Buchbesprechungen

Ohne Zusammenfassung     

Mathematical approaches to decompression

A flexible mathematical treatment of diver decompression has been developed by modifying the classical Haldanian model of inert gas transport. It is based on the assumption that inert gases will remain in solution in the tissues of a diver as long as a particular metastable limit is not exceeded,and that this limit varies with depth, nature of the inert gas,and the specific time constant of its transport in the body. Proposed metastable limits (M-values)of dissolved helium partial pressure have been developed empirically by the Experimental Diving Unit of the United States Navy. These limits permit the design by digital computer of decompression procedures expected to be safer than contemporary decompression tables for extended deep dives.

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Zusammenfassung Ein flexibles mathematisches Verfahren zur Überwachung der Dekompression bei Tauchern wurde entwickelt, durch Modifikation des klassischen Modells von Haldane für den Transport träger Gase.Es beruht auf der Annahme,dass träge Gase so lange in den Geweben eines Tauchers in Lösung bleiben, als eine bestimmte metastabile Grenze nicht überschritten wird. Diese Grenze ändert sich mit der Tiefe,der Natur des trägen Gases und der spezifischen Zeitkonstante seines Transports im Körper. Die vorgeschlagenen metastabilen Grenzen (M-Werte) des Partialdruckes von gelöstem Helium wurden empirisch entwickelt in der Experimental Diving Unit der Marine der Vereinigten Staaten.Diese Grenzen erlauben die Erfassung der Dekompressionsvorgänge durch Digital Computer und es wird angenommen, dass sie sicherer sind als die gebräuchlichen Dekompressions-Tabellen für langes Tieftauchen.

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Resume On a établi un procédé mathématique fléxible pour suivre les phénomènes de décompression chez les plongeurs.Pour ce faire, on a modifié le modèle classique de Haldane concernant le transport d'un gaz inerte. Comme base, on admet que les gaz inertes resteront en solution dans les tissues des plongeurs aussi longtemps qu'une limite métastatique n'est pas franchie.Cette limite varie avec la profondeur,la nature du gaz inerte et la constante de temps spécifique de son transport dans le corps. Les limites métastatiques proposées (valeurs-M)de la pression partielle de l'hélium dissous ont été déterminées empiriquement à l' "Expérimental Diving Unit"de la marine des Etats-Unis. Ces limites permettent de calculer les processus de décompression au moyen d'ordinateurs.On admet en outre que ce procédé est plus sûr que les tables de décompression usuelles, surtout dans le cas de plongées profondes et de longue durée.

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Based on a paper presented at the Forth International Biometeorological Congress, New Brunswick, N.J., 26 August – 2 September 1966.     

Target cells of vitamin D in the vertebrate retina

Using PAP technique, cellular localization of vitamin D-dependent calcium-binding protein (D-CaBP) was investigated in vertebrate retina with monospecific antisera against chick duodenal D-CaBP. In the chick retina, the receptor cells were positive. In the inner nuclear layer, horizontal cells and some bipolar cells were also positive. Some amacrine cells as well as different levels of the inner plexiform layer were also positive for D-CaBP. A few interspersed ganglion cells were positive but their axons forming the optic tract were negative. Müller's cells were negative. In 1-day-old chicks and 4-week-old rachitic chicks there was paucity and absence, respectively, of D-CaBP staining in horizontal cells. In the mouse, rat, and rabbit the receptors had only trace amounts of reaction product in their outer segment and pedicle. Horizontal cells were densely positive throughout their cellular body and processes. Some amacrine cells in the inner nuclear layer were positive. In the mouse and rat three horizontal levels of the outer plexiform layer were very prominent because of their dense staining for D-CaBP. Many ganglion cells were also positive along with their axons forming the optic nerve. In the rabbit, no positive layers were seen in the inner plexiform layer, and ganglion cells with their fibers were negative. In the frog retina there were smaller amounts of D-CaBP in the receptor cells and horizontal cells than that of the chick retina. Also, the fibers of the ganglionic cells were positive for D-CaBP. In all species studied, some amacrine cells were stained for D-CaBP. Because of its possible roles in membrane calcium transport and intracellular Ca++ regulation, it has perhaps similar functions in these positive cells. The synthesis of D-CaBP is dependent upon vitamin D. These positive cells are thus target cells of vitamin D.     

