Biomedical subjects

J Snel

Publications and source records attributed to J Snel.

At least 37 records · Page 2Linked to original sources

PubMed1998

Cerebral event-related potentials associated with selective attention to color: developmental changes from childhood to adulthood.

Event-related potentials were recorded from 80 participants ranging in age from 7 to 24 years while they attended selectively to stimuli with a specified color (red or blue) in an attempt to detect the occurrence of target stimuli. Color attention effects were identified as frontal selection positivity (FSP; 140-275 ms), selection negativity (SN; 150-300 ms), and N2b (200-450 ms), whereas target detection was reflected in P3b (300-700 ms). There were age-related decreases in the latencies of FSP, N2b, and P3b that paralleled decreases in reaction time and error rates. Also, the SN amplitude increased with advancing age, whereas both N2b and P3b showed changes in scalp topography. These results represent neurophysiological evidence that the efficiency of visual selective processes increases during childhood and adolescence. Developmental growth may take place at both relatively early and late levels of visual selective information processing.

Adolescent↗

PubMed1998

Heterogeneous suppression of experimentally induced colon cancer metastasis in rat liver lobes by inhibition of extracellular cathepsin B.

Metastatic rat colon cancer cells but not normal rat hepatocytes showed activity of cathepsin B on their plasma membranes. Activity was visualized in living cells with a new fluorogenic substrate, [Z-Arg]2-cresyl violet, and confocal microscopy. When these cancer cells were injected into the portal vein of rats, the animals developed tumors in the liver in a heterogeneous fashion. Three- to four-fold more tumors were found in the small caudate lobe than in the other three large lobes of the liver. Oral treatment with a selective water-soluble inhibitor of extracellular cathepsin B, Mu-Phe-homoPhe-fluoromethylketone, resulted in 60% reduction of the number of tumors and 80% reduction of the volume of tumors in the three large lobes whereas tumor development was not affected in the small caudate lobe. This study supports the conclusions that (a) extracellular cathepsin B plays a crucial but complex role in liver colonisation by rat colon carcinoma cells in vivo, (b) its selective inhibition suppresses tumor growth heterogeneously in the liver and (c) the caudate lobe of the liver is a relatively large risk factor for tumor development.

Amino Acid Chloromethyl Ketones↗

PubMed1998

Coping, personality and the development of a central pattern of body fat from youth into young adulthood: The Amsterdam Growth and Health Study.

OBJECTIVE: It has been suggested that coping behaviour, in particular a defeat reaction to stress, is a determinant of the central pattern of body fat. To verify this hypothesis, this study investigated if coping behaviour, and associated personality traits, are associated with a central pattern of body fat or total body fatness in a healthy population of males (n=83) and females (n=98) early in life. METHODS: Problem-focused, emotion-focused and type A behaviour were measured at the mean ages of 21 y and 27 y. Personality traits (inadequacy, social inadequacy, dominance, rigidity and debilitating anxiety), a central pattern of body fat (subscapular/triceps, (S/T) ratio) and total body fatness (sum of four skinfolds (SSF): biceps, triceps, subscapular, suprailiac) were measured six times between the ages of 13-27 y. RESULTS: In both genders, no association was found between either coping strategy and a central pattern of body fat or total body fatness. In males, type A behaviour was significantly negatively correlated with the S/T ratio (r = -0.27, P=0.01) after adjustment for total body fatness, at the mean age of 27 y. In a longitudinal analysis, adjusted for total body fatness, dominance and rigidity were negatively associated with the S/T ratio (beta = -0.09, 95% confidence interval (95% CI) (-0.17; -0.00) and beta = -0.11, 95% CI (-.19; -0.02), respectively) between the ages of 13-21 y in males. These associations of type A behaviour, dominance and rigidity, with a central pattern of body fat, were weaker and did not reach statistical significance with total body fatness. CONCLUSIONS: The results of this study justify further research on the association between coping behaviour, personality and the development of a central pattern of body fat.

Adaptation, Psychological↗

PubMed1998

Interactions between gut-associated lymphoid tissue and colonization levels of indigenous, segmented, filamentous bacteria in the small intestine of mice.

