Exploration of the strategies to enhance the regeneration of the optic nerve.

In adult mammals, only minimal regeneration of the optic nerve (ON) is possible. Both the low levels of intrinsic regeneration ability of retinal ganglion cells (RGCs) and the inhibitory glial environment of ON contribute to it. To explore the influence of these two factors on the extent of axon regeneration, two ON injury models were established. A conventional optic nerve crush model (ONC) is considered a high-inhibitory environment. A long-range optic nerve injury model (LI) is considered a low-inhibitory environment. Zymosan (Zy) was used to regulate the intrinsic regeneration capability of RGCs: the injection of zymosan represented a high state; no injection represented a low state. In the low-inhibitory environment, zymosan (LI + Zy group) significantly increased both the number of regenerated axons and the number of surviving RGCs, however the Relative A/R (representing the proportion of regenerated RGCs) was similar to the LI group (no zymosan injection).Furthermore, in the highly-inhibitory environment, although zymosan (ONC + Zy group) significantly increased the number of regenerated axons and the number of surviving RGCs, the relative A/R was significantly lower than that in the low-inhibitory environment (LI or LI + Zy groups). The results suggest that the low inhibitory environment may be more important for optic nerve regeneration. Binary regression analysis also demonstrated the similar results. Also, there was a clear synergy between the two factors. These indicate that both low inhibitory environments and high regeneration capability can enhance the regeneration of ON. A low inhibitory environment is greater essential.