Plate Assay to Determine Caenorhabditis elegans Response to Water Soluble and Volatile Chemicals

The nematode Caenorhabditis elegans is widely used for behavioral studies ranging from simple chemosensation to associative learning and memory. It is vital for such studies to determine optimal concentrations of attractive and aversive chemicals that C. elegans can sense. Here we describe a resource localization assay in which a chemical compound of interest is placed in two compartments of a quadrant plate in order to determine optimal concentrations of the chemical in behavioral studies. Using the assay, we determined the optimal concentration of a water-soluble attractant, KCl, as an unconditioned stimulus for the study of associative learning and memory. In this protocol, we also describe a chemotaxis assay using a square agar plate spotted with an aversive olfactory cue, 1-nonanol, as a conditioned stimulus.