ON direction-selective ganglion cells in the mouse retina

Two types of ganglion cells (RGCs) compute motion direction in the retina: the ON-OFF direction-selective ganglion cells (DSGCs) and the ON DSGCs. The ON DSGCs are much less studied mostly due to the low encounter rate. In this study, we investigated the physiology, dendritic morphology and synaptic inputs of the ON DSGCs in the mouse retina. When a visual stimulus moved back and forth in the preferred-null axis, we found that the ON DSGCs exhibited a larger EPSC when the visual stimulus moved in the preferred direction and a larger IPSC in the opposite, or null direction, similar to what has been found in ON-OFF DSGCs. This similar synaptic input pattern is in contrast to other well-known differences, namely: profile of velocity sensitivity, distribution of preferred directions, and different central projection of the axons. Immunohistochemical staining showed that the dendrites of ON DSGCs exhibited tight cofasciculation with the cholinergic plexus. These findings suggest that cholinergic amacrine cells may play an important role in generating direction selectivity in the ON DSGCs, and that the mechanism for coding motion direction is probably similar for the two types of DSGCs in the retina.