Unlike most other indigenous bacteria, segmented filamentous bacteria (SFB) are potent activators of the mucosal immune system. SFB are strongly anchored to the epithelial cells of the small intestine where they have a preference for mucosal lymphoid epithelium. Since SFB are only present in high numbers shortly after weaning, it was investigated whether an SFB-induced immune reaction results in the removal of these bacteria from the small intestine. A correlation was found between age and colonization levels in the small intestines of SFB monoassociated Swiss mice. Five-week-old athymic BALB/c (nu/nu) mice showed lower colonization levels than their heterozygous littermates, but the opposite was found at the age of 12 weeks. However, SFB inoculation of germfree Swiss mice resulted in higher colonization levels in 5-week-old mice when compared with 4-month-old mice. We conclude that SFB colonization levels in the small intestine are likely influenced by the activity of the mucosal immune system. However, an additional age-dependent factor that modulates SFB colonization levels cannot be excluded.

Age Factors↗

PubMed1998

Event-related potentials during visual selective attention in children of alcoholics.

Event-related potentials were recorded from 7- to 18-year-old children of alcoholics (COAs, n = 50) and age- and sex-matched control children (n = 50) while they performed a visual selective attention task. The task was to attend selectively to stimuli with a specified color (red or blue) in an attempt to detect the occurrence of target stimuli. COAs manifested a smaller P3b amplitude to attended-target stimuli over the parietal and occipital scalp than did the controls. A more specific analysis indicated that both the attentional relevance and the target properties of the eliciting stimulus determined the observed P3b amplitude differences between COAs and controls. In contrast, no significant group differences were observed in attention-related earlier occurring event-related potential components, referred to as frontal selection positivity, selection negativity, and N2b. These results represent neurophysiological evidence that COAs suffer from deficits at a late (semantic) level of visual selective information processing that are unlikely a consequence of deficits at earlier (sensory) levels of selective processing. The findings support the notion that a reduced visual P3b amplitude in COAs represents a high-level processing dysfunction indicating their increased vulnerability to alcoholism.

Adolescent↗

PubMed1997

Quantification of antigen-specific immunoglobulin A after oral booster immunization with ovalbumin in mice mono-associated with segmented filamentous bacteria or Clostridium innocuum.

Segmented filamentous bacteria (SFB) are known to stimulate the mucosal immune system. Here, the effect of SFB on oral booster immunization with ovalbumin was investigated. Mice mono-associated with SFB or Clostridium innocuum were sensitized by intraperitoneal administration of 100 micrograms ovalbumin with Freunds complete adjuvant. After 4 weeks, mice received 80 mg ovalbumin orally. A maximum IgA response was found 5 days after this booster immunization. Comparison of mice with SFB and mice with C. innocuum revealed a much higher level of IgA in the gut lumen and more IgA secreting cells in the lamina propria of the SFB-associated mice. However, no differences between both groups of animals were found in specific levels of IgA secreting cells or luminal IgA against ovalbumin. It is concluded that there is no enhancing effect of SFB after booster immunization when mice are primed intraperitoneally with ovalbumin.

Administration, Oral↗

PubMed1997

Caffeine effects on perceptual and motor processes.

The effects of a single dose of caffeine on specific information processing operations were examined by using a visual selective attention task in which subjects were asked to select between a left and right hand response on the basis of two different target letters. The target was presented on a predefined position in the visual field and was either presented alone or with flanker letters, calling for the correct, the incorrect or no specific response. A dose of 3 mg/kg body weight caffeine or lactose, dissolved in a cup of decaffeinated coffee, was administered double blind and deceptively to overnight abstinence coffee drinkers. Behavioural measures were supplemented by psychophysiological measures. The present results replicated the basic findings obtained in this paradigm. The results indicated that the time to localise the target decreased and response preparation started earlier after caffeine than after placebo. These caffeine effects did not interact with the time subjects spent on the task or with the reaction time distribution, which might be due to a high level of practice.

Adolescent↗

PubMed1997

The Amsterdam Growth and Health Longitudinal Study. The past (1976-1996) and future (1997-?).

