Referate

Ohne Zusammenfassung     

Intestinal barrier function in response to abundant or depleted mucosal glutathione in Salmonella-infected rats

Background  

Glutathione, the main antioxidant of intestinal epithelial cells, is suggested to play an important role in gut barrier function and prevention of inflammation-related oxidative damage as induced by acute bacterial infection. Most studies on intestinal glutathione focus on oxidative stress reduction without considering functional disease outcome. Our aim was to determine whether depletion or maintenance of intestinal glutathione changes susceptibility of rats to Salmonella infection and associated inflammation.     

Stimulation of human breast carcinoma cell invasiveness and urokinase plasminogen activator activity by glucose deprivation

Glucose deprivation has been shown to increase the invasive and metastatic potential of tumour cells. In the present study, we determined whether the enhanced tumour cell invasiveness resulting from glucose deprivation is linked to increased activity of enzymes required for extracellular matrix degradation. Results of in vitro invasion assays revealed that the invasiveness of human MDA-MB-231 and MCF-7 breast carcinoma cells and MCF-10A1 normal breast cells was, respectively, 3.9-, 2.9-, and 2.1-fold higher when they were incubated under glucose-deprivation (0.2 mM glucose) than when incubated under physiological blood glucose levels (5 mM). This effect of glucose deprivation on invasion correlated with increased urokinase plasminogen activator (uPA) and plasmin activity. Glucose deprivation did not increase the levels of gelatinase and plasminogen activator inhibitor-1 secretion, or the expression of cell-associated uPA receptor. To determine whether the increased invasiveness resulting from glucose deprivation is causally linked to increased uPA activity, invasion assays were conducted using MDA-MB-231 cells incubated in 0.2 mM or 5 mM glucose in the presence of a neutralising anti-uPA antibody. Results revealed that the anti-uPA antibody significantly inhibited invasion in a dose-dependent manner and to a much greater extent in cells incubated in 0.2 mM glucose than in cells incubated in 5 mM glucose. These results suggest that low glucose levels in malignant cancers increase tumour cell invasiveness by stimulating uPA and plasmin activity.     

Water deficiency induces evolutionary tradeoff between stress tolerance and chemical defense allocation that may help explain range limits in plants

What causes range limits is a central question in evolutionary ecology. Transplant studies indicate that areas just across range boundaries are often stressful. The recent Defense constraint (DC) hypothesis for plants states that the evolution of tolerance to stressful environments across a range boundary is constrained by allocation to chemical defense because of antagonistic crosstalk between abiotic and biotic stress signaling pathways that otherwise could be co‐opted for range expansion. Abscisic acid (ABA) drought stress tolerance and jasmonic acid/ethylene (JA/ET) defense signaling pathways, for example, are known to be antagonistic to one another in Arabidopsis and other species. To test the DC hypothesis, we examined quantitative genetic variation and co‐variation among marker‐inferred inbred lines and sib‐families of Boechera stricta, a close wild relative of Arabidopsis. The dynamics of the defense‐stress tolerance tradeoff was examined across 1) years that differed in precipitation, 2) drought and ABA treatments, and 3) a NPK nutrient supply gradient. In support of the DC hypothesis, we observed the tradeoff a) in the dry year, and b) in response to water deficiency, which c) was affected by ABA treatments, but the interaction between ABA and glucosinolate (GS) toxin levels was not significant. In contrast to the effects of water deficiency, d) the effect of lower NPK supply to cause the tradeoff was only marginally significant. Because an ABA‐mediated stress response is intrinsic to water deficient conditions and because of the known involvement of JA/ET in GS regulation, we suggest that these results provide circumstantial evidence implicating both of these pathways in the tradeoff and thus in the development of range limits.     

Broodcare or Egg Cannibalism by Parents and Helpers in Neolamprologus brichardi (Poll 1986) (Pisces: Cichlidae): a Study on Behavioural Mechanisms

In the cichlid species N. brichardi the young are tended by parent animals and broodcare helpers. No qualitative differences in the care are apparent. The regulation of eggcare by nonreproductive helpers is of especial interest as it excludes an endogenous component found in the parental care of other cichlids, based on sex and the reproductive cycle. The importance of the factors dominance, territory, size (age) experience, model and the continuous presence of eggs for helper eggcare disposition was examined experimentally. It was shown that subdominant inexperienced young fish will clean clutches, whereas dominants feed on them. Subdominant eggcleaners can be transformed into dominant eggfeeders; the change can be delayed or prevented by the continuous presence of eggs. Subdominant fish in a territory are more inclined to clean clutches than those in an aggregation. With growing experience (or size) helpers orient broodcare behaviour increasingly by a dominant model. Dominance and experience play no part however in broodpairs; here there are sex-dependent differences. In both sexes, eggcaring behaviour can be evoked only at the beginning of a breeding cycle. The disposition is bolstered by the presence of the clutch, and wanes after egg removal in females faster than in males. The tendency to continue eggcare can be strongly extended in both sexes by the continuous presence of eggs. Comparison with other cave-breeding cichlids showed that parental eggcare in these and N. brichardi was similarly regulated. Helper broodcare, however, is very differently regulated. These differences are discussed, as well as possible conclusions on the influence of endogenous and exogenous regulatory factors.     

Absolute versus per unit body length speed of prey as an estimator of vulnerability to predation

To study whether absolute (m/s) or relative (body lengths/s) speed should be used to compare the vulnerability of differently sized animals, we developed a simple computer simulation. Human 'predators' were asked to 'catch' (mouse-click) prey of different sizes, moving at different speeds across a computer screen. Using the simulation, a prey's chances of escaping predation depended on its speed (faster prey were more difficult to catch than slower prey of the same body size), but also on its size (larger prey were easier to catch than smaller prey at the same speed). Catching time, the time needed to catch a prey, also depended on both prey speed and prey size. Relative prey speed (body lengths/s or body surface/s) was a better predictor of catching time than was absolute prey speed (m/s). Our experiment demonstrates that, in contrast to earlier assertions, per unit body length speed of prey may be more 'ecologically relevant' than absolute speed. Copyright 1998 The Association for the Study of Animal Behaviour.