Pharyngeal Pumping in the Nematode C. elegans: Resolving Treatment Effects through Variability Assessment
Authors: Ortiz Brianna , Hincks Joshua , Vayndorf Elena , Taylor Barbara E. , Harris Michael B. 
Published: June 2021

In C. elegans, feeding is achieved through a well characterized behavior, pharyngeal pumping. This pumping is controlled by two pairs of pharyngeal motor neurons (MC and M3). Each pump cycle corresponds to the propagation of a single pharyngeal muscle action potential, initiated by MC and terminated by M3. Age‐related changes in tissue morphology and function, and a decline in C. elegans health are correlated with reduced rates of pharyngeal pumping. As such, pharyngeal pumping frequencies have been used to exemplify health‐ and age‐related decline in this model organism. Traditionally pharyngeal pumping has been assessed by eye, and reported as a pump rate, which is computed from the number of pumps observed divided by total recording time. Although rhythmic, pharyngeal pumping is both variable and periodic, traditionally pharyngeal pumping rate assessment does not consider underlying variability of pumping behavior. We have found that between‐subject variation in pumping frequency, and the relative coarseness of measures of occurrence frequency, interfere with the resolution of what could be subtle treatment effects between groups. The recently developed NemaMetrix ScreenChip system resolves individual pumping events by recording an electrical signature resulting from large voltage transients produced by pharynx muscle action potentials, the electropharyngeogram (EPG). We aimed to assess patterns of variability in EPG measurements to test the hypothesis that underlying variability could be a relevant and insightful index of functional decline in this model organism. In a companion presentation, we describe the theory and practice of normalization and variability assessments in EPG recordings. In this study, we used these analyses strategies to evaluate treatments known to influence pharyngeal pumping. Pharyngeal pumping is stimulated by the presence of bacterial food (E. coli) and/or the endogenous neuromodulator of feeding behavior, serotonin (5HT). Dose‐dependent increases in pumping are well characterized in this system. We recorded EPG in N2 wild‐type subjects treated with a range of 5HT concentrations (0, 2, 5 and 10 mM). We resolved both a dose‐dependent influence on pump frequency and pump variability, and we were able to resolve more subtle treatment effects through assessments of variability. Patterns of variability suggested variation on motor neuron pacing. Pharyngeal pumping is initiated by the MC motor neurons activating a levamisole‐sensitive (nicotinic) EAT‐2‐containing pharyngeal acetylcholine receptor. We compared EPG recordings between N2 wild‐type and eat‐2 [BT1] mutant strains. Again, subject groups were separated by pump frequency and pump variability, with variability suggesting differences in neuro‐muscular fidelity. We are completing levamisole dose‐response experiments, and results will be discussed. We suggest it may be possible to resolve more subtle aspects of functional decline in the C. elegans model from assessments of EPG variability than are possible from pharyngeal pumping frequencies alone.Support or Funding InformationWork reported in this publication was supported by the National Heart Lung and Blood Institute and National Institute of General Medical Sciences of the National Institutes of Health under awards 1R15HL126105, 1SC2GM112570 and three linked awards number RL5GM118990, TL4GM118992 and 1UL1GM118991. The work is solely the responsibility of the authors and does not necessarily represent the official view of the National Institutes of Health or any other funding body.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.