This article presents an overview of the Amsterdam Growth and Health Longitudinal Study (AGAHLS). This study was started in the 1970s, following a whole sample of 500 healthy 13-year-old boys and girls from two secondary schools. During the school period (12-17 years) annual measurements were performed with respect to anthropometrics, physiological and psychological parameters, lifestyle characteristics (activity, diet, smoking) and health parameters. A multiple longitudinal design was applied with overlapping birth cohorts and a cross-sectional measured control group to monitor for confounding factors such as time of measurement, cohort, dropout and testing effects. Emphasis is also placed on measures that enhance adherence of the subjects. The follow-up was extended with repeated measurements at age 21, 26 and 28. This enabled us to analyze the data with respect to tracking characteristics of biological and lifestyle variables over a period of 15 years between adolescence and adulthood and also to investigate quasi-causal relationships between the effects of a healthy lifestyle and indicators for cardiovascular diseases (CVD). Also new methods such as measurement of atherosclerosis and osteoporosis will be added and related to longitudinal measurements of the same subjects in the past. The main results that were obtained in the past are summarized and research questions for the near future are explained.

Adolescent↗

PubMed1997

No electrocortical evidence of automatic mismatch dysfunction in children of alcoholics.

The mismatch negativity (MMN) event-related potential (ERP) component is an automatic, attention-independent brain response to auditory stimulus change, which has been reported to be smaller in alcoholics relative to nonalcoholic controls. To determine whether MMN decrements might be a trait marker of alcoholism that is also present in nonalcoholic individuals at high risk for developing alcoholism, we investigated MMN in 9- to 18-year-old children of alcoholics (n = 20) and control children (n = 20) in three different stimulus conditions using a passive auditory oddball paradigm. There were no statistically significant between-group differences observed in amplitude, scalp topography, and peak latency of MMN. These findings, if replicated, suggest that reported MMN decrements in alcoholics most likely represent a state marker, and not a trait marker, of alcoholism. Also, inasmuch as another ERP component, the P300, is attention-dependent and reported to be smaller in children of alcoholics, the present results implicate that deviations in attentive, but not in automatic, information processing are associated with alcoholism vulnerability.

Adolescent↗

PubMed1996

Subject-related risk factors for sports injuries: a 1-yr prospective study in young adults.

The purpose of this study was to investigate the importance of subject-related risk factors for sports injuries, taking exposure time into account. At baseline in 182 healthy males and females (27 yr) the following subject-related risk factors were assessed: body mass index (BMI), maximal oxygen uptake (direct treadmill measurement), seven aspects of neuromotor fitness (MOPER fitness test), strength of the hamstring and quadriceps muscles (CYBEX), having sustained a sports injury in the 12 months preceding the baseline measurement ("previous injury"), and 16 psychological and psychosocial factors (measured with 8 standard, valid, and reliable questionnaires). For 1 yr, subjects were asked to make daily entries on a monthly log concerning all sports activities exceeding an intensity of 4 MET and all sustained sport injuries. Completed logs were returned by 139 subjects (75 males and 64 females). Fifty-one injuries were registered in 41 subjects. The overall incidence rate (IR) was 3.7 sports injuries per 1000 h of sports participation (95% confidence interval 2.8-4.9). For various subcategories, the following IR per 1000 h of sports participation were calculated: contact sports IR = 11.0 (95% CI 7.4-16.3); noncontact sports IR = 2.3% (95% CI 1.6-3.3); competition IR = 13.4 (95% CI 8.7-20.6); and training IR = 2.8 (95% CI 1.6-5.1). Data were analyzed by stepwise multiple logistic regression. The following five variables were independent and significant (P < 0.05) predictors of risk in sustaining a sport injury: dominance (odds ratio (OR) = 1.71; 95% CI = 1.44-2.03), vital exhaustion (OR = 1.85; CI = 1.22-2.86), stressful life events (OR = 1.84; 95% CI = 1.10-311); these ORs were calculated for an increase of 10% of the range of obtained scores, starting at minimum value. For total sporting time, the OR was calculated by taking the group with a total sporting time below the median (4050 h) as a reference (OR = 6.87; 95% CI = 2.09-22.55). For previous injury, subjects that had not sustained a sports injury in the 12 months preceding the baseline measurements served as a reference for the calculation of the OR (OR = 9.41; 95% CI = 2.80-31.58). These findings confirm that both exposure time and previous injury are more important predictors of sports injuries than psychological, psychosocial, physiological, and anthropometrical factors.

Adult↗

PubMed1996

Acute effects of caffeine on selective attention and visual search processes.

