Date of Award
Doctor of Philosophy (PhD)
The Drosophila larva offers a powerful model system to investigate the general principles by which the olfactory system processes behaviorally relevant sensory stimuli. The numerically reduced larval olfactory system relieves the formidable molecular and cellular complexity found in other organisms. This thesis presents a study in four parts that investigates molecular and neuronal mechanisms of larval odor coding. First, the larval odorant receptor (OR) repertoire was characterized. ORs define the olfactory receptive range of an animal. Each of the 21 larval olfactory sensory neurons (OSNs) expresses one or rarely two ORs, along with the highly conserved olfactory co-receptor Or83b. Second, odor response profiles of 11 larval OSNs were characterized by calcium imaging. A subset of larval neurons showed overlapping responses to the set of odorants tested, while other neurons showed either very narrow or very broad tuning. Third, the olfactory circuit for ethyl butyrate was investigated in detail. Three OSNs, expressing Or35a, Or42a and Or42b, responded with different sensitivity to ethyl butyrate. Second order projection neurons synapsing with each of these OSNs showed similar concentration tuning, but inhibitory interneurons showed high response thresholds and were only activated at high odor concentrations. We correlated these concentration-dependent response properties with larval chemotaxis behavior. Fourth, the relevance of olfaction to animals was investigated in competitive rearing experiments. Or83b mutants experienced a selective disadvantage when they had to forage for limiting food sources, particularly when competing against larvae with normal olfactory function. Thus, odor coding is achieved both by peripheral tuning and central circuit modulation.
Asahina, Kenta, "Cracking the Odor Code: Molecular and Cellular Deconstruction of the Olfactory Circuit of Drosophila Larvae" (2008). Student Theses and Dissertations. 196.