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H. Qian, K. R. Alexander; Comparison of Rabbit and Rat Cone Flicker ERGs. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1074.
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© ARVO (1962-2015); The Authors (2016-present)
Rats and rabbits are animal models commonly used in vision research. ERGs from both animals are dominated by ON-pathway activity. The purpose of this study was to characterize the cone flicker ERG of rabbit in comparison to previous results from rat obtained under identical test conditions.
Adult animals were anesthetized with ketamine and xylazine. The full-field stimulus consisted of 502-nm light whose luminance was modulated sinusoidally at 90% contrast. The stimulus mean luminance ranged from 25 to 350 cd/m2 and the temporal frequency ranged from 2 to 100 Hz. ERG responses were recorded from a chlorided silver wire electrode placed in the center of the cornea and connected to a Grass AC amplifier (bandwidth 0.3 to 300 Hz). The amplitudes and phases of the harmonic responses of the flicker ERG were derived from discrete Fourier transforms using Matlab.
In contrast to rat, where the fundamental response amplitude reached the noise level at approximately 50 Hz, the ERG of rabbit extended to at least 100 Hz. The fundamental response function of rabbit exhibited two limbs, with a high frequency region peaking at around 45 Hz. The response amplitude of rabbit at high stimulus frequencies varied in proportion to the mean luminance, whereas the ERG response at low frequencies was independent of mean luminance (Weber-law behavior). The phase-frequency function was shallower for rabbit (-12.3o + 0.4o/Hz) than for rat (-17.5o + 0.4o/Hz), indicating a shorter response delay for rabbit. In addition, there was also a large difference in the intercept of the phase-frequency function (-13o + 5o for rabbit and -73o + 2o for rat), which indicates that the rabbit flicker ERG mainly represents a differential response to a light stimulus, whereas the rat flicker ERG follows more directly the stimulus waveform. This difference was also evident in the light-adapted ERG elicited by a rectangular light pulse. Under these conditions, the rabbit ERG had a transient waveform, whereas the ERG response from rat was relatively sustained.
The cone flicker ERG of rabbit differs substantially from that of rat in terms of the frequency-response relationship and the waveform morphology. These differences likely represent different signal processing mechanisms of bipolar cells in these two ON-dominated retinas.
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