Abstract
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.