C. elegans will orient and travel in a straight uninterrupted path directly towards the negative pole of a DC electric field, a behavior referred to as electrotaxis1. Additionally, animals widen their approach angles proportionally to increasing field strength2. To elucidate the neural basis for this behavior, we examined populations of animals in a uniform field that is fixed in direction and magnitude. We have determined that C. elegans navigate in order to remain within a specific range of field strengths, which is the reason for the changes in their approach angles towards the negative pole.
eat-4 mutants are severely electrotaxis defective and addition of the wild-type
eat-4 gene in AWC neurons recovers the behavior. The pair of AWC neurons are functionally asymmetric in regard to chemotaxis and have been shown to express different genes. In particular, one of the AWC neurons expresses STR-2, a G-protein coupled receptor, and is referred to as AWCON. To test the role of the AWC neurons in electrotaxis behavior we examined the following mutant animals:
ceh-36, which are defective in the terminal differentiation of the AWC neurons,
inx-19, which have two AWCOFF/OFF neurons, and
nsy-1, which have two AWCON/ON neurons. We found that only
nsy-1 mutant animals are able to sense field gradients, suggesting AWCON is required for electrotaxis behavior. Although STR-2 is expressed only in AWCON,
str-2 mutants exhibit wild-type behavior indicating STR-2 is not an electroreceptor. Here, we demonstrated that AWCON functions as an electrosensory neuron allowing animals to sense and adjust approach trajectories angles to match the preferred field strength.Sukul NC, Croll NA. 1978. Influence of Potential Difference and Current on the Electrotaxis of Caenorhabditis elegans. J Nematol 10:314-317.</LI> Gabel CV, Gabel H, Pavlichin D, Kao A, Clark DA, Samuel AD. 2007. Neural circuits mediate electrosensory behavior in Caenorhabditis elegans. J Neurosci 27:7586-7596.</LI></OL>.