Picower Institute for Learning and Memory
Department of Brain & Cognitive Sciences
Massachusetts Institute of Technology
Host: Martin Chalfie
Title: Serotonergic Circuits that Control Persistent Behavioral States in C. elegans
Abstract: All animals must respond to the ingestion of food by generating adaptive behavioral responses. Previous studies have suggested a central role for neuromodulation in the regulation of feeding behaviors, but the causal links between food ingestion, neuromodulator release, neural circuit dynamics, and behavioral changes remain poorly characterized.
Using the simple nervous system of C. elegans, we examine how food ingestion engages neuromodulatory systems to drive changes in neural circuit dynamics and adaptive foraging behaviors. In our studies, we found that a serotonergic cell type, called NSM, directly detects the bacterial contents of the alimentary canal to signal an animal’s feeding state. We identified conserved ASIC family ion channels that mediate NSM’s sensory detection of bacteria in the alimentary canal, suggesting a new function for these conserved channels. Serotonin release by NSM drives stable dwelling states, in which animals exhibit slow locomotion while they feed. We performed large-scale calcium imaging in freely-moving animals and examined how the serotonergic system interacts with other neuromodulatory systems so that animals can switch between stable dwelling and roaming states while they forage for food. We found that the neurons that produce the neuromodulators serotonin and pigment dispersing factor (PDF) neuropeptide, which promote dwelling and roaming respectively, are reciprocally connected to the same sensorimotor network. This network displays winner-take-all dynamics that correspond to the stable dwelling and roaming states. Genetic studies showed that neuromodulator release promotes the stability and exclusivity of the network states that underlie roaming and dwelling. Cellular perturbations revealed that interactions between the sensorimotor and neuromodulatory circuits allow dynamic changes in food odors to drive behavioral state transitions in complex foraging environments.
These studies are yielding new mechanistic insights into how food ingestion alters large-scale neural activity patterns that underlie adaptive foraging decisions.