Synaptic pattern of nicotinic acetylcholine receptor α7 and β2 subunits on the direction-selective retinal ganglion cells in the postnatal mouse retina

Direction-selective retinal ganglion cells (DS RGCs) respond strongly to a stimulus that moves in their preferred direction, but respond weakly or do not respond to a stimulus that moves in the opposite or null direction. DS RGCs are sensitive to acetylcholine, and starburst amacrine cells (SACs) make cholinergic synapses on DS RGCs. We studied the distributions of nicotinic acetylcholine receptor (nAChR) α7 and β2 subunits on the dendritic arbors of DS RGCs to search for anisotropies that contribute to the directional preferences of DS RGCs. The DS RGCs from the retinas of postnatal mice (postnatal day P5, P10, and P15) were injected with Lucifer yellow, and injected cells were identified by their dendritic morphology. The dendrites of the DS RGCs were labeled with antibodies for either the nAChR α7 or β2 subunit as well as postsynaptic density protein-95 (PSD-95), visualized by confocal microscopy, and reconstructed from high-resolution confocal images. The distribution of nAChR subunits on the dendritic arbors in both the ON and OFF layers of the RGCs revealed an asymmetrical pattern on early postnatal day P5. However, the distributions of nAChR subunits on the dendritic arbors were not asymmetric on P10 and P15. Our results therefore provide anatomical and developmental evidence suggesting that the nAChR α7 and β2 subunits may involve in the early direction-selectivity formation of DS RGCs in the mouse retina.