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THE REFINEMENT OF RETINOTECTAL PROJECTION ON TECTAL WHOLE MOUNT DURING THE REGENERA- TION OF THE GOLDFISH OPTIC NERVE LABE- LED WITH Oil ANTEROGRADELY

Wang Zi-ren (Department of Biology, Lanzhou University, Lanzhou, 730000) Ronald L. Meyer (Developmental Biology Center, University of California, Irvine)  
The refinement of retinotectal projection during the regeneration of the goldfish optic nerve was studied with microin-jection of the lipophilic dye Dil (1,1-dioctadecyl-3, -3, -3', -3', -tetramethylindo-carbocyanine perchlorate) into the dorsal retina to label a few of retinal ganglion cells, which could be transported antero-gradely to their terminal arbors on the tectum. The regenerated optic nerve fibers on the tectal whole mount were examined at various time intervals (from 7 to 365 days) following an optic nerve crush. At the early regeneration stage (2 to 8 weeks postcrush), the regenerated optic fibers travelled in abnormal paths through both appropriate ventral and inappropriate dorsal hemitecta, but the majority of the fibers (about 60% to 70%) were found in the appropriate ventral hemitectum. At the late regeneration stage (2 months afterward postcrush), after refinement of regenerated optic fibers, the retinotectal projection was reestablished preciously as in the normal fish. Present study shows that the refinement of the retinotectal projection manifests in three major changes: 1) The disappearance of the regenerated optic fibers at the inappropriate tectal positions; 2) The disappearance of the side branches on the optic fiber shaft; 3) The formation of overlapping terminal arbors by the optic fibers that arrived at the retinotopic target. These results suggest that there may be two kinds of factors in the tectum: One is a common guiding factor which distributes over all the tectum and guides the regenerated optic fibers growing into the tectum at early regeneration; another is a position-specific neurotrophic factor which guides the regenerated optic fibers arriving at the retinotopic target at late regeneration.
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