Development of the optic nerve of the rat - Investigative ...

More documents

Recommendations

Info

Volume 14 Number 10 Rat optic nerve 741 Fig. 13. Postnatal tenth day. A, serpentine double-cell membrane which, led by a small cytoplasm of the glia cell (°), extends over a few axons (arrows). x40,000. B> axons are surrounded by a relatively large glia cell element (*) and by the double membranes (double arrows). x58,400. tain sparse micro-organelles. They consist of the electron lucent cytoplasm and are distinguishable from those of the astrocyte which contain rich filaments. These thin processes appear to produce myelin sheaths at a later date, Myelination. Myelination of the optic nerve begins at a relatively later stage. During the first postnatal week, fine processes of the oligodendroglia cell begin to extend profoundly in the space between axons. On the eighth and ninth days, when the diameter of the optic nerve measures about 200 ju and the development of the retinal photoreceptor elements is considerably advanced, the first sign of myelination is noted in the area immediately behind the globe and in the chiasm. The extending thin-cell processes begin to surround groups of axons. These thin processes become a double-cell membrane structure, eliminating the cytoplasmic matrix in several locations (Fig. 12). These seem to be the earliest myelin membrane. The early myelin membrane seems to attach to a group of axons instead of an individual fiber. The tip portion of the process which becomes the mesoaxon seems to preserve a small amount of the cytoplasm (Figs. 12 and 13, A). Also, the usual myelination process in which a few axons are surrounded by a large cytoplasm of the glia cell is occasionally found (Fig. 13, B). During the next few days the number of double-membrane structures increases markedly. Many axons are surrounded completely by these membranes and by layers of lamellar membranes. By the end of the second week, almost all axons are found to be surrounded by myelin sheaths (Fig. 14). The nodes of Ranvier, the area where cytoplasms of two oligodendroglia cells meet, are frequently found in this stage (Fig. 15). By the end of the third week, all axons become myelinated. Fine processes of the astrocytes then begin to fill in the spaces between the myelinated nerve fibers.
742 Kuioabara Investigative Ophthalmology October 1975 Fig. 14. Most axons are myelinated on the twelfth day. x8,000. O*e=»» Fig. 15. Early Ranvier's node in a 10-day-old rat. Two processes of the myelin-fomiing glia cells meet each other (arrow). x40 ; 000. Meninges and septa. The basal portions of the original neuroepithelial cells which have survived the early bionecrosis remain at the marginal zone of the stalk together with their basement membrane. These cells become tall and proliferate at their apical zone to differentiate into glia cells but they eventually become flat and form the outer limit of the optic nerve, the mantle glia. The cytoplasm of these cells is not distinguishable from that of the astrocyte. A thin connective tissue consisting of collagen fibers and a few fibroblasts is formed immediately outside of the basement membrane of the optic stalk on the fifteenth fetal day. This is the pia mater. The blood vessels around the optic nerve, the arachnoidal plexus, become significantly numerous during the first postnatal week. At about the same time, young mesenchymal cells begin to arrange in a circular pattern around the optic nerve and become the dura mater.
Page 1 and 2: Development of the optic nerve of t
Page 3 and 4: 734 Kuioabara Investigative Ophthal
Page 5 and 6: 736 Kuwabara Investigative Ophthalm
Page 7 and 8: 738 Kuwabara Investigntive Ophthalm
Page 9: 740 Kuwabara Investigative Ophthalm
Page 13 and 14: 744 Kuwabara Investigative Ophthalm

Development of the optic nerve of the rat - Investigative ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?