Growth stimulation and chemotropic attraction of rat retinal ganglion cell axons in vitro by co-cultured optic nerves, astrocytes and astrocyte conditioned medium

Abstract The effects of explants of optic nerves of different ontogenetic ages (P0-P14, adult), and of cultured astrocytes of various ages on the neurite regeneration of rat retinal ganglion cells (RGC) were assessed in vitro , using a three-dimensional culture system which allows the co-cultivation of various explants. Both co-cultured P0-P12 optic nerves and astrocyte cultures from P2 cerebral cortex stimulated the regeneration of neurites from the retinal explants after 3 days in culture. By contrast, P14 and older explants of the optic nerve, astrocytes from P17 optic nerve and astrocytes that had previously been grown in culture for more than 6 weeks had no effect on RGC neurite outgrowth. Moreover, both the P0–P12 optic nerve explants and the astrocytes from P2 cerebral cortex also seemed to have a chemotropic effect on the regenerating neurites, because the latter were longer on the side facing the co-explantat. The absence of a cellular bridge between retinal and optic nerve explants suggests that the effects are mediated by astroglia-derived diffusible neurite growth promoting factors. Accordingly, astrocyte-conditioned medium from P2 astrocytes also stimulated the outgrowth of neurites from the retinal explants. These findings show that immature astrocytes of a limited ontogenetic period release as yet unknown diffusible neurite growth-promoting factors which stimulate the regeneration of neurites from retinal explants.