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Christopher L Passaglia, XIAOLAN TANG, Radouil T Tzekov; Experimental evidence for a “crossed ERG” in rat. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):474.
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© ARVO (1962-2015); The Authors (2016-present)
We have identified a bioelectrical signal in the contralateral eye of rat evoked by stimulation of the ispsilateral eye, which was named the “crossed electroretinogram” (xERG). The purpose of this study was to present experimental evidence for the xERG.
6-8 months old Brown-Norway (male, 300-400g) rats were anesthetized with ketamine and xylazine and paralyzed with gallamine, while a series of 10ms full-field flashes were delivered in 3s intervals to one or both eyes under dark- and light-adapted conditions. Full-field ERGs and xERGs were recorded simultaneously from both eyes before and after experimental manipulations, which included intravitreal TTX injection into each eye and intraocular pressure (IOP) elevation of one eye using a 30g needle connected to a variable-height saline reservoir. In some experiments, the electrical activity of one optic nerve was recorded with a suction electrode while the other optic nerve was electrically stimulated.
TTX injection had significant effects on the treated eye, reducing the scotopic a-wave by 20-30% and the scotopic and photopic b-wave by 50-60% (n=6, p<0.05). In addition, the photopic b wave of contralateral untreated eye was significantly reduced (~35%). The xERG was quickly abolished by TTX injections in either eye, whereas control injections of saline had no effect. When IOP was raised from 20-80 mmHg, the b-wave gradually decreased and disappeared, followed by the a-wave. The xERG of the contralateral untreated eye also disappeared at similar IOP as the b-wave, but persisted in the treated eye even though the b-wave was eliminated. Both the ERG and xERG recovered to normal when IOP was lowered back to 20mmHg. A multi-peak compound action potential could also be recorded from the optic nerve of one eye after stimulation of the opposite nerve with electrical current.
There appears to be a direct electrophysiological connection between the two eyes of adult rats that is mediated by the spike discharges of retinal ganglion cells with axonal projections to the opposite eye. The resulting “crossed ERG” may be used to noninvasively investigate ganglion cell function and inter-ocular coordination of visual system responses in rat and perhaps other animals.
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