EXPRESSION OF C-JUN AS A RESPONSE TO DORSAL-ROOT AND PERIPHERAL-NERVESECTION IN DAMAGED AND ADJACENT INTACT PRIMARY SENSORY NEURONS IN THERAT

It was previously shown that the immediate early gene, c-jun, was high ly expressed over long periods, in both peripheral sensory and motor n eurons following axon damage or block of axoplasmic transport. Here we have examined the question of whether the expression of c-Jun protein is related to axon injury per se or to the process of axon growth. We have examined dorsal root ganglion (DRG) cells subjected to different manipulations which are associated with varying degrees of regrowth, as follows: (i) after peripheral nerve section, where it appears that all damaged neurons make some regenerative effort. 1 - 24 days after s ciatic nerve section and ligation most cells in L4/L5 DRG were c-Jun-p ositive; (ii) after section of the central processes of the DRG cells, which then showed a slow and limited regrowth of their axons towards, but not into, the spinal cord. This resulted in a variable, but signi ficant, expression of c-Jun in a small number of DRG cells; (iii) in i ntact sensory neurons that were offered the opportunity to sprout into adjacent denervated peripheral tissue. The sciatic nerve was ligated and the response of cells in the L3 ganglia (many of which project to the saphenous nerve) was measured. A small but significant number of c ells were c-Jun-positive; (iv) in intact sensory neurons that were off ered the opportunity to sprout centrally into partialy denervated neur opil of the spinal cord. We examined neurons in the L3 DRG after rhizo tomy of the adjacent L4/L5 dorsal roots. Previous work suggests that s ensory neurons show at best a very limited growth under these conditio ns. No significant increase was seen in c-Jun expression in these case s. These results suggest that c-Jun expression is closely correlated w ith growth and regeneration, and not simply a consequence of neuronal injury.