De novo formation of axon-like processes from axotomized retinal ganglion cells which exhibit long distance growth in a peripheral nerve graft in adult hamsters.

Damaged axons in the central nervous system of the adult mammal can be stimulated to regenerate extensively into a peripheral nerve graft. It was generally believed that the new axonal sprouts which extend into the graft arose from the injured proximal axonal stumps. However, when retinal ganglion cells of the adult hamster were axotomized by crushing the optic nerve and the proximal axonal stump was not in direct apposition to the graft, a new axon-like process could be seen to be emitted from either the cell soma or dendrite and extended in the graft for at least 1-2 cm. This axon-like process was distinct from the original injured axon which could still be seen to course towards the optic disc in the retina. Evidently, even a fully differentiated central nervous system neuron of the adult mammal retains a great degree of morphological plasticity so that if the original axon is discouraged to regrow after injury, other parts of the neurons can act as favourable sites for the sprouting of a new axon-like process.