Vidal Pizarro Ivonne, Swain Gary P, Selzer Michael E
University of Pennsylvania, Institute of Neurological Sciences, Philadelphia, Pennsylvania 19104, USA.
J Comp Neurol. 2004 Feb 2;469(2):298-310. doi: 10.1002/cne.11013.
After spinal cord transection, axons regenerate both in larval and adult lampreys. It is not known to what degree cells proliferate, even in the uninjured animal. Therefore, we have determined the prevalence of mitosis in the lamprey central nervous system (CNS). Bromodeoxyuridine (BrdU) was injected and incorporated for 4 hours into 2- to 5-year-old larvae, animals undergoing metamorphosis, and young adults. Labeled cells were counted in the rhombencephalon (where most supraspinal projecting neurons are located) and spinal cord. A mitotic index (MI) was calculated as the percentage of nuclei that were labeled. There was a seasonal variation in mitotic activity, with higher MIs occurring in summer. Within the summer, there was an additional transient spike in mitosis, especially in the rhombencephalon. There was no correlation between age and MI within the range of developmental stages examined. Baseline MIs in the rhombencephalon and spinal cord were approximately 0.15% and 0.20%, respectively. In most animals, the highest mitotic rates in both the rhombencephalon and spinal cord were seen in the ependyma, but many labeled cells were found in nonependymal regions as well. During the summer spike, almost all of the additional mitosis in the rhombencephalon was in the ependyma, but this finding was not true in the spinal cord. Many BrdU-labeled cells in the spinal cord and rhombencephalon were also stained by monoclonal antibodies specific for lamprey glial keratin but were never labeled by anti-neurofilament antibodies. These results suggest that (1) neurogenesis is uncommon in the lamprey CNS; (2) during most of the year, baseline gliogenesis occurs mainly in the ependyma with substantial contribution by nonependymal areas. During the summer, a spike of mitotic activity occurs in the ependyma of the rhombencephalon and throughout the spinal cord.
脊髓横断后，幼体和成年七鳃鳗的轴突都会再生。即使在未受伤的动物中，细胞增殖的程度也尚不清楚。因此，我们测定了七鳃鳗中枢神经系统（CNS）中有丝分裂的发生率。将溴脱氧尿苷（BrdU）注射到2至5岁的幼体、正在变态的动物和年轻成体中，并使其掺入4小时。对菱脑（大多数脊髓以上投射神经元所在的部位）和脊髓中的标记细胞进行计数。计算有丝分裂指数（MI），即标记细胞核的百分比。有丝分裂活性存在季节性变化，夏季的MI较高。在夏季，有丝分裂还有一个额外的短暂高峰，尤其是在菱脑中。在所检查的发育阶段范围内，年龄与MI之间没有相关性。菱脑和脊髓的基线MI分别约为0.15%和0.20%。在大多数动物中，菱脑和脊髓中最高的有丝分裂率出现在室管膜，但在非室管膜区域也发现了许多标记细胞。在夏季高峰期间，菱脑中几乎所有额外的有丝分裂都发生在室管膜，但在脊髓中并非如此。脊髓和菱脑中许多BrdU标记的细胞也被七鳃鳗神经胶质角蛋白特异性单克隆抗体染色，但从未被抗神经丝抗体标记。这些结果表明：（1）七鳃鳗中枢神经系统中神经发生并不常见；（2）在一年中的大部分时间里，基线神经胶质生成主要发生在室管膜，非室管膜区域也有很大贡献。在夏季，菱脑的室管膜和整个脊髓中会出现有丝分裂活性高峰。
