In the retina, the direction of a moving object is encoded by starburst amacrine cells (SACs) and ON-OFF direction selective ganglion cells (ooDSGCs). Multiple neural circuits have accounted for the underlying mechanisms of direction selectivity. We previously found that the cholinergic feedback circuit through α7-nicotinic acetylcholine receptors (α7-nAChRs) in bipolar cells mediates direction selectivity in SACs. We investigated whether distinct visual stimuli differently affected cholinergic feedback through α7-nAChRs. We conducted two-photon Ca 2+ imaging using Ca 2+ indicators of Oregon Green BAPTA-1 for SACs and GCaMP6s/f for ooDSGCs. We generated an AAV viral vector inserting the ProD1 promoter and GCaMP6. Ca 2+ transients were recorded in response to “long” distance and “local” traveling bars. The involvement of nAChRs was assessed using an α7-nAChR antagonist, methyllycaconitine (MLA), and a non-α7-nAChR antagonist, hexamethonium (HEX). The intraocular injection of the ProD1-AAV into C57BL/J mouse eyes resulted in GCaMP6 expression only by ooDSGCs. The “long” stimulus elicited direction selectivity in ooDSGCs higher than the “local” stimulus did, independent of motion speeds. In SACs, a “long” stimulus also evoked higher direction selectivity than a “local” stimulus. Pharmacological dissection revealed that MLA reduced “long”-evoked direction selectivity, whereas HEX had no effect on SAC direction selectivity. Overall, we found that the long-distance traveling stimulus activates outside of receptive fields for SACs and ooDSGCs to enhance direction selectivity for those cells. In conjunction with our previous results, the 7-nAChRs in bipolar cells likely mediate the signals of a long-distance moving bar to enhance direction selectivity in SACs and ooDSGCs.
Bohl et al. (Tue,) studied this question.