Abstract
[Objective] To confirm the validity of chronic pain model due to a soft tissue lesion, we examined and compared pain behaviors occurring at the site of the lesion and a remote area.
[Methods] To produce muscle lesion in rats, lipopolysaccharide (LPS, 2 μg/kg, 100 μl) and 6% hypertonic saline (HS, 100 μl, five consecutive injections at 90-minite intervals) were injected into the unilateral gastrocnemius muscle at 24-hour intervals. Then, measurements for the muscle pain threshold and mechanical hypersensitivity of the hind paw were performed bilaterally.
[Results] A combined treatment with LPS and HS to the unilateral muscle developed long-persisting pain behaviors in the hind paws bilaterally, lasting more than 10 weeks. On the other hand, pain behavior at the injected site disappeared within 1 week after treatment.
[Conclusion] The pain behavior occurring beyond the site of the lesion persists even after the disappearance of pain in the muscle, showing a similar pattern in the development of chronic pain seen in humans.
