Anatomical and physiological studies have shown that the zebrafish is a useful model of vertebrate visual function. Anatomy has shown that the zebrafish possess the traditional three cone types (S-, M-, and L- cones), and a fourth cone type that is sensitive to ultraviolet light (U-cones). Physiologically, the adult zebrafish appears to have a complex visual system with color opponent mechanisms. Anatomical results suggest that the zebrafish may be a good model of retinal development as well. The zebrafish retina develops in a sequential manner and is immature at hatch. Bilotta et al. (1996) also found that the retina was functionally immature in larvae zebrafish. In addition, after exposure to abnormal light rearing conditions, larvae zebrafish showed deficits in visual behavior, even though there appears to be no effect on the gross morphology of the young zebrafish retina. The purpose of the present study was to use a physiological approach to assess retinal development and the effects of abnormal light rearing conditions. Larvae zebrafish were raised under three light rearing conditions: constant light (LL), constant dark (DD), and normal cyclic light (LD) for six days following fertilization. After six days, the animals were placed back into normal cyclic light. Three ages were tested: 6-8, 13-15, and 21-24 dpf. The method used to assess retinal function was the electroretinogram (ERG). Comparisons were made across the three age groups and the three conditions. Differences in the ERG waveforms and spectral sensitivities across the three ages were found. The 6-8 and 13-15 dpf subjects were less sensitive than the 21-24 dpf group. Also, the 21-24 dpf had adult-like U- and S-cone function, but were missing the L-M and the M-S opponent mechanisms found in the adult. Deficits from the light rearing conditions were seen immediately following exposure (6-8 dpf). The LL condition subjects showed the greatest deficit in the ultraviolet and short-wavelength areas, and the DD condition subjects showed a slight deficit across the entire spectrum. At 13-15 dpf, the LL and DD groups showed an increase in sensitivity and by 21-24 dpf the differences that had been apparent were gone. The results of this study show that the zebrafish is a good model for vertebrate retinal development and function. Thus, the behavioral developmental trend that is seen in other vertebrates is also present in the zebrafish. In addition, the zebrafish is adversely affected by abnormal light rearing environments. The pattern of damage that was seen in primates appears to be present in the zebrafish. However, unlike the primates, the zebrafish appears to be capable of regeneration, thereby suggesting that the zebrafish would be a viable model for light environment effects and regeneration.
| Identifer | oai:union.ndltd.org:WKU/oai:digitalcommons.wku.edu:theses-1321 |
| Date | 01 August 1998 |
| Creators | Saszik, Shannon |
| Publisher | TopSCHOLAR® |
| Source Sets | Western Kentucky University Theses |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Masters Theses & Specialist Projects |
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