Immunohistochemical study on the developing optic nerves in human embryos and fetuses

For the purpose of investigating the time of development and myelination of the optic nerve, we applied immunohistochemical stains to the optic nerves of 26 human embryos and fetuses aged 6-39 weeks. The minimum diameter of the optic nerve's cross section increased with the development of embryos; 0.15 mm at the 9th week, 0.4 mm at the 11th week, 1.5 mm at the 24th week, and 2.1 mm at the 32nd week. With regard to myelin basic protein (MBP), the localization could not be observed at 28 gestational weeks. The MBP was proved to be positive in oligodendrocytes of the optic nerve at the age of the 32nd gestational week. The localization of glial fibrillary acidic protein (GFAP) was proved partially in astrocytes around the optic nerve in the case of 24 gestational weeks. The remarkable localization of GFAP-positive astrocytes inside the nerve fibers was proved at the 27th gestational week. The histological appearance of GFAP-positive cells advanced to that of MBP-positive ones after 8 weeks interval. The degree of MBP staining was less marked than that of GFAP in examined fetal cases. These results suggest that astrocytes and oligodendrocytes correlate to the developmental growth and myelination of the optic nerves during the fetal development.