Rod contributions to the electroretinogram of the dark‐adapted developing zebrafish

Abstract

Anatomical studies of the developing zebrafish retina have shown that rods approach maturity at about 15 days postfertilization (dpf). Past work has examined the photopic spectral sensitivity function of the developing zebrafish, but not spectral sensitivity under darkadapted conditions. This study examined rod contributions to the dark-adapted spectral sensitivity function of the ERG b-wave component in developing zebrafish. ERG responses to stimuli of various wavelengths and irradiances were obtained from dark-adapted fish at 6-8, 13-15, 21-24, and 27-29 dpf. The results show that dark-adapted spectral sensitivity varied with age. Spectral sensitivity functions of the 6-8 and 13-15 dpf groups appeared to be cone dominated and contained little or no rod contributions. Spectral sensitivity functions of the 21-24 and 27-29 dpf groups appeared to have both rod and cone contributions. Even at the oldest age group tested, the darkadapted spectral sensitivity function did not match the adult function. Thus, consistent with anatomical findings, the rod contributions to the ERG spectral sensitivity function appear to develop with age; however, these contributions are still not adult-like by 29 dpf, which is contrary to anatomical work. These results illustrate that the zebrafish is an excellent model for visual development.

Zebrafish: A model system for the study of eye genetics

“…In zebrafish larvae, the regular spread of cone opsin expression into the dorsal and temporal retina is in contrast to the sporadically distribution of rod opsin across the retina (Raymond et al, 1995;Schmitt and Dowling, 1996;Fadool, 2003). The first detectable rod responses by ERG appear between 15 to 21 dpf (Saszik et al, 1999;Bilotta et al, 2001).…”

“…It is also likely that mutations specifically affecting rods were not detected in the previous larval screens. Based upon the ERG and visual-evoked behaviors, rod function usually cannot be detected prior to 21 dpf (Saszik et al, 1999;Bilotta et al, 2001) whereas most screens are conducted at 5 dpf. To detect changes in the rods, alternative approaches needed to be developed.…”

Behavioral genetic approaches to visual system development and function in zebrafish

“…At this stage there is little or no rod function detectable, and rods are first found to be functional in the ERG at 21 dpf (Bilotta et al, 2001). The rod contributions to the ERG spectral sensitivity function develop with age and are still not adult-like by 29 dpf, despite mature rod morphology seen anatomically (Bilotta et al, 2001). This is a clear indication that the retina is still maturing during young fry stages.…”

“…Its development closely follows the morphologic maturation of the retina. By 5 dpf, electroretinograms (ERG) containing all the components of a typical vertebrate ERG can be recorded (Branchek, 1984;Brockerhoff et al, 1995;Hughes et al, 1998;Saszik et al, 1999;Bilotta et al, 2001;Seeliger et al, 2002).…”

“…Although expression of rhodopsin is clearly detectable in young larvae, rod photoreceptors are not morphologically mature until relatively late stages (15 dpf; Branchek and Bremiller, 1984). At this stage there is little or no rod function detectable, and rods are first found to be functional in the ERG at 21 dpf (Bilotta et al, 2001). The rod contributions to the ERG spectral sensitivity function develop with age and are still not adult-like by 29 dpf, despite mature rod morphology seen anatomically (Bilotta et al, 2001).…”