Jones Shawn P, Rahimi Omid, O'Boyle Michael P, Diaz Daniel L, Claiborne Brenda J
Department of Biology, University of Texas at San Antonio, San Antonio, Texas 78249, USA.
Hippocampus. 2003;13(3):413-27. doi: 10.1002/hipo.10121.
Most granule neurons in the rat dentate gyrus are born over the course of the first 2 postnatal weeks. The resulting heterogeneity has made it difficult to define the relationship between dendritic and axonal maturation and to delineate a time course for the morphological development of the oldest granule neurons. By depositing crystals of the fluorescent label Dil in hippocampal field CA3, we retrogradely labeled granule neurons in fixed tissue slices from rats aged 2-9 days. The results showed that all labeled granule cells, regardless of the age of the animal, exhibited apical dendrites. On day 2, every labeled neuron had rudimentary apical dendrites, and a few dendrites on each cell displayed immature features such as growth cones, varicosities, and filopodia. Some cells displayed basal dendrites. By day 4, the most mature granule neurons had longer and more numerous apical branches, as well as various immature features. Most had basal dendrites. On days 5 and 6, the immature features and the basal dendrites had begun to regress on the oldest cells, and varying numbers of spines were present. On day 7, the first few adult-like neurons were seen: immature features and basal dendrites had disappeared, all dendrites reached the top of the molecular layer, and the entire dendritic tree was covered with spines. These data show that dendritic outgrowth occurs before, or concurrent with, axon arrival in the CA3 target region, and that adult-like granule neurons are present by the end of the first week.
大鼠齿状回中的大多数颗粒神经元在出生后的前两周内产生。由此产生的异质性使得难以确定树突和轴突成熟之间的关系，也难以描绘最老的颗粒神经元形态发育的时间进程。通过在海马CA3区沉积荧光标记物Dil的晶体，我们对2 - 9日龄大鼠固定组织切片中的颗粒神经元进行了逆行标记。结果显示，所有标记的颗粒细胞，无论动物年龄大小，均表现出顶端树突。在第2天，每个标记的神经元都有原始的顶端树突，每个细胞上的一些树突表现出不成熟的特征，如生长锥、膨体和丝状伪足。一些细胞显示出基底树突。到第4天，最成熟的颗粒神经元有更长、更多的顶端分支，以及各种不成熟的特征。大多数有基底树突。在第5天和第6天，最老的细胞上的不成熟特征和基底树突开始消退，出现了数量不等的棘。在第7天，首次观察到一些类似成年的神经元：不成熟特征和基底树突消失，所有树突到达分子层顶部，整个树突树布满棘。这些数据表明，树突生长发生在轴突到达CA3靶区域之前或同时，并且在第一周结束时出现类似成年的颗粒神经元。
