c-Jun expression after axotomy of corneal trigeminal ganglion neurons is dependent on the site of injury

The proto-oncogene c-Jun has been implicated in the control of neuronal res ponses to injury and in axonal growth during regenerative processes. We hav e investigated the expression of c-Jun during normal terminal remodelling i n trigeminal ganglion neurons innervating the cornea and after acute injury of epithelial nerve terminals or parent axons. Remodelling and rearrangeme nt, or damage limited to corneal epithelium endings, was not a trigger for activation of c-Jun expression. However, injury of parent axons in the stro ma or in the orbital ciliary nerves induced c-Jun expression in 50% of the population of corneal neurons, which included all of the large myelinated a nd 20% of the small neuropeptide-containing corneal neurons. This suggests that c-Jun expression in trigeminal ganglion neurons is not associated with normal remodelling or regeneration of peripheral nerve terminals, and that it takes place only when parent axons are injured. A substantial number of damaged neurons do not express c-Jun, indicating that in primary sensory n eurons, injury and regeneration may not always be coupled to the expression of this protooncogene.