C. elegans Responds to Chemical Repellents by Integrating Sensory Inputs from the Head and the Tail

Abstract

The phasmids are bilateral sensory organs located in the tail of Caenorhabditis elegans and other nematodes. The similar structures of the phasmids and the amphid chemosensory organs in the head have long suggested a chemosensory function for the phasmids. However, the PHA and PHB phasmid neurons are not required for chemotaxis or for dauer formation, and no direct proof of a chemosensory function of the phasmids has been obtained. C. elegans avoids toxic chemicals by reversing its movement, and this behavior is mediated by sensory neurons of the amphid, particularly, the ASH neurons. Here we show that the PHA and PHB phasmid neurons function as chemosensory cells that negatively modulate reversals to repellents. The antagonistic activity of head and tail sensory neurons is integrated to generate appropriate escape behaviors: detection of a repellent by head neurons mediates reversals, which are suppressed by antagonistic inputs from tail neurons. Our results suggest that C. elegans senses repellents by defining a head-to-tail spatial map of the chemical environment.

Ultraviolet-A triggers photoaging in model nematode Caenorhabditis elegans in a DAF-16 dependent pathway

“…When the worms exposed to UV-A, this network system have partially damaged as the time of exposure increased. This was attributed to the depletion of the activity of ASH neurons (Sambongi et al 1999) or the increased activity of PHA and PHB phasmid neurons (Hilliard et al 2002). The osmosensation assay results also suggest the damage in neural network, since it is also chiefly mediated by ASH neurons (Srinivasan et al 2008).…”

“…Hilliard et al (2002) stated that sensation of a repellent placed on the tail region of the worm and subsequent reversal be mediated by a head-to-tail spatial map. When the worms exposed to UV-A, this network system have partially damaged as the time of exposure increased.…”

“…Drop assay was performed with a method developed by Hilliard et al (2002) with some modifications. Briefly, worms after exposure to UV-A for 2, 4, or 6 h were allowed to crawl on unseeded NGM plates.…”

Generation and modulation of chemosensory behaviors in C. elegans

“…Ablation of the ASE neurons reduces but does not completely abolish the ability of worms to chemotax towards a point source of aqueous attractants including NaCl, while perturbation of ASE function, together with ADF, ASG, and ASI results in a more complete defect [72] (Table 1). Intriguingly, it has been shown that in ASE-ablated animals, the ability to respond to decreases in salt concentration is abolished, [104] whereas animals continue to respond to concentration increases, perhaps via the ADF, ASG, and ASI neurons [77]. It will be interesting to determine whether the ability to respond to positive or negative changes in concentration is segregated to different chemosensory neurons, to the left/right members of a neuron pair, or is a property of downstream components of the chemosensory circuit.…”

“…To date, no specific chemosensory functions have been assigned to the inner labial chemosensory neurons. However, the PHA and PHB phasmid chemosensory neurons may sense chemical repellents and antagonize ASH-mediated avoidance behaviors [104] (Table 1).…”