Reese B E, Colello R J
Neuroscience Research Institute, University of California, Santa Barbara 93106.
Neuroscience. 1992;46(2):419-29. doi: 10.1016/0306-4522(92)90062-7.
The present study has examined the birthdates of neurons in the retinal ganglion cell layer of the adult rat. Rat fetuses were exposed to tritiated thymidine in utero to label neurons departing the mitotic cycle at different gestational stages from embryonic days 12 through to 22. Upon reaching adulthood, rats were either given unilateral injections of horseradish peroxidase into target visual nuclei in order to discriminate (1) ganglion cells from displaced amacrine cells, (2) decussating from non-decussating ganglion cells, and (3) alpha cells from other ganglion cell types; or, their retinae were immunohistochemically processed to reveal the choline acetyltransferase-immunoreactive amacrine cells in the ganglion cell layer. Retinae were embedded flat in resin and cut en face to enable reconstruction of the distribution of labelled cells. Retinal sections were autoradiographically processed and then examined for neurons that were both tritium-positive and either horseradish peroxidase-positive or choline acetyltransferase-positive. Tritium-positive neurons in the ganglion cell layer were present in rats that had been exposed to tritiated thymidine on embryonic days E14-E22. Retinal ganglion cells were generated between E14 and E20, the ipsilaterally projecting ganglion cells ceasing their neurogenesis a full day before the contralaterally projecting ganglion cells. Alpha cells were generated from the very outset of retinal ganglion cell genesis, at E14, but completed their neurogenesis before the other cell types, by E17. Tritium-positive, horseradish peroxidase-negative neurons in the ganglion cell layer were present from E14 through to E22, and are interpreted as displaced amacrine cells. Choline acetyltransferase-positive displaced amacrine cells were generated between E16 and E20. Individual cell types showed a rough centroperipheral neurogenetic gradient, with the dorsal half of the retina slightly preceding the ventral half. These results demonstrate, first, that retinal ganglion cell genesis and displaced amacrine cell genesis overlap substantially in time. They do not occur sequentially, as has been commonly assumed. Second, they demonstrate that the alpha cell population of retinal ganglion cells and the choline acetyltransferase-immunoreactive population of displaced amacrine cells are each generated over a limited time during the periods of overall ganglion cell and displaced amacrine cell genesis, respectively. Third, they show that the very earliest ganglion cells to be generated in the temporal retina have exclusively uncrossed optic axons, while the later cells to be generated therein have an increasing propensity to navigate a crossed chiasmatic course.
本研究检测了成年大鼠视网膜神经节细胞层中神经元的出生日期。将大鼠胎儿在子宫内暴露于氚标记的胸腺嘧啶核苷，以标记在胚胎第12天至22天不同妊娠阶段离开有丝分裂周期的神经元。成年后，对大鼠进行以下操作：要么向目标视觉核单侧注射辣根过氧化物酶，以区分（1）神经节细胞与移位无长突细胞，（2）交叉的与非交叉的神经节细胞，以及（3）α细胞与其他类型的神经节细胞；要么对其视网膜进行免疫组织化学处理，以显示神经节细胞层中胆碱乙酰转移酶免疫反应性无长突细胞。将视网膜平铺包埋在树脂中并进行面切，以便重建标记细胞的分布。对视网膜切片进行放射自显影处理，然后检查同时为氚阳性且辣根过氧化物酶阳性或胆碱乙酰转移酶阳性的神经元。在胚胎第14 - 22天暴露于氚标记胸腺嘧啶核苷的大鼠的神经节细胞层中存在氚阳性神经元。视网膜神经节细胞在胚胎第14天至20天之间生成，同侧投射的神经节细胞在对侧投射的神经节细胞停止神经发生前一整天就停止了神经发生。α细胞从视网膜神经节细胞发生的最初阶段即胚胎第14天开始生成，但在其他细胞类型之前，于胚胎第17天完成神经发生。神经节细胞层中氚阳性、辣根过氧化物酶阴性的神经元在胚胎第14天至22天均有出现，被解释为移位无长突细胞。胆碱乙酰转移酶阳性的移位无长突细胞在胚胎第16天至20天之间生成。各细胞类型呈现大致的中心 - 外周神经发生梯度，视网膜的背侧半部略早于腹侧半部。这些结果表明，第一，视网膜神经节细胞发生和移位无长突细胞发生在时间上有很大重叠。它们并非如通常所认为的那样依次发生。第二，它们表明视网膜神经节细胞的α细胞群体和移位无长突细胞的胆碱乙酰转移酶免疫反应性群体分别在整个神经节细胞和移位无长突细胞发生期间的有限时间内生成。第三，它们表明颞侧视网膜中最早生成的神经节细胞仅有不交叉的视神经轴突，而其中较晚生成的细胞有越来越大的倾向走交叉的视交叉路径。
