Toxicity of dioxin to developing teeth and salivary glands : An experimental study

Dioxins are ubiquitous environmental poisons having unequivocal adverse health effects on various species. The majority of their effects are thought to be mediated by the aryl hydrocarbon receptor (AhR). Developing human teeth may be sensitive to dioxins and the most toxic dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is developmentally toxic to rodent teeth. Mechanisms of TCDD toxicity can be studied only experimentally. The aim of the present thesis work was to delineate morphological end points of developmental toxicity of TCDD in rat and mouse teeth and salivary glands in vivo and in vitro and to characterize their cellular and molecular background. Mouse embryonic teeth and submandibular gland explants were grown in organ culture without/with TCDD at various concentrations, examined stereomicroscopically and processed for histological examination. The effects of TCDD on cellular mechanisms essential for organogenesis were investigated. The expression of various genes eliciting the response to TCDD exposure or involved in tooth and salivary gland development was studied at the mRNA and/or protein levels by in situ hybridization and immunohistochemistry. Association of the dental effects of TCDD with the resistance of a rat strain to TCDD acute lethality was analyzed in two lactationally exposed rat strains. The effect of TCDD on rat molar tooth mineralization was studied in tissue sections. TCDD dose- and developmental stage-dependently interfered with tooth formation. TCDD prevented early mouse molar tooth morphogenesis and altered cuspal morphology by enhancing programmend cell death, or apoptosis, in dental epithelial cells programmed to undergo apotosis. Cell proliferation was not affected. TCDD impaired mineralization of rat molar dental matrices, possibly by specifically reducing the expression of the mineralization-related dentin sialophosphoprotein gene shown in cultured mouse teeth. The impaired mineralization of rat teeth was accompanied by decreased expression of AhR and the TCDD-inducible xenobiotic-metabolozing enzyme P4501 A1 (CYP1A1), suggesting mediation of the TCDD effect by the AhR pathway. The severe interference by TCDD with rat incisor formation was independent of the genotypic variation of AhR determining the resistance of a rat strain to TCDD acute lethality. The impairment by TCDD of mouse submandibular gland branching morphogenesis was associated with CYP1A1 induction and involved blockage of EGF receptor signalling. In conclusion, TCDD exposure is likely to have activated the AhR pathway in target organs with the consequent activation of other signalling pathways involving developmentally regulated genes. The resultant phenotype is organ specific and modified by epithelial-mesenchymal interactions and dependent on dose as well as the stage of organogenesis at the time of TCDD exposure. Teeth appear to be responsive to TCDD exposure throughout their development.

Magnetic superconductors: Model theories and experimental properties of rare-earth compounds

Superconducting and magnetically long-range ordered states were believed to be mutually exclusive phenomena. The discovery of rare-earth compounds in recent years, which exhibit both superconductivity and magnetic ordering (ferromagnetic, antiferromagnetic or sinusoidal), has led to considerable theoretical and experimental work on such systems. In the present article, we give a review of various theoretical models and important experimental results. In the theoretical sections, we start with the Abrikosov-Gorkov pair breaking theory for dilute alloys and discuss its improvement in the work of Müller-Hartmann and Zittartz. Then, in the context of magnetic superconductors, various microscopic theories that have been advanced are presented. These predict re-entrant behaviour in some systems (ferromagnetic superconductors) and coexistence regions in others (particularly antiferromagnetic superconductors). Following this, phenomenological generalized Ginzburg-Landau theories for two kinds of orders (superconducting and magnetic) are presented. A section dealing with renormalization group analysis of phase diagrams in magnetic superconductors is given. In experimental sections, the properties of each rare-earth compounds (ternary as well as some tetranery) are reviewed. These involve susceptibility, heat capacity, resistivity, upper critical field, neutron scattering and magnetic resonance measurements. The anomalous behaviour of the upper critical field of antiferromagnetic superconductors near the Néel temperature is discussed both in theory sections and experimental section for various systems.

Heat-Capacity Measurements - Progress In Experimental-Techniques

The heat capacity of a substance is related to the structure and constitution of the material and its measurement is a standard technique of physical investigation. In this review, the classical methods are first analyzed briefly and their recent extensions are summarized. The merits and demerits of these methods are pointed out. The newer techniques such as the a.c. method, the relaxation method, the pulse methods, the laser flash calorimetry and other methods developed to extend the heat capacity measurements to newer classes of materials and to extreme conditions of sample geometry, pressure and temperature are comprehensively reviewed. Examples of recent work and details of the experimental systems are provided for each method. The introduction of automation in control systems for the monitoring of the experiments and for data processing is also discussed. Two hundred and eight references and 18 figures are used to illustrate the various techniques.

Productivity and marketing enhancement for peanut in Papua New Guinea and Australia

Enhance productivity of peanuts in Papua New Guinea and Australia. Also the application of remote sensing technologies to enhance profitability in peanut systems.

Rice flower integrating production and marketing

This book contains guidelines on market-driven production for export markets, with information on how the marketing chain operates and what risks are involved. Using rice flower as an example, the book gives growers strategies to enhance their market performance and improve the profitability of their enterprises. It outlines some practical suggestions for marketing rice flower in Japan, the United States, Taiwan and Hong Kong as well as in Australia, and also provides a draft standard for rice flower for export markets.

