Figure 1.
The ON pathway cross-inhibits the OFF pathway via the AII amacrine cell. ON and OFF pathways start at the top of the diagram and continue to the bottom: the cone synapses onto both ON and OFF cone bipolar cells, which provide excitatory glutamatergic inputs (+) to ON and OFF ganglion cells, respectively. A cross-inhibitory circuit goes from left to right: the ON bipolar cell is coupled electrically to the AII amacrine cell, which inhibits (−) the OFF bipolar cell and the OFF ganglion cell. The ON bipolar cell receives feedback inhibition from a GABAergic amacrine cell. Note that, while recording excitatory currents, the inhibitory inputs to the OFF ganglion cell were blocked by voltage clamping at the reversal potential for chloride (Vm = ECl). Synaptic blockers are indicated in red (l-AP4, TPMPA, MFA, strychnine, and CNQX + d-AP5).