Figure 5. Circuitry for lateral GABAergic inhibition and possible pathway for inhibition of inhibition without direct amacrine-to-amacrine synaptic contact.

A, circuitry for lateral GABAergic inhibition. Many studies have shown a local GABA inhibition extending about 200 μm beyond the ganglion cell dendritic field. The narrow amacrine cell is too narrow; the wide amacrine cell is too broad and transient. This suggests that the inhibitory interneuron is likely to be the medium amacrine cell. Right, possible pathway for inhibition of inhibition without direct amacrine-to-amacrine synaptic contact. The right-most medium interneuron inhibits the bipolar cell that provides excitation to the left medium amacrine cell thereby reducing the activity of the left amacrine cell. This pathway allows for inhibition of inhibition without a direct inhibitory synapse between medium amacrine cells. MF: medium field amacrine cell.