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L Xu, SL Ball, KR Alexander, NS Peachey; Pharmacological Analysis of the Rat Cone Electroretinogram . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1814.
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Purpose: The electroretinogram (ERG) of the rat cone system has proven useful for evaluating experimental treatments for retinal disease. However, the relative contributions of the different retinal cell types to the rat cone ERG have not been determined. Here, we address this issue using a pharmacological approach. Methods: ERGs were recorded from Sprague-Dawley rats under ketamine/xylazine anesthesia. Pharmacological agents dissolved in saline were injected into the vitreous, and cone ERGs were recorded approximately 2 hours later. In different experiments, we used 2-amino-4-phosphonobutyric acid (L-AP4), sodium aspartate (ASP), piperidine dicarboxylic acid (PDA) or vehicle (saline) alone. Stimulus flashes of varying durations were superimposed upon a steady rod-desensitizing adapting field. Results: In response to light, rat cone photoreceptor activity, isolated by treatment with ASP or L-AP4+PDA, generated an ERG component of negative polarity that was substantially smaller than the human cone photoreceptor response under identical recording conditions. The response of the cone DBCs, estimated by subtraction of L-AP4-treated responses from those obtained after saline injection, contributed a positive potential of large amplitude to the rat cone ERG. In comparison, the response of the HBCs, estimated by subtracting responses recorded after PDA from those obtained after saline injection, and by subtracting responses recorded after L-AP4 from those obtained after ASP, was of small amplitude, with a negative polarity at stimulus onset and a positive polarity at stimulus offset. Conclusion: The relative contributions of the DBC- and HBC- driven responses to the rat cone ERG are distinctly different from those underlying the primate ERG response (Sieving et al., Vis Neurosci 1994;11: 519-532). While DBCs and HBCs make a substantial contribution to the primate cone ERG, the rat cone ERG response is dominated by the DBC component, and HBCs make only a minor contribution.
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