Neural Substrates of Experience in Caenorhabditis elegans Olfactory Learning

One essential function of the nervous system is to modulate behavioral response based on experience. In the past decades, increasing amount of studies has characterized the mechanisms underlying experience-dependent modulation of neural circuits. However, it is not entirely clear how the nervous system translates experience into a modulatory signal. The over-arching goal of my thesis work is to contribute to our understanding of this important neuroscience question. I address this question by using a form of aversive olfactory learning in Caenorhabditis elegans. While C. elegans feeds on bacteria, it is susceptible to infectious bacteria. Ingestion of these pathogens makes the animal ill and leads to a slow death over time. Previous work in my advisor’s laboratory has shown that C. elegans learns to avoid the smell of the infectious bacteria after ingestion and this experience-dependent olfactory plasticity depends on the serotonin signaling from a pair of serotonergic neurons called ADF and the serotonin signaling is upregulated by pathogen stress stimuli. ADF acts in a neuronal network to play an essential role in regulating the aversive olfactory learning. Because serotonin signal responds to a variety of environmental stresses in many animals, including mammals, I use the C. elegans aversive olfactory training as a model to characterize the molecular and cellular mechanisms underlying the regulation of serotonin signaling by aversive experience.