Partial sciatic nerve transection induced tyrosine hydroxidase immunoreactive axon sprouting around both injured and spared dorsal root ganglion neurons which project to the gracile nucleus in middle-aged rats.

After partial sciatic nerve transection (PSNT), sympathetic axons sprout into the lumbar dorsal root ganglia (DRG), a phenomenon implicated in neuropathic pain. We asked whether sympathetic sprouting is directed to injured or spared DRG neurons and whether these neurons project to the gracile nucleus. Using combined fluorescent dye tracing and tyrosine hydroxylase (TH) immunohistochemistry, we found that 4 weeks after PSNT in rats 8-10 months old, 51% of the neurons surrounded by TH-immunoreactive (IR) axons were spared, while 43% were injured. Seventy-nine percent projected to the gracile nucleus. Sympathetic sprouting induced by PSNT is not directed preferentially to injured or spared DRG neurons, but does show a preference for DRG neurons projecting to the gracile nucleus.