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R. L. Chappell, I. Anastassov, A. Sergaeva, H. Ripps; Evidence that Retinal Zinc Has a Role in Surround Enhancement of Response to a Modulated Spot of Light. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1038.
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© ARVO (1962-2015); The Authors (2016-present)
Surround inhibition is a well known phenomenon, but the process by which the response to a modulated spot of light can be enhanced by the addition of steady surround illumination remains an enigma. In the present study, we examined the possibility that retinal zinc has a role in the surround enhancement response.
The electroretinogram (ERG) and horizontal cell intracellular responses were recorded from skate (Raja erinacea) eyecup preparations. Responses were digitized and analyzed using p-ClampTM and OriginTM software. Pharmacological agents in skate Ringer were topically applied.
Simultaneously recorded ERG and horizontal cell responses revealed that the horizontal cell response to a sinusoidally modulated 1mM diameter spot of light was mirrored in oscillations observed in the ERG. Since the enhancement of the amplitude of the response to the modulated spot by addition of steady surround (1.4mm ID, 3mm OD) illumination could be observed in ERG recordings, we used the ERG response to probe the pharmacology of the surround enhancement effect. When skate Ringer containing 100µM histidine plus 200µM picrotoxin was applied for approximately 10min, the peak-to-peak ERG response of the sinusoidally modulated spot which had been enhanced by some 40% (41.2% ±5.8% increase, N=8) by the addition of a steady surround showed no such enhancement (-15.9% ±4.6% decrease, N=5). However, exposure to 200µM picrotoxin alone produced no substantial reduction of the surround enhancement effect which increased by 31.8% ±13.4% (N=3).
Use of the ERG facilitated pharmacological investigation of the enhancement of a sinusoidally modulated spot of light to the addition of steady annular surround illumination. The finding that surround enhancement is blocked by the application of histidine (a membrane-impermeant chelator of endogenous zinc) and picrotoxin (a GABA blocker) but not by picrotoxin alone, suggests that labile zinc (Zn2+) has a role in surround enhancement of responses to a modulated spot of light.
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