Abstract
The nervous system of the nematode Caenorhabditis elegans is comprised of 302 neurons. Although the structure of the nervous system is quite different from that of vertebrates or insects, many evolutionally conserved molecules are used in the neural circuits. C. elegans use chemosensation to survive in a continuously changing environment. They migrate to comfortable places by smelling for bacterial food and approaching the source of the smell. They also sense noxious stimuli, such as toxic chemicals and mechanical stimuli, and avoid them. Some of the chemotaxis responses are altered by prior chemical exposure in a given context (i. e., high population density, bacterial infection, and food status). Sugar derivatives termed ascarosides are continuously secreted from C. elegans and used as mediators of population density information in the plasticity of chemotaxis response. Evolutionally conserved molecules, such as components of insulin and monoamine signaling pathways, function in neural circuits to regulate chemotaxis plasticities.
C. elegans has been used as a useful model animal not only in molecular genetics studies but also in physiological studies using live imaging of neurons. In this review, I introduce the overall structure of the nervous system and regulatory mechanisms of neural circuits and molecular pathways in chemical sensation and information processing to generate an appropriate sensory response.
