COMPARISON OF SYMPATHETIC SPROUTING IN SENSORY GANGLIA IN 3 ANIMAL-MODELS OF NEUROPATHIC PAIN

Sympathetic postganglionic fibers sprout in the dorsal root ganglion ( DRG) after peripheral nerve injury. Therefore, one possible contributi ng factor of sympathetic dependency of neuropathic pain is the extent of sympathetic sprouting in the DRG after peripheral nerve injury. The present study compared the extent of sympathetic sprouting in the DRG as well as in the injured peripheral nerve in three rat neuropathic p ain models: (I) the chronic constriction injury model (CCI); (2) the p artial sciatic nerve ligation injury model (PSI); and (3) the segmenta l spinal nerve ligation injury model(SSI). All three methods of periph eral nerve injury produced behavioral si,ans of ongoing and evoked pai n with some differences in the magnitude of each pain component. The d ensity of sympathetic fibers in the DRG was significantly higher at al l examined postoperative times than controls in the SSI model. while i t was somewhat higher than controls only at the last examined postoper ative time (20 weeks) in the CCI and PSI models. Therefore, data sugge st that. although sympathetic changes in the DRG may contribute to neu ropathic pain syndromes in the SSI model, other mechanisms seem to be more important in the CCI and PSI models at early times following peri pheral nerve injury.