Microfluidic-based Tools and Methods for Complex Chemosensory-based Behavioral Studies in C. elegans

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Rouse, Tel Mitchel
Lu, Hang
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There is a great interest in studying behavior and the underlying biological basis for behaviors in small model organisms. Some properties of C. elegans that greatly facilitate genetic investigations are its small size, relatively simplistic ‘brain’, complex repertoire of behaviors, and ease of isogenic population studies. In order to take full advantage of these characteristics, it is desirable to have methods for analyzing behaviors of large populations of animals in well-controlled environments. One set of behaviors extensively used to investigate numerous phenomena in neurobiology within C. elegans deals with the navigation of chemical environments (chemotaxis). Studies based on C. elegans chemotaxis are used in investigating chemosensation, innate preferences, learning, memory, and more. We have improved upon previous microfluidic and computer-vision technologies to advance C. elegans chemosensation and chemotaxis studies to answer more sophisticated biological questions. One developed method is a microfluidic device capable of monitoring animal neuronal activity in vivo while delivering multiple chemical stimuli to animals at sub-second speeds in any desired order without cross-contamination. This method facilitates investigations as to how complex environmental stimulus changes are encoded within a simple, well-characterized nervous system at relevant behavioral timescales. The second developed method is a microfluidic platform and accompanying software capable of tracking a population of C. elegans freely navigating well-controlled, spatial chemical environments over long timescales. Via this method, complete behavioral and stimulus experience history profiles can be generated for each animal within a population. This enables correlations to be made between acute chemotaxis behaviors and animal stimulus histories and provides additional insight as to how a series of acute chemotaxis behaviors results in long-term preference choices. We demonstrate the power and utility of the hardware and software developed for chemosensory-based behavioral studies by investigating starvation associative learning in C. elegans. Within our developed platform, we recapitulated wild-type (WT) learning phenotypes, recapitulated a previously known learning-defective phenotype of the insulin/IGF-1 signaling (IIS) pathway mutant, ins-1, and then utilized behavioral analyses and developed platform capabilities to test multiple hypotheses to explain the observed phenotypic differences between WT and ins-1. The developed capabilities and findings in this work should facilitate further elucidation of the role of INS-1 in the regulation of starvation plasticity. Taken together, the developed technologies in this thesis will allow for more powerful and sophisticated experiments for investigating chemosensory-based phenomena in neurobiology.
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