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Xiaolan TANG, Radouil T Tzekov, Christopher L Passaglia; Further evidence of interocular signal transfer in the rodent visual system. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
We recently identified a novel bioelectrical signal in the contralateral eye of rats evoked by stimulation of the ispsilateral eye called the “crossed electroretinogram” (xERG). This study further investigates the anatomical and physiological origins of the xERG in rats and its existence in mice.
Brown-Norway rats (n=8, male, 300-400g) and C57BL/6 mice (n=2, male, 25-30g) were anesthetized with ketamine. Rats were paralyzed with gallamine. Animals were dark-adapted for 4 hours prior to data collection. Electroretinogram (ERG) and xERG records were then acquired simultaneously from both eyes under dark-adapted and light-adapted conditions with a series of 10ms full-field flashes delivered with an interstimulus interval of 3s to one or both eyes. Flash intensity was varied over 6 log units. Visual evoked potential (VEP) records were also acquired from rats with active electrodes inserted into the skull over the visual cortex (3mm lateral and 7mm posterior to bregma). Fluorescent dye rhodamine was injected intravitreally in one eye of 7 rats, and 5-7 days after injection the retinas of both eyes were extracted and labeled cells in the non-injected eye were imaged and counted.
Rat ERG (b-wave) and VEP (N1-P2) amplitudes both increased in proportion to flash intensity under photopic and scotopic illumination. The correlation coefficient averaged 0.85 and 0.92 for the two illumination conditions, respectively. In contrast, none of the xERG components (xP1, xN1, xP2) differed markedly in amplitude under scotopic or photopic conditions for the range of flash intensities tested. Monocular stimulation evoked a xERG in the non-flashed eye of mice as well. The signal was 3-5 folder larger and differed in waveform from that of rats as it lacked the xP1 component. Monocular dye injection in rats labeled a small number (<10) of retinal ganglion cells in the opposite eye, preferentially in the nasal side.
The xERG in rats reflects interocular crosstalk via retino-retinal optic nerve projections. Volume conduction of visually-evoked retinal or cortical signals from the flashed eye is not involved. A xERG is also recorded in mice, another animal known to have retino-retinal connections.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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