Abstract
The survival of all animals is critically dependent on their ability to detect and respond appropriately to environmental cues. It is particularly important for animals to integrate information such as internal state and contextual cues in order to generate flexible and adaptive behaviors. One of the most important sensory modalities is olfaction; animals rely on olfaction to locate food sources, avoid pathogens and predators, and communicate with each other. However, a given odorant can elicit attractive or repulsive responses depending on context, intensity, and experience. How odor valence is robustly but flexibly encoded in neural circuits remains to be fully explored. Using the small nematode Caenorhabditis elegans, I have characterized a context- and concentration-dependent olfactory plasticity paradigm to a subset of bacterial food-produced medium-chain alcohols such as 1-hexanol. Specifically, I show that the behavioral response of C. elegans to 1-hexanol is inverted from attraction to avoidance in the presence of saturating levels of a second attractive bacteria-produced chemical. I have found that, by engaging distinct intracellular signal transduction pathways, the single AWC sensory neuron pair can invert its odorant response sign and drive context-dependent changes in behavioral preference to an odorant. In addition, I have also described a push-pull opposing component circuit that drives concentration-dependent behavioral preference to hexanol. The results described in this dissertation suggest that sensory neurons can dynamically encode the hedonic valences of stimuli and that odor discrimination can take place at the level of sensory neurons.