1. Followers of the leech command-like neuron Tr2 discovered using a FRET-based voltage indicator Adam L. Taylor Garrison W. Cottrell David Kleinfeld William B. Kristan, Jr.

2. Tr2 terminates swimming

3. Tr2 swim-termination pathways

4. Voltage-sensitive dye imaging Impale one Tr2 Inject current pulses to elicit bursts of spikes at 1 Hz Image a midbody ganglion, look for cells with activity at 1 Hz

5. Imaging reveals Tr2 targets

8. Optical recordings are very sensitive High sensitivity due to FRET-based voltage-sensitive dyes

9. Tr2 spikes elicit 1-1 EPSPs Connections are monosynaptic, chemical

10. 256 and 54 stop swimming

11. Cell morphologies

12. Conclusions Using FRET-based voltage-sensitive dyes, we found three novel Tr2 targets: 256, 252, and 54 Two of these cells, cells 256 and 54, terminate swimming when driven strongly This suggests that these cells play a role in Tr2-induced swim stops We haven’t connected Tr2 to the swim CPG yet, but we’ve moved the ‘cloud’ back one layer Optical recording is a very efficient way of finding synaptic targets

13. Acknowledgements Tim Cacciatore Tito Gonzalez Roger Tsien Aurora Biosciences Corporation (now Panvera Ltd.) La Jolla Interfaces in Science, Burroughs Wellcome Fund National Institutes of Health GM08107