning, this paper presents a semantics and proof theory of a system for defeasible argumentation. Arguments are expressed in a logic-programming language with both weak and strong negation, conflicts between arguments are decided with the help of priorities on the rules. An important feature of the system is that these priorities are not fixed, but are themselves defeasibly derived as conclusions within the system. Thus debates on the choice between conflicting arguments can also be modelled. The semantics of the system is given with a fixpoint definition, while its proof theory is stated in dialectical style, where a proof takes the form of a dialogue between a proponent and an opponent of an argument: an argument is shown to be justified if the proponent can make the opponent run out of moves in whatever way the opponent attacks.

A twin-pronged attack on complex traits

Abstract: Before one starts the hunt for quantitative trait loci (QTLs) for a complex trait it is necessary to show that the trait is genetically influenced. This evidence is most likely to come from the classical twin study—the demonstration that monozygotic twins are more similar for the trait than dizygotic twins. The strengths and weaknesses of twin studies are discussed, and it is suggested that, far from becoming irrelevant with advances in molecular biology, they can improve the efficiency of QTL detection and play an important role in unravelling developmental genetic mechanisms

Willingness to Sacrifice in Close Relationships

Abstract: The authors advance an interdependence analysis of willingness to sacrifice. Support for model predictions was revealed in 6 studies (3 cross-sectional survey studies, 1 simulation experiment, 2 longitudinal studies) that used a novel self-report measure and a behavioral measure of willingness to sacrifice. Willingness to sacrifice was associated with strong commitment, high satisfaction, poor alternatives, and high investments; feelings of commitment largely mediated the associations of these variables with willingness to sacrifice. Moreover, willingness to sacrifice was associated with superior couple functioning, operationalized in terms of level of dyadic adjustment and probability of couple persistence. In predicting adjustment, willingness to sacrifice accounted for significant variance beyond commitment, partially mediating the link between commitment and adjustment; such mediation was not significant for persistence.

IL-12-deficient dendritic cells, generated in the presence of prostaglandin E2, promote type 2 cytokine production in maturing human naive T helper cells.

Abstract: We studied to what extent the presence of an inflammatory mediator PGE2, during the development of dendritic cells (DC) affects their subsequent ability to induce Th1- and Th2-type cytokines in maturing naive Th cells. PGE2 (10(-9)-10(-6) M) did not alter the morphology or the expression of class II MHC and costimulatory molecules on DC obtained from monocytes in the presence of granulocyte-macrophage CSF and IL-4, although at concentrations above 10(-8) M, PGE2 prevented the acquisition of CD1a marker. Both control DC and DC maturing in the presence of PGE2 (PGE2-DC) were potent stimulators of naive Th cells. In contrast to control DC, which produced high amounts of IL-12 and trace amounts of IL-10, PGE2-DC produced no IL-12 and high amounts of IL-10 when stimulated in the absence of PGE2. This distinct cytokine profile of PGE2-DC was stable for at least 48 h of additional culture in the absence of PGE2. Control DC induced the development of Th0-like cells from superantigen-activated naive Th cells, whereas PGE2-DC promoted the development of Th cells that produced high amounts of IL-4 and IL-5. Experiments using IL-12-neutralizing Abs or rIL-12 indicated a crucial role of IL-12 deficiency in the induction of type 2 cytokine profiles. These findings suggest that elevated levels of PGE2 promote type 2 Th responses by stably impairing the ability of maturing DC to produce IL-12. Since type 2 Th responses are protective in several Th1-related autoimmune disorders, PGE2-DC may be considered for use in immunotherapy.

Kinetics of response in lymphoid tissues to antiretroviral therapy of HIV-1 infection

Abstract: In lymphoid tissue, where human immunodeficiency virus–type 1 (HIV-1) is produced and stored, three-drug treatment with viral protease and reverse transcriptase inhibitors markedly reduced viral burden. This was shown by in situ hybridization and computerized quantitative analysis of serial tonsil biopsies from previously untreated adults. The frequency of productive mononuclear cells (MNCs) initially diminished with a half-life of about 1 day. Surprisingly, the amount of HIV-1 RNA in virus trapped on follicular dendritic cells (FDCs) decreased almost as quickly. After 24 weeks, MNCs with very few copies of HIV-1 RNA per cell were still detectable, as was proviral DNA; however, the amount of FDC-associated virus decreased by ≥3.4 log units. Thus, 6 months of potent therapy controlled active replication and cleared >99.9 percent of virus from the secondary lymphoid tissue reservoir.

Financial System Architecture

Abstract: This article builds a theory of financial system architecture. We ask: what is a financial market, what is a bank, and what determines the economic role of each? Starting with basic assumptions about primitives--the types of agents and the nature of the informational asymmetries--we provide a theory that explains which agents coalesce to form banks and which trade in the capital market. It is shown that borrowers of higher observable qualities access the financial market. Moreover, a financial system in its infancy will be bank-dominated, and increased financial market sophistication diminishes bank lending. Article published by Oxford University Press on behalf of the Society for Financial Studies in its journal, The Review of Financial Studies.