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F. Tremblay, J. Nason, B. Maleki; Shaping of GERG, PERG and MFERG by APB– and PDA–Sensitive Cells in the Pig Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2247.
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Purpose: To investigate the retinal origins of the multifocal ERG (MFERG), pattern ERG (PERG), and Ganzfeld ERG (GERG) by using pharmacological agents known to block APB– and PDA–sensitive circuits in the pig retina. Methods: 15 Hampshire Durco Cross pigs were anesthetized and paralyzed with intravenous ketamine (20–25mg/kg/h) and gallamine (25mg/kg/h) at 5 to 10 weeks of age. Pupils were dilated with atropine (0.04 mg/kg IM) and ERG recordings were obtained from a monopolar contact lens electrode referenced to the ipsilateral eyelid. The stimuli for the MFERG consisted of 103 non–scaled, high contrast hexagons presented with an m–sequence of 2 14 –1. Pattern ERG stimuli were 60 x 60 deg, 2.1 Hz phase–reversing checkerboards (99% contrast) with checks subtending 12.5 to 0.3 deg. Ganzfeld ERG stimuli were 10 cd/m2 flashes against a photopic background of 30 cd/m2. Following the first series of ERG recordings, intravitreal injections with either 2–amino–4–phosphonobutyric acid (APB) or cis–2,3–piperidinedicarboxilic acid (PDA), to achieve vitreal concentrations of 1mM and 5 mM respectively. A second series of ERG recordings was obtained, 1.5 hr post–injection. Results: After injection of APB, GERGs showed an overall decrease in amplitude of the b–wave, and a small increase in the a–wave, along with preservation of the oscillatory potentials (OPs) and the photopic negative response. In the PERG, APB decreased the amplitude of the P50 but increased the N95 amplitude. The MFERG showed an increase in amplitude of the first negative component, a decrease in amplitude of several late components, and an overall delay in implicit times of all components. After injection of PDA, GERGs showed a small decrease in the amplitude of the a–wave, without affecting the b–wave. As well, PDA significantly reduced all OPs. In the PERG, PDA decreased the amplitude of the N95 without affecting the P50 significantly. In the MFERG, PDA decreased the amplitude of both early and late components, but did not change any of the implicit times. It did, however, significantly reduce high frequency components. Conclusions: The affect of APB and PDA on the GERG and mfERG is consistent with previous results obtained with monkeys and rats, although some species specific differences must be considered. To our knowledge, this is the first study to look at the affect of APB and PDA on the pERG in any species. As such, we have demonstrated a differential influence of ON and OFF–pathway bipolar cells on the generation of the P50 and N95.
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