• Kazutoshi Hirose, Nahoko Iwakura, Sumihisa Orita, Masaomi Yamashita, Gen Inoue, Kazuyo Yamauchi, Yawara Eguchi, Nobuyasu Ochiai, Shunji Kishida, Junichi Nakamura, Masashi Takaso, Tetsuhiro Ishikawa, Gen Arai, Masayuki Miyagi, Hiroto Kamoda, Yasuchika Aoki, Ryo Hiwatari, Jun Kakizaki, Toshikazu Kunishi, Motoaki Kono, Takane Suzuki, Tomoaki Toyone, Kazuhisa Takahashi, Kazuki Kuniyoshi, and Seiji Ohtori.
• Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan.
• Eur Spine J. 2010 Oct 1; 19 (10): 1746-52.

AbstractPathomechanisms of injured-nerve pain have not been fully elucidated. Radicular pain and chronic constriction injury models have been established; however, producing these models is complicated. A sciatic nerve-pinch injury is easy to produce but the reliability of this model for evaluating pain behavior has not been examined. The current study evaluated pain-related behavior and change in pain markers in the dorsal root ganglion (DRG) of rats in a simple, sciatic nerve-pinch injury model. In the model, the sciatic nerve was pinched for 2 s using forceps (n = 20), but not injured in sham-operated animals (n = 20). Mechanical and thermal hyperalgesia were measured every second day for 2 weeks using von Frey filaments and a Hargreaves device. Calcitonin gene-related peptide (CGRP), activating transcription factor-3 (ATF-3), phosphorylated p38 mitogen activated protein (Map) kinase (p-p38), and nuclear factor-kappa B (NF-κB; p65) expression in L5 DRGs were examined at 4 and 7 days after surgery using immunohistochemistry. The proportion of neurons immunoreactive for these markers was compared between the two groups. Mechanical (during 8 days) and thermal hyperalgesia (during 6 days) were found in the pinch group rats, but not in the sham-operated animals (p < 0.05); however, hyperalgesia was not significant from days 10 to 14. CGRP, ATF-3, p-p38, and NF-κB expression in L5 DRGs was upregulated in the nerve-injured rats compared with the sham-operated rats (p < 0.01). Our results indicate that a simple sciatic nerve pinch produced pain-related behavior. Upregulation of the pain-marker expression in the nerve-injury model suggested it could be used as a model of pain. However, it was not considered as suitable for long-term studies.

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