Grant P, Ma P M
J Comp Neurol. 1986 Aug 15;250(3):364-76. doi: 10.1002/cne.902500309.
The rotated eye paradigm has been a major experimental test of the neuronal specificity model for the development of ordered retinotectal connections in amphibians. In most studies, however, no optic fiber pathways were traced from rotated eyes and correlated with visuotectal projections. As an initial approach to this question, optic fibers from eyes rotated at different embryonic stages were traced with 3H-proline autoradiography. Three experimental series were prepared: in situ eye rotations, isochronic transplants of eyes rotated between embryos at the same stage, and heterochronic transplants of eyes rotated between embryos at different stages. Single or multiple optic fiber pathways developing from rotated eyes are identified by their sites of entry and trajectory in the brain. These include a normal chiasmatic (CH) pathway, and three aberrant pathways, identified as trigeminal (TR), diencephalic (DI), and oculomotor (OC). The latter three enter the brain ipsilaterally, some crossing contralaterally via commissural pathways. Depending on stage and type of operation, TR pathways develop in 50-100% of the animals, while CH pathways are more common after rotation at stage 21/22. The surgical procedure affects the initial trajectory of fibers from the retina, perturbs guidance cues in the surrounding orbit, and determines the patterns of optic pathways that develop. In most cases, optic fibers follow motor (oculomotor) or sensory (trigeminal) nerves, usually the first fibers encountered near the orbit by axonal pioneers exiting the retina. Evidently, optic fibers exhibit no pathway selectivity; any axon serves as a guidance cue. Tecta are innervated in about 50% of the cases, usually by fibers following abnormal trajectories from CH and OC pathways. The results suggest that the development of ordered visuotectal projections from rotated eyes is a complex process that may be independent of the trajectory of fiber arrival. Unless pathways and visuotectal maps are directly compared in each animal, however, the question remains open because we still do not know which anomalous pathways, if any, correlate with ordered projections.
旋转眼范式一直是对两栖动物有序视网膜-脑顶盖连接发育的神经元特异性模型的一项主要实验测试。然而，在大多数研究中，没有从旋转眼中追踪到视神经纤维通路并将其与视觉-脑顶盖投射相关联。作为解决这个问题的初步方法，用³H-脯氨酸放射自显影术追踪了在不同胚胎阶段旋转的眼睛的视神经纤维。制备了三个实验系列：原位眼旋转、同一阶段胚胎间旋转眼的等时移植以及不同阶段胚胎间旋转眼的异时移植。从旋转眼中发育出的单条或多条视神经纤维通路通过它们在脑中的进入部位和轨迹来识别。这些通路包括正常的交叉（CH）通路以及三条异常通路，分别确定为三叉神经（TR）、间脑（DI）和动眼神经（OC）通路。后三条通路同侧进入脑内，有些通过连合通路对侧交叉。根据手术阶段和类型，TR通路在50% - 100%的动物中发育，而在第21/22阶段旋转后CH通路更常见。手术操作会影响来自视网膜的纤维的初始轨迹，扰乱周围眼眶中的引导线索，并决定发育的视神经通路模式。在大多数情况下，视神经纤维沿着运动（动眼神经）或感觉（三叉神经）神经走行，通常是轴突先驱离开视网膜时在眼眶附近遇到的第一批纤维。显然，视神经纤维没有表现出通路选择性；任何轴突都可作为引导线索。在大约50%的情况下脑顶盖会被神经支配，通常是由沿着来自CH和OC通路的异常轨迹的纤维支配。结果表明，从旋转眼中发育出有序的视觉-脑顶盖投射是一个复杂的过程，可能与纤维到达的轨迹无关。然而，除非在每只动物中直接比较通路和视觉-脑顶盖图谱，否则这个问题仍然悬而未决，因为我们仍然不知道哪些异常通路（如果有的话）与有序投射相关。
