Identification of neural circuits by imaging coherent electrical activity with FRET-based dyes

We show that neurons that underlie rhythmic patterns of electrical output m ay be identified by optical imaging and frequency-domain analysis. Our cont rast agent is a two-component dye system in which changes in membrane poten tial modulate the relative emission between a pair of fluorophores. We demo nstrate our methods with the circuit responsible for fictive swimming in th e isolated leech nerve cord. The output of a motor neuron provides a refere nce signal for the phase-sensitive detection of changes in fluorescence fro m individual neurons in a ganglion. We identify known and possibly novel ne urons that participate in the swim rhythm and determine their phases within a cycle. A variant of this approach is used to identify the postsynaptic f ollowers of intracellularly stimulated neurons.