Referate

Ohne Zusammenfassung     

Coactivation of leg reflexes in the stick insect

Each leg of a standing stick insect acts as a height controller. The leg contains several joints. Most of these joints are known to be controlled by feedback loops which are the basis of resistance reflexes (review Bässler 1983). This leads to the question of whether the resistance reflex of the whole leg can be understood as a simple, vectorial sum of the individual reflexes provided by the different joints, or whether additional properties emerge by simultaneous stimulation of several joints. Force measurements were performed while passively moving the middle leg tarsus of a fixed stick insect (Carausius morosus) stepwise to different positions. From the dynamic and static forces the torques developed by each joint were calculated. They were compared with the torques developed when only a single joint was moved by the same amount. The comparison shows that for a large range of positions there are no differences between both situations. Differences occur in two cases. First, the muscle system controlling the coxa-trochanter joint seems to be more strongly excited when the entire leg is moved than when only the one joint is moved. This change increases the linearity of the whole system for small deviations from the zero position. Second, the torque developed by the extensor tibiae system for negative steps (corresponding to increased body height), and the levator of coxa and trochanter for positive steps, decreases rather than increases when the whole leg is moved to extreme positions. This contributes to a decrease in the slope of the force-height characteristic and thus to a more non-linear behaviour of the whole system for the extreme positions. It is well known that the amplification factors of resistance reflexes in the leg show a large variation (Bässler 1972a; Kittmann 1991). Our results indicate that any change of the amplification factor influences the reflexes in all leg joints in the same way.     

Spatial distribution patterns of interphase centromeres during retinoic acid-induced differentiation of promyelocytic leukemia cells

BACKGROUND: The pericentromeric heterochromatin is an important element for the regulation of gene silencing. Its spatial distribution during interphase appears to be cell-type specific. This study analyzes three-dimensional (3D) centromere distribution patterns during cellular differentiation along the neutrophil pathway. METHODS: Differentiation of the promyelocytic leukemia cell line NB4 was induced by retinoic acid. Centromeres in interphase nuclei were visualized by immunofluorescence staining of centromere-associated proteins with CREST serum. 3D images of nuclei were obtained by confocal microscopy. Automated methods for the segmentation of point-like objects in 3D images were implemented to detect the position of centromeres. Features of centromere localization patterns were determined by constructing the minimal spanning tree of the centromere distribution. RESULTS: In differentiated NB4 cells, the number of centromere conglomerates (chromocenters) was decreased and the distance between chromocenters was increased as compared with untreated controls. The nuclear volume did not differ between the two groups. CONCLUSIONS: The measured rearrangement of centromeres indicates a progressive clustering of heterochromatin and a global remodeling of interphase chromosome territories during differentiation of NB4 cells. The developed methods for the analysis of 3D centromere distribution patterns provide the opportunity for a fast and objective analysis of heterochromatin remodeling.     

Phytochemicals in Fruit and Vegetables: Health Promotion and Postharvest Elicitors

Inverse associations between fruit and vegetable intake and chronic diseases, such as different types of cancer and cardiovascular disease, have been demonstrated in numerous epidemiological studies. Phytochemicals have been indicated to be responsible for this observed protective effect. Application of postharvest elicitors can trigger distinct changes in the plant's secondary metabolism. Thus, targeted postharvest elicitor treatments may be used to obtain fruit and vegetables enriched with phytochemicals for sale as fresh market products or used as raw material for functional foods and supplements, thereby promoting higher consumption of these health-promoting substances.

     

Stimulation of Vesicular-Arbuscular Mycorrhizal Fungi by Mycotrophic and Nonmycotrophic Plant Root Systems

Transformed root cultures of three nonmycotrophic and one mycotrophic plant species stimulated germination and hyphal growth of the vesicular-arbuscular mycorrhizal fungus Glomus etunicatum (Becker & Gerd.) in a gel medium. However, only roots of the mycotrophic species (carrot) supported continued hyphal exploration after 3 to 4 weeks and promoted appressoria formation by G. etunicatum.