Ravi Chander, Prathyusha2023-04-2820232023-04-28http://hdl.handle.net/1828/15044In the mammalian retina, the orientation-selective (OS) and direction-selective (DS) information are generally thought to be relayed to higher visual centers via distinct ganglion cell types. Contrary to this notion, here I report that classic ON-OFF direction-selective ganglion cells (DSGCs) that are known to encode the four cardinal directions, also encode orientation of static stimuli. The DSGC’s preferred orientations was always orthogonal to its preferred-null axis defined by moving stimuli. To evaluate the synaptic mechanisms underlying orientation selectivity a combination of electrophysiological, optogenetic, and gene knock-out techniques were used to assess the functional properties of all four types of ON-OFF DSGCs. Cumulative results from multiple approaches revealed that the glutamate input to all four types of DSGCs was tuned to the vertical axis. This relies on signals from a specific presynaptic source (the bipolar cell type 5A; BC5A), which appear to be electrically coupled to vertically oriented processes of wide-field amacrine cells. By contrast, the GABAergic inhibition mediated largely by starburst amacrine cells was tuned either along the horizontal or vertical axis, consistent with their well-defined asymmetric wiring pattern. Thus, distinct combinations of inhibition and excitation underlie orientation selectivity in the nasal/temporal and dorsal/ventral coding DSGC populations, only the latter critically relying on the starbursts. Together, my work provides novel insights into how feature selectivity emerges in the hierarchical network in the retina.enAvailable to the World Wide WebDirection-selectiveOrientation-selectiveElectrophysiologyOptogeneticsAsymmetric inhibitionVertical excitationOS is orthogonal to the P-N axisdv-DSGCsnt-DSGCsSACsBC5AsWACsGap-junction couplingCx36 gap-junctionsGenetic knockoutThesis