Effects of APB, PDA, and TTX on ERG responses recorded using both multifocal and conventional methods in monkey....

Results from studies of human subjects suggest that the multifocal ERG technique developed by Erich Sutter and colleagues has considerable potential for assessment of retinal function in both the clinic and laboratory. While the utility of this measure depends to a large extent upon an understanding of the physiological origin for the different response components, relatively little is known in this regard. For the experiments described in this report, we made ERG recordings using both multifocal and conventional methods. Intravitreal injections of APB, PDA, and TTX were used to identify contributions from activity in ON pathway, OFF pathway, and third order retinal neurons, respectively. The results show that photoreceptor activity makes a small direct contribution to 1st and 2nd order multifocal photopic luminance responses. TTX-sensitive activity in third order retinal neurons contributes to both 1st and 2nd order responses with relatively greater contribution to the 2nd order response. Blockade of TTX-sensitive activity in third order cells produces effects on the 2nd order response which are very similar to changes observed in eyes suffering selective loss of retinal ganglion cells resulting from experimental glaucoma. Effects of these intravitreally injected test agents were also determined, in the same recording session, for flash, 30 Hz flicker, and oscillatory potential responses.