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Biomedical subjects

G Wolters

Publications and source records attributed to G Wolters.

At least 19 recordsLinked to original sources
PubMed2005

The environment influences whether high-fat foods are associated with palatable or with unhealthy.

This study investigated whether relatively automatic evaluations of food differ between situations and between obese people and lean controls. These evaluations were assessed in the affective priming paradigm (APP) -- a response latency based measure for associations. In Experiment 1, we either focused participants (33 obese and 26 lean controls) on the palatability (restaurant condition) or on the healthiness (health condition) of food, prior to the APP. Independent of weight-status, relatively automatic evaluations of food were based on palatability in the restaurant condition, and on health in the health condition. So, the current focus of attention can shape the way foods are evaluated relatively automatically. In Experiment 2, craving was induced in participants (27 obese and 29 lean controls). Unexpectedly, the craving induction did not achieve its goal of focusing on the palatability of food in general, but just for low-fat foods, possibly because of the health-emphasizing environment -- a hospital. Interestingly, obese people showed a stronger palatability priming effect with increasing levels of initial craving. For normal weight controls the effect was in the same direction, but missed significance. In our environment, palatability of food may be too salient, and health may not be salient enough, influencing automatic food-evaluations.

Adult↗
PubMed2005

Early associations with food in anorexia nervosa patients and obese people assessed in the affective priming paradigm.

Two experiments are reported that used the affective priming paradigm (Fazio, R. H., Sanbonmatsu, D. M., Powell, M. C., & Kardess, F. R. (1986). On the automatic activation of attitudes. Journal of Personality and Social Psychology, 50, 229-238) to uncover associations with food at a relatively automatic level. Experiment 1 tested the hypothesis that anorexia nervosa (AN; n=22) patients would show less sensitivity to the palatability of foods than unrestrained lean controls (n=27). Results indeed suggested that AN patients did not display a liking of palatable foods over unpalatable foods, whereas unrestrained controls did. Experiment 2 tested the hypothesis that obese people (n=27) would show more sensitivity to the palatability of (high-fat) palatable foods than unrestrained lean controls (n=27) would. However, results suggested that the priming effect was based on health concerns, in that participants showed a preference for low-fat palatable foods over high-fat palatable foods. Average speed of responding and context are discussed as variables influencing the affective priming effect. Taken together, results suggest that food evaluations at a relatively automatic level are controlled by an interaction between participant characteristics, stimuli characteristics, and the specific context.

Affect↗
PubMed2001

A cortical mechanism for binding in visual working memory.

Luck and Vogel (1997) showed that the storage capacity of visual working memory is about four objects and that this capacity does not depend on the number of features making up the objects. Thus, visual working memory seems to process integrated objects rather than individual features, just as verbal working memory handles higher-order "chunks" instead of individual features or letters. In this article, we present a model based on synchronization and desynchronization of reverberatory neural assemblies, which can parsimoniously account for both the limited capacity of visual working memory, and for the temporary binding of multiple assemblies into a single pattern. A critical capacity of about three to four independent patterns showed up in our simulations, consistent with the results of Luck and Vogel. The same desynchronizing mechanism optimizing phase segregation between assemblies coding for separate features or multifeature objects poses a limit to the number of oscillatory reverberations. We show how retention of multiple features as visual chunks (feature conjunctions or objects) in terms of synchronized reverberatory assemblies may be achieved with and without long-term memory guidance.

Humans↗
PubMed1997

Full versus divided attention and implicit memory performance.

Effects of full and divided attention during study on explicit and implicit memory performance were investigated in two experiments. Study time was manipulated in a third experiment. Experiment 1 showed that both similar and dissociative effects can be found in the two kinds of memory test, depending on the difficulty of the concurrent tasks used in the divided-attention condition. In this experiment, however, standard implicit memory tests were used and contamination by explicit memory influences cannot be ruled out. Therefore, in Experiments 2 and 3 the process dissociation procedure was applied. Manipulations of attention during study and of study time clearly affected the controlled (explicit) memory component, but had no effect on the automatic (implicit) memory component. Theoretical implications of these findings are discussed.

Adult↗
PubMed1996

Information processing during general anesthesia: evidence for unconscious memory.

Memory for words presented during general anesthesia was studied in two experiments. In Experiment 1, surgical patients (n = 80) undergoing elective procedures under general anesthesia were presented shortly before and during surgery with words via headphones. At the earliest convenient time after surgery (within 5 h) and 24 h later, memory was tested by asking patients to complete auditorily presented word stems with the first word that came to mind and to leave out words they remembered having heard earlier (exclusion task). Moreover, patients were requested to perform a "yes/no" forced-choice recognition task to assess recognition memory for both the pre- and intraoperative words. Memory for the material presented during anesthesia was demonstrated immediately after surgery and 24 h later by means of both tasks. In a second similar experiment (n = 80), the results were replicated. These findings show that anesthetized patients can process information that was presented intraoperatively.

Adolescent↗
PubMed1995

Implicit memory for stimuli presented during inhalation anesthesia in children.

