| 501. |
- Wahlstrom, E., et al.
(författare)
-
Size-dependent foraging efficiency, cannibalism and zooplankton community structure
- 2000
-
Ingår i: Oecologia. ; 123:1, s. 138-148
-
Tidskriftsartikel (refereegranskat)abstract
- To examine size-dependent food web interactions in systems with cannibalism, we compared the abundances of zooplankton and phytoplankton over 2 years in four lakes with cannibalistic perch (Perca fluviatilis ) of which two also supported the top predator pike (Esox lucius). The abundance of perch 2 years and older was lower in lakes with pike than in lakes with only perch. In contrast, the abundance of small perch (young-of-the-year and I-year old) was lower in lakes with only perch suggesting that intense cannibalism reduced these size classes to low levels in lakes lacking pike. Functional response experiments with differently sized perch and zooplankton showed that the attack rate of small perch susceptible to cannibalism was much higher than that of large cannibalising perch. The optimal body size of perch with respect to attack rate was also lower for small zooplankton prey than for large zooplankton. The zooplankton communities in lakes with only perch were dominated by the relatively small species Ceriodaphnia quadrangula and Bosmina spp. and total zooplankton biomass was higher in these lakes than in lakes with both pike and perch. In contrast, the mean size of cladoceran zooplankton was largest in lakes with both pike and perch owing to a dominance of the large zooplankton species Holopedium gibberum in these lakes. We relate these patterns to (1) the low foraging efficiency of large perch on small zooplankton and (2) the low abundance of small zooplanktivorous perch (due to cannibalism) in lakes with only perch. The differences in zooplankton community structure also resulted in different seasonal dynamics of phytoplankton between lakes. Cannibalism introduces a vertical heterogeneity to food webs that causes consumer-resource dynamics that are not predictable from linear food chain models.
|
|
| 502. |
- Walker, B R, et al.
(författare)
-
Independent effects of obesity and cortisol in predicting cardiovascular risk factors in men and women.
- 2000
-
Ingår i: Journal of Internal Medicine. - 0954-6820 .- 1365-2796. ; 247:2, s. 198-204
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: Recent data suggest that higher plasma cortisol may be associated with hypertension and insulin resistance in otherwise healthy men, as it is in Cushing's syndrome. However, obesity in women is associated with lower plasma cortisol concentrations. This study sought to establish whether plasma cortisol is associated with cardiovascular risk factors in women as it is in men, and whether these relationships in either sex are confounded by obesity.DESIGN: A population-based cross-sectional study.SETTING: The MONICA study in northern Sweden.SUBJECTS: From a target cohort of 2500, 1921 subjects took part and 226 were randomly selected because they attended between 07.00 and 09.00 h after an overnight fast. A 75 g oral glucose tolerance test was performed and blood sampled at baseline and 2 h after glucose.RESULTS: Plasma cortisol was lower in relatively obese subjects: in men, this was observed only in the 2 h sample (r = -0.23, P = 0.02) and in women only in the fasting sample (r = -0.26, P < 0.01). Simple regression analysis did not identify relationships between plasma cortisol and blood pressure, serum lipids, fasting insulin or glucose tolerance. However, after adjusting for the effect of obesity by multiple regression, higher plasma cortisol was independently associated with higher diastolic blood pressure in men (r = 0.21, P = 0.04) but not in women, and higher fasting serum triglyceride levels in women (r = 0.28, P < 0. 001) but not in men.CONCLUSIONS: Increasing obesity and plasma cortisol concentrations make independent and sex-specific contributions to variations in blood pressure and aspects of the insulin resistance syndrome. Adverse cardiovascular risk is greatest in those with the combination of obesity and failure to downregulate plasma cortisol levels.
|
|
| 503. |
|
|
| 504. |
- Wang, Ke, et al.
(författare)
-
Phase Behavior and Phase Structure of a Cationic Fluorosurfactant in Water
- 2000
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 16:3, s. 1042-9
-
Tidskriftsartikel (refereegranskat)abstract
- The phase behavior of the cationic fluorocarbon surfactant 1,1,2,2-tetrahydroperfluorodecylpyridinium chloride in water has been studied using small-angle X-ray and 2H NMR spectroscopy as the main techniques. The following phase sequence was found: micellar (L1), hexagonal (HI), centered rectangular (R; spacegroup c2mm) and centered trigonal (T, spacegroup Rm) with increasing surfactant concentration. At higher concentrations evidence for random mesh phase and a lamellar phase was found, at high temperatures a bicontinuous cubic phase was found. Compared to a cationic hydrocarbon surfactant of similar hydrophobicity, the occurrence of the intermediate phases is more extensive in the phase diagram, and the fluorocarbon surfactant prefers to form intermediate phases instead of a cubic phase. The surface curvature of the aggregates changes from highly curved cylindrical structures of the hexagonal phase to the planar bilayer structure of the lamellar phase over a sequence of geometries that allow the average of the mean curvature to change gradually as water content is decreased.
|
|
| 505. |
- Weber, M., et al.
