Circadian Rhythm of the Electroretinogram in Rats

Abstract

We examined the diurnal changes in the electroretinogram (ERG) in rats to clarify whether a circadian rhythm exists in the retinal function.

ERGs were continuously recorded every 4 hours for 2 days from freely moving male Jcl: Wistar rats (4-7 months old) via electrodes implanted into the sclera of the left eye, and the amplitude and latency of the a-wave and b-wave and wavelet index (calculated from O1, O2, and O3 amplitudes) were determined. Under a 12-hour light/dark cycle (lights on from 7:00 to 19:00), the amplitude of the a-wave and b-wave and wavelet indices increased during the dark phase with maximum values at 23:00 or 3:00 and decreased during the light phase with minimum values at 11:00 or 15:00. In contrast, the latency of the a-wave and b-wave decreased during the dark phase with minimum values at 23:00 or 3:00 and increased during the light phase with maximum values at 11:00 or 15:00. A similar pattern of diurnal ERG changes was also observed under conditions of both continuous dark and continuous light. Therefore, the diurnal changes in the ERG were considered to be related to circadian rhythm of the retinal function. Additionally, the pattern of diurnal ERG changes was reversed one month after the 12-hour light/dark cycle was reversed (lights on from 19:00 to 7:00), suggesting light is one of the environmental synchronizers of circadian rhythm.

These results indicate that circadian rhythm of the retinal function similar to that of locomotor activity, which increases during the dark phase and decreases during the light phase, exists in the rat.