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James Kuchenbecker, Scott Greenwald, Maureen Neitz, Jay Neitz; S-cone Electroretinograms in Old and New World Primates Recorded Using Two Methods. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3706.
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© ARVO (1962-2015); The Authors (2016-present)
Using the exchange of two lights that lie along a tritan line makes it possible to isolate pure S-cone electroretinogram (ERG) signals. Here, we compare the pure S-cone ERG using silent substitution with a method in which “S-cone ERGs” are obtained to short wavelength flashes in the presence of intense long wavelength adaptation. Results were compared in an Old World (OW) primate (baboon) and a New World (NW) primate (squirrel monkey) to evaluate the possibility of differences in S-cone circuitry between the two primate groups that have been proposed to explain reported neuroanatomical differences.
An LED Ganzfeld system was used (Q450; Roland Consult, modified by replacing 450 with a 420 nm LED). A tritan pair of lights was alternated at 1 Hz with a 50% duty cycle. A tritan pair that completely isolated S-cone responses for each individual animal was found by making small adjustments to the relative intensities of the two lights while taking advantage of the striking differences in the temporal characters of L/M vs. S-cone ERG signals. For comparison, “S-cone ERGS” were recorded in response to the 420 nm LED in the presence of steady adaption from an amber LED (~590 nm peak).
Compared to L/M, S-cone ERGs have very distinct temporal characteristics. The component waves also have strikingly different relative amplitudes including a much smaller a-wave and absent d-wave which can be explained by the absence of S-cone specific off-bipolar cells in primates. In comparison to the pure S-cone ERGs obtained with silent substitution, long wavelength adaptation can reduce but does not eliminate L/M contamination.
Using silent substitution we recorded pure S-cone ERGs to investigate differences between S-cone and L/M cone mediated signals very early in the visual pathway. The temporal peak of both the S-cone a- and b-wave is slower indicating the sluggishness of S-cone temporal responses observed in human psychophysics has its origins in the outer retina and, at least, partly in the cones themselves. The robust off-bipolar cells signals in both the a- and d-waves elicited by L/M cone stimulation are absent in the pure S-cone ERG with no evidence for the species differences predicted from the anatomy in which off-midget bipolars have been proposed to contact S-cones in OW but not NW primates.
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