Coombs Julie L, Van Der List Deborah, Chalupa Leo M
Neurobiology, Physiology & Behavior, College of Biological Sciences, University of California, Davis, California 95616, USA.
J Comp Neurol. 2007 Aug 20;503(6):803-14. doi: 10.1002/cne.21429.
Quantitative methods were used to assess dendritic stratification and other structural features of developing mouse retinal ganglion cells from birth to after eye opening. Cells were labeled by transgenic expression of yellow fluorescent protein, DiOlistics or diffusion of DiI, and subsequently imaged in three dimensions on a confocal microscope followed by morphometric analysis of 13 different structural properties. At postnatal day 1 (P1), the dendrites of all cells ramified across the vertical extent of the inner plexiform layer (IPL). By P3/4, dendrites were largely confined to different strata of the IPL. The stratification of dendrites initially reflected a retraction of widely ramifying dendritic processes, but for the most part this was due to the subsequent vertical expansion of the IPL. By P8, distinct cell classes could be recognized, although these had not yet attained adult-like properties. The structural features differentiating cell classes were found to follow three different developmental trends. The mean values of one set of morphological parameters were essentially unchanged throughout postnatal development; another set of measures showed a rapid rise with age to adult values; and a third set of measures first increased with age and later decreased, with the regressive events initiated around the time of eye opening. These findings suggest that the morphological development of retinal ganglion cells is regulated by diverse factors operating during different but overlapping time periods. Our results also suggest that dendritic stratification may be more highly specified in the developing mammalian retina than has been previously realized.
采用定量方法评估出生至睁眼后发育中小鼠视网膜神经节细胞的树突分层及其他结构特征。通过黄色荧光蛋白的转基因表达、染料弹丸法或DiI扩散对细胞进行标记，随后在共聚焦显微镜上进行三维成像，接着对13种不同的结构特性进行形态计量分析。出生后第1天（P1），所有细胞的树突在内网状层（IPL）的垂直范围内分支。到P3/4时，树突主要局限于IPL的不同层。树突的分层最初反映了广泛分支的树突过程的退缩，但在很大程度上这是由于IPL随后的垂直扩展。到P8时，可以识别出不同的细胞类别，尽管这些细胞尚未具备成年细胞的特性。发现区分细胞类别的结构特征遵循三种不同的发育趋势。一组形态学参数的平均值在整个出生后发育过程中基本保持不变；另一组测量值随年龄迅速上升至成年值；第三组测量值首先随年龄增加，随后下降，退化事件在睁眼时左右开始。这些发现表明，视网膜神经节细胞的形态发育受不同但重叠时间段内起作用的多种因素调控。我们的结果还表明，在发育中的哺乳动物视网膜中，树突分层可能比之前所认识的更为高度特化。
