Dynamics of Neural Activity During Chemotaxis in Caenorhabditis Elegans

Abstract

The nervous system of an animal must control and coordinate locomotion in a changing and often unpredictable environment in order to survive. When a Caenorhabditis elegans navigates its environment, the nervous system can modulate the animal’s behaviors to locate and track chemoattractive gradients to find food. Even though the physical wiring diagram of the nervous system of C. elegans was completed 25 years ago, it provides little information as to how interneurons integrate signals to produce complex behavior. Which neurons and what dynamics of activity patterns are important in controlling chemotaxis. Working with Dr. Askin Kocabas and Dr. Zengcai Guo, we used optogenetics and new optical tools to perturb neural activity directly in freely moving animals to evoke chemotactic behavior. We discovered that controlling the activity in just one pair of interneurons (AIY) is sufficient to manipulate the animal to locate, turn towards and track a virtual light gradient. Since AIY interneurons are post-synaptic to most chemosensory neurons, the activity patterns in AIY might be important for signal processing and coordinating locomotion during chemotaxis. Working with Jeffrey Lee, Dr. Askin Kocabas and Abdullah Yonar, we next investigated how AIY communicates environmental information with its downstream neurons AIZ, RIA, and RIM to control behavior. Using a calcium imaging system built in the laboratory, we found that all of them respond to bacterial odor. Optogenetic stimulation results suggested that AIZ and RIA control gradual turning and RIM controls reversal. Combining the knowledge from the literature, we proposed a possible functional connection network among neurons important for sensing chemoattractive odor. Although C. elegans only has 302 neurons, we still do not understand how neurons transmit signals nor what role certain neurons have in controlling behavior. The results presented here shed light on the dynamics of the neural activity underlying chemotaxis, and can guide approaches in further research of neural circuits in C. elegans and other organisms.