金鱼再生的视神经在顶盖投射精确化的DiI顺行标记研究

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

本文用微量显微注射法,在金鱼视网膜的背侧用亲脂类荧光染料DiI标记少量神经节细胞,通过顺行标记研究了视神经再生过程中视网膜顶盖投射的精确化过程。在损伤视神经后的不同时期观察了再生视神经纤维在顶盖整装片上的分布。在再生早期它们以超出正常的途径由背腹两侧进入顶盖,广泛分布。但其中大部分仍分布于顶盖腹侧的靶区。在再生晚期通过精确化,重建如正常鱼一样精确的视网膜顶盖投射。这个精确化过程表现在以下三方面:(1)再生于顶盖错误区域的再生视神经纤维的消失;(2)再生早期视神经纤维主干上生长的侧部分支的消失;(3)到达靶区的再生视神经纤维形成重迭的终末分支。由以上结果推测,顶盖中可能存在两类不同的因子:一类是普通诱向因子,存在于整个顶盖中,它在再生早期引导再生的视神经纤维长入顶盖。另一类是神经营养因子,它具区域特异性,在再生晚期引导视神经纤维到达顶盖靶区,形成精确的视网膜顶盖投射。

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.