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Merging methods to map synaptic connections

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02/24/23 | Merging methods to map synaptic connections

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A team led by Josh Lillvis, a research scientist in the Saalfeld Lab, and former Janelia Group Leader Barry Dickson, now a professorial research fellow at the Queensland Brain Institute, developed a fast and easy method for mapping synaptic connections between individual neurons. The method uses tissue expansion and light sheet microscopy to rapidly reconstruct selected circuits across many animals with single-synapse resolution.

This video shows an example of automatic detection of presynaptic sites in a single optic lobe L2 neuron. L2 neurons were labeled by a membrane reporter. A single L2 neuron was semiautomatically segmented and an L2 mask was generated. Presynaptic sites, labeled by the protein BRP, were automatically classified and assigned to the L2 neuron. Credit: Lillvis et al.

Traditional methods used to reconstruct brain wiring diagrams generate a complete, detailed connectome but are expensive and time-consuming so they can only be used for mapping the connections in a single animal.

To relate the structure and function of neural networks to behavior, scientists need to be able to map the wiring diagrams of many animals – a task that would be virtually impossible using traditional connectome methods.

The new method uses genetic tools to label neurons of interest in fruit flies and expansion microscopy, developed by Janelia Principal Scientist Paul Tillberg, to expand the sample to a resolution allowing individual synaptic connections can be observed.

This video shows how the method identifies connections between SAG neurons and pC1 neurons by identifying the contact between the pC1 postsynaptic site and the SAG presynaptic sites. SAG neurons are labeled by a membrane reporter. SAG neurons are semiautomatically segmented and an SAG mask was generated. Presynaptic sites labeled by the protein BRP were automatically classified and assigned to SAG neurons. pC1 postsynaptic sites were automatically classified and connections between pC1 postsynaptic sites and SAG presynaptic sites were automatically generated. Credit: Lillvis et al.

Lattice light sheet microscopy, a technique developed by Janelia Senior Fellow Eric Betzig, is then used to image the expanded brain tissue. The team also developed new computational methods that are used to identify the synaptic connections.

The new method, published in eLife, allows researchers to map selected circuits quickly and easily for multiple animals across different conditions and behavioral states, enabling comparison across animals that can be used to correlate structure, function and behavior.




Joshua L Lillvis, Hideo Otsuna, Xiaoyu Ding, Igor Pisarev, Takashi Kawase, Jennifer Colonell, Konrad Rokicki, Cristian Goina, Ruixuan Gao, Amy Hu, Kaiyu Wang, John Bogovic, Daniel E Milkie, Linus Meienberg, Brett D Mensh, Edward S Boyden, Stephan Saalfeld, Paul W Tillberg, Barry J Dickson. “Rapid reconstruction of neural circuits using tissue expansion and light sheet microscopy.” eLife, published October 26, 2022. DOI: 10.7554/eLife.81248