Individual glomeruli mediate innate olfactory attraction and aversion in Drosophila

Abstract: In the Drosophila olfactory system, as in many other organisms, different odorants activate specific patterns of glomeruli, but the mechanisms by which these patterns are transformed and eventually read out to lead to behavior remain unknown. One outstanding question is the degree to which the responses of the second order projection neurons are derived from direct receptor input, as opposed to interneurons that receive input from multiple glomeruli. Using mutants for two receptors in conjunction with PN imaging, we found that the cognate receptor neurons are the main driver of PN responses. To address the question of how glomerular patterns elicit behavior, we used genetic tools to dissect the contribution of each glomerulus that is activated by the food odorant apple cider vinegar. This odorant triggers robust innate attraction at a low concentration, which activates six glomeruli. We found that two of these glomeruli were necessary and sufficient for this behavior. At a higher concentration, apple cider vinegar becomes markedly less attractive. We found that one glomerulus, which is activated by the higher concentration, was responsible for the switch in behavior. These results show that innate attraction and repulsion to a food odorant is mediated by individual glomeruli rather than the combination of activated glomeruli