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Upregulation of NaV1.7 in Dorsal Root Ganglia After Intervertebral Disc Injury in Rats

Sadamasu, Aya MD; Sakuma, Yoshihiro MD; Suzuki, Miyako MD, PhD; Orita, Sumihisa MD, PhD; Yamauchi, Kazuyo MD, PhD; Inoue, Gen MD, PhD; Aoki, Yasuchika MD, PhD; Ishikawa, Tetsuhiro MD, PhD; Miyagi, Masayuki MD, PhD; Kamoda, Hiroto MD, PhD; Kubota, Gou MD; Oikawa, Yasuhiro MD; Inage, Kazuhide MD; Sainoh, Takeshi MD; Sato, Jun MD; Nakamura, Junichi MD, PhD; Toyone, Tomoaki MD, PhD; Takahashi, Kazuhisa MD, PhD; Ohtori, Seiji MD, PhD

doi: 10.1097/BRS.0000000000000229
Basic Science

Study Design. Animal study.

Objective. To investigate pain-related expression of NaV1.7 in dorsal root ganglia (DRG) innervating intervertebral discs.

Summary of Background Data. The pathophysiology of discogenic low back pain is not fully understood. Prostaglandins and cytokines produced by degenerated discs can cause pain, but nonsteroidal anti-inflammatory and steroid medications are often ineffective at pain reduction. Tetrodotoxin-sensitive, voltage-gated sodium (NaV) channels are associated with sensory transmission in primary sensory nerves, and the NaV1.7 channel has emerged as an attractive analgesic target. The purpose of this study was to investigate pain-related expression of NaV1.7 in DRG innervating intervertebral discs.

Methods. Using a rodent model of disc puncture, we labeled DRG neurons innervating L5–L6 discs with FluoroGold neurotracer (n = 20). Half of the rats (n = 10) underwent intervertebral disc puncture using a 23-gauge needle (puncture group), and the other half underwent non-puncture sham surgery (non-puncture group). Seven and 14 days after surgery, DRGs from the L1 to L6 levels were harvested, sectioned, and immunostained for NaV1.7, and the proportion of NaV1.7-immunoreactive DRG neurons was evaluated.

Results. NaV1.7 was expressed in DRG neurons innervating intervertebral discs from L1 to L5. The ratio of NaV1.7-expressing DRG neurons to total FG-labeled neurons was 7.2% and 7.6% at 1 and 2 weeks after surgery, respectively, in the non-puncture group and 16.2% and 16.3% at 1 and 2 weeks, respectively, in the puncture group. The upregulation of NaV1.7 after puncture was significant at both 1 and 2 weeks after surgery (P < 0.01).

Conclusion. We found that disc injury increases NaV1.7 expression in DRG neurons innervating injured discs. NaV1.7 may be a therapeutic target for pain control in patients with lumbar disc degeneration.

Level of Evidence: N/A

Recently, sodium channel NaV1.7 has emerged as an attractive analgesic target. We evaluated pain-related expression of NaV1.7 in dorsal root ganglia (DRG) neurons innervating punctured intervertebral discs in rats. Disc injury increased NaV1.7 expression in DRG neurons. NaV1.7 may be a therapeutic target for pain in patients with disc degeneration.

Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan.

Address for correspondence and reprint requests to Seiji Ohtori, MD, PhD, Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan; E-mail: sohtori@faculty.chiba-u.jp

Acknowledgment date: September 10, 2013. First revision date: December 10, 2013. Acceptance date: December 29, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

No relevant financial activities outside the submitted work.

© 2014 by Lippincott Williams & Wilkins