Refine
Has Fulltext
- yes (214)
Is part of the Bibliography
- yes (214)
Year of publication
- 1993 (214) (remove)
Document Type
- Journal article (160)
- Book article / Book chapter (27)
- Conference Proceeding (11)
- Review (8)
- Book (4)
- Complete part of issue (2)
- Jahresbericht (1)
- Other (1)
Keywords
- Anorganische Chemie (11)
- Toxikologie (11)
- Organische Chemie (8)
- Physiologische Chemie (8)
- Immunologie (7)
- Psychologie (6)
- Virologie (6)
- Biochemie (5)
- Infektionsbiologie (4)
- Neurobiologie (4)
Institute
- Theodor-Boveri-Institut für Biowissenschaften (28)
- Institut für Psychologie (bis Sept. 2007) (24)
- Institut für Pharmakologie und Toxikologie (20)
- Institut für Anorganische Chemie (17)
- Institut für Virologie und Immunbiologie (16)
- Institut für Molekulare Infektionsbiologie (13)
- Physikalisches Institut (13)
- Institut für Organische Chemie (9)
- Institut für Klinische Neurobiologie (8)
- Klinik und Poliklinik für Allgemein-, Viszeral-, Gefäß- und Kinderchirurgie (Chirurgische Klinik I) (8)
Die Arbeit geht von der allgemeinen Feststellung aus, daß die Repräsentation von Wissen der Reduktion des Aufwandes von zu erwartenden Informationsverarbeitungsprozessen dient. Es werden verschiedene Anforderungen an die menschliche Informationsverarbeitung betrachtet, und es wird jeweils gefragt, welche Eigenschaften die Wissensrepräsentation haben muß, um diesen Anforderungen zu genügen. Im einzelnen werden die Objektwahrnehmung, die anschauliche Vorstellungstätigkeit, die Aufmerksamkeitssteuerung, die Erkennung semantischer Relationen, die Handlungskontrolle und der Erwerb von Wortbedeutungen betrachtet. Es wird die Schlußfolgerung gezogen, daß eine Repräsentation in diskreten symbolischen Einheiten der Dynamik der Wissensnutzung unter den verschiedenen Anforderungen wenig gerecht wird. Es scheint naheliegender, Wissen direkt in Handlungseinheiten zu repräsentieren. Solche Einheiten sollten Informationen über einzelne Handlungen mit Informationen über Situationskontexte verbinden, in denen die Handlungen erfolgreich verwendet worden sind. Die Vorteile einer solchen handlungsorientierten Wissensrepräsentation werden diskutiert.
Wben irradiated at 360 nm, furocoumarins with a hydroperoxide group in a side chain effciently give rise to a type of DNA damage that can best be explained by a photoinduced generation of hydroxyl radicals from the excited pbotosensitizers. The observed DNA damage profiles, i.e. the ratios of single-strand breaks, sites of base loss (AP sites) and base modifications sensitive to fonnamidopyrimidine-DNA glycosylase (FPG protein) and endonuclease m, are similar to the DNA damage profile produced by hydroxyl radicals generated by lonizing radiation or by xanthine and xanthine oxidase in the presence of Fe(III)-EDTA. No such damage is observed with the corresponding furocoumarin alcohols or in the absence of near-UV radiation. The damage caused by the photo-excited hydroperoxides is not influenced by superoxide dismutase (SOD) or catalase or by D2O as solvent. The presence of t-butanol, however, reduces both the formation of single-strand breaks and of base odifications sensitive to FPG protein. The cytotoxicity caused by one of the hydroperoxides in L5178Y mome lymphoma cells is found to be dependent on the near-UV irradiation and to be much higher than that of the corresponding alcohol. Therefore the new type of photoinduced damage occurs inside cells. Intercalating photosensitizers with an attached hydroperoxide group might represent a novel and versatile class of DNA damaging agents, e.g. for phototherapy.
