The optimum spot MK-2206 stimulus was 100–200 μm in diameter, similar to the dendritic field size (192.8 ± 2.7 μm; n = 42; Figures 1G and S1). When we presented moving stimuli (a 400 μm spot moving in

8 directions at 1000 μm/s), DSGCs responded to the leading (ON) and trailing (OFF) edges of the spot with a burst of spikes (Figure 2B). Stimuli moving in the centrifugal (soma to dendrite) direction evoked the maximal response, whereas those moving in the centripetal direction (dendrite to soma) evoked weaker responses (Figure 2B). The direction of preferred response was consistent from cell to cell and always pointed toward the temporal pole, parallel to the dendritic tree (Figures 2B–2D). The DS indices (DSIs; see Experimental Procedures) for ON and OFF responses were 0.45 ± 0.03 and 0.52 ± 0.03, respectively (n = 42; note DSI ranges from 0 to 1, with larger values indicating stronger directional selectivity). Plotting the angle of the DSI against that of the AI for ON and OFF responses/dendritic trees (Figure 2E) yielded

striking correlations www.selleckchem.com/products/chir-99021-ct99021-hcl.html with slopes of 0.96 (R2 = 0.92) and 0.97 (R2 = 0.94), respectively. These findings contrast with previous reports that found ON-OFF DSGC dendrites to be either symmetric or asymmetric but randomly oriented with respect to the preferred direction (Yang and Masland, 1994 and Huberman et al., 2009; but see Kim et al., 2008 for OFF DSGCs). The strong correlation between morphological and functional asymmetries observed here suggests that dendrites play a role in computing direction. Although our results clearly demonstrate that GFP+ cells in the Hb9::eGFP retina belong to a unique set of polarized DSGCs that code anterior motion, it is not clear if asymmetries are CYTH4 present in ganglion cells

that code other directions. To test this possibility, we next recorded from GFP− DSGCs in the Hb9::eGFP retina (Figure S2). In a random sample of 14 cells, we found that 4 displayed asymmetry comparable to the GFP+ cells. In these cells, asymmetry appeared to be orientated in the same direction as the preferred responses (Figure S2). In the general population, however, only a weak correlation between the orientation of dendrites and response preference was observed for ON but not for OFF dendrites (R2 = 0.20 and 0.03 for ON and OFF, respectively; Figure S2). Without knowing whether asymmetric cells belong to a specific population of DSGCs or if they are part of a population with varying morphologies, it is difficult to establish the functional significance of these findings. Hence, the identification of a genetic marker that labeled a specific population of asymmetrical DSGCs in this study was pivotal in establishing the functional relevance of morphological specializations.