Description

In Caenorhabditis elegans, serotonin (5-HT) activates and controls pharyngeal pumping in response to food (Horvitz et al., 1982; Sze et al., 2000; Song and Avery 2012).  Tryptophan hydroxylase, the enzyme required for serotonin biosynthesis, is encoded by the gene tph-1.  Worms with a tph-1 deletion mutation exhibit phenotypes associated with a lack of serotonin-signaling, including reduced pharyngeal pumping (Sze et al., 2000; Avery and Horvitz 1990; Song and Avery 2012). We used a microfluidic electropharyngeogram (EPG) recording platform (NemaMetrix) and associated software (NemAnalysis) to measure pharyngeal pumping in C. elegans tph-1 mutants in the presence of bacterial food (100 mg/ml E. coli OP50 in M9 buffer), following a 2-hr fasting period. Prior research has shown that a fasting period (e.g., 2-4-hr) induces elevated feeding rates for worms upon re-introduction to bacterial food (Lemieux and Ashrafi 2015). We chose to measure pharyngeal pumping during this elevated feeding phase due to our hypothesis that tph-1 animals would exhibit lower pumping rates than control worms.   Pumping was recorded for 2-minute durations over three independent trials (total N2 n = 90; tph-1 n = 92).  C. elegans tph-1 mutants exhibited significantly lower pharyngeal pumping rates than N2 control animals (A, N2 = 3.46 ± 0.19 Hz; tph-1 = 0.89 ± 0.10 Hz; mean ± SEM; *** p < 0.0001, 2-tailed students t-test).  Pumping frequency data were pooled in A; see B for a comparison of each experimental trial.