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Synaptic circuits of the fly's medulla

Tracing visual pathways from the fly's compound eye has been blocked for decades by the complexity of the second neuropile, the medulla. Extending our previous work on the synaptic circuits in the first neuropile, the lamina, we are now using serial-section EM of the medulla to reconstruct the synaptic circuits of the medulla.

Working from long series of sections cut by Zhiyuan Lu, Shin-ya and Satoko Takemura, aided by undergraduates such as Matthew Murphy, have traced the profiles of various cells in the distal medulla as well as their input neurons. These are lamina cells L1-L5, photoreceptors R7 and R8, medulla cell T1, and centrifugal cells C2, C3. Their work has recently been reported (see ref. 134), and is continuing as part of a visiting scientist program at the Janelia Farm Research Campus of the Howard Hughes Medical Institute, where Shin-ya is a postdoctoral fellow. In collaboration with a team leader there, Mitya Chklovskii, who is developing algorithms for the automatic recognition of cell profiles from EM sections and their reconstruction in 3-D, we are developing methods for automatic reconstruction of synaptic circuits in different brain regions of Drosophila.

This work is also continuing at Dalhousie University. For example, in collaboration with the group of Chi-Hon Lee at the National Institute of Child Health and Human Development of the NIH, we are examining the circuits underlying colour vision in Drosophila (see ref. 136). Using genetic reagents available only in Drosophila, we can label neurons to identify their connections, interrupt their function, and then examine the behavioral outcome in the fly's vision. This establishes the direct causal basis of behaviour, identified neuron by identified neuron.