A continuous and automated method for the analysis of food intake behaviour

Abstract

C. elegans has become a promising model to study food-associated diseases and behaviors, and food intake regulatory mechanisms. Food intake depends on two motions: the cycle contraction of pharynx (pumping) and the isthmus peristalsis. These feeding motions can be modulated by the worm's internal state and environmental cues. Feeding rate is proportional to the worm pharyngeal pumping, easily observed under a stereoscope. Direct quantification of pumps per minute has been widely used for studying food intake and its underlying modulation. Alternatively, food intake can be measured indirectly using fluorescent bacteria. However, these methods are short-term, time-consuming and unsuitable for independent measurements of high numbers of animals. Automated and long-term methods to study food intake are desirable. Although some particular devices and long-term methods based on food clearance assays have been reported, they fail in the automated and/or continuous aspects. Here we describe a method for the analysis and continuous monitoring of worm feeding in 96-well plates. This method is based on a bioluminescence assay that we previously described for measurement of developmental timing in C. elegans. We measure bioluminescence in reporter strains that constitutively and ubiquitously express luciferase. The substrate of the reaction, luciferin, is added in the food, and bioluminescence signal from individual animals reports worm differential behaviors in food intake. We hypothesize that differential food intake phenotypes, among mutants and during ageing, may be proven as differences in bioluminescence signal patterns. To validate our system we have monitored bioluminescence in eat-2 mutants. EAT-2 functions post-synaptically in pharyngeal muscle, regulating the rate of pharyngeal pumping. We observe that the bioluminescence signal is reduced in eat-2 mutants. To further validate this method, other mutants and conditions are under study. We will present evidence for the suitability of our method to monitor food intake and dissect underlying regulatory mechanisms.