Department of Psychology
Master of Arts
The visual system processes information at various levels. Initial processing takes place in the retina, which then sends information to the optic tectum, the first visual brain center in lower vertebrates, for further processing. There were two main goals of this study. The first goal was to obtain tectal evoked responses (TER) from adult zebrafish and to compare them to previous electroretinogram (ERG) spectral sensitivity data (Bilotta & Harrison, 1999). The second purpose of this study was to examine neural regeneration in the adult zebrafish at various times post-crush and to compare visual processing of these subjects to the normal subjects. The optic nerve tracts of the zebraflsh's right eye were damaged via optic nerve crush and subjects were tested at one of 5 times post-crush: 3, 14, 28, 42, or 90 days post-crush (dpc). Complete TER spectral sensitivity functions were obtained (n=10) and compared to ERG data. The TER ON-response was consistently about one log unit less sensitive than the ERG bwave (ON-response) across the entire spectrum (320-640 nm). The results show that the cone contributions to TER and ERG responses were different, particularly at the short and middle wavelengths. TER OFF-response sensitivity and the ERG d-wave sensitivity were both sensitive to ultraviolet and short wavelengths, but the TER OFF-response sensitivity dropped considerably to the middle and long wavelengths. Thus, it appears that the retina and the tectum process visual information differently. In addition to comparing ERG and TER responses, TER spectral sensitivity functions were obtained for 90 dpc subjects (n=7) and compared to the control data. No significant differences were found between the TER ON-response of the 90 dpc and the control subjects. In fact, their respective spectral sensitivities appear to have the same cone contributions. The only difference was that there was more variability in the 90 dpc subjects than in control subjects. However, the OFF-responses of the control subjects were considerably more sensitive to the ultraviolet wavelengths than the OFF-responses of the 90 dpc subjects. The results show that there was a general trend in optic nerve regeneration over time. This study has provided valuable information about the differences and similarities in visual processing of different levels of the visual system. In addition, this study has demonstrated the successful repair of the functional properties of CNS neurons in this species. All of this information further enhances the usefulness of the zebrafish as a model for vision science and neuroscience.
McDowell, Angela, "Analysis of Zebrafish Optic Tectum Visual Processing Before and After Optic Nerve Crush" (2002). Masters Theses & Specialist Projects. Paper 624.