ABSTRACT

This chapter describes two main appetite control behaviors, hunger and satiety, in C. elegans and discusses the molecular mechanisms underlying them. The feeding organ of C. elegans is a pharynx, a neuromuscular tube responsible for sucking bacteria into the worm from outside, concentrating them, and grinding them up. Hunger is the internal state that results from a lack of nutrients and that motivates the behavioral response. Hungry animals seek food and are eager to eat when they encounter food. The best understood hunger signal in mammals is ghrelin, an endogenous ligand for growth hormone receptor. Kang and Avery showed that one of the downstream processes that the muscarinic signal initiates as a starvation response is autophagy. The opioid system has been observed in invertebrates; biochemical approaches such as immunocytochemistry and radioimmunoassay detected opioids in many invertebrate animals including planarians. Satiated animals stop eating, decrease exploratory behavior, and often fall asleep, a pattern called the "behavioral sequence of satiety".