A proximal retinal component in the primate photopic ERG a-wave.
OBJECTIVE
The monkey photopic ERG was studied during administration of glutamate analogs to determine whether the photopic a-wave derives exclusively from photoreceptors.


METHODS
Monkey photopic ERGs were elicited using 200-msec flashes or 30-microseconds xenon photostrobe flashes on a steady light-adapting background of 40 cd/m2 (3.3 log scotopic troland). Intravitreal injections of APB, PDA, or both were given to block transmission to depolarizing and hyperpolarizing second-order retinal neurons, respectively.


RESULTS
After injecting PDA to block light responses of horizontal cells and hyperpolarizing bipolar cells, part of the photopic a-wave was eliminated. The PDA-sensitive component, presumed to be due to activity postsynaptic to cones, was responsible for the photopic a-wave threshold and dominated the response over the initial 1 to 1.5 log units of intensity. For brighter stimuli, this component made a constant contribution to the photopic a-wave. A non-PDA-sensitive contribution to the a-wave, presumed to originate directly from cones, was first evident 1 to 1.5 log units above photopic a-wave threshold. It progressively dominated the a-wave at higher intensities, particularly at early time points after the flash. Injecting PDA almost eliminated the photopic a-wave elicited with bright xenon photostrobe flashes that are commonly used for human clinical ERG diagnostic testing, indicating that this a-wave may contain significant postreceptoral activity.


CONCLUSIONS
The primate photopic ERG a-wave derives, in part, from retinal activity postsynaptic to cone photoreceptors, particularly for stimuli near the photopic ERG threshold that are typically used for human clinical studies.
Bush
R A
RA
W. K. Kellogg Eye Center, University of Michigan, Ann Arbor 48105.
Sieving
P A
PA
D000613:Aminobutyrates / Q000008:administration & dosage; D000818:Animals; D004596:Electroretinography; D007267:Injections; D007395:Interneurons / Q000502:physiology; D008252:Macaca fascicularis; D008253:Macaca mulatta; D016202:N-Methylaspartate / Q000008:administration & dosage; D010775:Photic Stimulation; D010875:Pipecolic Acids / Q000008:administration & dosage; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D014822:Vitreous Body
D000613:Aminobutyrates; D010875:Pipecolic Acids; C029262:2,3-piperidinedicarboxylic acid; D016202:N-Methylaspartate; C012729:2-amino-4-phosphonobutyric acid