AMOUNT OF SYMPATHETIC SPROUTING IN THE DORSAL-ROOT GANGLIA IS NOT CORRELATED TO THE LEVEL OF SYMPATHETIC DEPENDENCE OF NEUROPATHIC PAIN IN A RAT MODEL

Incomplete peripheral nerve injury often leads to neuropathic pains, s ome of which are relieved by sympathectomy, and results in sympathetic postganglionic nerve fiber sprouting in the dorsal root ganglion (DRG ). This study was performed to see whether the sprouting in the DRG pl ays a key role in the sympathetic dependence of neuropathic pain. To t his aim, we compared two groups of rats, both of which were subjected to unilateral transection of the inferior and superior caudal trunks a t the levels between the S1 and S2, S2 and S3, and S3 and S4 spinal ne rves, with respect to sympathetic fiber sprouting; one group showed ne uropathic pain behaviours (i.e. mechanical and cold allodynia signs) w hich were very sensitive to phentolamine, alpha adrenergic blocker, an d the other group exhibited no sensitivity. Immuno-histochemical stain ing with tyrosine hydroxylase antibody or the S1-S3 DRGs was not corre lated with the sensitivity to phentolamine. These results suggest that the degree of sympathetic dependence of neuropathic pain is not a fun ction of the extent of the sympathetic postganglionic nerve fiber spro uting in the DRG. (C) 1998 Elsevier Science Ireland Ltd.