Fig. 7. Macaque starburst amacrine cells show center-surround receptive-field structure that is insensitive to GABAa receptor antagonists.

a Starburst whole-cell current-clamp recording (cell imaged in Supplementary Fig. 5e) shows a resting membrane potential ~75 mV on a high photopic background (~ 10⁵ photoisomerizations/cone/sec) and large amplitude depolarizing response (~40 mV) to 0.5 s, 100% contrast, square wave pulse stimulus. With increasing spot diameter (inset at top; 50–720 µm diameter; color coded) the response becomes more transient (black trace, 720 µm diam spot) and the sustained response component is lost. A characteristic feature of the starburst response to this stimulus is a large, spike-like transient that appears as the stimulus is enlarged to fill the receptive-field center. b, c Starburst spatial tuning (100% sinusoidal contrast modulation of spots of varied diameter at 2 Hz), fit with a center-surround Difference-of-Gaussians receptive-field model (line fit to data; n = 27 cells; center diam, 208 ± 76; surround diam, 360 ± 156); 2D profile of model fit is shown in c; small icon shows starburst soma and dendritic tree at same scale as model. d Surround response isolated by annular stimuli; increasing the inner diameter of the annulus from 20 to 400 µm (icons at center; top to bottom panels; 2 Hz square wave modulation) eliminates the ON-center depolarization (top panel) and isolates a pure OFF-surround depolarization (bottom panel). e Surround OFF depolarization is not eliminated by bath application of GABAa receptor antagonist (SR 95331(GABAzine); 10 µM; n = 4; 8 ± 3% reduction).