The effect of chronic decentralization on the enkephalin immunoreactive plexus around penile ganglionic neurons

Target organ responses to sympathetic nerve stimulation are altered following partial decentralization of the pelvic plexus in the rat. One possible explanation for the new responses is that nerve injury has led to a reorganization of synaptic connections within pelvic ganglia. Since one measure of synaptic influence is the occurrence of a pericellular plexus of varicose fibers around autonomic ganglion cells, the present study has used immunocytochemistry for enkephalin (ENK), a peptide present in nerve fibers in the pelvic plexus, to follow changes in the innervation of penile ganglionic neurons after interruption of preganglionic pathways. Penile ganglion cells were located by the injection of the tracer Fluorogold into the penile crura. Four days after lesion of the pelvic nerve, innervation of penile neurons falls from 76% to 20%. This number increases however, to 31% in chronically (6 weeks) lesioned animals. In the totally decentralized ganglia, ENK immunoreactive (IR) fibers enclose fewer than 12% of the penile neurons 4 days after nerve lesion. However, this value rises to 35% in the chronically decentralized pelvic ganglion. Therefore, recovery of an enkephalin plexus occurs irrespective of whether the pelvic nerve, or both the hypogastric and pelvic nerve have been cut. Although these findings suggest sprouting within partially decentralized ganglia, the similar incidence of an ENK plexus in ganglia subjected to chronic partial or total decentralization indicates that preganglionic fibers are not responsible for the emergent fibers.