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).
DMM or sham surgery was performed in 10-week-old male C57BL/6 wild-type or Pirt-GCaMP3
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.
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.