An Amacrine Cell Circuit for Signaling Steady Illumination in the Retina.

Decades of research have focused on the circuit connectivity between retinal neurons, but only a handful of amacrine cells have been described functionally and placed in the context of a specific retinal circuit. Here, we identify a circuit where inhibition from a specific amacrine cell plays a vital role in shaping the feature selectivity of a postsynaptic ganglion cell. We record from transgenically labeled CRH-1 amacrine cells and identify a postsynaptic target for CRH-1 amacrine cell inhibition in an atypical retinal ganglion cell (RGC) in mouse retina, the Suppressed-by-Contrast (SbC) RGC. Unlike other RGC types, SbC RGCs spike tonically in steady illumination and are suppressed by both increases and decreases in illumination. Inhibition from GABAergic CRH-1 amacrine cells shapes this unique contrast response profile to positive contrast. We show the existence and impact of this circuit, with both paired recordings and cell-type-specific ablation.