(författare)
-
Preserved slow conducting corticomotoneuronal projections in ALS patients with autosomal recessive D90A CuZn-SOD mutation.
- 2000
-
Ingår i: Brain. - : Oxford University Press (OUP). - 0006-8950 .- 1460-2156. ; 123:7, s. 1505-1515
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, a subgroup of the amyotrophic lateral sclerosis (ALS) syndrome associated with mutations in the gene encoding the free radical scavenging enzyme CuZn-superoxide dismutase (CuZn-SOD, SOD1) has been identified. Some 67 different mutations have been reported worldwide to date, comprising about one-fifth of familial ALS cases in the populations studied. The autosomal recessively inherited D90A CuZn-SOD mutation has been associated with a very slowly progressive, clinically distinct phenotype, and is neurophysiologically characterized by very slow central motor conduction. It is not known which physiological and/or biochemical mechanisms are responsible for the different clinical course. To delineate ALS associated with this particular CuZn-SOD mutation from ALS without mutations, we performed a detailed neurophysiological study of the corticomotoneuronal function using peristimulus time histograms (PSTHs) in eight ALS patients homozygous for the D90A CuZn-SOD mutation. The results were compared with those obtained in 12 non-hereditary ALS patients and 11 healthy subjects. PSTHs were constructed from three to seven different, voluntarily recruited motor units of the extensor digitorum communis muscle (EDC) in each patient. The onset latency, number of excess bins, duration and synchrony of the primary peak were analysed. All measurements differed significantly between healthy controls and the D90A patients (P < 0.0007). The mean onset latency of the primary peak in D90A patients was 35.3 ms, compared with 24.2 ms for non-hereditary ALS patients and 19.3 ms for normal subjects (P < 0.0000). Delayed primary peaks in the D90A patients were desynchronized and characteristically preceded by a marked suppression phase. This suppression phase was not seen in non-hereditary ALS patients. We conclude that the mainly slow conducting and/or polysynaptic corticomotoneuronal connections are preserved in the D90A homozygous cases, and that the cortical and possibly spinal inhibitory circuitry is preserved. These events may partially protect the motor neurons, slowing down the degenerative process.
|
|
| 506. |
- Werner, Thomas, et al.
(författare)
-
A family of peptidoglycan recognition proteins in the fruit fly Drosophila melanogaster.
- 2000
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 97:25, s. 13772-13777
-
Tidskriftsartikel (refereegranskat)abstract
- Peptidoglycans from bacterial cell walls trigger immune responses in insects and mammals. A peptidoglycan recognition protein, PGRP, has been cloned from moths as well as vertebrates and has been shown to participate in peptidoglycan-mediated activation of prophenoloxidase in the silk moth. Here we report that Drosophila expresses 12 PGRP genes, distributed in 8 chromosomal loci on the 3 major chromosomes. By analyzing cDNA clones and genomic databases, we grouped them into two classes: PGRP-SA, SB1, SB2, SC1A, SC1B, SC2, and SD, with short transcripts and short 5'-untranslated regions; and PGRP-LA, LB, LC, LD, and LE, with long transcripts and long 5'-untranslated regions. The predicted structures indicate that the first group encodes extracellular proteins and the second group, intracellular and membrane-spanning proteins. Most PGRP genes are expressed in all postembryonic stages. Peptidoglycan injections strongly induce five of the genes. Transcripts from the different PGRP genes were found in immune competent organs such as fat body, gut, and hemocytes. We demonstrate that at least PGRP-SA and SC1B can bind peptidoglycan, and a function in immunity is likely for this family.
|
|
| 507. |
- Westerberg, Kristina, 1953-, et al.
(författare)
-
Municipal middle managers : psychosocial work environment in a gender-based division of labor
- 2000
-
Ingår i: Scandinavian Journal of Management. - : Elsevier. - 0956-5221 .- 1873-3387. ; 16:2, s. 189-208
-
Tidskriftsartikel (refereegranskat)abstract
- The purpose of the reported study was to explore how 245 municipal middle managersperceived their psychosocial and physical work environments, and to examine psychosomaticreactions and job satisfaction in departments engaged in di!erent types of activity, also tocompare male and female managers in these respects. The way in which psychosomaticreactions and job satisfaction were related to the psychosocial and physical work environmentswas also investigated. The results indicated a di!erence between departments depending on thetype of activity. Departments concerned with care and education, i.e. care of the elderly, childcare and schools showed a tendency to lower values for psychosocial work environment factorsand more psychosomatic reactions than the departments geared more towards maintenanceand production, i.e. street maintenance, the power plant department and the recreation o$ce.In the departments concerned with children, female managers were in a majority. In the streetmaintenance department, the recreation o$ce and the power plant department, male managerspredominated. Compared to the men, the women had a higher level of education, lower salaries,more reactions of a psychosomatic nature, lower job satisfaction and a less satisfying psychosocialwork environment. The only department with an equal number of male and femalemanagers was the schools department. Here there were no di!erences between men and womenin the factors studied. Two partial correlations were computed in order to separate theimportance of type of activity and sex to the work environment factors and outcome variables.This indicated that the type of activity was more important than biological sex. The genderingof work activities is therefore also discussed and further investigations are suggested. ( 2000Elsevier Science Ltd. All rights reserved.
|
|
| 508. |
- Westerlund, L, et al.
