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Nat Neurosci,
2008]
Small, high-impedance neurons with short processes, similar to those found in the soil nematode Caenorhabditis elegans, are predicted to transmit electrical signals by passive propagation. However, we have found that certain neurons in C. elegans fire regenerative action potentials. These neurons resembled Schmitt triggers, as their potential state appears to be bistable. Transitions between up and down states could be triggered by application of the neurotransmitter glutamate or brief current pulses.
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Development,
2021]
A dynamic pattern of histone methylation and demethylation controls gene expression during development, with some processes such as formation of the zygote involving large-scale reprogramming of methylation states. A new paper in Development investigates how inherited histone methylation regulates developmental timing and the germline/soma distinction in <i>Caenorhabditis elegans</i> To hear more about the story we caught up with first author and postdoctoral researcher Brandon Carpenter, and his supervisor David Katz, Associate Professor in the Department of Cell Biology at Emory University School of Medicine in Atlanta, Georgia.
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Environmental Toxicology and Risk Assessment: Implications for Environmental Decisions, American Society for Testing and Materials, Standard Technical Publication 1403,
2001]
A comparison of the acute LC50s for five metals between the standard test organism Eisenia fetida and the soil nematode Caenorhabditis elegans was made. Although the test with C. elegans is shorter (24 h vs. 2 weeks) and uses less soil or testing medium (2.33 g vs. 200 g dry weight) than that for E. fetida, LC50s were comparable for the earthworm and the nematode. The current study further investigated similarities by extending the exposure time to 48 h. Comparisions were made to 24-h C. elegans data, published E. fetida data, and U.S. Environmental Protection Agency (EPA) allowable concentrations. The nitrate salts of Pb, Ni, Cd, Zn, and Cu were used to generate LC50s. Two naturally occurring soils in Georgia were chosen to compare different soil properties on the metals' toxicity. Tifton soil was sampled from the southern region of Georgia and is characterized by relatively high sand and low clay and soil organic matter (SOM) contents. Cecil soil, in contrast, is found in the Piedmont region of Georgia and is characterized by relatively high amounts of clay and SOM. As anticipated, extending the exposure time to 48 h significantly increased the toxicity (i.e. decreased the LC50s) of the metals compared to published 24-h C. elegans data. Physical-chemical properties of soils are known to affect the binding of polyvalent metals and thus the bioavailability and toxicity of these metals. Increasing clay and SOM contents allow for an increased capacity to bind metals. For this reason, LC50s were higher in Cecil than in Tifton soil. Because tests using C. elegans are rapid, reliable, and generate data comparable to that of the earthworm, we suggest further studies that may lead to the standardization of the nematode for use as a soil toxicity-testing organism.
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Environ Toxicol Chem,
2003]
Current regulation of metals in soils is based on total metal concentrations rather than on actual exposure concentrations. Considering the extreme variation in soil physicochemical properties, total concentrations are not reflective of the availability and resultant toxicity of metals in different soils. In this study, the availability of Cd, Cu, Ni, Pb, and Zn to the free-living soil nematode Caenorhabditis elegans was assessed after 24-h exposure in three soils using a sequential soil extraction procedure. Albany soil, sampled from southern Georgia, USA, is characterized by a high sand content, whereas Cecil soil from the Piedmont region of Georgia contains higher fractions of clay and organic matter. The final soil was an American Society for Testing and Materials (ASTM) artificial medium composed of peat, kaolin clay, sand, and calcium carbonate. Based on their compositions, ASTM medium would sorb metals most strongly and Albany soil the least strongly. In fact, 24-h lethal concentrations to 50% (LC50s) of nematodes for the five metals as determined by the total metal concentration followed this trend. In addition, water-extractable metals were lowest in ASTM medium and highest in Albany soil when spiked at the same concentrations. Our data show the need to consider soil type when performing toxicological tests and establishing site-specific metal concentrations in soil.
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Tropenmed Parasitol,
1980]
Two species of Nearctic black fly, Simulium decorum and S. pictipes, exhibit partial susceptibility to infection with the bovine parasite, Onchocerca lienalis, when inoculated intrathoracically with microfilariae. In addition, a proportion of S. decorum females will support the development of the human parasite, O. volvulus, to the third larvae stage. Infection rates with second- or third-stage larvae seven or more days after varied among geographic strains of S. decorum, ranging from 6.5% in a strain from northern New York State to 48.7% in a strain from Georgia. The average number of larvae per infected female ranged from 1.00 to 1.78 in the three strains examined. Partial susceptibility to O. lienalis was found to persist in colonized strains of s. decorum, and cryopreserved microfilariae of this parasite retained their infectivity. Seven or more days after inoculation with microfilariae of the Guatemalan strain of O. volvulus, 16.7% of the females of S. decorum harbored second- or third-stage larvae. Development of O. lienalis and O. volvulus proceeded normally in these black flies, and moderate increases in susceptibility rate and number of infective larvae were noted in response to increased microfilarial dosages.