• Takanori Omae, Junichi Nakamura, Seiji Ohtori, Sumihisa Orita, Kazuyo Yamauchi, Shuichi Miyamoto, Shigeo Hagiwara, Shunji Kishida, and Kazuhisa Takahashi.
• a Department of Orthopaedic Surgery , Graduate School of Medicine, Chiba University , Chiba City , Chiba , Japan.
• Mod Rheumatol. 2015 Jan 1; 25 (6): 931-6.

ObjectivesTo determine the direct effects of intra-articular injection of nerve growth factor (NGF) into normal rat hips and the time course of pain-related mediator appearance.MethodsUsing 36 numbers of 8-week-old male Sprague-Dawley rats, 30 μl of 1% Fluoro-Gold solution (FG) (Sham-operated group; n = 12), 30 μl of 1% FG with 50 μg/ml NGF (NGF50 group; n = 12), and 30 μl of 1% FG with 100 μg/ml NGF (NGF100 group; n = 12) were injected into the left hip joints. Neurons in the dorsal root ganglion (DRG) labeled with FG, and FG and calcitonin gene-related peptide-immunoreactivity (CGRP-IR) were counted. The synovia in the left hip joint was examined histologically.ResultsThe NGF50 and NGF100 groups showed evidence of synovitis without cartilage degeneration compared with the Sham-operated group. At 7 days, the proportions of CGRP-IR FG-labeled to total FG-labeled neurons were 12%, 18%, and 36% in the Sham-operated, NGF50, and NGF100 groups, respectively. At 14 days, the proportions were 13%, 22%, and 35% in the Sham-operated, NGF50, and NGF100 groups, respectively. At 7 and 14 days, the NGF50 and NGF100 groups showed a significantly higher proportion of CGRP-IR FG-labeled neurons than the Sham-operated group.ConclusionsIntra-articular administration of NGF into the hip joint produces a novel rat model for hip pain.

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