Axon Regeneration in Vitro on Physiologically Relevant Substrata

The study of axon growth in culture is limited by a poor understanding of the relative contribution of each of a complex array of factors, which include diffusible, axon growth-modulating molecules and substrate-bound guidance cues available to developing and regenerating neurons in vivo. With the objective of more closely mimicking in vivo conditions, one approach we have exploited employs thin cryosections of appropriate regions of unfixed nervous tissue as culture substrata for the growth of regenerating neurons. By using this technique it is possible to culture different populations of neurons on substrata in which environmental growth-modulating factors are preserved. This form of bioassay has facilitated the study of the different neurite outgrowth responses of neurons both from different sources and at different developmental ages on varying native substrata. Using this method we have demonstrated that mature dorsal root ganglion neurons (DRG) will regrow axons only on predegenerated sciatic nerve in vitro, while immature DRG extend neurites on both intact and degenerated sciatic nerve. In contrast, both mature and neonatal DRG fail to regenerate on either fully myelinated mature optic nerve or unmyelinated embryonic optic nerve. Moreover, neonatal retinal ganglion cells do not regenerate on any of these substrata.