Skoff R P, Price D L, Stocks A
J Comp Neurol. 1976 Oct 1;169(3):313-34. doi: 10.1002/cne.901690304.
The time of origin for astrocytes and oligodendrocytes in rat optic nerve was studied by 3H-thymidine autoradiographic techniques similar to those used in dating the time of origin for neurons. This study shows that astrocytes are formed throughout late embryonic and all of postnatal development, while oligodendrocytes are generated only during the postnatal period. A few astroglia undergo their final cell division as early as 15.5 days of gestation, but most astrocytes are not generated until the first week of postnatal development. Although the final cell division for more than half of the astrocytes takes place before the end of the first postnatal week, fully mature, fibrous astrocytes are not observed in electron micrographs until after 14 days of age. This time lag implies that the differentiation of these early generated cells takes place gradually over a 2-to 3-week interval. Oligodendroglia begin their final division a day or two before the onset of myelination (6-7 days postnatal), but the vast majority are produced during the period of myelinogenesis. After almost all of the axons have been myelinated, oligodendrocytes are still being generated in small numbers. These late forming cells are generally less differentiated in appearance than those formed earlier; this suggests that the degree of differentiated of oligodendrocytes may be dependent upon the number of axons available for myelination. As with astrocytes, oligodendrocytes show a lag of about two weeks from the time of final cell division until they transform into morphologically differentiated cells. In transverse sections of the optic nerve heavily labeled neuroglia are randomly distributed, indicating there are no temporal-radial gradients for the individual cell types. This observation taken together with the other information obtained from the present and the previous study (Stoff et al., '76) strongly suggest that the factors controlling gliogenesis are different from those governing neuronogenesis.
采用与确定神经元起源时间时所用的类似的³H-胸腺嘧啶核苷放射自显影技术，研究了大鼠视神经中星形胶质细胞和少突胶质细胞的起源时间。这项研究表明，星形胶质细胞在整个胚胎后期及出生后发育阶段都在形成，而少突胶质细胞仅在出生后时期产生。少数星形胶质细胞早在妊娠15.5天时就进行了最后一次细胞分裂，但大多数星形胶质细胞直到出生后发育的第一周才产生。虽然超过一半的星形胶质细胞的最后一次细胞分裂在出生后第一周结束前发生，但直到14日龄后，电子显微镜照片中才观察到完全成熟的纤维性星形胶质细胞。这段时间间隔意味着这些早期产生的细胞的分化在2至3周的时间内逐渐发生。少突胶质细胞在髓鞘形成开始前一两天（出生后6 - 7天）开始其最后一次分裂，但绝大多数是在髓鞘形成期产生的。几乎所有轴突都已髓鞘化后，仍有少量少突胶质细胞在产生。这些后期形成的细胞在外观上通常比早期形成的细胞分化程度低；这表明少突胶质细胞的分化程度可能取决于可供髓鞘化的轴突数量。与星形胶质细胞一样，少突胶质细胞从最后一次细胞分裂到转化为形态学上分化的细胞也有大约两周的延迟。在视神经的横切面上，标记严重的神经胶质细胞随机分布，表明各细胞类型不存在时间-径向梯度。这一观察结果与从本研究及先前研究（斯托夫等人，1976年）获得的其他信息一起，强烈表明控制胶质细胞生成的因素与控制神经元生成的因素不同。
