A high accuracy linear rate meter.

By implementing analog computer techniques using digital circuits, an instantaneous rate meter was built with approximately 100 times the accuracy of commercially available rate meters. The circuit is accurate to within +/- 0.2 events/min over a range of rates of 0.2-900 epm. Modifications can be made to provide a digital display of rate. The circuit design techniques used in developing the rate meter may be used to generate a wide variety of functions of time with very high accuracy.     

Benthic Diatoms as Indicators of Stream Sediment Concentrationin Hong Kong

Diatoms are photosynthetic unicellular, eukaryotic, microorganisms (algae) that are distinguished by their silicified (SiO₂‐nH₂O) cell walls. They have often been employed to assess salinity, pH, and nutrient conditions. Our data suggest that, they may also be used to assess suspended solid levels in streams. The ratio of motile to attached benthic diatoms from five different stream sites in Hong Kong was correlated with the level of suspended solids for each of these sites. Sites with high concentrations of suspended solids had a high percentage of motile diatoms on their rocks while sites with low concentrations of suspended solids had a high percentage of attached (non‐motile) diatoms on their rocks. When water carried by a stream has a high concentration of suspended solids, benthic diatoms in the stream are often covered in a layer of silt. Those diatoms that are motile are able to get on top of this silt layer while attached diatoms cannot. If the silt layer is not washed away, the attached diatoms perish and the percentage of motile diatoms increases. Thus, streams with high concentrations of suspended solids display a higher proportion of motile diatoms than do clear water streams with low concentrations of suspended solids. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of calf endometrium nuclei on human estradiol receptor complex; an in vitro study.

A heterogenous system was created containing purified calf endometrium nuclei and cytosol from adult human uterine tissue to test whether calf endometrium nuclei are able to convert the 4S-form of the estradiol receptor complex into the well known 5S form extracted under high salt conditions from uterine nuclei.Quite in contrast to the receptor hormone complex from immature tissue the complex from mature uterine tissue is translocated in a temperature independent step into calf endomertium nuclei.     

Regulation of cytochrome P450 in the central nervous system

The role of brain P450 in the physiology, pharmacology and toxicology of the brain is the subject of this study. Cytochrome P450 was isolated from the brains of rats and quantitated spectrally. The contribution of the known hepatic forms of the enzyme to the forms constitutive in the brain as well as those which are induced by hormones are xenobiotics were characterized on Western blots. We have found that the level of P450 in the brain is increased during pregnancy and lactation, by partial hepatectomy and by ethanol. In each case the profile of P450s induced is different. In pregnancy and lactation the P450 content of the hypothalamic preoptic area and olfactory lobes were increased up to 10-fold and the only subfamily identified on Western blots was 4A. There was no detectable 1A, 2A, 2B, 2C, or 2E1. Ethanol increases the level of brain P450 3- to 5-fold and P450 2C, 2E1 and 4A are induced. Upon partial hepatectomy P450 1A, 2C and 4A were detected on Western blots but there was no 2E1. The inducibility of these forms of P450 in the brain suggests that there is in situ metabolism of steroids, fatty acids, prostaglandins, ethanol and other xenobiotics in the brain and raises questions about the role of brain P450 in the development of tolerance to drugs and the neurotoxicity of xenobiotics. More importantly, the action of neurotransmitters such as dopamine which utilize fatty acid metabolites as intracellular mediators, could be influenced by the levels of 2C and 4A P450s.     

