Wilm C, Fritzsch B
Faculty of Biology, University of Bielefeld, FRG.
Brain Behav Evol. 1990;36(5):271-99. doi: 10.1159/000115313.
Adult bony fish possess only a small ipsilateral retinofugal projection, if any. Experimental manipulation, such as unilateral enucleation, can lead to an enhancement of this projection. We examined the patterns of, as well as the conditions for the development and maintenance of an enhanced ipsilateral retinofugal projection (EIRP) after nerve crush, after enucleation, and after various combinations of both types of surgery in juvenile and adult Haplochromis burtoni (Cichlidae). Retinal projections were labeled either unilaterally with horseradish perixodase, or with the lipophilic fluorescent dye DiI in aldehyde-fixed animals, or bilaterally with differently colored fluorescent dextran amines. Unilateral nerve crush always leads to the regeneration of retinofugal fibers to the contralateral tectum but spares some contralateral diencephalic nuclei. In addition, unilateral or bilateral nerve crush in many cases, and unilateral enucleation in some cases, leads to the development of an EIRP to the ipsilateral diencephalon and tectum. This EIRP persists (4 months and longer postoperatively) in only 10% of the unilaterally enucleated animals, in none of the animals subjected to unilateral nerve crush and in 79% of the animals subjected to bilateral nerve crush. All unilaterally enucleated animals in which the remaining, contralateral optic nerve was crushed develop and maintain an EIRP. These data suggest that nerve crush alone is sufficient to cause regenerating fibers to project, at least transiently, to the ipsilateral side of the brain. When the normal contralateral projection is either absent or in the process of regeneration, an EIRP can be maintained. In the latter case, alternate bands or patches of ipsi- and contralateral fibers in the tectum may result. Ipsilateral fibers follow unusual pathways by recrossing at the rostral diencephalon. Likewise, regenerating contralateral retinal fibers grow differently in this area; here, where the optic-nerve projection is reorganized into the optic tract, many regenerating fibers are deflected to the ipsilateral side of the brain. Despite atypical routes taken by some fibers, the EIRP nevertheless ends only in specific retinorecipient areas. An EIRP develops independently of the age of the animal, independently of the time lapse between enucleation and nerve lesion, and independently of persisting debris. However, in animals receiving an optic nerve lesion a long time after unilateral enucleation, the size of the EIRP and its tectal extent are reduced compared to that in animals enucleated around the same time as receiving the crush of the contralateral optic nerve.
成年硬骨鱼即便有同侧视网膜外投射，也十分微弱。诸如单侧眼球摘除等实验性操作可增强这种投射。我们研究了幼年和成年布氏朴丽鱼（丽鱼科）在神经挤压、眼球摘除以及两种手术的不同组合之后，同侧视网膜外投射增强（EIRP）的发展和维持模式及条件。视网膜投射可通过用辣根过氧化物酶单侧标记，或在醛固定动物中用亲脂性荧光染料DiI标记，或用不同颜色的荧光葡聚糖胺双侧标记。单侧神经挤压总是会导致视网膜外纤维向对侧顶盖再生，但会保留一些对侧间脑核。此外，在许多情况下，单侧或双侧神经挤压以及在某些情况下的单侧眼球摘除，会导致向同侧间脑和顶盖发展出EIRP。这种EIRP仅在10%的单侧眼球摘除动物中持续存在（术后4个月及更长时间），在单侧神经挤压的动物中无一持续存在，而在双侧神经挤压的动物中有79%持续存在。所有单侧眼球摘除且对侧剩余视神经被挤压的动物都会发展并维持EIRP。这些数据表明，仅神经挤压就足以使再生纤维至少短暂地投射到脑的同侧。当正常的对侧投射缺失或处于再生过程中时，EIRP可以维持。在后一种情况下，顶盖中同侧和对侧纤维可能会形成交替的条带或斑块。同侧纤维通过在前脑间脑处再次交叉而遵循异常路径。同样，再生的对侧视网膜纤维在该区域的生长也不同；在这里，视神经投射重新组织成视束，许多再生纤维偏向脑的同侧。尽管一些纤维走了非典型路径，但EIRP仍然仅在特定的视网膜接受区域终止。EIRP的发展与动物年龄无关，与眼球摘除和神经损伤之间的时间间隔无关，也与残留碎片无关。然而，在单侧眼球摘除很长时间后接受视神经损伤的动物中，与在单侧眼球摘除同时接受对侧视神经挤压的动物相比，EIRP的大小及其在顶盖中的范围会减小。
