EMBRYONIC OPTIC-NERVE TISSUE FAILS TO SUPPORT NEURITE OUTGROWTH BY CENTRAL AND PERIPHERAL NEURONS IN-VITRO

The failure of axon regeneration in the injured mammalian central nerv ous system has been ascribed, in part, to the inhibitory effects of my elin proteins. To investigate the influence of myelination on neurite growth and regeneration by both central nervous system and peripheral nervous system neurons, isolated rat neonatal retinal ganglion cells a nd adult and neonatal dorsal root ganglion neurons were cultured on cr yostat sections of both immature unmyelinated and mature fully myelina ted adult rat optic nerve. In agreement with earlier studies using neo natal peripheral neurons, the adult optic nerve failed to support neur ite outgrowth from any of the neurons tested. A new finding was that t issue sections from unmyelinated optic nerve (aged embryonic days 18 a nd 20, and postnatal days 1 - 3), also failed to support the growth of neurites from neonatal retinal ganglion cells and both neonatal and a dult dorsal root ganglion neurons. Neonatal retinal ganglion cells als o failed to extend neurites on sections of pre-degenerated sciatic ner ve, a tissue shown in our previous work to be a good substratum for su pporting neurite growth for both neonatal and adult DRG neurons. These results suggest that cells in the immature optic nerve either express widely acting axon growth inhibitory molecules unrelated to previousl y described myelin proteins, or do not synthesize appropriate axon gro wth promoting molecules. They also reveal that, for axon regeneration, central nervous system and peripheral sensory neurons require distinc t substratum interactions.