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 17A degrees C, and then shifted to 20A degrees C condition. Based on the ability of nematodes to trace the temperature of 20A degrees C, exposure to 10 mu M of all examined metals and 2.5 mu M Pb and Hg caused significant decrease of associative learning behavior at time intervals of 5 and 18 h; however, exposure to 2.5 mu M Cu, Zn, and Ag did not influence associative learning behavior. Moreover, exposure to 2.5 and 10 mu M of examined metals did not influence body bend and thermotaxis to cultivation temperature, whereas exposure to 50 mu M 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.