Long-term increase in the levels of c-jun mRNA and jun protein-like immunoreactivity in motor and sensory neurons following axon damage.

The immediate early genes c-fos, c-jun and NGFI-A are rapidly and transiently expressed in neurons of the superficial dorsal horn following noxious sensory stimulation. However, using either in situ hybridisation to map mRNA or specific antibodies to detect the protein products we were unable to detect any change in expression of those genes in stimulated dorsal root ganglion cells or motor neurons. In contrast levels of c-jun mRNA and protein-like immunoreactivity (but not c-fos or NGFI-A) are massively increased within dorsal root ganglion cells and motor neurons following sciatic nerve section or crush. However, these changes are neither rapid nor transient. Increased gene product is seen at 24 h but not 2 h after nerve damage and these levels are maintained up to seven days later. These results suggest that there are multiple routes for the control of c-jun gene expression within the nervous system and that c-jun may play a key role in the neuronal response to injury.