Abstract
In Drosophila melanogaster, olfactory projection neurons (PNs) deliver odor information from antennal lobe (AL) to two higher brain centers: mushroom body(MB) and lateral horn (LH). Numerous evidences implicate key roles of the MB and its downstream circuits in olfactory learning and memory,but little is known about the roles of the LH. Here, I characterized more than 100 GAL4 lines containing LH related neurons and constructed a comprehensive connectivity map for predicting odor information flow. Based on morphology and polarity of individual neurons, I classified LH neurons into 2 classes, 7 families and 22 types. Immunohistochemical labeling of 22 types of LH neurons showed that only 5 types were GABAergic: LHD/V-LN1, LHD/V-LN2, LHD-PN4, LHD-PN5 and MB-C5 neurons. I focused on studying LH-PNCalyx neurons (four types: MB-C4 to -C7) connecting between LH and MB calyx. To understand innate function, I activated each neuron with optogenetics. and found that activation of MB-C4 and MB-C7, but not MB-C5 and MB-C6, triggered attraction behavior. Furthermore, using GFP reconstitution across synaptic partners (GRASP) labeling, I showed that MB-C4 neurons connected with AL-PN and LH local neurons at the LH and with AL-PN and MB neurons at the calyx. In conclusion, I constructed a map of LH circuits and showed that innate olfactory attraction may involve MB-C4 neurons.