OLFACTORY PROCESSING IN OVIPOSITION BEHAVIOR OF DROSOPHILA MELANOGASTER
Chin, Sonia G
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How does the brain make sense of complex mixtures of smells? An animal’s olfactory system is capable of detecting and distinguishing hundreds (perhaps thousands) of chemicals, and translating those inputs into useful behaviors. We study olfaction in the vinegar fly Drosophila melanogaster, an animal that uses its olfactory system to guide nearly all aspects of its life. The study of olfactory perception at its primary level of sensation is complicated by the possibility that monomolecular odorants typically activate many different olfactory receptors. This lack of a simple odorant-OSN match has made deciphering olfactory coding challenging. We have developed a novel chemogenetic approach to specifically activate genetically defined subsets of OSNs using a highly tuned odorant-receptor pair (geosmin and Or56a). Using this tool, we systematically tested how the individual activations of 23 of the fly’s 62 OSN types each contribute to egg laying, an ethologically important behavior for flies. We found that in six of the 23 cases, flies perceived OSN activation as a negative oviposition cue. Previous studies have demonstrated that the lateral horn, a higher order olfactory brain region innervated by secondary projection neurons (PNs), seems to sort information into two categories: food and pheromone. Examining the morphology of the PNs that synaptically partner with each class of negative oviposition OSNs revealed the novel finding that female fly brains use segments of, rather than whole, PNs to encode a negative oviposition domain in the lateral horn.