Subcellular pathways through VG3 amacrine cells provide regionally tuned object-motion-selective signals in mouse retina.

We combined subcellular calcium imaging and connectomic reconstruction to understand the flow of information through a plexus of excitatory VGluT3-expressing mouse retinal amacrine cells (VG3s). We found that VG3s received inputs from all nearby bipolar cell types but exhibited a strong preference for the fast type 3a bipolar cells. We used our connectivity map and physiological recordings to predict the influence of these bipolar cells on different types of RGCs innervated by VG3s and found that the depth of retinal ganglion cell (RGC) dendritic arbor stratification determined the RGCs view of bipolar cells through the VG3 plexus. We also found that both VG3s and their RGC targets were often innervated by the same bipolar cells. RGCs that extend processes into the middle layers of the inner plexiform layer, therefore, encounter a plexus of small object motion selective glutamatergic excitation that is complementary to the local bipolar cell input.