Odor guided behavior and its modulation in the fruit fly Drosophila melanogaster
Geosmin is produced by a group of microbes, is highly aversive to Drosophila. We furthermore showed that Drosophila has one type of sensory neurons expressing an odorant receptor (OR 56a) that is extremely sensitive and fully dedicated to detect this compound. The Geosmin detection System is conserved across the genus Drosophila. Exploiting aversivespecific circuits could be an efficient method for manipulating disease vectors as well as agricultural pests. Next I showed that flies exhibit increased attraction to ethyl acetate, to another food odor, even to a repellent and pheromone after starvation. All odors evoked stronger physiological responses in starved flies with the effects being most pronounced at low odor concentrations. I investigated, which molecular players could be involved in such modulation. Conducting RNAi knockdown experiments with some the identified genes coupled with a quantitative olfactory assay to identify regulators of such modulation. Only silencing the CCHamide1 receptor resulted in an abolished starvation effect, suggesting a major role in starvation-induced modulation. This study shows that the fly’s antennal olfactory sensing neurons (OSNs) seem to be constantly tuned to current needs. There are Inhibitory projection neurons (iPNs) target the LH exclusively and bypass the Mushroom body (MBc). By using a specific driver line (MZ699) we were able to investigate the impact of this inhibitory pathway on olfactory processing within the LH. We performed calcium imaging experiments and found three domains with different highly stereotypic response patterns in lateral horn (LH). The posterior medial domain (LH PM domain) was strongly activated by innately attractive odorants, while the anterior lateral domain was mainly activated by repellent odorants. The third anterior medial domain (LH AM domain) was valence independent and mainly coded for odorant intensity. Do these iPNS decode odor features and govern decision making? By selectively silencing iPNs (via interrupting GABA synthesis) we were able to reduce the flies’ attraction to almost all attractive odorants.