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Shen, Ching-Han

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Shen

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Ching-Han

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Shen, Ching-Han
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    Controlling Interneuron Activity in Caenorhabditis Elegans to Evoke Chemotactic Behaviour
    (Nature Publishing Group, 2012) Kocabas, Askin; Shen, Ching-Han; Guo, Zengcai V.; Ramanathan, Sharad
    Animals locate and track chemoattractive gradients in the environment to find food. With its small nervous system, Caenorhabditis elegans is a good model system in which to understand how the dynamics of neural activity control this search behaviour. Extensive work on the nematode has identified the neurons that are necessary for the different locomotory behaviours underlying chemotaxis through the use of laser ablation, activity recording in immobilized animals and the study of mutants. However, we do not know the neural activity patterns in C. elegans that are sufficient to control its complex chemotactic behaviour. To understand how the activity in its interneurons coordinate different motor programs to lead the animal to food, here we used optogenetics and new optical tools to manipulate neural activity directly in freely moving animals to evoke chemotactic behaviour. By deducing the classes of activity patterns triggered during chemotaxis and exciting individual neurons with these patterns, we identified interneurons that control the essential locomotory programs for this behaviour. Notably, we discovered that controlling the dynamics of activity in just one interneuron pair (AIY) was sufficient to force the animal to locate, turn towards and track virtual light gradients. Two distinct activity patterns triggered in AIY as the animal moved through the gradient controlled reversals and gradual turns to drive chemotactic behaviour. Because AIY neurons are post-synaptic to most chemosensory and thermosensory neurons, it is probable that these activity patterns in AIY have an important role in controlling and coordinating different taxis behaviours of the animal.
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    Dynamics of Neural Activity During Chemotaxis in Caenorhabditis Elegans
    (2015-09-28) Shen, Ching-Han; Lichtman, Jeffrey; Engert, Florian; Schier, Alex
    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.