Visualization of Peripheral Neuron Sensitization in a Surgical Mouse Model of Osteoarthritis by In Vivo Calcium Imaging

• Published in: Arthritis & rheumatology (Hoboken, N.J.) Vol. 70; no. 1; pp. 88 - 97
• Main Authors: Miller, Rachel E., Kim, Yu Shin, Tran, Phuong B., Ishihara, Shingo, Dong, Xinzhong, Miller, Richard J., Malfait, Anne‐Marie
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.01.2018
• Subjects: Biocompatibility; Biomedical materials; Calcium; Calcium imaging; Destabilization; Dorsal root ganglia; Hyperalgesia; Imaging; In vivo methods and tests; Knee; Mechanical stimuli; Meniscus; Mice; Neurons; Nociceptors; Osteoarthritis; Pain perception; Rodents; Sensory neurons; Stimuli; Surgery
• ISSN: 2326-5191; 2326-5205
• DOI: 10.1002/art.40342

Objective To develop a method for analyzing sensory neuron responses to mechanical stimuli in vivo, and to evaluate whether these neuronal responses change after destabilization of the medial meniscus (DMM). Methods DMM or sham surgery was performed in 10‐week‐old male C57BL/6 wild‐type or Pirt‐GCaMP3+/‐ mice. All experiments were performed 8 weeks after surgery. Knee and hind paw hyperalgesia were assessed in wild‐type mice. The retrograde label DiI was injected into the ipsilateral knee to quantify the number of knee‐innervating neurons in the L4 dorsal root ganglion (DRG) in wild‐type mice. In vivo calcium imaging was performed on the ipsilateral L4 DRG of Pirt‐GCaMP3+/‐ mice as mechanical stimuli (paw pinch, knee pinch, or knee twist) were applied to the ipsilateral hind limb. Results Eight weeks after surgery, mice subjected to DMM had more hyperalgesia in the knee and hind paw compared to mice subjected to sham surgery. Intraarticular injection of DiI labeled similar numbers of neurons in the L4 DRG of mice subjected to sham surgery and mice subjected to DMM. Increased numbers of sensory neurons responded to all 3 mechanical stimuli in mice subjected to DMM, as assessed by in vivo calcium imaging. The majority of responses in mice subjected to sham surgery and mice subjected to DMM were in small to medium‐sized neurons, consistent with the size of nociceptors. The magnitude of responses was similar between mice subjected to sham surgery and mice subjected to DMM. Conclusion Our findings indicate that increased numbers of small to medium‐sized DRG neurons respond to mechanical stimuli 8 weeks after DMM surgery, suggesting that nociceptors have become sensitized by lowering the response threshold.