Experience-dependent plasticity of a highly specific olfactory circuit in Drosophila melanogaster

Drosophila melanogaster encounters a variety of odor cues signaling potentially harmful threats through-out its life, which are detected by highly specialized olfactory circuits enabling the animal to avoid them. We studied whether such crucial neuronal pathways are hard-wired or can be modulated by experience. Using long-term exposure to high concentrations of geosmin, an indicator of potentially lethal microorganisms, we demonstrate at the single-cell level that the underlying neuronal circuitry undergoes structural changes in the antennal lobe, while higher brain centers remain unaffected. In particular, second-order neurons show neurite extensions and synaptic remodeling after the exposure period, whereas olfactory sensory neurons and glia cells remain unaffected. Flies that were exposed to geosmin tolerate this innately aversive odorant in general choice and oviposition assays. We show that even a highly specific olfactory circuit is plastic and adaptable to environmental changes.