Action potentials are necessary for wide-field inhibitory signals in the inner plexiform layer of amphibian retina

Purpose: To determine whether action potentials are necessary for certain types of lateral signaling in the inner plexiform layer in amphibian retinas. Ganglion cells are inhibited by moving stimuli in the receptive field surround (change-sensitive inhibition), which is believed to be mediated by wide-field amacrine cells. It has been postulated that the wide-field amacrine cells, which are glycinergic, use action potentials to signal information laterally in the IPL. Methods: Light-evoked responses of On-Off ganglion cells were measured by intracellular recording in superfused eyecups of mudpuppy and tiger salamander, and in tiger salamander retinal slices using whole-cell patch clamp recording. Results: In the eyecup, ganglion cell responses to spot stimuli in the receptive field center were reduced when the receptive field surround was illuminated with a stationary broken annulus (windmill) pattern (steady surround inhibition) and was further reduced when the windmill was spinning (change-sensitive inhibition). Change-sensitive inhibition was blocked by strychnine (2 μM) and by tetrodotoxin (500 nM). In retinal slices, full-field light stimuli caused small, transient EPSCs and IPSCs in ganglion cells. Picrotoxin (150 μM) increased EPSCs and blocked the GABA-mediated component of the IPSCs. The remaining light-evoked inhibitory current, which reversed near the chloride equilibrium potential, was blocked by strychnine and tetrodotoxin. Conclusion: Transient wide-field glycinergic input to amphibian ganglion cells requires action potentials, presumably in wide-field transient amacrine cells.