Department of Integrative Biology and Physiology, Howard Hughes Medical Institute, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Curr Biol. 2013 Feb 18;23(4):301-6. doi: 10.1016/j.cub.2012.12.038. Epub 2013 Jan 24.
Carbon dioxide (CO(2)) elicits an attractive host-seeking response from mosquitos yet is innately aversive to Drosophila melanogaster despite being a plentiful byproduct of attractive fermenting food sources. Prior studies used walking flies exclusively, yet adults track distant food sources on the wing. Here we show that a fly tethered within a magnetic field allowing free rotation about the yaw axis actively seeks a narrow CO(2) plume during flight. Genetic disruption of the canonical CO(2)-sensing olfactory neurons does not alter in-flight attraction to CO(2); however, antennal ablation and genetic disruption of the Ir64a acid sensor do. Surprisingly, mutation of the obligate olfactory coreceptor (Orco) does not abolish CO(2) aversion during walking yet eliminates CO(2) tracking in flight. The biogenic amine octopamine regulates critical physiological processes during flight, and blocking synaptic output from octopamine neurons inverts the valence assigned to CO(2) and elicits an aversive response in flight. Combined, our results suggest that a novel Orco-mediated olfactory pathway that gains sensitivity to CO(2) in flight via changes in octopamine levels, along with Ir64a, quickly switches the valence of a key environmental stimulus in a behavioral-state-dependent manner.
二氧化碳（CO2）能引起蚊子的吸引力反应，但对黑腹果蝇来说，尽管它是有吸引力的发酵食物来源的大量副产品，但天生是厌恶的。先前的研究仅使用行走的苍蝇，但成年苍蝇在飞行中跟踪遥远的食物源。在这里，我们展示了在磁场中系绳的苍蝇可以在飞行中自由绕偏航轴旋转，主动寻找狭窄的 CO2羽流。经典 CO2 感应嗅觉神经元的遗传破坏不会改变飞行中的 CO2 吸引力;然而，触角消融和 Ir64a 酸传感器的遗传破坏确实如此。令人惊讶的是，必需嗅觉核心受体（Orco）的突变在行走时不会消除 CO2 厌恶，但会消除飞行中的 CO2 跟踪。生物胺章鱼胺在飞行中调节关键的生理过程，阻断章鱼胺神经元的突触输出会改变 CO2 的效价，并在飞行中引起厌恶反应。总之，我们的研究结果表明，一种新的 Orco 介导的嗅觉途径，通过改变章鱼胺水平，在飞行中对 CO2 产生敏感性，再加上 Ir64a，以行为状态依赖的方式快速切换关键环境刺激的效价。