The influence of a single dose of caffeine was evaluated in focused and divided attention conditions of a visual selective search task in which subjects had to perform controlled search processes to locate a target item. Search processes were manipulated by varying display load. A dose of 3 mg/kg body weight caffeine or lactose, dissolved in a cup of decaffeinated coffee, was administered double blindly and deceptively to overnight abstinent coffee drinkers. Behavioral measures were supplemented by event-related potentials (ERPs). Subjects reacted faster in the caffeine condition. The P3b peak latency decreased after caffeine in the low display load condition and in the focused attention condition, indicating that the effects of caffeine are dependent on the number of relevant display items, not on the total number of display items presented. Search processes, as reflected in a negative ERP deflection, were not affected by caffeine.

Adult↗

PubMed1996

Biological maturation and the distribution of subcutaneous fat from adolescence into adulthood: the Amsterdam Growth and Health Study.

OBJECTIVE: To analyze differences in the development of a trunk-oriented fat distribution pattern between 13 and 27 years of age in individuals who either matured rapidly or slowly in adolescence. DESIGN: Longitudinal, observational, four annual measurements between 1977 and 1980 and additional measurements in 1985 and 1991. SUBJECTS: 79 boys, 98 girls, health Caucasian schoolchildren, classified as rapidly, normally or slowly maturing. MEASUREMENTS: biceps, triceps, subscapular, suprailiac skinfolds resulting in two skinfold ratios, body mass index, skeletal age, peak height velocity (for boys only), age at menarche. RESULTS: No statistically significant differences were found between rapidly and slowly maturing boys and girls, based on the skeletal age or the peak height velocity. Girls with a relatively early menarche showed significant higher mean skinfold ratios between 13 and 27 years of age than girls with a relatively late menarche. CONCLUSION: Skeletal maturation of boys and girls and peak height velocity (only measured in boys) are not associated with a trunk-oriented fat distribution pattern between 13 and 27 years of age. Only a relatively early menarche in girls seems to be associated with a trunk-oriented fat distribution pattern from adolescence into adulthood.

Adipose Tissue↗

PubMed1995

Aging, caffeine, and information processing: an event-related potential analysis.

Structural and energetic processes in information processing were studied in young and elderly subjects. A visually focussed selective search task was used, in which subjects had to select relevant information, followed by controlled memory search processes to locate a target item. Caffeine was used to manipulate the energetic state of the subjects. During task performance event-related potentials (ERPs) and reaction time (RT) were recorded. Subjects were 15 young and 15 elderly healthy, non-smoking, moderate caffeine consumers (250-600 mg/day). Before the experimental sessions they abstained from caffeine for > or = 12 h. In the experiment subjects received 250 mg caffeine or placebo dissolved in decaffeinated coffee. RT data seem to indicate that aging effects are at least partly due to a shift in the speed-accuracy trade-off. ERP results provide evidence for decreased levels of energy resources in the elderly. The identification of relevant information and stimulus evaluation processes were delayed in the elderly, suggesting an additional effect of aging on structural processes. Caffeine improved performance and increased the amplitude of the N1, N2b, and P3b, in both young and old subjects. These results suggest that caffeine makes more energy resources available for task performance. The effects of aging on P3b latency were counteracted by caffeine. Other caffeine effects did not differ significantly between young and elderly subjects.

Adolescent↗

PubMed1995

Comparison of 16S rRNA sequences of segmented filamentous bacteria isolated from mice, rats, and chickens and proposal of "Candidatus Arthromitus".

Segmented filamentous bacteria (SFB) are nonpathogenic bacteria that are commonly found attached to the intestinal walls of many animals. Until now, these bacteria have not been cultured in vitro. Recently, a 16S rRNA sequence analysis revealed that SFB isolated from mice represent a distinct subline within the Clostridium subphylum of the gram-positive bacteria. Since SFB isolated from mice, rats, and chickens are known to be host specific, we investigated the phylogenetic relationships among SFB obtained from these three hosts. Total DNAs from the intestinal floras of chickens and rats were used as templates for PCR amplification of 16S rRNA genes. PCR products were cloned and screened by a dot blot hybridization procedure to identify homologous sequences that cross-reacted with mouse SFB-specific oligonucleotide probes. A phylogenetic analysis of these 16S ribosomal DNA sequences revealed that SFB isolated from these three hosts form a natural group, which is peripherally related to the genus Clostridium sensu stricto (group I Clostridium). The SFB obtained from chickens, rats, and mice had closely related, albeit different, 16S rRNA gene sequences. The observed levels of 16S rRNA sequence divergence, ca. 1.5 to 3%, together with host specificity, suggest that SFB isolated from mice, rats, and chickens represent different species and that coevolution of the SFB and their hosts occurred. "Candidatus Arthromitus" is proposed as the provisional generic name for this group of organisms.