During general inhalation anesthesia, neutral phrases including either the color blue or yellow combined with one of two objects, ball or kite, were repeatedly presented to 36 children undergoing eye surgery. Postoperative testing with a coloring and two-choice task was performed to detect preferences for the colors and objects presented under anesthesia. No preference attributable to implicit memory could be demonstrated, and there was no explicit recollection of intraoperative events. Memory of intraoperative events occurring during inhalation anesthesia was not demonstrated with the present methodology in young children.

Anesthesia, Inhalation↗
PubMed1993

Expression and characterization of a structural and functional domain of the mannitol-specific transport protein involved in the coupling of mannitol transport and phosphorylation in the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli.

The mannitol-specific transport protein in Escherichia coli, EIImtl, consists of three structural and functional domains: a hydrophilic EIII-like domain (the A domain); a hydrophobic transmembrane domain (the C domain); and a second hydrophilic domain (the B domain) which connects the A and C domains together. The A domain contains the first phosphorylation site, His554, while the B domain contains the second phosphorylation site, Cys384. The phosphoryl group which is needed for the active transport of mannitol is sequentially transferred from P-enolpyruvate via the two phosphorylation sites to mannitol bound to the substrate binding site. In this paper, the expression, purification, and initial characterization of the B domain, IIBmtl, are described. Oligonucleotide-directed mutagenesis was used to produce an amber stop codon (TAG) and HindIII restriction site in a flexible loop between the B and A domains in the subcloned gene fragment coding for IIBAmtl (van Weeghel et al., 1991c). The gene fragment coding for IIBmtl was then subcloned behind strong promoters, located in two different expression/mutagenesis vectors, which directed the expression of the 15.3-kDa polypeptide in Escherichia coli. The domain was purified from E. coli crude cell extracts by using Q-Sepharose Fast Flow, S-Sepharose Fast Flow, and hydroxylapatite column steps. This purification procedure resulted in 1 mg of pure IIBmtl/g of cell, wet weight. The purified B domain was analyzed in vitro for its catalytic activity with membranes containing the phosphorylation site mutant form of EIImtl, C384S, and with the transmembrane domain, IICmtl. The B domain, together with purified IIA, was able to restore the P-enolpyruvate-dependent phosphorylation activity of the membrane-bound C domain. Steady-state mannitol phosphorylation kinetics at saturating EI, HPr, and IIAmtl yielded an apparent Km of P-IIBmtl for IICmtl of 200 microM and an apparent Vmax of 71 nmol of mtl-P min-1 mg of membrane protein)-1. This Vmax value is comparable to that of wild-type EIImtl measured under the same experimental conditions.

Base Sequence↗
PubMed1993

Implicit memory during balanced anaesthesia. Lack of evidence.

The effect of the number of presentations on implicit memory for words was studied in anaesthetised patients. During standardised, balanced anaesthesia, 81 surgical patients were presented with less common specimens of familiar word categories. For each of three word categories the number of word presentations varied between the patients (0 (control), 5, or 30 presentations). Postoperatively, repetition priming was tested by asking patients to generate exemplars for each of the word categories. No implicit memory for the words presented during anaesthesia was found and consequently no effect of number of word presentations could be demonstrated. It is suggested that this finding, which contradicts previous results, may be caused by the relatively low familiarity of the words used.

Adult↗
PubMed1992

Design of a polyurethane membrane for the encapsulation of islets of Langerhans.

A semipermeable membrane for the encapsulation of the islets of Langerhans, consisting of a microporous polymer network, has been developed. The polyurethane network was formed by cross-linking a mixture of linoleic acid and a linear poly(etherurethane) with dicumyl peroxide. Cross-linking the polyurethane impedes the formation of hard domains. Miocroporosity was introduced by adding salt crystals of different sizes before cross-linking and leaching it out afterwards. To optimize the permeability and immunoprotectivity, membranes were prepared with three different porosities. Membranes of this material were filled with islets of Langerhans and implanted in the peritoneal cavity of rats. Short-term in vivo experiments in rats show that membranes with pores in the range 0.3-0.7 micron and a wall thickness of about 8 microns were permeable for insulin and glucose and protected the islets of Langerhans against the cells of the immunological system.

Animals↗
PubMed1990

Mental arithmetic: effects of calculation procedure and problem difficulty on solution latency.

In this chronometric study of mental arithmetic, problems with sums greater than 20 and less than 100 were presented to third-grade subjects (age 8-9). It is argued that such problems are calculated by using procedures in which the problem is broken down into subproblems for which solutions are retrieved from a declarative knowledge base. Important bottlenecks in this process are the processing capacity (since only one subproblem can be handled at a time) and the storage capacity of working memory (since the original problem and all outcomes of subproblems have to be retained). Therefore it can be hypothesized that arithmetic procedures and types of problems that necessitate more subproblems will lead to longer solution times. Both hypotheses were confirmed. Significant interactions between types of problems and arithmetic procedures show an increasing difference in solution time between the procedures with increasing problem difficulty. It can be concluded that for the type of problems studied, arithmetic procedures requiring a smaller number of subproblems lead to better performance.

