Effects of decompression on neuropathic pain behaviors and skin reinnervation in chronic constriction injury

Decompression is an important therapeutic strategy to relieve neuropathic pain clinically; there is, however, lack of animal models to study its temporal course of neuropathic pain behaviors and its influence on nerve regeneration to sensory targets. To address these issues, we established a model of decompression on rats with chronic constriction injury (CCI) and investigated the effect on skin reinnervation. Animals were divided into a decompression group, in which the ligatures were removed, and a CCI group, in which the ligatures remained at postoperative week 4 (POW 4). At this time point, the skin innervation indexes of protein gene product 9.5 (PGP 9.5), substance P (SP), and calcitonin gene-related peptide (CGRP) were reduced in both groups to similar degrees. Beginning from POW 6, the decompression group exhibited significant reductions of thermal hyperalgesia and mechanical allodynia compared to the CCI group (p < 0.001). At POW 8, neuropathic pain behaviors had completely disappeared in the decompression group, and the decompression group had a higher skin innervation index of SP than the CCI group (0.45 ± 0.05 vs. 0.16 ± 0.03, p < 0.001). These indexes were similar in both groups for PGP 9.5 (0.32 ± 0.09 vs. 0.14 ± 0.04, p = 0.11) and CGRP (0.38 ± 0.06 vs. 0.21 ± 0.07, p = 0.09). These findings demonstrate the temporal changes in the disappearance of neuropathic pain behaviors after decompression and suggest that decompression causes different patterns of skin reinnervation for different markers of skin innervation.