Toxigenic Potential of Some Fusarium Isolates from Southeast Asia

The isolation and characterization of 10 isolates of six Fusarium spp. from plant and soil samples collected in Southeast Asia is reported. The ability of these isolates to produce trichothecenes both in liquid cultures (CZ, GYEP, and MYRO) and on rice was assessed, and their toxigenic potential was examined by skin assay and gavage studies with culture filtrates. Although culture filtrates of all the isolates caused minor damage to test animals, only that of F. equiseti DAOM 189762 produced trichothecenes.     

Mycotoxicoses of domestic animals and their diagnosis

Mycotoxins have been named "agents in search of a disease," and the considerable progress in analytical methodology over the last 10 years has not changed this very much. The following are factors that contribute to the difficulty of making a diagnosis: (1) nonspecificity of lesions; (2) masking of mycotoxic effects by secondary effects, e.g., through immunosuppression; (3) late appearance of a lesion, e.g., bone marrow damage or neoplasia; (4) interaction of several mycotoxins or presence of other toxicants or deficiency states; (5) species variation in the response to the mycotoxin(s); (6) difficulty of linking a late appearing effect with a demonstrable cause; (7) low doses of mycotoxins may cause stimulating effects; and (8) not being aware of the potential of a mycotoxin as a causative factor in disease. The mycotoxins of major importance in Canada are trichothecenes, ochratoxin, zearalenone, and ergot. It is concluded that the significance of mycotoxins for animals in Canada is likely generally underestimated.     

Brugia pahangi: effects upon the flight capability of Aedes aegypti.

Aedes aegypti mosquitoes were adversely affected by infections of the filarial worm Brugia pahangi. Infected mosquitoes flew significantly shorter distances and showed marked reductions in total flight time during 24-hr flight mill tests compared to uninfected controls. Total flight range and duration flown by infected mosquitoes remained relatively constant throughout the infection process, while control mosquitoes flew further and longer with increasing time after their blood meal. Furthermore, a significantly greater number of infected mosquitoes either died or were rendered incapable of flight. Of flying and nonflying mosquitoes with 6-day-old or older infections dissected for parasite burdens, the nonflying group contained significantly more worms. Results of this study indicate that developing filarial larvae within this mosquito vector reduce its ability to survive and to transmit its infection by reducing its flight capabilities. Conclusions from this study relate only to A. aegypti homozygous for the gene fm which is fully susceptible to this filarial parasite.     

Electron spin resonance studies on the lipid-protein interaction between cardiolipin and anti-cardiolipin antibodies.

Electron spin resonance measurements were performed in order to investigate the influence of anti-cardiolipin antibodies on cardiolipin-containing liposomes. The physical state of the lipid structures and the alterations caused by the interaction with specific antibody were determined by measuring the freedom of motion of spin-labeled stearic acid derivatives incorporated into the lipid structures. The interaction of the cardiolipin-containing liposomes with the anti-cardiolipin antibodies reduced the mobility of the spin-labeled stearic acid probe I (12, 3), whose nitroxide group is assumed to be located near the polar region of the lipid bilayer. The restricted mobility, which qualitatively resembles the interaction of cardiolipin liposomes with calcium ions, is probably the result of a tighter packing of the polar groups in their crystalline array. The binding sites of the cardiolipin structures for anti-cardiolipin antibodies and Ca2 ions seem to be identical. As indicated by the spin-labeled stearic acid probe I (1, 14), the apolar region of the lipid bilayer is not affected by the interaction of the cardiolipin-containing liposomes with the anti-cardiolipin antibodies.     

Development of a fluorescent probe for the study of nucleosome assembly and dynamics

To develop a probe for use in real-time dynamic studies of nucleosomes, core histones (from Drosophila) were conjugated to a DNA-intercalating dye, thiazole orange, by a reaction targeting Cys 110 of histone H3. In the absence of DNA, the conjugated histones are only very weakly fluorescent. However, upon reconstitution into nucleosomes by standard salt dialysis procedures, the probe fluoresces strongly, reflecting its ability to intercalate into the nucleosomal DNA. The probe is also sensitive to the nature of the DNA-histone interaction. Nucleosomes reconstituted by stepwise salt dialysis give a fluorescence signal quite different from that of the species formed when DNA and histones are simply mixed in low salt. In addition, changing either the DNA length or the type of sequence (nucleosome positioning sequences versus random DNA of the same size) used in the reconstitution alters the resulting fluorescence yield. The results are all consistent with the conclusion that a more rigid, less flexible nucleosome structure results in less fluorescence than a looser structure, presumably due to structural constraints on dye intercalation. This probe should be well suited to analyzing nucleosome dynamics and to following factor-mediated assembly and remodeling of nucleosomes in real time, particularly at the single-molecule level.     

