Robinson S R, Horsburgh G M, Dreher B, McCall M J
Department of Anatomy, University of Sydney, N.S.W., Australia.
Brain Res. 1987 Oct;432(2):161-74. doi: 10.1016/0165-3806(87)90041-1.
In albino rabbits aged from the 16th postconceptional day (16PCD) to adulthood, the number of axons in the optic nerves were estimated from sample areas totalling 1-12% of the cross-sectional area of the nerve. On the 16PCD there are about 20,000 axons in the optic stalk. The number of axons in the retrobulbar part of the optic nerve reaches a peak value of 766,000 on the 23PCD, and then decreases to about 350,000 by the 32PCD (the day of birth). The number of axons does not change between the 32PCD and 50PCD, but thereafter it slowly decreases, reaching the adult number (294,000) by the 84PCD. A similar trend is apparent in pigmented animals. Thus, on the 25PCD there are 736,000 axons in the retrobulbar part of the optic nerve and the number decreases to 428,000 by the 31PCD. In the adult pigmented rabbit there are 280,000 axons in the optic nerve. In animals younger than the 32PCD, growth cones are present, and the number of axons in the prechiasmal part of the optic nerve was 8-22% lower than in the retrobulbar part of the same nerve. These observations suggest that there is a continued outgrowth of axons from the eye towards the target nuclei. By the 32PCD, the numbers of axons in the retrobulbar and prechiasmal parts of the nerve were very similar, suggesting that by this age all axons had reached the chiasm. The numbers of retinal ganglion cells (RGCs) labelled by massive injections of horseradish peroxidase into the retino-recipient nuclei were estimated in albino rabbits aged from the 24PCD to adulthood. RGCs were counted in evenly spaced sample areas totalling 4-11% of the retinal area. On the 24PCD, the number of labelled RGCs (500,000) was lower than the number of axons in the optic nerve (probably because not all RGC axons had reached their target nuclei by this age). However, by the 27PCD the number of labelled RGCs (550,000) was very similar to the number of prechiasmal axons (568,000). At all ages thereafter, the numbers of both RGCs and axons were very similar, with adult RGC numbers (about 291,000) being reached by the 85PCD. We conclude that axon loss in the rabbit optic nerve after the 27PCD is almost certainly due to the elimination (presumably death) of the parent RGCs, and we suggest that RGC death is also the most likely cause of axon loss prior to the 27PCD.(ABSTRACT TRUNCATED AT 400 WORDS)
在从孕后第16天（16PCD）到成年期的白化兔中，从占神经横截面积1% - 12%的样本区域估计视神经中的轴突数量。在16PCD时，视柄中有约20,000条轴突。视神经球后部分的轴突数量在23PCD时达到峰值766,000条，然后到32PCD（出生日）时降至约350,000条。在32PCD和50PCD之间轴突数量不变，但此后逐渐减少，到84PCD时达到成年数量（294,000条）。有色动物中也有类似趋势。因此，在25PCD时，视神经球后部分有736,000条轴突，到31PCD时数量降至428,000条。成年有色兔的视神经中有280,000条轴突。在小于32PCD的动物中存在生长锥，视神经视交叉前部分的轴突数量比同一神经球后部分少8% - 22%。这些观察结果表明，轴突从眼睛向靶核持续生长。到32PCD时，神经球后和视交叉前部分的轴突数量非常相似，表明到这个年龄所有轴突都已到达视交叉。在从24PCD到成年期的白化兔中，通过向视网膜接受核大量注射辣根过氧化物酶来估计视网膜神经节细胞（RGC）的数量。在占视网膜面积4% - 11%的均匀间隔样本区域中计数RGC。在24PCD时，标记的RGC数量（500,000个）低于视神经中的轴突数量（可能是因为到这个年龄并非所有RGC轴突都已到达其靶核）。然而，到27PCD时，标记的RGC数量（550,000个）与视交叉前轴突数量（568,000个）非常相似。此后在所有年龄段，RGC和轴突的数量都非常相似，到85PCD时达到成年RGC数量（约291,000个）。我们得出结论，27PCD后兔视神经中的轴突损失几乎肯定是由于亲代RGC的消除（可能是死亡）所致，并且我们认为RGC死亡也是27PCD之前轴突损失最可能的原因。（摘要截短至400字）
