Injury-induced long-term expression of immediate early genes in the rat superior cervical ganglion.

Using in situ hybridization histochemistry and immunocytochemistry the induction of immediate early genes (IEGs) was studied in the rat superior cervical ganglion (SCG) after deafferentation, axotomy and sialectomy (removal of the submandibular gland). Control SCGs showed very low levels of IEGs, whereby Fos proteins were found in 1% and Jun protein in 6% of neurons, but not in non-neuronal cells. Denervation and axotomy induced c-fos, NGFI-A, c-jun, jun B and jun D mRNA expression for up to 6 days in non-neuronal cells, whereas in sympathetic neurons the expression of only c-jun mRNA was induced after axotomy and sialectomy. The induction of Fos and Jun proteins by neuronal injury was demonstrated by immunocytochemistry. The results indicate that neuronal injury induces IEGs mainly in non-neuronal cells and that in neurons only c-jun is induced after axotomy. It is hypothesized that the induction of IEG other than c-jun in neurons after brain injury is an indirect event unrelated to the neuronal response to injury.