Abstract
Purpose. 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-μsec 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. Conclusion. 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.
Original language | English (US) |
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Pages (from-to) | 635-645 |
Number of pages | 11 |
Journal | Investigative Ophthalmology and Visual Science |
Volume | 35 |
Issue number | 2 |
State | Published - 1994 |
Externally published | Yes |
Keywords
- 2-amino-4-phosphonobutyric acid
- a-wave
- Cis-2,3-piperidine-dicarboxylic acid
- cones
- depolarizing bipolar cells
- electroretinography
- hyperpolarizing bipolar cells
- photopic ERG
- primate
ASJC Scopus subject areas
- Ophthalmology
- Sensory Systems
- Cellular and Molecular Neuroscience