嗅覺密碼可以分為型態構造上和生理功能上兩大部分。在果蠅嗅覺神經網路定位上發現在第一級到第三級嗅覺神經都保存著很大的一致性。而其中投射神經(projection neuron)軸突末梢在側號角(lateral horn)更具有明顯的分佈模式(stereotype)，而這個區域推測其主要功能是辨識不同的氣味。不過此投射神經軸突在蕈狀體(mushroom body)內分佈卻具備較大的彈性和歧異性。後續在功能影像(functional image)的研究發現在觸角突(antennal lobe)和蕈狀體皆具有一致的嗅覺誘導圖譜(odor evoke map)，推測投射神經軸突末梢在蕈狀體也應具有固定的分佈模式。在本實驗我們將重點放在蕈狀體杯狀構造中的嗅覺密碼，我們使用flip-out和MARCM技術產生單一投射神經的3D立體影像，另外再加以DiD染色使我們能辨識蕈狀體杯狀構造中四個樹突區域(dendritic field)，最後計算每個單一投射神經軸突末梢其bouton在杯狀構造四個區域的分佈模式。我們發現投射神經在杯狀構造中比以往僅觀察神經網路圖譜具有更大的一致性和更固定的分佈模式。如果我們大量去統計每個嗅球(glomerulus)延伸出來的投射神經我們就有機會解開構造上的嗅覺密碼。在本實驗中我們發現有一群特定從DL4嗅球延伸出來的投射神經，其軸突末端皆延伸到蕈狀體和側號角以外的區域，而且具有很高的比例在蕈狀體杯狀構造中的四摺疊區域(four-fold domain)中形成bouton。我們推測這群特定的投射神經具備和其他投射神經不同的功能並且扮演重要的角色。

The coding of the olfaction is separated into anatomical and physiological parts. Mapping olfactory circuits in Drosophila found highly conservation from first-order to third-order neurons. Projection neurons have striking stereotype axon branching in the lateral horn, which is indicated for recognition of smell. However the axon patterns in the mushroom body which is functioned in learning and memory seems to be more variable and plastic. Further studies of functional images in the calyx reveals a stereotype order evoked map, indicate the axon pattern of projection neuron has a stereotype connection to the calyx. Here we focus on the olfactory code in mushroom body calyx, using MARCM and flip-out technique to generate single projection neuron pattern, and DiD counterstaing to identify four dendritic fields in the calyx, with a quantitative analysis of bouton distribution from each single projection neuron. After the quantification of bouton numbers in each dendritic field, it shows more stereotypy than the branching pattern along. We can generate an olfactory code in anatomy by a large scale of screening of all the patterns from each glomerulus. We also found a subset of projection neurons from the DL4 glomerulus, has an axon pattern always project out of mushroom body and lateral horn, with a high ratio of a few number boutons in four fold domain. Our results suggest projection neuron from DL4 has distinct but important function different from other projection neurons.

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