The Journal of comparative neurology
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Peripheral nerve injury has been shown to result in sympathetic fibre sprouting around dorsal root ganglia (DRG) neurons. It has been suggested that this anomalous sympathetic fibre innervation of the DRG plays a role in neuropathic pain. Other studies have suggested an interaction between sympathetic and sensory fibres more peripherally. ⋯ It is noteworthy that, although, by week 6 post-MN lesions, SP-IR fibre reinnervation of the lower lip was occurring, the DbetaH-IR fibres still were present in the upper dermis. Quantification revealed that the migration and branching of the DbetaH-IR fibres into the upper dermis occurred gradually and was most significant at 4 weeks post-MN lesions, as demonstrated by the fact that the DbetaH-IR fibres were found 169.6 +/- 91.4 microm away from the surface of the skin compared with 407.1 +/- 78.4 microm away in sham-operated animals. These findings suggest that the ectopic innervation of the upper dermis by sympathetic fibres may be important in the genesis of neuropathic pain through the interactions of sympathetic and SP-containing sensory fibres.