Hayes W P, Meyer R L
Developmental Biologcy Center, University of California, Irvine 92717.
J Comp Neurol. 1988 Aug 22;274(4):516-38. doi: 10.1002/cne.902740404.
The distribution of normal and regenerating retinal fibers and synapses was studied on tectum in goldfish by light (LM) and electron microscopy (EM). Since labeling of the early regenerating fibers was previously reported to be difficult, a new 'cold-fill' HRP labeling protocol was developed, which labeled regenerating optic fibers and terminals on tectum as early as 14 days after nerve crush when they first arrive on tectum. In order to characterize the laminar distribution of optic afferents in normal fish and in fish regenerating for 14-240 days, EM photomontages of areas 14 microns wide by 160 microns deep through the HRP-labeled primary optic innervation layer (S-SO-SFGS) were constructed. The time points in regeneration that were examined spanned the period in which others have shown that an initially diffuse retinotopic map becomes spatially restricted. At the LM level regenerating optic fibers were restricted to the optic lamina. They reinnervated tectum in an anterior to posterior sequence as previously seen with autoradiography. In addition, at 14 days, some "pioneer" optic fascicles were found to have already grown to posterior tectum where they gave rise to branches with boutonlike terminations and growth-cone-like processes. Form the ultrastructural analysis it was clear that optic fibers and terminals observed strict laminar boundaries as they partitioned themselves in the optic laminae (S, SO and SFGS) in both normal and regenerating fish. The behavior of optic fibers was lamina specific with respect to synapse formation and the orientation of fiber outgrowth. As early as 14 days regeneration, optic fibers made synapses onto the four types of postsynaptic profiles observed in normal fish. Numerous optic terminals were labeled at 14 days, and there appeared to be no waiting period between fiber ingrowth to the SO and synapse formation in the S and SFGS. At 14-60 days, atypical synaptic contacts which appear to be nascent synapses were made by labeled optic fibers in fascicles and by growth-cone-like processes. By 21-30 days, the density of optic terminals was high and there were many more fasciculated optic fibers in the SFGS than normal as late as 350 days. These findings suggest that optic fiber lamination is highly constrained by tectal cues, that fibers rapidly regenerate many synaptic terminals before retinotopic map refinement is complete, and that fibers have a strong affinity for each other.
通过光学显微镜（LM）和电子显微镜（EM）研究了金鱼视顶盖中正常和再生视网膜纤维及突触的分布。由于先前报道早期再生纤维的标记很困难，因此开发了一种新的“冷灌流”HRP标记方案，该方案在神经挤压后14天，即再生的视神经纤维和终末首次到达视顶盖时，就能对其进行标记。为了描述正常鱼和再生14 - 240天的鱼中视神经传入纤维的层状分布，构建了通过HRP标记的初级视神经支配层（S - SO - SFGS）、宽14微米、深160微米区域的EM照片拼接图。所检查的再生时间点涵盖了其他人已表明最初弥散的视网膜拓扑图在空间上变得受限的时期。在光学显微镜水平，再生的视神经纤维局限于视神经层。它们从前向后依次重新支配视顶盖，这与先前放射自显影所见一致。此外，在14天时，发现一些“先驱”视神经束已经生长到视顶盖后部，在那里它们产生带有纽扣状终末和生长锥样突起的分支。从超微结构分析可以清楚地看出，在正常鱼和再生鱼中，视神经纤维和终末在视神经层（S、SO和SFGS）中自我分隔时都遵循严格的层界。视神经纤维在突触形成和纤维生长方向上具有层特异性。早在再生14天时，视神经纤维就与正常鱼中观察到的四种类型的突触后轮廓形成突触。在14天时，大量视神经终末被标记，并且从纤维长入SO到在S和SFGS中形成突触之间似乎没有等待期。在14 - 60天时，标记的视神经纤维束和生长锥样突起形成了似乎是新生突触的非典型突触接触。到21 - 30天时，则密度很高，并且直到350天，SFGS中紧密成束的视神经纤维比正常情况多得多。这些发现表明，视神经纤维的分层受到视顶盖线索的高度限制，在视网膜拓扑图细化完成之前，纤维迅速再生许多突触终末，并且纤维之间具有很强的亲和力。
