Fujimori K E, Takeuchi K, Yazaki T, Uyemura K, Nojyo Y, Tamamki N
Department of Anatomy, Fukui Medical University, Matsuoka, Japan.
J Comp Neurol. 2000 Feb 14;417(3):275-88. doi: 10.1002/(sici)1096-9861(20000214)417:3<275::aid-cne2>3.0.co;2-7.
In the telencephalon, the corticospinal (CS), callosal, and hippocampal commissural neurons are the major types of neurons that have axons crossing the midline of the brain. To understand the mechanisms involved in crossing the midline structure and to examine whether the expression patterns of L1 and TAG-1 in the commissural neurons are similar to those in the spinal cord, we investigated L1 and TAG-1 expression in these neurons in rats by using a double-labeling technique involving retrograde labeling and in situ hybridization. Expression of L1 messenger RNA was detected in the retrogradely labeled CS projection neurons by 1,1;-dioctadecyl-3,3, 3;,3;-tetramethylindocarbocyanine perchlorate (DiI) injection into the pons at embryonic day (E) 19, but expression of TAG-1 messenger RNA was not detected in these neurons. Also, after their axons crossed the pyramidal decussation, continued expression of L1 but no expression of TAG-1 in the CS projection neurons was shown by an additional double-labeling experiment involving DiI injection into the spinal cord at postnatal day (P) 1. An immunohistochemical study showed that L1 was continuously present in each level of the CS tract at E21 and P3, but TAG-1 immunoreactivity was not found in any level at any stage. Finally, we examined the expression of L1 and TAG-1 messenger RNAs in the callosal and hippocampal commissure neurons after their axons had crossed the midline by using the double-labeling technique. In both cases, hybridization signals of the L1 and TAG-1 messenger RNAs were observed in the retrogradely labeled neurons at P3. These results suggest that the roles of L1 and TAG-1 in the formation of the commissures in the forebrain are different from their roles in the spinal cord.
在端脑中，皮质脊髓（CS）、胼胝体和海马连合神经元是轴突穿过脑中线的主要神经元类型。为了了解参与穿过中线结构的机制，并研究连合神经元中L1和TAG-1的表达模式是否与脊髓中的相似，我们通过使用涉及逆行标记和原位杂交的双重标记技术，研究了大鼠这些神经元中L1和TAG-1的表达。通过在胚胎第19天（E19）将1,1'-二油酰基-3,3,3',3'-四甲基吲哚羰花青高氯酸盐（DiI）注入脑桥，在逆行标记的CS投射神经元中检测到L1信使核糖核酸的表达，但在这些神经元中未检测到TAG-1信使核糖核酸的表达。此外，在其轴突穿过锥体交叉后，通过在出生后第1天（P1）将DiI注入脊髓的另一项双重标记实验表明，CS投射神经元中L1持续表达而TAG-1无表达。免疫组织化学研究表明，在E21和P3时，L1在CS束的各个水平持续存在，但在任何阶段的任何水平均未发现TAG-1免疫反应性。最后，我们通过使用双重标记技术，在胼胝体和海马连合神经元的轴突穿过中线后，检测了L1和TAG-1信使核糖核酸的表达。在这两种情况下，在P3时，在逆行标记的神经元中均观察到L1和TAG-1信使核糖核酸的杂交信号。这些结果表明，L1和TAG-1在前脑连合形成中的作用与其在脊髓中的作用不同。
