Thread by @darbly

New @biorxivpreprint on synapse-resolution reconstruction of motor control circuits in the Drosophila ventral nerve cord (VNC) led by @jasper_tms, @davidhildebrand, and Brett Graham. A great collaboration with the labs of @casa_tuthill & @janfunkey. 1/n
biorxiv.org/content/10.110…

The VNC has circuits that sense & control the fly's limbs, similar to the spinal cord. Although it accounts for ~1/3 of the central nervous system, our understanding of the anatomy and function of the VNC has lagged behind our understanding of the fly brain. vid E. Dickinson 2/n

To reconstruct the connectivity of neuronal circuits underlying behavior, we developed GridTape to automate the collection of sections for transmission electron microscopy. We used GridTape to collect 4400 sections of a fly VNC in 28 continuous hours. 3/n

We built a GridTape-compatible electron microscope to image over 20 million synapse-resolution images in 2 months. You can see the aligned dataset yourself at catmaid.virtualflybrain.org Thanks to @virtualflybrain for publicly hosting the dataset! 4/n

We reconstructed all the motor neurons controlling the legs, wings, halteres, and neck; as well as the axons of hundreds of sensory neurons projecting into the VNC from the body. We make these publicly available (see the link above) to serve as a foundation for future work. 5/n

We found that most motor neurons had unique and recognizable branching patterns. This let us find left-right pairs of motor neurons that likely control the same muscle in opposite legs. Identifiability of motor neurons is a key advantage to studying motor control in the fly. 6/n

One highlight was finding a class of sensory neurons with huge-diameter axons that synapse on specific leg motor neurons on both sides of the body. We believe these are bilateral campaniform sensillum (bCS) neurons that encode changes in the load on the legs. 7/n

We wanted to know if bCS axons target their synapses to particular types of motor neurons. By registering the EM dataset to a standardized VNC atlas, we can compare any EM reconstructed neurons to neurons imaged with light microscopy. 8/n

Indeed, these sensory neurons specifically target motor neurons that control rapid flexion of the leg, but avoid synapsing onto motor neurons that produce slow movements. These motor neuron types were recently characterized by @singlephotons et al (biorxiv.org/content/10.110…). 9/n

Our evidence suggests that bCS neurons are poised to drive fast, synchronous leg flexion in response to changes in load on the legs. We expect future functional experiments will further characterize the role of these neurons in behavior. 10/n

We are grateful for the support of @AllenInstitute @IARPAnews @neurowitz @RJVneurotech @NINDSnews @NIMHgov @NIH & the efforts of those who made it possible including @aaron_t_kuan, @lathomas42, @TriNguy81821638, @julia_buhmann, @singlephotons, Brendan Shanny & @LuxelCorp. 11/end