Ott Matthias, Bellintani-Guardia Breno
Institute for Anatomy, University of Tübingen, Osterbergstrasse 3, 72074 Tübingen, Germany.
Vis Neurosci. 2003 May-Jun;20(3):273-83. doi: 10.1017/s0952523803203060.
Retinal ganglion cells (RGCs) usually increase their dendritic field area with postnatal retinal growth. The mechanisms that regulate the postnatal shape of dendritic arbors in the growing retina are not well understood. Quantitative studies suffer from the difficulty of labeling specific subpopulations of RGCs selectively including their dendritic processes. In this study, we labeled displaced retinal ganglion cells (DGC) that are known to project to the accessory optic system (AOS) in juvenile and adult chameleons by retrograde transport of dextran amines. The complete population of DGCs was quantitatively screened for the effects of postnatal retinal growth on cell morphology, dendritic field coverage, and dendritic arbor size. The adult eye contained 2000 DGCs/retina. This number was already present at birth. The smaller size of the hatchling eye (approximately 1/3 of the adult size) led to higher densities of DGCs. The greatest accumulation of juvenile DGCs (two-fold higher compared to the adult) was found in the periphery of the retina where the greatest surface expansion was observed. DGC dendritic field areas were adjusted proportionally to this expansion in order to maintain a constant dendritic coverage. The increase of dendritic fields was mediated by two putative passive mechanisms: First, an elongation of individual dendrites similar to previous reports of postnatal RGC development in the retina of goldfish and chicks. Second, and more prominent, we observed that neighboring dendrites were pulled apart from each other. This resulted in a looser spacing of the initially tightly packed dendrites of each dendritic arbor. This dispersal of dendrites over a larger area was, due to its passive nature, proportional to the increase of the retinal surface and preserved a constant dendritic coverage irrespective of the animal's age and eye size.
视网膜神经节细胞（RGCs）通常会随着出生后视网膜的生长而增加其树突野面积。目前对于调节视网膜生长过程中树突分支出生后形态的机制尚不清楚。定量研究面临着选择性标记包括其树突过程在内的特定RGC亚群的困难。在本研究中，我们通过葡聚糖胺的逆行运输标记了幼年和成年变色龙中已知投射到副视系统（AOS）的移位视网膜神经节细胞（DGC）。对整个DGC群体进行了定量筛选，以研究出生后视网膜生长对细胞形态、树突野覆盖范围和树突分支大小的影响。成年眼中每个视网膜含有2000个DGC。这个数量在出生时就已存在。幼体眼睛较小（约为成年眼睛大小的1/3）导致DGC密度更高。在视网膜周边发现幼年DGC的积累最多（比成年时高出两倍），而视网膜周边的表面扩张最大。DGC的树突野面积与这种扩张成比例地调整，以保持恒定的树突覆盖范围。树突野的增加由两种假定的被动机制介导：第一，单个树突的伸长，类似于先前关于金鱼和小鸡视网膜中出生后RGC发育的报道。第二，更显著的是，我们观察到相邻的树突彼此拉开。这导致每个树突分支最初紧密排列的树突间距变宽。由于其被动性质，树突在更大面积上的这种分散与视网膜表面的增加成比例，并且无论动物的年龄和眼睛大小如何，都能保持恒定的树突覆盖范围。