Diethylstilbestrol alters the morphology and calcium levels of growth cones of PC12 cells in vitro
(1993)
Diethylstilbestrol (DES) is a synthetic estrogen with carcinogenic properties. DES is known to alter cytoskeletal components, including the organization of actin stress fibres in C6 rat glioma cells. ln a test of the hypothesis that DES disrupts actin Filaments of growth cones in neuron-like cells, DES-induced changes in filopodial lengths were quantified in rat pheochromocytoma (PC12) cells in vitro. DES significantly altered growth cone morphology, with collapse of growth cone filopodia and neurite retraction invariably occurring at a concentration of 10 MikroM. At 5 MikroM DES, transient reductions in total filopodiallengths occurred. At DES concentrations of 0.1 nM and 1 nM, reductions in total filopodiallengths occurred in a fraction of growth cones. Evidence exists which shows that growth cone activity and morphology are intimately linked to Ieveis of intracellular, free calcium and that DES increases such levels. Measurements of free intracellular calcium levels by fluorescence microscopy, at times concurrent with the DES-induced reduction in total filopodial lengths, showed that calcium levels were indeed significantly increased by 10 MirkoM DES. Labelling of filamentaus actin (f-actin) with FITC-phalloidin showed that the f-actin distribution in growth cones exposed to DES could not be differentiated from the distribution found in spontaneously retracting growth cones. Tagether with evidence which showed that growth cone motility was not affected, the results are taken to indicate that DES, rather than acting directly on the cytoskeleton, exerts its effects indirectly, by a calcium-induced destabilization of actin filaments in the growth cone.
Autolyzed, antigen-extracted, allogeneic (AAA) bone was prepared from human cortical bone and its morphologic, biomechanical, and osteoinductive properlies were compared with untreated (frozen) as well as lyophilized human bone. Scanning electron microscopy revealed removal of inprganic calcium phosphates and persistence of shrunken collagen fibrils on the surface of AAA bone matrix. Biomechanical testing of differently prepared bone samples showed that lyophilization increased both the modulus of elasticity (P < .00001) and the compressive strength (P < .00001 ). Depending on the depth of decalcification in the preparation of AAA bone, both measured values decreased in rehydrated AAA bone compared with untreated bone {P < .00001 ). Completely demineralized and rehydrated AAA bone was soft, flexible, and showed very little compressive strength. Differences in biomechanical behavior between samples drilled longitudinally or perpendicularly to the diaphyseal bone axis were observed. Xenogeneic human bone samples were implanted in muscle pouches of Sprague-Dawley rats for 6 weeks. AAA bone implants showed chondrogenesis and osteogenesis in 50% of the cases, while untreated or lyophilized bone implants induced no new cartilage or bone formation. As decalcification exposed xenogeneic organic matrix components, AAA bone implants provoked the highest inflammatory reaction. When AAA bone samples were implanted in immunosuppressed rats, the inflammatory reaction was suppressed and 94o/o of the implants showed endochondral bone formation. The chondroinductivity of the bone samples also was tested in vitro using neonatal rat muscle tissue to avoid interference with inflammatory cells and secreted cytokines. In this assay, 68°/o of AAA bone samples induced chondroneogenesis, while untreated as weil as lyophilized bone samples failed to induce any cartilage formation. The results clearly dernonstrafe that AAA bone has osteoinductive properties. Biomechanical stability of AAA bone implants depends on the degree of demineralization. Thus, they can be prepared in an appropriate manner for different indications in oral and maxillofacial surgery.
Known mutagens and carcinogens in the dict were compiled and the risk of cancer was estimated on the basis of average exposure Ievels in Switzerland and carcinogenic potencies from rodent bioassays. The analysis showed that, except for a1cohol, the sum of all known dietary carcinogens could only explain a few percent of the cancer deaths attributed by epidemiologists to dietary factors. The discrepancy was explained by a "carcinogenicity" of excess macronutrients. This hypothesis was based on an evaluation of dietary restriction experiments in rats and mice, where a dramatic reducing effect on spontaneaus tumour formation was seen. From these experiments, a "carcinogenic potency" was deduced for food in excess (TD50 approximately 16 g/kg per day). Ovemutrition in Switzerland was converted into excess food intake and the cancer risk estimated on the basis ofthe TD50 value. The resulting risk of60,000 cases per one million lives wou1d aJlow to explain by overnutrition almost all "diet-related" cancer deaths in humans.