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不同氣味劑分子已知能夠同時激發幾個不同類別的嗅覺神經元，說明存在一個組合編碼。 通過進行一項新的行為測定，并用最先進的方法對果蠅的特定神經元進行基因控制，Julia Semmelhack和 Jing Wang發現，低濃度引誘劑的吸引力完全依賴于一兩個神經元中心或嗅小球。他們所采用的引誘劑為蘋果醋，用來指示果蠅喜歡的食物源——腐爛的水果。在低濃度時，蘋果醋觸發了6個嗅小球，并對果蠅有一種強烈的自然吸引力。當6個嗅小球中的2個（DMA1 和 VA2）通過基因手段“關掉”時，吸引力被大大減小。嗅覺的一個共同特征是，大多數氣味隨著其強度增加會變得不太適宜，最終會變得討嫌。 這項研究揭示了該現象在神經元層面上的一個可能的基礎，因為較高濃度的蘋果醋會激發更多的嗅小球，因而其吸引力會減小。 薦原始出處： Nature 459, 218-223 (14 May 2009) | doi:10.1038/nature07983 Select Drosophila glomeruli mediate innate olfactory attraction and aversion Julia L. Semmelhack1 & Jing W. Wang1 1 Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093, USA Fruitflies show robust attraction to food odours, which usually excite several glomeruli. To understand how the representation of such odours leads to behaviour, we used genetic tools to dissect the contribution of each activated glomerulus. Apple cider vinegar triggers robust innate attraction at a relatively low concentration, which activates six glomeruli. By silencing individual glomeruli, here we show that the absence of activity in two glomeruli, DM1 and VA2, markedly reduces attraction. Conversely, when each of these two glomeruli was selectively activated, flies showed as robust an attraction to vinegar as wild-type flies. Notably, a higher concentration of vinegar excites an additional glomerulus and is less attractive to flies. We show that activation of the extra glomerulus is necessary and sufficient to mediate the behavioural switch. Together, these results indicate that individual glomeruli, rather than the entire pattern of active glomeruli, mediate innate behavioural output. (責任編輯：Doctor001) |
