Ornithine decarboxylase activity in dorsal root ganglia of regenerating frog sciatic nerve

Ornithine decarboxylase (ODC) activity was studied in dorsal root ganglia (DRG) of regenerating frog sciatic nerve. There was a significant increase in activity two days after a crush lesion of the nerve 2.5 cm distal to the DRG. The increase reached a maximum after 7 days, then declined but remained above control levels for at least 9 days. An endoneural injection of vinblastine, a potent inhibitor of retrograde and orthograde axonal transport, between the DRG and the crush inhibited the increase in ODC. In contrast, injections of vinblastine into undamaged nerves failed to affect ODC. The increase in ODC and also the regenerative properties of the nerve could be prevented by daily i.p. injections of alpha-difluoromethyl ornithine. We suggest that a signal is formed at the site of injury in the sciatic nerve. This signal is conveyed to the DRG by retrograde axonal transport where it initiates the events leading to an increase in ODC. This increase appears to be necessary for the regeneration of sensory fibers in the frog sciatic nerve.