Valverde F, López-Mascaraque L, Santacana M, De Carlos J A
Laboratorio de Neuroanatomía Comparada, Instituto Cajal (CSIC), Madrid, Spain.
J Neurosci. 1995 Jul;15(7 Pt 1):5014-24. doi: 10.1523/JNEUROSCI.15-07-05014.1995.
In the rat, the deepest neocortical layer forms a conspicuous cell band known as layer Vlb. Cells in layer Vlb are among the first to differentiate, and it has been regarded as an homolog to the subplate of primates and carnivores. Cell death has been considered a universal feature of subplate cells. In order to assess the validity of this assertion, we examined the sequence of generation and the extent of cell death in layer Vlb. This was achieved using injections of 3H-thymidine and two methods for the direct visualization of apoptotic figures. Single injections of 3H-thymidine were performed between E12 and E15 (E0 is the day of insemination), and brains were examined at different postnatal ages between P1 and P63. The number of heavily labeled cells were counted in layer Vlb in six standard, equally spaced coronal sections in each brain. Single injections at E12 labels about 3% of the entire population of layer Vlb cells, 17% at E13, 30% at E14, and < 1% at E15. Our results indicate that the absolute number of heavily labeled cells in layer Vlb remains constant. The analysis of variance (one-way ANOVA) showed that the difference among the group means was not significant from P1 to P63 after injections at either E12, E13, or E14. In order to confirm these results, we evaluated the distribution of pyknotic (apoptotic) cell bodies in the neocortex. Apoptotic cells were visualized in Nissl preparations and by histochemical staining using an in situ apoptosis detection kit. The analysis was performed in rats from E18 to P15. Both methods gave comparable results. We found that the amount of cell death in layer Vlb is neither particularly prominent nor significantly different from that which occurs in the remaining neocortical layers, apart from layer II and in the white matter of the corpus callosum. We conclude that neuronal death does not play any significant role in the rodent subplate.
在大鼠中，新皮层最深层形成一条明显的细胞带，称为Vlb层。Vlb层中的细胞是最早分化的细胞之一，它被认为是灵长类动物和食肉动物的亚板层的同源物。细胞死亡一直被认为是亚板层细胞的一个普遍特征。为了评估这一断言的正确性，我们研究了Vlb层细胞的生成顺序和细胞死亡程度。这是通过注射3H-胸腺嘧啶核苷以及两种直接观察凋亡细胞形态的方法来实现的。在胚胎第12天到第15天（E0为受精日）之间进行单次3H-胸腺嘧啶核苷注射，并在出生后第1天到第63天的不同年龄检查大脑。在每只大脑的六个标准、等间距冠状切片中计数Vlb层中标记严重的细胞数量。在胚胎第12天单次注射标记约3%的Vlb层细胞总数，第13天为17%，第14天为30%，第15天小于1%。我们的结果表明，Vlb层中标记严重的细胞绝对数量保持恒定。方差分析（单因素方差分析）表明，在胚胎第12天、第13天或第14天注射后，从出生后第1天到第63天，各组均值之间的差异不显著。为了证实这些结果，我们评估了新皮层中固缩（凋亡）细胞体的分布。在尼氏染色标本中以及使用原位凋亡检测试剂盒进行组织化学染色来观察凋亡细胞。分析在胚胎第18天到出生后第15天的大鼠中进行。两种方法得到了可比的结果。我们发现，Vlb层中的细胞死亡量既不特别突出，与其余新皮层层（除了第II层和胼胝体白质）发生的细胞死亡量也没有显著差异。我们得出结论，神经元死亡在啮齿动物亚板层中不发挥任何重要作用。
