Brunso-Bechtold J K, Casagrande V A
J Neurosci. 1982 May;2(5):589-97. doi: 10.1523/JNEUROSCI.02-05-00589.1982.
Three characteristics distinguish the six layers of the adult tree shrew dorsal lateral geniculate nucleus (LGN). First, interlaminar spaces divide the nucleus into cell layers. Second, input from the two eyes projects to the nucleus such that two layers (1 and 5) receive input from the ipsilateral retinal and four layers (2, 3, 4, and 6) receive input from the contralateral retina. Finally, distinct cytological features characterize individual layers. In this report, we describe the postnatal development of LGN layers in the tree shrew in terms of the development of these three characteristics. At birth, the nucleus appears homogenous in Nissl-stained sections. Thus, no interlaminar spaces are present and all cells look similar in shape, size, and staining intensity. However, autoradiographic data show that, at birth, retinal afferents are segregated in an adult-like pattern. Interlaminar spaces begin to be evident between layers innervated by opposite eyes on postnatal day 2. Several days later, interlaminar spaces between layers innervated by the same eye (i.e., the borders of layer 3) appear, while the others continue to widen. Although some cytological maturation begins before interlaminar space formation, it is not until interlaminar spaces are apparent that features such as differential staining intensity and cell size can be used to distinguish individual layers. The results suggest that the three characteristics that define LGN layers in the tree shrew may be temporally separate events in the developing nucleus. Thus, retinal afferents are segregated prior to interlaminar space formation which, in turn, is initiated prior to final maturation of the cytological features that characterize the cell layers. This may indicate a degree of developmental independence among these maturational events.
成年树鼩背外侧膝状核（LGN）的六层结构有三个特征。首先，层间间隙将该核分为细胞层。其次，来自双眼的输入投射到该核，使得两层（1层和5层）接收同侧视网膜的输入，四层（2层、3层、4层和6层）接收对侧视网膜的输入。最后，各层具有独特的细胞学特征。在本报告中，我们根据这三个特征的发育情况描述了树鼩LGN各层的出生后发育。出生时，在尼氏染色切片中该核看起来是均匀的。因此，不存在层间间隙，所有细胞在形状、大小和染色强度上看起来都相似。然而，放射自显影数据表明，出生时视网膜传入纤维以类似成年的模式分离。出生后第2天，由对侧眼支配的层之间的层间间隙开始明显。几天后，由同侧眼支配的层之间的层间间隙（即3层的边界）出现，而其他间隙继续扩大。虽然一些细胞学成熟在层间间隙形成之前就开始了，但直到层间间隙明显时，诸如不同的染色强度和细胞大小等特征才能用于区分各层。结果表明，定义树鼩LGN各层的这三个特征在发育中的核中可能是在时间上分开的事件。因此，视网膜传入纤维在层间间隙形成之前就已分离，而层间间隙的形成又在表征细胞层的细胞学特征最终成熟之前开始。这可能表明这些成熟事件之间存在一定程度的发育独立性。
