Study design: Retrograde neurotracing and immunohistochemical investigation of brain-derived neurotrophic factor (BDNF)-related sensory innervation of punctured lumbar intervertebral discs (IVDs) in rat dorsal root ganglia (DRG).
Objective: To investigate the association between BDNF and sensory innervation of multiple-punctured lumbar IVD in rats.
Summary of background data: BDNF--a neurotrophin in DRG neurons--is anterogradely transported to the spinal cord and transmits pain signals. Its presence in the peripheral sites of degenerative IVDs has been recently reported, although its association with discogenic pain remains unclear.
Methods: Forty female Sprague-Dawley rats were equally divided into four groups: naïve, sham, and two agent-treated groups (vehicle [saline-treated] group and anti-BDNF [anti-BDNF antibody] group). L5-L6 IVDs of the agent-treated rats were exposed and injured by repeated punctures. The retrograde neurotracer Fluoro-Gold (FG) and treatment agents were intradiscally applied. In the sham group, FG alone was applied onto uninjured IVD. One week later, L1-L3 DRGs were harvested and immunolabeled for the inflammatory pain-related calcitonin gene-related peptide (CGRP), that is, the pain marker. The proportions of FG-labeled CGRP-immunoreactive (-ir) DRG neurons were assessed. Each L5-L6 IVD was resected for measuring the BDNF concentration using enzyme-linked immunosorbent assay.
Results: FG-labeled DRG neurons were almost equally prevalent at each DRG level. The proportions of FG-labeled CGRP-ir DRG neurons in the two agent-treated groups were significantly elevated (average 37.9% ± 7.2% and 25.4% ± 9.1%; vehicle and anti-BDNF groups, respectively; P < 0.05) in comparison with the naïve and sham groups (19.6% ± 1.3% and 19.2% ± 3.6%, respectively) and were significantly decreased in the anti-BDNF group in comparison with the vehicle group (P < 0.05). BDNF concentrations were elevated maximally in the vehicle group (18.5 ± 5.2 pg/g) but suppressed in the anti-BDNF group (14.0 ± 3.0 pg/g).
Conclusion: Direct intradiscal application of the anti-BDNF antibody significantly suppressed both CGRP production and the local concentration of BDNF. Our results indicate a possible association between the local production of BDNF and the pathophysiology of discogenic pain.