Child↗
PubMed1988

Selenium, rubidium and zinc in human semen and semen fractions.

The levels of selenium, rubidium and zinc were determined in samples of semen, seminal plasma and spermatozoa from men with suspected infertility, together with several parameters of semen quality. The proportion of whole semen selenium present in sperm increased with increasing sperm count from 0 to 40%. For rubidium 98 +/- 4% and for zinc 95 +/- 8% of the total amount in semen was contained in seminal plasma. In seminal plasma a positive correlation was found between the levels of zinc and selenium, and between the levels of zinc and rubidium, indicating that, like zinc, selenium and rubidium in seminal plasma also derive mainly from the prostate gland. Semen quality parameters, such as sperm motility, vitality, speed and morphology, were not correlated with the contents of the three elements in either whole semen or seminal plasma. As the seminal content of selenium is dependent on the proportion of prostatic secretion in seminal plasma and on the sperm count, and both factors can vary considerably, the selenium level of whole semen does not appear to be a suitable parameter for investigation of the relationship between selenium and semen quality. Provisional measurements suggest lower sperm selenium levels at abnormally low or high sperm counts.

Humans↗
PubMed1987

An enzyme-immunoassay for antibodies against hepatitis B core antigen: characteristics and clinical validation.

An enzyme-immunoassay (EIA) for antibodies to hepatitis B core antigen (anti-HBc) was developed. The new test uses undiluted samples, incubated directly into an HBcAg coated well. Three alternative test procedures are possible. The stability of reagents was studied and a preclinical evaluation was performed intramurally. An assay correlation study was organised. We report the results of the external evaluation performed at 4 centres. A mean analytical sensitivity of 1.1, 1.2 and 0.36 PEI units/ml anti-HBc was found for procedure I (1 h/1 h/30 min), procedure II (30 min/30 min/30 min) and procedure III (16-20 h/1 h/30 min), respectively. In total, 5288 determinations on serum or plasma from various patients and healthy individuals were performed: 10% with procedure I, 52% with procedure II and 38% with procedure III. The qualitative (positive or negative) results were compared with those found with tests used routinely at the centres--47% with Corzyme (Abbott) and 53% with Corab (Abbott)--in a first screening. A final evaluation was made taking into account the repeatability of the results. Based on all results together, the agreement between the new EIA for anti-HBc and the routine tests was 97.6% at the first screening and increased to 99.0% after further evaluation.

Blood Donors↗
PubMed1985

Detection of hepatitis B virus DNA in serum and relation with the IgM class anti-HBc titers in hepatitis B virus infection.

Sera from four groups of patients wtih different serologic markers of HBV infection were examined for HBV DNA using molecular hybridization technique and for IgM class anti-HBc using an ELISA based on the antibody capture principle. Results of HBV DNA assay were generally in good agreement with the presence of HBeAg. However, HBV DNA was found in 13% of anti-HBe+ sera and in one patient with anti-HBc as a sole marker. IgM anti-HBc was detected at high titers in acute hepatitis B patients and was also present during the "window-period." This marker was also found, though less frequently when other markers for HBV infectivity were absent, in chronic hepatitis B patients and healthy carriers. From these findings we conclude that the HBV DNA assay provides a reliable method of detecting the infectious agent, particularly in anti-HBe+ sera and sera with anti-HBc as a sole marker. The assay for IgM anti-HBc is useful for establishing the diagnosis of recent infection in patient with anti-HBc as a sole marker, and during acute hepatitis with very high aminotransferase values, a condition in which HBV DNA may be undetectable.

Acute Disease↗
PubMed1985

Improved ELISA for the detection of HBsAg.

A sandwich ELISA for hepatitis B virus surface antigen (HBsAg) was developed using monoclonal anti-HBs for the solid phase and horse-radish peroxidase labelled sheep anti-HBs. The sensitivity was approx. 0.3 U/ml HBsAg, in the standard test procedure, comprising two incubation steps of 1 h at 37 degrees C, or in a shortened procedure comprising two incubation steps of 30 min at 50 degrees C. A slightly reduced sensitivity (approx. 0.5 U/ml) was obtained when the two incubations were combined in a one-step incubation for 1 h at 37 degrees C. All three procedures were completed by an incubation for 30 min at room temperature with peroxide and tetra-methylbenzidine. The number of false positives obtained when donor sera were screened was below 0.5%. False positive reactions occurred more frequently, but still to a limited extent, when previously selected sera containing rheumatoid factor or other possibly interfering factors were tested with the standard procedure. Most sera containing factors that interfere with a commercial ELISA for HBsAg using sheep anti-HBs coated plates, were negative. Rheumatoid factor positive sera seldom gave false positive results. The lower detection limit became approx. 0.1 U/ml when the cut-off was reduced, while the number of false positives in a donor population only increased to 1.5%. The results obtained with reagents from four different batches indicate a stability of up to 4 wk at 37 degrees C and for at least 26 wk at 4 degrees C.

Carrier State↗