Asymmetric connections with starburst amacrine cells underlie the upward motion selectivity of J-type retinal ganglion cells.

Motion is an important aspect of visual information. The directions of visual motion are encoded in the retina by direction-selective ganglion cells (DSGCs). ON-OFF DSGCs and ON DSGCs co-stratify with starburst amacrine cells (SACs) in the inner plexiform layer and depend on SACs for their direction selectivity. J-type retinal ganglion cells (J-RGCs), a type of OFF DSGCs in the mouse retina, on the other hand, do not co-stratify with SACs, and how direction selectivity in J-RGCs emerges has not been understood. Here, we report that both the excitatory and inhibitory synaptic inputs to J-RGCs are direction-selective (DS), with the inhibitory inputs playing a more important role for direction selectivity. The DS inhibitory inputs come from SACs, and the functional connections between J-RGCs and SACs are spatially asymmetric. Thus, J-RGCs and SACs form functionally important synaptic contacts even though their dendritic arbors show little overlap. These findings underscore the need to look beyond the neurons' stratification patterns in retinal circuit studies. Our results also highlight the critical role of SACs for retinal direction selectivity.