During their development, neurons extend long axonal processes to synapse on specific target neurons. This growth capacity is lost in the mature central nervous system of mammals so that when an axon such as an optic axon is severed, it can no longer regrow to restore functional connections. We have found culture conditions, however, that allow adult mouse optic axons to regenerate in vitro indicating that they retain the inherent capacity to grow. Molecular comparison with embryonic optic fibers reveal that adult fibers differ in intracellular axonal proteins and cell surface receptors that regulate growth and mediate interactions with the glial cells of the mature nervous system. A specific axon-glia interactions may be the cause of regenerative failure in adult mammals.
