Complete Freund's adjuvant-induced intervertebral discitis as an animal model for discogenic low back pain.
BACKGROUND
Although numerous animal models for low back pain associated with intervertebral disk (IVD) degeneration have been proposed, insufficient data have been provided to make any conclusions regarding pain. Our aim in this study was to determine the reliability of complete Freund's adjuvant (CFA) injection into the rat spine as an animal model representing human discogenic pain.


METHODS
We studied IVD degenerative changes with pain development after a 10-microL CFA injection into the L5-6 IVD of adult rats using behavioral, histologic, and biochemical studies. Serial histologic changes were analyzed to detect degenerative changes. Expression of calcitonin gene-related peptide (CGRP), prostaglandin E (PGE), and inducible nitric oxide synthase (iNOS) were determined using immunohistochemistry or real-time polymerase chain reaction as support data for pain development. In addition, CGRP immunoreactivity (ir) at the IVD was considered indirect evidence of neural ingrowth into the IVD.


RESULTS
There was a significant increase of the hindpaw withdrawal response in the CFA group until 7 wk postoperatively (P < 0.05). Histologic analyses revealed progressive degenerative changes of the disks without any damage in adjacent structures, including nerve roots. In the CGRP-ir staining study, the bilateral dorsal horns and IVD had positive ir after intradiscal CFA injection. CGRP mRNA expression was increased in the dorsal root ganglion (DRG) at 2 and 4 wk, whereas PGE and iNOS mRNAs were markedly increased at 2 wk. The increment of CGRP expression was higher in allodynic rats compared with nonallodynic rats.


CONCLUSIONS
Intradiscal CFA injection led to chronic disk degeneration with allodynia, which was suggested by pain behavior and expression of pain-related mediators. The increment of CGRP, PGE, and iNOS also suggest pain-related signal processing between the IVD and the neural pathway in this animal model. This animal model may be useful for future research related to the pathophysiology and development of novel treatment for spine-related pain.
Lee
Min
M
Department of Biomedical Science, Korea University Graduate School, Seoul, Korea.
Kim
Byung-Jo
BJ
Lim
Eun Jeong
EJ
Back
Seung Keun
SK
Lee
Ju-Han
JH
Yu
Sung-Wook
SW
Hong
Sung-Ha
SH
Kim
Joo Han
JH
Lee
Sang-Heon
SH
Jung
Woon-Won
WW
Sul
Donggeun
D
Na
Heung Sik
HS
D000818:Animals; D001522:Behavior, Animal; D015740:Calcitonin Gene-Related Peptide / Q000235:genetics / Q000378:metabolism; D015299:Discitis / Q000139:chemically induced / Q000150:complications* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D004195:Disease Models, Animal; D005620:Freund's Adjuvant / Q000008:administration & dosage; D006930:Hyperalgesia / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D007150:Immunohistochemistry; D007278:Injections, Spinal; D007403:Intervertebral Disc / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D017116:Low Back Pain / Q000209:etiology* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D008297:Male; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism; D010147:Pain Measurement; D017288:Pain Threshold; D016133:Polymerase Chain Reaction; D011458:Prostaglandins E / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D015398:Signal Transduction; D013997:Time Factors; D016474:Weight-Bearing
D011458:Prostaglandins E; D012333:RNA, Messenger; D005620:Freund's Adjuvant; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D015740:Calcitonin Gene-Related Peptide