Sympathectomy induces c-Jun in adult trigeminal neurons: an immunohistochemical and tract-tracing study.

The induction of the immediate early gene product c-Jun was investigated in trigeminal ganglia following surgical removal of the superior cervical ganglion (SCG). A 5-fold increase in c-Jun-immunoreactive neurons was detected by 48 h post-surgery in ipsilateral trigeminal ganglia of sympathectomized rats. This increase persisted for 6 days. When examined 4 months after sympathectomy, c-Jun expression had returned to basal levels. The possibility that trigeminal neurons project to the SCG, and therefore induce c-Jun by being axotomized by sympathectomy, was also examined using retrograde fluorescent tracing. A very limited number of trigeminal neurons were retrogradely labeled from the SCG. These data indicate that c-Jun induction occurs in sensory neurons following perturbations to sympathetic ganglia, and that trigeminal neurons may project to the SCG, but that c-Jun induction cannot be ascribed to axotomy following surgical sympathectomy. Thus, these findings support anatomical and functional interconnections between the sensory and autonomic nervous systems. The relationship of c-Jun induction with plasticity phenomena is discussed.