Abstract
Purpose:
Emran et al (2010) reported that the amplitudes of the electroretinograms (ERGs) recorded from isolated eyes of larval zebrafish were normal throughout the day, but were almost absent after several hours of darkness at night. The purpose of our study was to confirm this circadian rhythm of the ERGs in living zebrafish.
Methods:
Initially, zebrafish (Danio rerio) were kept in a 14:10 light:dark cycle (room fluorescent light, 9:00 to 23 hours). ERGs were elicited by stimulus intensities of 790 mW/m2 and durations of 1000 msec. The ERGs were recorded with an Ag/AgCl wire electrode that was inserted into a glass micropipette filled with E3 medium. A glasspipette electrode was positioned in the center of the cornea and a reference electrode was an Ag/AgCl pellet that placed beneath the larvae body. The zebrafish was anesthetized by 3-aminobenzoic acid methylester and placed on its side on a moisture sponge with one eye facing toward a light. We recorded ERGs of larval (5 days postfertilization) zebrafish at 9:00, 14:00, 19:00, 24:00, 2:00, 6:00, and 14:00 h. We also recorded the ERGs after three hours of dark-adaptation at 2:00 and at 14:00 hours. We recorded 3 animals for each time.
Results:
As reported by Emran et al, the b-wave amplitudes were smaller at night than during the day; average, 365.3 μV at 14:00 h, 151.1 μV at 23:00 h, 28.7 μV at 2:00 h, and 25.3 μV at 6:00 h. At 9:00 h the next morning, the amplitude was larger at 70.3 μV. The ERG amplitudes recorded after three hours dark-adaptation were always lager at 14:00 h (61.2 μV) than at 2:00 h (25.3 μV). The implicit times of the b-wave tended to be prolonged at night; 87.7 msec at 14:00 h, 100.7 msec at 23:00 h, 152.3 msec at 2:00 h, 95.5 msec at 6:00 h.
Conclusions:
These results suggested that there are significant differences in the ERG amplitudes and implicit times recorded at day and at night not only in isolated eyes but also in the living larval zebrafish. Additional experiments are planned to determine the physiological basis for this circadian change in the ERGs.
Keywords: 510 electroretinography: non-clinical •
688 retina •
427 aqueous