Projection targeting with phototagging to study the structure and function of retinal ganglion cells.

Understanding the structure-function relationships across neurons is challenging, particularly when circuits are composed of dozens of distinct cell types. We refined an approach, called "projection targeting with phototagging", that allows simultaneous elucidation of the projections, morphology, and visual response properties of diverse retinal ganglion cell (RGC) types in the mammalian retina. The approach combines retrograde virally mediated phototagging of RGCs, microscopy, and large-scale multi-electrode array (MEA) measurements. Importantly, the approach does not rely on transgenic animals and thus is potentially generalizable across species. We validated this approach in rats by targeting retinal projections to the superior colliculus (SC). We showed that multiple RGC types project to the SC and that these results in rats align well with prior findings from transgenic mouse studies.