Direct single injection of p38 mitogen-activated protein kinase inhibitor does not affect calcitonin gene-related peptide expression in dorsal root ganglion neurons innervating punctured discs in rats.
STUDY DESIGN.: Immunohistological analysis of punctured disc after application of a p38 MAP kinase inhibitor. OBJECTIVE.: To examine effect of direct application on dorsal root ganglion (DRG) neurons innervating damaged rat discs. SUMMARY OF BACKGROUND DATA.: Degeneration of lumbar discs is one cause of low back pain. Pathogenesis may involve sensory nerve ingrowth into disc inner layers; tumor necrosis factor-alpha (TNF-alpha) is thought to be a major inducer of ingrowth. Because p38 mitogen-activated protein kinase (p38) upregulates TNF-alpha expression and may play a crucial role in pain sensation, we investigated the effect of one injection of inhibitor on expression of the pain-related neuropeptide calcitonin gene-related peptide (CGRP). METHODS.: The neuro-tracer fluoro-gold was applied to the surfaces of L4/5 discs to label the innervating DRG neurons (n = 30). Of 30 rats, 10 were controls, whereas the other 20 were the experimental model (i.e., discs were punctured with 23-gauge needle). P38 specific inhibitor or saline was applied simultaneously (n = 10 each, Puncture + inhibitor and puncture + saline groups). Fourteen days postsurgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP. Proportion of CGRP-immunoreactive DRG neurons was evaluated in all groups. RESULTS.: Fluoro-gold-labeled neurons innervating the L4/5 disc were distributed throughout L1 to L6 DRGs in all groups. Proportions of labeled neurons positive for CGRP were 15.2% +/- 8% (controls), 27.2% +/- 10% (puncture + saline), and 25.2% +/- 8% (puncture + inhibitor). Proportion of immunoreactive neurons was significantly increased in the puncture groups compared with controls. However, there was no significant difference between the 2 puncture groups (P > 0.1). CONCLUSION.: In this model, CGRP was upregulated in DRG neurons innervating the damaged disc. However, a direct single application of p38 inhibitor did not suppress CGRP expression in innervating DRG neurons. Future research with p38 inhibitor in this model should evaluate multiple or systemic administration of inhibitor.
Hayashi
Yasushi
Y
Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.
Ohtori
Seiji
S
Yamashita
Masaomi
M
Yamauchi
Kazuyo
K
Inoue
Gen
G
Suzuki
Munetaka
M
Orita
Sumihisa
S
Eguchi
Yawara
Y
Ochiai
Nobuyasu
N
Kishida
Shunji
S
Takaso
Masashi
M
Fukui
Yu
Y
Wakai
Ken
K
Kuniyoshi
Kazuki
K
Ishikawa
Tetsuhiro
T
Arai
Gen
G
Miyagi
Masayuki
M
Kamoda
Hiroto
H
Aoki
Yasuchika
Y
Takahashi
Kazuhisa
K
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism*; D002452:Cell Count; D005727:Ganglia, Spinal / Q000187:drug effects / Q000378:metabolism*; D007150:Immunohistochemistry; D007403:Intervertebral Disc / Q000293:injuries / Q000294:innervation* / Q000378:metabolism; D008159:Lumbar Vertebrae / Q000293:injuries / Q000294:innervation / Q000378:metabolism; D008297:Male; D056325:Neuronal Tract-Tracers; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013266:Stilbamidines; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; C104334:FR 167653; D056325:Neuronal Tract-Tracers; D047428:Protein Kinase Inhibitors; D011720:Pyrazoles; D011725:Pyridines; D013266:Stilbamidines; D014409:Tumor Necrosis Factor-alpha; D048051:p38 Mitogen-Activated Protein Kinases; D015740:Calcitonin Gene-Related Peptide