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X. Luo, L. J. Frishman; Pharmacological Dissection of the Pattern ERG (PERG): Insight From Using Uniform Fields. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2177.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the retinal pathway origins of the PERG with help of uniform field stimuli.
Transient PERGs and uniform field ERGs were recorded from anesthetized macaques before and at least 1 hour after intravitreal injections of l-APB (2-amino-4-phosphonobutyric acid, 1.6-2.0 mM), TTX (tetrodotoxin, 1-2 µM), and PDA (cis-2,3-piperidinedicarboxylic acid, 3.3-3.8 mM) to block ON pathway, Na+-dependent spiking activity, and hyperpolarizing 2nd and all 3rd order neuron responses. Pharmacologic effects initially were confirmed using ganzfeld flash ERGs. The PERG stimulus was a 1 cy/deg contrast reversing checkerboard. PERG and uniform field stimuli were presented using the same display monitor (contrast: 84%, mean lum.: 55 cd/m2, 2 Hz sq wave modulation). The PERG was also simulated by averaging ON and OFF responses to uniform fields.
The PERG contained an early positive wave P1 (counterpart of P50 in humans) around 50 ms after pattern reversal, and a negative wave N2 (human N95) around 110 ms. ON responses to the uniform field contained a b-wave followed by a photopic negative response (PhNR); OFF responses contained a brief d-wave and a PhNR. Simulated N2 was the average of ON and OFF response PhNRs, and simulated P1 was the average of the early ON and OFF responses including b- and d-waves. Agents that removed (TTX) or nearly removed (> 80% for PDA, N=2) PhNRs in uniform field responses also removed N2 in PERG and simulations. APB removed the ON PhNR. As a result, both PERG N2 and simulated N2 dropped ~50% (SE=9.7% and 5.1%, respectively; N=4). TTX also altered early responses including b- and d-waves, causing a 50% drop in PERG P1 and a 15% drop in simulated P1. APB removed positive ON and enhanced OFF responses, while PDA did the reverse. For both agents, ON response effects were more prominent. Simulated P1 dropped ~60% (SE=6.3%, N=4) after APB whereas P1 became larger after PDA in PERG (123% and 460% of control in two animals) and simulation (150% and 300%).
APB, TTX and PDA had similar effects on PERG and simulated PERG from ON and OFF responses. Uniform field ERGs improved understanding of the pathway origins of the PERG.
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