Kirby M A, Steineke T C
Department of Pediatrics, School of Medicine, Loma Linda University, CA 92350.
Vis Neurosci. 1992 Dec;9(6):603-16. doi: 10.1017/s095252380000184x.
The morphology of retinal ganglion cells within the central retina during formation of the fovea was examined in retinal explants with horseradish-peroxidase histochemistry. A foveal depression was first apparent in retinal wholemounts at embryonic day 112 (E112; gestational term is approximately 165 days). At earlier fetal ages, the site of the future fovea was identified by several criteria that included peak density of ganglion cells, lack of blood vessels in the inner retinal layers, arcuate fiber bundles, and the absence of rod outer segments in the photoreceptor layer. Prior to E112, the terminal dendritic arbor of retinal ganglion cells within the central retina extended into the inner plexiform layer and were located directly beneath their somas of origin or at most were slightly displaced from it. For example, at E90 the mean horizontal displacement of the geometric center of the dendritic arbor from the somas of cells within 600 microns of the estimated center of the future fovea was 4.1 microns (S.D. 2.7, range 1.0-10.0, n = 97). Following formation of the foveal depression the dendritic arbors of cells were significantly displaced from their somas. For example, at E138 the mean displacement was 41.2 microns (S.D. 12.2, range 12.0-56.0, n = 97). The displacement of the dendritic arbor which occurred during this period was not accounted for by areal growth of the dendritic arbor, the somas, or the retina, but was produced by the lengthening of the primary dendritic trunk. Moreover, no significant displacement was observed within the remaining 1.5-6.5 mm of the central retina. These observations provide evidence supporting early speculations that the formation of the foveal pit occurs, in part, by the radial migration of ganglion cells from the center of the fovea during its formation. Our analyses suggest that this migration occurs by the lengthening of the primary dendrite presumably by the addition of membrane. This migration is in a direction opposite to the inward movement of photoreceptors that occurs during late fetal and early postnatal periods (Packer et al., 1990, Journal of Comparative Neurology 298, 472-493).
利用辣根过氧化物酶组织化学技术，在视网膜外植体中检测了中央视网膜内视网膜神经节细胞在中央凹形成过程中的形态。在胚胎第112天（E112；妊娠期约165天），视网膜整体标本中首次出现中央凹凹陷。在更早的胎儿期，未来中央凹的位置可通过几个标准来确定，包括神经节细胞的峰值密度、视网膜内层无血管、弓形纤维束以及光感受器层无视杆外段。在E112之前，中央视网膜内视网膜神经节细胞的终末树突分支延伸至内网状层，且直接位于其起源的胞体下方，或者最多仅与其稍有偏移。例如，在E90时，在距未来中央凹估计中心600微米范围内的细胞，其树突分支几何中心相对于胞体的平均水平偏移为4.1微米（标准差2.7，范围1.0 - 10.0，n = 97）。中央凹凹陷形成后，细胞的树突分支明显与其胞体发生了偏移。例如，在E138时，平均偏移为41.2微米（标准差12.2，范围12.0 - 56.0，n = 97）。在此期间发生的树突分支偏移并非由树突分支、胞体或视网膜的面积增长所致，而是由初级树突干的延长产生的。此外，在中央视网膜剩余的1.5 - 6.5毫米范围内未观察到明显的偏移。这些观察结果为早期推测提供了证据，即中央凹坑的形成部分是由于在其形成过程中神经节细胞从中央凹中心进行径向迁移。我们的分析表明，这种迁移是通过初级树突的延长发生的，推测是通过添加膜实现的。这种迁移方向与胎儿后期和出生后早期发生的光感受器向内移动方向相反（Packer等人，1990年，《比较神经学杂志》298，472 - 493）。
