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Title: Role of the SAA and SMB neurons in locomotion in the nematode Caenorhabditis elegans, with a focus on steering
Author: Kalogeropoulou, Elpiniki
ISNI:       0000 0004 7233 7315
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2018
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The nematode C. elegans can orient itself towards sensory cues. Two mechanisms of orientation have been observed in the worm; pirouettes and steering. Past studies have identified a number of neurons that contribute to either orientation strategy. Here I investigate the role of the motor neuron SMB and the interneuron SAA in locomotion, with a focus on steering. SMB motor neurons have been postulated to be part of the steering circuit. SAA interneurons, which are close to and highly synaptically connected with the SMB motor neurons, have not been previously explored. Here, for the first time, the function of SAA in locomotion is investigated. I report the generation of integrated transgenic lines where the SMB neuron and/or the SAA neuron are genetically ablated. A two-component ablation system was used to genetically ablate the neurons by targeted expression of a reconstituted caspase specifically in these neurons. Imaging confirmed targeted ablation. The SMB- and SAA- ablated strains demonstrate similar phenotypes different to those of the wild type in both probabilistic and deterministic locomotion. The phenotypes suggest that SMB and SAA suppress pirouettes, while also facilitating steering, and regulate the amplitude of sinusoidal movement and omega turns. Double ablation mutants revealed that these two neurons are integral to steering, but are not the sole head neurons regulating the amplitude of undulatory movement. Dorsal asymmetric ablation strains revealed differing contributions of SMB and SAA to each orientation strategy. The expression of the trp-1, trp-2 and trp-4 genes encoding known stretch receptors suggests that these neurons might also have a proprioceptive function. Calcium imaging on the SMB neurons revealed increased activity of these neurons after the onset of omega turns. Using these results I proposed a new neural network model that integrates both orientation strategies, and a testable model for head movement.
Supervisor: Cohen, Netta ; Hope, Ian Sponsor: EPSRC
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available