Direct excitatory and lateral inhibitory synaptic inputs to amacrine cells in the tiger salamander retina.

Two distinct synaptic currents in amacrine cells were measured using whole cell patch clamp in retinal slices. Synaptic activity was elicited with transretinal current passed from photoreceptors to ganglion cells to depolarize bipolar cell terminals. Recordings made in line with the stimulating electrodes revealed inward synaptic currents that reversed near O mV, positive to spike threshold. Recording 400 micron lateral to the stimulating electrodes revealed synaptic currents that reversed near-60 mV, negative to spike threshold. The lateral signal was blocked by tetrodotoxin and strychnine. A current with reversal potential similar to the lateral input was elicited by direct application of glycine to the amacrine cells. The results suggest that bipolar, but not amacrine input can elicit spikes in neighboring amacrine cells, that amacrine cells are mutually inhibitory and the inhibitory lateral transmission is limited to the extent of processes of the excited, spiking cell.