Habitat structure versus food abundance: the importance of sparse vegetation for the common redstart Phoenicurus phoenicurus

As many other birds breeding in agricultural areas, the common redstart declined strongly in many Central European countries over the last 60 years. The destruction of traditionally managed orchards, an important breeding habitat in Central Europe, is a relevant cause. An additional factor for the decline of this species could be the intensified management of the ground vegetation in orchards through reducing food availability and lowering prey detectability and accessibility. In this study we examined the importance of surfaces with sparse vegetation for the location of redstart territories and for foraging. To validate the results of these field studies we made habitat-choice experiments in aviaries with captive birds. Territories occupied by redstarts in orchards of northwestern Switzerland contained a significantly higher proportion of surfaces with sparse vegetation than unoccupied control sites. Redstarts made almost five times more hunting flights into experimentally established ruderal vegetation strips than into adjacent unmown meadows. No difference was observed when the meadow was freshly mown. Vegetation height and the proportion of open ground surface correctly predicted the vegetation type for hunting in 77% of the cases. Experiments in aviaries offering two types of sparse vegetation and a dense meadow supported the results of the field experiments. Even a four-fold increase of the food abundance in the meadow did not lead to a noticeable change in preference for the sparse vegetation types. For the conservation of the common redstart, not only traditionally managed orchards with tall trees with cavities should be preserved but also areas with sparse vegetation should be favored.     

Endothelial‐derived thrombospondin‐1 promotes macrophage recruitment and apoptotic cell clearance

Rapid apoptotic cell engulfment is crucial for prevention of inflammation and autoimmune diseases and is conducted by special immunocompetent cells like macrophages or immature dendritic cells. We recently demonstrated that endothelial cells (ECs) also participate in apoptotic cell clearance. However, in contrast to conventional phagocytes they respond with an inflammatory phenotype. To further confirm these pro‐inflammatory responses human ECs were exposed to apoptotic murine ECs and changes in thrombospondin‐1 (TSP‐1) expression and in activation of intracellular signalling cascades were determined by real‐time qPCR, immunoblotting and immunocytochemistry. Human primary macrophages or monocytic lymphoma cells (U937) were incubated with conditioned supernatant of human ECs exposed to apoptotic cells and changes in activation, migration and phagocytosis were monitored. Finally, plasma levels of TSP‐1 in patients with anti‐neutrophil cytoplasmic antibody(ANCA)‐associated vasculitis (AAV) were determined by ELISA. We provided evidence that apoptotic cells induce enhanced expression of TSP‐1 in human ECs and that this increase in TSP‐1 is mediated by the mitogen‐activated protein kinases (MAPK) ERK1 and 2 and their upstream regulators MEK and B‐Raf. We also showed that plasma TSP‐1 levels are increased in patients with AAV. Finally, we showed that conditioned supernatant of ECs exposed to apoptotic cells induces pro‐inflammatory responses in monocytes or U937 cells and demonstrated that increased TSP‐1 expression enhances migration and facilitates engulfment of apoptotic cells by monocyte‐derived macrophages or U937 cells. These findings suggest that under pathological conditions with high numbers of uncleared dying cells in the circulation endothelial‐derived elevated TSP‐1 level may serve as an attraction signal for phagocytes promoting enhanced recognition and clearance of apoptotic cells.     

Comparison of analytical and inverse finite element approaches to estimate cell viscoelastic properties by micropipette aspiration

The viscoelastic properties of cells are important in predicting cell deformation under mechanical loading and may reflect cell phenotype or pathological transition. Previous studies have demonstrated that viscoelastic parameters estimated by finite element (FE) analyses of micropipette aspiration (MA) data differ from those estimated by the analytical half-space model. However, it is unclear whether these differences are statistically significant, as previous studies have been based on average cell properties or parametric analyses that do not reflect the inherent experimental and biological variability of real experimental data. To determine whether cell material parameters estimated by the half-space model are significantly different from those predicted by the FE method, we implemented an inverse FE method to estimate the viscoelastic parameters of a population of primary porcine aortic valve interstitial cells tested by MA. We found that inherent differences between the analytical and inverse FE estimation methods resulted in statistically significant differences in individual cell properties. However, in cases with small pipette to cell radius ratios and short loading periods, model-dependent differences were masked by experimental and cell-to-cell variability. Analytical models that account for finite cell-size and loading rate further relaxed the experimental conditions for which accurate cell material parameter estimates could be obtained. These data provide practical guidelines for analysis of MA data that account for the wide range of conditions encountered in typical experiments.