The C.elegans Pharynx

Hi all,
I work with the C.elegans and am using it for Anthelminthic Assay. I work with a Stereomicroscope which has a maximum magnification of 4X. Under this magnification, it is difficult at times to detect the Pharyngeal pulsation. I have one doubt about the C.elegans Pharynx. Does it continuously pulsate even in the absence of the Bacterial feed? Or does it pulsate only in the presence of the Feed? Or does it pulsate because of the Body contractions and expansions while the worm moves? Can anybody in the community, come out with an explanation for this???

Hi KrittiK,

Before I give you an answer, please allow me to introduce several resources you can use to provide you with more immediate answers.

  1. - this is a great site from Dave Hall and colleagues that describe C. elegans anatomy. In addition, there are early but seminal worm publications, such as John White’s “The Mind of a Worm” in which the wiring diagram of the nervous system was described.
  2. - an online resource that is basically a review of C. elegans research and methods
  3. textpresso (can get there by clicking on Literature Search on Wormbase or on Leon Avery’s C. elegans WWW): this allows you to search through worm papers a sentence at a time.

I did a quick search in the pharynx section of WormAtlas and here will paste the relevant info for your question:
“The pharynx has intrinsic myogenic activity that is regulated by its nervous system. The nervous system, in turn, integrates internal signals such as the animal’s nutritional status and external signals such as the presence or absence of food (Avery and Horvitz, 1989; Franks et al., 2006). In the absence of food, the pharynx pumps approximately once every second, whereas in the presence of food the rate increases to about four pumps per second. Also, a well-fed worm suspended in liquid will pump only in the presence of bacteria, whereas a starved worm keeps pumping, albeit slowly and irregularly, in the absence of food and accelerates its pumping in the presence of lower amounts of bacteria compared to a well-fed worm (Avery et al., 1993). The pumping rate of the pharynx is also modulated by the somatic sensory system; for example, pumping is briefly inhibited upon sensing a light touch to the body (Chalfie et al., 1985; Avery and Thomas., 1997).”

We also have stereoscopes with a max zoom of 4x (+10x of eyepieces = 40x total). Pumping is visible, but I would imagine one with a higher zoom would work better. I believe people have also used an inverted microscope with a 20x lens to visualize worms on agar plates.