Three levels of lateral inhibition: A space-time study of the retina of the tiger salamander

The space-time patterns of activity generated across arrays of retinal neur ons can provide a sensitive measurement of the effects of neural interactio ns underlying retinal activity. We measured the excitatory and inhibitory c omponents associated with these patterns at each cellular level in the reti na and further dissected inhibitory components pharmacologically. Using per forated and loose patch recording, we measured the voltages, currents, or s piking at 91 lateral positions covering similar to 2 mm in response to a fl ashed 300-mu m-wide bar. First, we showed how the effect of well known late ral inhibition at the outer retina, mediated by horizontal cells, evolved i n time to compress the spatial representation of the stimulus bar at ON and OFF bipolar cell bodies as well as horizontal cells. Second, we showed, fo r the first time, how GABA(C) receptor mediated amacrine cell feedback to b ipolar terminals compresses the spatial representation of the stimulus bar at ON bipolar terminals over time. Third, we showed that a third spatiotemp oral compression exists at the ganglion cell layer that is mediated by feed forward amacrine cells via GABA(A) receptors. These three inhibitory mechan isms, via three different receptor types, appear to compensate for the effe cts of lateral diffusion of activity attributable to dendritic spread and e lectrical coupling between retinal neurons. As a consequence, the width of the final representation at the ganglion cell level approximates the dimens ions of the original stimulus bar.