Probabilistic modeling of selective stimulation of the human sciatic nerve with a flat interface nerve electrode

Ankle control is critical to both standing balance and efficient walking. The hypothesis presented in this paper is that a Flat Interface Nerve Electrode (FINE) placed around the sciatic nerve with a fixed number of contacts at predetermined locations and without a priori knowledge of the nerve's underlying neuroanatomy can selectively control each ankle motion. Models of the human sciatic nerve surrounded by a FINE of varying size were created and used to calculate the probability of selective activation of axons within any arbitrarily designated, contiguous group of fascicles. Simulations support the hypothesis and suggest that currently available implantable technology cannot selectively recruit each target plantar flexor individually but can restore plantar flexion or dorsiflexion from a site on the sciatic nerve without spillover to antagonists. Successful activation of individual ankle muscles in 90% of the population can be achieved by utilizing bipolar stimulation and/or by using a cuff with at least 20 contacts.     

Ion diffusion potentials across mycoplasma membranes determined by a novel method using a carbocyanine dye

The influence of transmembrane ion fluxes on mycoplasma membrane potentials was studied. Electric membrane potential was calibrated vs fluorescence intensity of a potential-sensitive carbocyanine dye according to delta psi = (RT/F) X log([aIN(1 - IN) - b]/Kint), where IN = I/I0, I0 = maximal fluorescence intensity (obtained for delta psi----infinity), and a and b are constants. Fluorescence intensity was calibrated vs membrane potential by inducing a K+ diffusion potential. The calibration procedure was based on the assumption that in the presence of valinomycin the membrane potential was determined entirely by K+ diffusion. Then the dependence of fluorescence intensity on the external K+ concentration, Kext, could be described by Ival = I0[1 + a/(Kext + b)]-1. For Mycoplasma mycoides subsp. capri and enterococci, the constants were determined from experimental data using nonlinear least-squares computer-assisted methods. The validity of our assumption was proved using the "null-point" method. Here the Ca2+ ionophore A23187 and varying external Ca2+ concentrations were used to change the membrane potential experimentally. K+ and Na+ diffusion potentials significantly contributed to mycoplasma membrane potential whereas Cl- had no influence. Under growth conditions the mycoplasma membrane potential was estimated to be delta psi = -68 mV.     

Expression of RAGE and HMGB1 in Thymic Epithelial Tumors,Thymic Hyperplasia and Regular Thymic Morphology

Recently, a role of the receptor for advanced glycation endproducts (RAGE) in myasthenia gravis was described. RAGE and its ligand high mobility group box 1 (HMGB1) play key roles in autoimmunity and cancer. To test whether these molecules are involved in patients with thymic abnormalities we applied immunohistochemical analysis in 33 cases of thymic epithelial tumors, comprising 27 thymomas and 6 thymic carcinomas, and 21 nonneoplastic thymuses. Both molecules were detected in neoplastic epithelial cells: RAGE staining was most intense in WHO type B2 thymomas and thymic carcinomas (p<0.001). HMGB1 nuclear staining was strongest in A and AB, and gradually less in B1 = B2>B3>thymic carcinoma (p<0.001). Conversely, HMGB1 cytoplasmic staining intensities were as follows: A and AB (none), B1 (strong), B2 (moderate), B3 and thymic carcinoma (weak); (p<0.001). Fetal thymic tissue showed a distinct expression of RAGE and HMGB1 in subcapsular cortical epithelial cells which was found in 50% of myasthenic patients. Furthermore RAGE and HMGB1 were expressed in thymocytes, macrophages, Hassall''s corpuscles, thymic medulla, and germinal center cells in myasthenic patients. Immunohistochemistry results were complemented by systemic measurements (immunosorbent assay): serum levels of soluble RAGE were significantly reduced in patients with epithelial tumors (p = 0.008); and in invasive tumors (p = 0.008). Whereas RAGE was equally reduced in thymic hyperplasia and epithelial tumors (p = 0.003), HMGB1 was only elevated in malignancies (p = 0.036). Results were most pronounced in thymic carcinomas. Thus, RAGE and HMGB1 are involved in the (patho-)physiology of thymus, as evidenced by differentiated thymic and systemic expression patterns that may act as diagnostic or therapeutic targets in autoimmune disease and cancer.