Effects of metal exposure on associative learning behavior in nematode Caenorhabditis elegans

In the present study, the thermotaxis model was used to evaluate the effects of metal exposure at different concentrations on associative learning behavior in nematodes. The examined nematodes were cultured at 25 or 17 degrees C, and then shifted to 20 degrees C condition. Based on the ability of nematodes to trace the temperature of 20 degrees C, exposure to 10 microM of all examined metals and 2.5 microM Pb and Hg caused significant decrease of associative learning behavior at time intervals of 5 and 18 h; however, exposure to 2.5 microM Cu, Zn, and Ag did not influence associative learning behavior. Moreover, exposure to 2.5 and 10 microM of examined metals did not influence body bend and thermotaxis to cultivation temperature, whereas exposure to 50 microM of examined metals caused significant reduction of body bend and thermotaxis to cultivation temperature. Furthermore, Pb and Hg were the more toxic among the examined metals, with severe toxicity on associative learning behavior, thermotaxis, and locomotion behavior in nematodes.