Collateral sprouting and responsiveness to nerve growth factor of ageing neurons.

Loss of neuronal plasticity and/or alterations in neuronal targets with ageing can induce degenerative phenomena in the nervous system. To study the possible contribution of reduced neuronal plasticity to age-related neurodegeneration, we examined the sprouting response to aged rat iridial nerves on in oculo grafts of peripheral tissues taken from young and old animals. Contrary to previous observations in young hosts, both young and old transplants became re-innervated by host nerves to a similar extent, with a nerve density which was typical of old target tissue in situ. Nerve growth factor treatment increased the innervation density on all transplants. However, the increase was significant only on young target tissues.