GROWTH-STIMULATION AND CHEMOTROPIC ATTRACTION OF RAT RETINAL GANGLION-CELL AXONS IN-VITRO BY COCULTURED OPTIC NERVES, ASTROCYTES AND ASTROCYTE CONDITIONED MEDIUM

The effects of explants of optic nerves of different ontogenetic ages (P0-P14, adult), and of cultured astrocytes of various ages on the neu rite regeneration of rat retinal ganglion cells (RGC) were assessed il l vitro, using a three-dimensional culture system which allows the eo- cultivation of various explants. Both co-cultured P0-P12 optic nerves and astrocyte cultures from P2 cerebral cortex stimulated the regenera tion 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 cultu re For more than 6 weeks had no effect on RGC neurite outgrowth. Moreo ver, both the P0-P12 optic nerve explants and the astrocytes from P2 c erebral cortex also seemed to have a chemotropic effect on the regener ating neurites, because the latter were longer on the side being the c o-explantat. The absence of a cellular bridge between retinal and opti c nerve explants suggests that the effects are mediated by astroglia-d erived diffusible neurite growth promoting factors. Accordingly, astro cyte-conditioned medium from P2 astrocytes also stimulated the outgrow th of neurites from the retinal explants. These findings show that imm ature astrocytes of a limited ontogenetic period release as yet unknow n diffusible neurite growth-promoting factors which stimulate the rege neration of neurites from retinal explants. Copyright (C) 1996 ISDN.