Gustatory Behaviour in Caenorhabditis elegans

The nematode C. elegans is an ideal model-organism to study the genetics of behaviour (Brenner, 1974). It is capable of sensing salts and we discriminate three different responses: it is attracted to low salt concentrations (Ward, 1973; Dusenbery et al., 1974), it avoids high salt concentrations that give osmotic problems (Culotti & Russell, 1978), and the response to NaCl shows plasticity: normally attractive salt concentrations are avoided after pre-exposure to salt (Saeki et al., 2001; Jansen et al., 2002). The goal of this study was to unravel the molecular mechanisms and the cellular circuitry behind the different responses of C. elegans to NaCl. A candidate gene approach was used in which mutants for 123 genes were tested for their role in salt responses. A complete overview of all genes tested is given in the Chapter 5. We found 22 genes involved in attraction, 57 genes involved in avoidance and 87 genes involved in gustatory plasticity. Several of the most interesting results were followed up and are discussed in this thesis. In Chapter 1, a summary is given of what is known about the molecular mechanisms of taste, an introduction to C. elegans as a model organism, and a brief overview of the C. elegans nervous system and neurotransmission. Furthermore, various sensory behaviours of C. elegans and their plasticity are discussed. Chapter 2 focuses on chemotaxis to NaCl and discusses five newly identified genes, which function in two genetic pathways that mediate NaCl chemotaxis. Chapter 3 discusses the role of G protein signalling in gustatory plasticity and identifies multiple neurons as well as a genetic pathway involved in this process. Chapter 4 discusses the roles of different neurotransmitters in the different responses of C. elegans to NaCl. An overall discussion and summary are given in the final chapter. Taken together, this study provides new insights into the processes of NaCl chemotaxis and its plasticity in C. elegans. We expect that these insights can be extrapolated to mammals.

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