(författare)
-
Early life-stage mortality in zebrafish (Danio rerio) following maternal exposure to polychlorinated biphenyls and estrogen
- 2000
-
Ingår i: Environmental Toxicology and Chemistry. - 0730-7268. ; 19:6, s. 1582-8
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, specific polychlorinated biphenyl (PCB) congeners were examined far embryo and early life stage mortality in zebrafish (Danio rerio). A set of eight PCBs and two hydroxylated PCBs and 17 beta-estradiol were tested. Of the compounds tested, 4'-OH-PCB30 (hydroxylated polychlorinated biphenyl) and PCB 104 were found to be highly toxic to embryos following maternal exposure and transfer to the oocyte. It was also observed that 17 beta-estradiol exposure resulted in a high incidence of embryo mortality. Analysis of estrogen receptor levels during embryonic development showed increased mRNA (ribonucleic acid) levels from the 1K stage to 50% epiboly. Following injection of the different compounds, the estrogen receptor mRNA levels were also analyzed in adult male fish to determine if there was a correlation between embryo mortality and estrogenicity of the studied PCBs. The two PCBs that were highly embryo toxic were observed to be estrogenic.
|
|
| 509. |
- Westlund, Per-Olof
(författare)
-
Line shape analysis of NMR powder spectra of (H2O)-H-2 in lipid bilayer systems
- 2000
-
Ingår i: JOURNAL OF PHYSICAL CHEMISTRY B. ; 104:25, s. 6059-64
-
Tidskriftsartikel (refereegranskat)abstract
- A NMR line shape/spin relaxation model is developed for (H2O)-H-2 studies of structure and dynamics of the lipid-water interfaces of phosphatidylcholine bilayers. A line shape function describing the orientational dependence of (H2O)-H-2 is derived. In addition, also expressions of the observed quadrupole splitting and the spin-lattice relaxation rate are derived within the same dynamic model. The model comprises two chemically interchanging fractions of water namely, "free", and "bound". There are four molecular parameters characterizing the "bound" water of the lipid water interface, namely, (1) the fraction water molecules bound to lipid molecules, (2) the local water order parameter S-0(Pd), (3) the order parameter S-0(dD) which describes the averaged "bound" water, and an effective correlation time (4) tau(c), characterizing water translational diffusion at the interface. This model allows for analyzing quadrupole splittings, spin-lattice relaxation rates, and water powder line shapes. Thus, dynamics as well as structural information about the water molecules residing in the water lipid interface may be extracted. In the reinterpretation of (H2O)-H-2 powder spectra obtained for lamellar phases of dipalmitoylphosphatidylcholine (DPPC), the results clearly indicate that S-0(dD)(L-alpha) > S-0(dD)(L-beta') when comparing the liquid crystalline phase with 10-11 water molecules per lipid molecule and the gel phase with 3.5-4.2 water molecules per lipid molecule. Whereas the order of the perturbed water is similar in both phases, S-0(Pd)(L-alpha) approximate to S-0(Pd)(L-beta'). The lateral diffusion is characterized by a correlation time tau(c) > 60 ns but cannot be determined without measuring the spin-lattice relaxation measurements.
|
|
| 510. |
- Wiberg, Karin, et al.
(författare)
-
The Enantioselective Bioaccumulation of Chiral Chlordane and -HCH Contaminants in the Polar Bear Food Chain
- 2000
-
Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 34:13, s. 2668-74
-
Tidskriftsartikel (refereegranskat)abstract
- The enantiomer ratios (ERs) of -HCH and chlordane related compounds (CHLs) were examined in the polar bear food chain (arctic cod-ringed seal-polar bear), using chiral gas chromatography-mass spectrometry (GC-MS). The cod showed near-racemic mixtures (ER = 1) for most of the compounds. In contrast, ERs in ringed seal and polar bear were frequently nonracemic (ER 1), due to enantiomer-specific biotransformation. As (+)--HCH was transferred up the food chain, it became more abundant relative to (-)--HCH. For the CHLs, there was no uniform trend for the ER changes and the increasing trophic level. Apparent chiral biomagnification factors (BFs) were calculated and up to a 20-fold difference in the BF between enantiomers was found. Analysis of chiral BFs relative to CB-153 indicated that oxychlordane was formed by ringed seal and metabolized by polar bears. However, the ERs did not change significantly as a result of these biotransformations. Multivariate statistical methods revealed the clustering of sample categories and were used to investigate the relationships between the ERs, chemical residue concentrations, and biological data. ERs were important variables for the sample groupings and for the class separation of male/female seals and fat/liver tissues. The variance in the cytochrome P450 CYP2B protein content of bear liver could be explained by the variances in chemical residue data. In this analysis the ERs were of secondary importance. The ERs of some highly recalcitrant CHLs in polar bear adipose showed linear relationships with the age of the bears.
|
|
