Aspartate-induced dissociation of proximal from distal retinal activity in the mudpuppy

The effects of aspartate (Asp) on the ERG and on neuronal, glial, and K+ responses were monitored continuously in the superfused mudpuppy eyecup. Asp induced a time-dependent sequence of events which may be divided into three stages: Stage 1, initially, light-evoked responses throughout the retina are depressed; Stage 2, distal responses (horizontal, bipolar, and K+ responses) return to near pre-drug amplitudes and there is a simultaneous ERG enhancement, but responses in the proximal retina remain suppressed; Stage 3, a second depression of retinal responses leads to a-wave isolation. The dissociation of distal from proximal responses observed during Stage 2 strongly supports the hypothesis that the ERG b-wave results from events arising in the distal retinal network.