Evidence for a ganglion cell contribution to the primate electroretinogram(ERG): Effects of TTX on the multifocal ERG in macaque

To assess the contribution of spiking inner retinal neurons to the multifoc al electroretinogram (ERG), recordings were made from four monkeys (Macaca mulatta) before and after intravitreal injections of tetrodotoxin (TTX). TT X blocks all sodium-based action potentials and thus terminates spiking act ivity of amacrine and ganglion cells. TTX eliminated a large component from the control responses, and this TTX-sensitive component was present as ear ly as 10 ms after the stimulus. Before injection with TTX, the 103 focal ER G responses varied in waveform across the retina. After TTX, the response w aveforms were largely independent of retinal position, indicating that it w as primarily the TTX-sensitive component of the control response that was d ependent upon retinal location. Given that retinal ganglion cells compose a sizable proportion of the retinal elements that produce action potentials, it is likely that part of the TTX-sensitive component is due to the spilli ng activity of these cells. Further, the systematic change in waveform of t he TTX-sensitive component with distance from the optic nerve head suggests that part of the TTX-sensitive component may originate from the activity o f the ganglion cell axons. Based on these findings, there is reason to be o ptimistic that the multifocal technique can be employed to study the effect s of glaucoma and other diseases that affect the inner retina.