Odorant-selective genes and neurons mediate olfaction in C. elegans

Generation and modulation of chemosensory behaviors in C. elegans

“…Fifth, to further emphasize the importance of avoiding noxious chemicals, the ability to sense noxious chemicals is largely segregated from the ability to respond to attractive chemicals at the level of the sensory neurons themselves (Table 1). Thus, the ASH, ADL, and AWB neurons mediate aversive behaviors more or less exclusively, whereas attraction is mediated by the remaining eight pairs of amphid chemosensory neurons [58, 65,71,72,[89][90][91]. This organization is similar to observations in the mammalian and Drosophila gustatory system, where sensory cells responding to sugars and other palatable compounds are segregated from those sensing bitter and hence, toxic compounds [92][93][94][95][96][97].…”

“…Chemotactic ability allows C. elegans to locate food sources or mates, and to avoid predators. In the laboratory, chemotaxis behaviors can be assayed simply by placing a single animal or populations of animals on an agar plate containing a point source of a chemical, and quantifying the number of animals at the source after a period of time [69][70][71][72]. Under these conditions, C. elegans exhibits robust chemotaxis behavior towards a wide range of chemicals at a range of concentrations.…”

“…First, similar to other olfactory systems, low concentrations of chemicals are sensed by smaller numbers of neurons than higher concentrations [83] (Table 1). Second, the same chemical may act as a repellent at one concentration, and as an attractant at a different concentration [70,71,[84][85][86]. Third, even at low concentrations, the ability to sense a particular chemical may be distributed among several neurons.…”

“…Thus, the left ASE neuron is the primary sensor of Na + ions, whereas the right ASE neuron responds to Cl − and K + [98] (Table 1). On the other hand, while both the left and right AWC neurons sense benzaldehyde, either the left or the right AWC neuron responds to the volatile odorant butanone, and the other neuron responds to 2,3-pentanedione [71,99] (Table 1). The advantages of assigning the sensory functions stochastically as in the AWC neurons [100], or via a developmentally hardwired mechanism as for the ASE neurons [101][102][103] is not immediately obvious.…”

“…In the background of a high constant concentration of one chemical, animals fail to respond to a point source of that chemical, but continue to respond to other chemicals sensed by that neuron type [71]. Similarly, prolonged exposure to one odorant decreases the response to that odorant while sparing responses to other chemicals sensed by that neuron [142,[145][146][147].…”