INTRODUCTION: Radiculopathy in lumbar disc herniation is induced by both nerve root inflammation and mechanical compression. Glial cell line‐derived neurotrophic factor (GDNF) is one of the neurotrophins synthesized and expresses in satellite glial cells for 28 days after application of nucleus pulposus (NP) in rats. GDNF might act to recover neural damage through GDNF family receptor (GFR) alpha‐1 and to improve neuropathic pain. Growth associated protein (GAP)‐43 is a marker of nerve regeneration. The aim of this study was to investigate the relationship between painrelated behavior and nerve regeneration after application of NP.
METHODS: Adult female Sprague‐Dawley rats (n=94) were used. Animals were divided into two groups. In the NP group. NP harvested from the tail was applies to the left L5 dorsal root ganglion (DRG). In the sham group, NP was not applied to the DRG. Mechanical withdrawal thresholds were measured using von Frey test for 56 days. Expression of GAP 43 and GFR alpha‐1 in DRG neurons were examined by immunohistochemistry. Statistical analysis was performed by Bonferroni test and unpaired student t‐test (significant level: p<0.05).
RESULTS: The mechanical withdrawal threshold in the NP groups was significantly decreased for 35 days compared with the sham group (p<0.05). There was no significant difference of the threshold between two groups from day 42 to 56. The expression of GFR alpha‐1 increased in the NP group at day 14. GAP 43 expression in the NP group increased significantly compared with the sham group from day 14 to 35 (p<0.05).
DISCUSSION: The GAP 43 expression increased after expression of GDNF and GFR alpha‐1, and lasted from 14 to 35 days. This reaction of regeneration might improve the threshold 42 days after application of NP. GDNF and/or GDNF family receptor might be the potential target to improve radiculapathy in lumbar disc herniation.