New molecular strategies for prevention of fibroproliferative vascular disease : An experimental approach to restenosis

Vascular intimal hyperplasia is a major complication following angioplasty. The hallmark feature of this disorder is accumulation of dedifferentiated smooth muscle cells (SMCs) to the luminal side of the injured artery, cellular proliferation, migration, and synthesis of extracellular matrix. This finally results in intimal hyperplasia, which is currently considered an untreatable condition. According to current knowledge, a major part of neointimal cells derive from circulating precursor cells. This has outdated the traditional in vitro cell culture methods of studying neointimal cell migration and proliferation using cultured medial SMCs. Somatostatin and some of its analogs with different selectivity for the five somatostatin receptors (sst1 through sst5) have been shown to have vasculoprotective properties in animal studies. However, clinical trials using analogs selective for sst2/sst3/sst5 to prevent restenosis after percutaneous transluminal coronary angioplasty (PTCA) have failed to show any major benefits. Sirolimus is a cell cycle inhibitor that has been suggested to act synergistically with the protein-tyrosine kinase inhibitor imatinib to inhibit intimal hyperplasia in rat already at well-tolerated submaximal oral doses. The mechanisms behind this synergy and its long-term efficacy are not known. The aim of this study was to set up an ex vivo vascular explant culture model to measure neointimal cell activity without excluding the participation of circulating progenitor cells. Furthermore, two novel potential vasculoprotective treatment strategies were evaluated in detail in rat models of intimal hyperplasia and in the ex vivo explant model: sst1/sst4-selective somatostatin receptor analogs and combination treatment with sirolimus and imatinib. This study shows how whole vessel explants can be used to study the kinetics of neointimal cells and their progenitors, and to evaluate the anti-migratory and anti-proliferative properties of potential vasculoprotective compounds. It also shows how the influx of neointimal progenitor cells occurs already during the first days after vascular injury, how the contribution of cell migration is more important in the injury response than cell proliferation, and how the adventitia actively contribute in vascular repair. The vasculoprotective effect of somatostatin is mediated preferentially through sst4, and through inhibition of cell migration rather than of proliferation, which may explain why sst2/sst3/sst5-selective analogs have failed in clinical trials. Furthermore, a brief early oral treatment with the combination of sirolimus and imatinib at submaximal doses results in long-term synergistic suppression of intimal hyperplasia. The synergy is a result of inhibition of post-operative thrombocytosis and leukocytosis, inhibition of neointimal cell migration to the injury-site, and maintenance of cell integrity by inhibition of apoptosis and SMC dedifferentiation. In conclusion, the influx of progenitor cells already during the first days after injury and the high neointimal cell migratory activity underlines the importance of early therapeutic intervention with anti-migratory compounds to prevent neointimal hyperplasia. Sst4-selective analogs and the combination therapy with sirolimus and imatinib represent potential targets for the development of such vasculoprotective therapies.

Internet marketing capabilities and international market growth

The Internet has been shown to facilitate elements of internationalisation such as information accumulation and network opportunities. However, there is limited understanding of how the Internet combined with marketing capabilities drives international market growth. This study, based on a sample of 224 Australian firms, develops and tests, using structural equation modelling (SEM), a conceptual model of Internet marketing capabilities and international market growth. Results indicate that firms deploying Internet marketing capabilities will benefit due to the reduction of information uncertainty and increased capacity to develop international network capabilities. Moreover, Internet marketing capabilities indirectly lead to international market growth when the firm has a high level of international strategic orientation and international network capabilities. Overall, Internet marketing capabilities enhance the firm's ability to generate other internal capabilities within the firm, which in turn have a positive impact on the international market growth of the firm.

Plasma-enhanced synthesis of bioactive polymeric coatings from monoterpene alcohols: A combined experimental and theoretical study

This paper describes the synthesis and characterization of a novel organic polymer coating for the prevention of the growth of Pseudomonas aeruginosa on the solid surface of three-dimensional objects. Substrata were encapsulated with polyterpenol thin films prepared from terpinen-4-ol using radio frequency plasma enhanced chemical vapor deposition. Terpinen-4-ol is a constituent of tea tree oil with known antibacterial properties. The influence of deposition power on the chemical structure, surface composition, and ultimately the antibacterial inhibitory activity of the resulting polyterpenol thin films was studied using X-ray photoelectron spectroscopy (XPS), water contact angle measurement, atomic force microscopy (AFM), and 3-D interactive visualization and statistical approximation of the topographic profiles. The experimental results were consistent with those predicted by molecular simulations. The extent of bacterial attachment and extracellular polymeric substances (EPS) production was analyzed using scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). Polyterpenol films deposited at lower power were particularly effective against P. aeruginosa due to the preservation of original terpinen-4-ol molecules in the film structure. The proposed antimicrobial and antifouling coating can be potentially integrated into medical and other clinically relevant devices to prevent bacterial growth and to minimize bacteria-associated adverse host responses.