Analysis of the sensory responses of parasitic nematodes using electrophysiology

Use of the electrophysiological technique to examine the sensory perception of live, intact nematodes has provided detailed analysis of responses to known concentrations of test chemicals. The use of larger nematodes, such as the animal-parasite Syngamus trachea, enabled direct extracellular recordings from individual sensilla; with smaller nematodes, the recording electrode was inserted close to the cephalic region. Extracellular recordings from the cephalic region of second-stage juveniles and males of the potato cyst nematodes, Globodera rostochiensis and Globodera pallida, were obtained after exposure to a variety of semiochemicals, including sex pheromones and certain putative phagostimulatory compounds. The responses of adult females of the animal-parasitic nematode, Brugia pahangi, to some possible host cues, and the inhibition by ivermectin of the response to a known allelochemical were investigated. Exposure to acetylcholine was used to compare the concentration-dependent responses of second-stage juveniles of G. rostochiensis and adult females of B. pahangi and the insect-parasitic nematode Leidynema appendiculata. Use of a perfusion system enabled sequential exposure of individual nematodes to different test chemicals or to different concentrations of the same chemical. Incubating second-stage juveniles of G. rostochiensis for 24 h in a mAb showing specificity to amphidial secretions resulted in blocking of the normal response to host root diffusates. The potential of the electrophysiology technique for analysing perturbation of sensory perception is discussed.