Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology Jena, Germany.
Front Physiol. 2014 Feb 20;5:59. doi: 10.3389/fphys.2014.00059. eCollection 2014.
Odor information is predominantly perceived as complex odor blends. For Drosophila melanogaster one of the most attractive blends is emitted by an over-ripe banana. To analyze how the fly's olfactory system processes natural blends we combined the experimental advantages of gas chromatography and functional imaging (GC-I). In this way, natural banana compounds were presented successively to the fly antenna in close to natural occurring concentrations. This technique allowed us to identify the active odor components, use these compounds as stimuli and measure odor-induced Ca(2+) signals in input and output neurons of the Drosophila antennal lobe (AL), the first olfactory neuropil. We demonstrate that mixture interactions of a natural blend are very rare and occur only at the AL output level resulting in a surprisingly linear blend representation. However, the information regarding single components is strongly modulated by the olfactory circuitry within the AL leading to a higher similarity between the representation of individual components and the banana blend. This observed modulation might tune the olfactory system in a way to distinctively categorize odor components and improve the detection of suitable food sources. Functional GC-I thus enables analysis of virtually any unknown natural odorant blend and its components in their relative occurring concentrations and allows characterization of neuronal responses of complete neural assemblies. This technique can be seen as a valuable complementary method to classical GC/electrophysiology techniques, and will be a highly useful tool in future investigations of insect-insect and insect-plant chemical interactions.
气味信息主要被感知为复杂的气味混合物。对于黑腹果蝇来说，最有吸引力的混合物之一是由过熟的香蕉散发出来的。为了分析果蝇的嗅觉系统如何处理天然混合物，我们将气相色谱和功能成像（GC-I）的实验优势结合起来。通过这种方式，将接近自然存在浓度的天然香蕉化合物连续呈现给果蝇的触角。这项技术使我们能够识别出活性气味成分，使用这些化合物作为刺激物，并测量果蝇触角叶（AL）中输入和输出神经元的气味诱导 Ca(2+)信号，AL 是第一个嗅觉神经节。我们证明，天然混合物的混合物相互作用非常罕见，仅在 AL 输出水平发生，导致混合物的表示非常线性。然而，关于单个成分的信息在 AL 内的嗅觉回路中被强烈调制，导致单个成分的表示与香蕉混合物之间的相似性更高。这种观察到的调制可能以一种独特的方式调整嗅觉系统，以区分气味成分，并提高对合适食物来源的检测。因此，功能 GC-I 可以分析实际上任何未知的天然气味混合物及其在相对出现浓度下的成分，并能够描述完整神经组合的神经元反应。这项技术可以被视为对经典 GC/电生理学技术的一种有价值的补充方法，并且在未来昆虫-昆虫和昆虫-植物化学相互作用的研究中将是一个非常有用的工具。
