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James N Ver Hoeve, Brittany Glatting, Kimberly B McIntyre, Brian J Christian, T Michael Nork, Charlene B Y Kim; Gender Differences in Anesthetized Primate ERG and Full-field Flash VEP. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5130.
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To describe gender-related differences in the flash-evoked cortical potential and the electroretinogram in the anesthetized primate.
As part of baseline screening, a total of 300 male and 268 female cynomolgus macaque monkeys (Macaca fascicularis) was evaluated using an ERG protocol based on the ISCEV standard with the addition of cortical evoked response to flash stimuli. Animals were sedated with ketamine and medetomidine . Rod dark-adapted 0.01 cd-s m-2 ERG (DA 0.01), mixed rod/cone dark-adapted (DA 2.7), and light-adapted cone (LA 2.7, LA 30 Hz) ERGs were recorded from each animal. ERG signals were recorded from dilated eyes via monopolar contact lens electrodes. Flash visual evoked potentials (FVEPs) were elicited by LA 2.7 flashes delivered at 4.1 Hz. FVEPs were recorded from two channels over the occipital scalp referenced to vertex. The distributions of response parameters were evaluated and the means were compared using parametric statistics.
The distribution of ERG B-wave amplitudes in both females and males was normalized with a log transform. Mean female ERG B-wave amplitudes exceeded those of males by 7-9% for DA 0.01, DA 2.7 and LA 2.7 conditions (p’s < 0.001). Latency-to-peak (implicit time, IT) of the A- and B-waves did not differ by gender with the exception of shorter ITs in females for the DA 2.7 flash A-wave. The FVEP waveform consisted of a small voltage negative (~1 mcV) wave with an IT of 25 ms (N25), a positive voltage wave peaking at 50 ms (P50), a large voltage N61 wave, and a prominent P94 wave. Female P94 amplitudes exceeded males’ on average by 33 percent. Female FVEP RMS exceeded that of males by 56% (p<0.001). No significant correlations existed between FVEP measures and any ERG measure.
This study provides normative data on full-field ERG and the FVEP from a large sample of male and female monkeys. The FVEP is a technically relatively simple test that can play an important role in the functional assessment of visual pathways in pre-clinical pharmaceutical development. These data provide a reference for evaluating the FVEP in this setting. As found similarly in studies of awake humans, female monkeys have a slightly larger amplitude ERG B-wave compared with males. The basis of the difference between males and females in ERG and VEP amplitude remains to be elucidated.
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