Imaging tools to assess circuit connectivity and function in zebrafish

Neuronal circuits arise from the activity-dependent formation and elimination of synapses during development. Activity-dependent synaptic wiring has been studied extensively in peripheral sensory and motor neurons where the goal is to be excited or to excite. However, in the central nervous system, neural circuits are comprised of neurons that both excite and inhibit common targets and so activity-dependent wiring must be coordinated during development to achieve an appropriate balance of excitation and inhibition. To better understand this process, it would help to simultaneously monitor the activity of excitatory and inhibitory populations and their synaptic connections to common targets during development. In this exploratory R21 proposal, we will develop a genetic strategy to monitor activity-dependent changes in excitatory and inhibitory premotor synaptic connectivity in the developing zebrafish spinal cord. We will use a genetically-encoded sensor developed in Drosophila melanogaster that uses a synaptobrevin-based GFP, YFP or CFP reconstitution across synaptic partners to simultaneously label connections in different colors and monitor their activity levels (Syb-XRASP). In Aim 1 we will validate the CFP, YFP and GFP variants of Syb-XRASP at the neuromuscular junction of developing zebrafish. In Aim 2, we will use Syb-XRASP to monitor the assembly of connections of premotor neurons within excitatory Chx10-labeled V2a population and inhibitory En1-labeled V1 population. Together, these aims will allow us to assess the formation of connections from motor neurons to muscles, from single V2a and V1 interneurons to all motor neurons, and from all V2a and V1 interneurons to single motor neurons. These experiments will provide an unprecedent view of how connections are formed during the development of circuits comprised of excitatory and inhibitory neurons.