Jeyarasasingam G, Snider C J, Ratto G M, Chalupa L M
Section of Neurobiology, Physiology and Behavior and the Center for Neuroscience, University of California, Davis 95616-0657, USA.
J Comp Neurol. 1998 May 11;394(3):335-43.
At maturity, ON and OFF alpha ganglion cells in the cat retina are arrayed in regular mosaics, with adjacent cells commonly forming ON-OFF pairs. In the present study, we investigated the role of activity-mediated ganglion cell death in the formation of such cellular patterns. Because direct measures of ganglion cell mosaics are problematic in the developing retina, we examined the distributions of ON and OFF alpha cells in the postnatal cat retina by assessing the degree to which cells in closest proximity were of opposite sign (i.e., ON-OFF pairs). Computer simulations demonstrated that superimposition of two regular distributions results in a high incidence (approximately 90%) of opposite sign pairs. This is also the case for ON and OFF alpha cells in the mature retina, reflecting the high degree of regularity exhibited by this cell class. In contrast, during the first postnatal month, alpha cells displayed a much lower incidence of opposite sign pairs (approximately 60%), comparable to the superimposition of two simulated random distributions. We also show that there is a 20% loss of alpha cells in the central retina during postnatal development and that this magnitude of loss is sufficient to form regular distributions of ON and OFF cells. To assess the influence of sodium voltage-gated activity on this developmental process, intraocular injections of tetrodotoxin (TTX) were made during the postnatal period of alpha cell loss. When the TTX-treated animals reached maturity, there was a dose-related decrease in the incidence of opposite sign pairs, without any appreciable change in cell density. Moreover, the regularity index of ON and OFF cells was significantly lower than normal in the TTX-treated retinas. These findings demonstrate that a spatially selective pattern of ganglion cell loss contributes to the formation of regular ON and OFF ganglion cell distributions and that such cell loss is regulated by retinal activity.
在成熟时，猫视网膜中的ON和OFFα神经节细胞呈规则镶嵌排列，相邻细胞通常形成ON-OFF对。在本研究中，我们调查了活动介导的神经节细胞死亡在这种细胞模式形成中的作用。由于在发育中的视网膜中直接测量神经节细胞镶嵌存在问题，我们通过评估最接近的细胞具有相反信号（即ON-OFF对）的程度，来检查出生后猫视网膜中ON和OFFα细胞的分布。计算机模拟表明，两个规则分布的叠加会导致相反信号对的高发生率（约90%）。成熟视网膜中的ON和OFFα细胞也是如此，反映了这一细胞类型所表现出的高度规则性。相比之下，在出生后的第一个月，α细胞显示出相反信号对的发生率要低得多（约60%），类似于两个模拟随机分布的叠加。我们还表明，在出生后发育过程中，中央视网膜中的α细胞有20%的损失，并且这种损失程度足以形成ON和OFF细胞的规则分布。为了评估钠电压门控活动对这一发育过程的影响，在α细胞损失的出生后时期进行了眼内注射河豚毒素（TTX）。当用TTX处理的动物达到成熟时，相反信号对的发生率出现剂量相关的下降，而细胞密度没有任何明显变化。此外，在经TTX处理的视网膜中，ON和OFF细胞的规则指数明显低于正常水平。这些发现表明，神经节细胞损失的空间选择性模式有助于形成规则的ON和OFF神经节细胞分布，并且这种细胞损失受视网膜活动调节。
