Functional interrogation of neuronal connections by chemoptogenetic presynaptic ablation.

Most neurons are embedded in multiple circuits, with signaling to distinct postsynaptic partners playing functionally different roles. The function of specific connections can be interrogated using synaptically localized optogenetic effectors; however, these tools are often experimentally difficult to validate or produce paradoxical outcomes. We have developed a system for photoablation of synaptic connections originating from genetically defined neurons based on presynaptic localization of the fluorogen-activating protein dL5** that acts as a photosensitizer when bound to a cell-permeable fluorogen dye. Using the well-mapped zebrafish escape circuit as a readout, we first show that cytoplasmically expressed dL5** enables efficient spatially targeted neuronal ablation using near-infrared light. We then demonstrate that spatially patterned illumination of presynaptically localized dL5** (syp-dL5) can effectively disconnect neurons from selected downstream partners, suppressing postsynaptic responses and producing precise behavioral deficits. This technique should be applicable to almost any genetically tractable neuronal circuit, enabling refined manipulation of functional connectivity within the nervous system.