A novel rat model of hip pain by intra-articular injection of nerve growth factor-characteristics of sensory innervation and inflammatory arthritis

Abstract

Objectives. To 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.

Methods. Using 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.

Results. The 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.

Conclusions. Intra-articular administration of NGF into the hip joint produces a novel rat model for hip pain.

Keywords:

• Experimental study
• hip joint
• intra-articular injection
• nerve growth factor

Acknowledgements

The source of support in the form of grants or industrial support: The corresponding author, JN, received Grants-in-Aid for Scientific Research (Research Project Number: 25870125) for this work. The other authors do not receive any funding or financial support that may be perceived to have biased the study.

Conflict of interest

None.