Animals↗

PubMed1994

Influence of caffeine on information processing stages in well rested and fatigued subjects.

The effects of caffeine on different information processing stages were examined by using choice reaction time tasks. Independent variables were stimulus degradation, stimulus-response compatibility, time-uncertainty, state of the subject, and caffeine treatment. The task variables were assumed to affect the following processing stages; encoding, response selection and motor preparation, respectively. A 200 mg dose at the beginning of the experiment and a maintenance dose of 50 mg caffeine or lactose half-way through the session were administered to well rested and fatigued subjects, double-blind and deceptively. Behavioural measurements, event-related potentials (ERPs) and mood questionnaires were used to assess caffeine effects. The data showed that caffeine shortened reaction time. This effect showed an interaction with stimulus degradation and time uncertainty. In addition, ERP results supported the view that caffeine increases cortical arousal and perceptual sensitivity. Stimulating effects of caffeine were mainly located at input and output stages of the information processing system. Central processes were unaffected by caffeine. Fatigued subjects showed larger improvements in performance after caffeine than well-rested subjects. The results also indicated that caffeine effects were not stimulating in all subjects: 6 out of 30 subjects did not show arousing effects of caffeine.

Adolescent↗

PubMed1994

Influence of caffeine on selective attention in well-rested and fatigued subjects.

Effects of caffeine were studied in a visual focused selective search task in well-rested and fatigued subjects. A dose of 200 + 50 mg caffeine or placebo, dissolved in decaffeinated coffee, was administered in a double-blind and deceptive fashion. The task was to detect a target letter on one diagonal of a visual display designated as relevant and ignore stimuli presented on the irrelevant diagonal. Behavioral measures were supplemented by event-related potential (ERP) measures. Subjects reacted faster in the caffeine condition. Caffeine enhanced the N1 and the N2b components. Selection of relevant information apparently was more adequate in this condition. Search negativity was not affected by caffeine. Caffeine effects on the P3 elicited by target letters were more pronounced in the fatigued than in the well-rested subjects, indicating that the effects of caffeine are dependent on the state of the subject. The results suggest that caffeine has specific rather than general effects on information processing.

Adolescent↗

PubMed1994

Children of alcoholics: attention, information processing and event-related brain potentials.

Recent studies on biological markers and risk factors for alcoholism have distinguished between nonalcoholic individuals with a family history of alcoholism and those without such a family history on measures of event-related brain potentials. The main finding of these "high-risk" studies is a smaller amplitude of the P300 component in males with a history of paternal alcoholism. This relationship between P300 amplitude and a family history of paternal alcoholism has been observed in adults and children. Consequently, several authors have suggested that a reduced P300 amplitude could serve as a vulnerability marker for alcoholism. We address several conceptual and methodological issues involved in the study of event-related potentials in children at high risk for alcoholism. Subsequently, the ongoing high-risk study of the Amsterdam Institute for Addiction Research is described briefly.

Adult↗

PubMed1990

Age-related differences in timing of position and velocity identification.

The aim of this investigation was to study age-related differences in timing of position and velocity identification in a laboratory task. The skills required for performing this task are thought to be similar to those needed in real traffic situations. From this perspective, the results of this study may be taken into account in studies on accident analysis and prevention. To control for differences in the conscious experience of time and for simple reaction time to visual stimuli, young (25-34) and old (58-70) adults had to produce timed periods of 20 seconds and to time the arrival of a visible moving object at its goal. In these simple tasks no differences were found between young and old subjects. In the proper, more complex experiment, timing of position and velocity identification of a moving object were assessed with or without feedback on timing and velocity in the same old and young group. The object, moving from left to right at a constant velocity, was shown on a video screen during the first 40% of its trajectory. The moving object could have any of four (fixed) velocities which were presented in blocks with a regular or a mixed order. By pushing a button subjects estimated at which time the object would have reached the marked end of a trajectory. In a condition without feedback on timing of position, the timing error of older adults was higher than that of young adults and particularly with higher object velocities.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