RAPID SPROUTING OF SYMPATHETIC AXONS IN DORSAL-ROOT GANGLIA OF RATS WITH A CHRONIC CONSTRICTION INJURY

We compared the time-course of sympathetic nerve sprouting into the L4 -6 dorsal root ganglia (DRG) of adult rats following a chronic constri ction injury (CCI) made on the sciatic nerve, or following sciatic ner ve transection at the same site. We also tested the rats for changes i n threshold for withdrawal from mechanical and thermal stimuli deliver ed to the hindpaws. We found sympathetic sprouting in DRG by 4 days fo llowing CCI, paralleling the decreases in mechanosensory threshold and preceding changes in thermal thresholds. However, with sciatic nerve transection, sympathetic sprouting was not detectable until 14 days af ter nerve injury. Thus, after CCI, sympathetic sprouting occurs with a sufficiently rapid time-course for it to play a role in the genesis o f neuropathic pain. We suggest that the more rapid sprouting seen afte r CCI than after resection is due to the availability of products of W allerian degeneration, including nerve growth factor, to both spared a nd regenerating axons following CCI, but not following resection. (C) 1997 International Association for the Study of Pain.