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S. M. Petersen-Jones, G. Shaw, F. Montiani-Ferreira; Analysis of the Chick Electroretinogram. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1072.
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To characterize the chick ERG in detail.
Dark-adapted flash ERG and light-adapted flash and long-flash ERGs were recorded from normal chicks before and after intravitreal aspartate, APB, PDA or NMDA.
Pre drug administration ERGs. At lower flash intensities the dark-adapted a-wave was of greater amplitude than that of the light-adapted ERG. The dark-adapted b-wave intensity:response curve initially increased with flash intensity and then reached a plateau, whereas the light-adapted b-wave peaked at a higher stimulus intensity and then showed a typical "photopic hill", with decreased amplitude in response to increased stimulus intensity. Aspartate. This removed inner retinal components leaving the PIII response. Comparison with the light-adapted a-wave suggested a post-receptoral effect which acts to increase the a-wave amplitude at low flash intensities and decrease it at higher intensities. APB. APB eliminated the b-wave. There was no significant difference in the light- or dark-adapted a-wave amplitudes prior to APB administration compared to after drug administration. PDA. PDA significantly reduced the light-adapted a-wave at all intensities greater than 1 log cdS/m2. It tended to reduce the photopic hill effect of the light-adapted b-wave. PDA almost completely removed the a-wave, increased the b-wave amplitude and virtually eliminated the d-wave of the long-flash ERG. NMDA. Administration of NMDA smoothed the b-wave due to suppression of OPs. There was a significant increase in the dark-adapted b-wave amplitude in response to brighter stimuli. There was no significant difference in the light-adapted flash ERG amplitudes between the preinjection recordings and following NMDA administration. NMDA reduced the d-wave of the long-flash ERG.
The chick a-wave has a major component that is removed by PDA suggesting it originates from the activity of OFF bipolar cells or horizontal cells. The chick dark-adapted b-wave I:R function reaches a plateau in response to brighter flashes, blocking third order neurons prevents formation of a plateau allowing further increase in b-wave amplitude with increased flash intensity. Third order neurons appear to modulate the light-adapted b-wave I:R to a lesser extent, although both blocking OFF bipolar cell/horizontal cells and third order neurons tends to reduce the photopic hill effect. The d-wave is virtually eliminated by PDA and NMDA suggesting that it may originate from third order neurons of the OFF pathway.
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