Regeneration of the abdominal postganglionic sympathetic system

The abdominal sympathetic system is unique in that its postganglionic axons do not directly innervate gastrointestinal smooth muscle layers but exert their effects through the enteric nervous system. The purpose of the present study was to examine the ability of neurons in abdominal sympathetic ganglia to regenerate after axonal injury and to determine whether reinnervation occurs after the removal of ganglia. Axons from the celiac ganglion and superior mesenteric ganglion complex (CG/SMG) of adult female BALB/c mice were crushed or the ganglion complex was removed. Immunohistochemistry, western blotting and in situ hybridization were performed to examine the changes in tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP-43) in the duodenum and the sympathetic ganglia. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling and injection of the tracer dye, fluorogold were also performed. After crushing the nerve, TH in the duodenum disappeared and reappeared within 90 days. In the CG/SMG, TH decreased and increased as in the duodenum, while the expression of GAP-43 changed in the opposite direction. Nerve crushing caused cell death to limited number of neurons in the CG/SMG. The removal of CG/SMG decreased TH in the duodenum and stomach, but 180 days later TH-positive innervation was recovered. Fluorogold injection revealed that the inferior mesenteric ganglion reinnervated the stomach. Therefore, postganglionic sympathetic nerves in the abdomen are able to regenerate and reinnervation occurs even after the removal of sympathetic ganglia.