Abstract
Purpose:
We have encountered a new phenomenon of bioelectrical activity in the contralateral eye when visually stimulating the ipsilateral eye of rats. This phenomenon was named “crossed electroretinagram” (xERG), and the aim of this study was to investigate its light-dependent properties.
Methods:
6-8 months old Brown-Norway (n=6, male, 300-400g) rats were anesthetized with ketamine and xylazine and paralyzed with gallamine. Animals were dark-adapted for 4 hours prior to ERG recording. Full-field ERG and xERG were then obtained simultaneously from both eyes under dark-adapted and light-adapted conditions with 10ms full-field flashes delivered at luminance intensities varying over 2 log units and interstimulus intervals of 3, 5 and 10s.
Results:
The xERG consisted of three waves: a positive peak (xP1), a negative trough (xN1), and a second positive peak (xP2). The latency of the scotopic and photopic xP1 peaks were 99.4 ± 2.1 ms and 110.4 ± 4.6 ms, respectively. The latencies of the xN1 and xP2 peaks were more variable, falling in the range of 100-300ms and 300-400 ms, respectively. The xP1, xN1, and xP2 amplitudes of the scotopic xERG were 6.4 ± 1.2, 8.4 ± 1.1 and 7.4 ± 0.8 mV, respectively. The photopic xERG components were similar in amplitude: 6.3 ± 0.7, 6.0 ± 1.0 and 6.4 ± 1.7 mV, respectively. Neither the scotopic nor the photopic xERG amplitudes were markedly affected by changes in stimulus intensity or flash interval over the range tested. The xERG closely approximated the difference in full-field ERG responses to monocular and binocular stimulation.
Conclusions:
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” was relatively insensitive to variations in stimulus parameters compared to the full-field ERG. This newly established phenomenon offers a promising tool for studying ganglion cell function and visual signal processing noninvasively.