Influence of Age
•Axons grow during embryonic development.
•Axons can regenerate early in development but not in the adult CNS.
•What is the reason for this developmental loss of regenerative ability?
–Environment?
–Neuron-intrinsic?
A general rule of thumb is that the younger the animal, the better the regenerative ability.  However, in assessing regeneration it is necessary to recognize that some axons have not yet developed at the time that a lesion is made.  Thus the subsequent appearance of these axons distal to a lesion reflects developmental processes and not regeneration, since the axon was never interrupted.