Clipping Hind Paws Under Isoflurane Sedation as a Useful Tool for Evaluation of Chronic Pain in CCI Animals

Background: Several behavioral tests have been devised to assess pain in rodent models, one of which is the Chronic constriction injury (CCI) model of the sciatic nerve, including the sensitivity of the paw evaluated through reflex reactions to heat or mechanical stimuli. However, because of their high restless activity and responsiveness to humans, it is tough to give the moving animals consistent stimuli to get consistent and reliable reactions. Methods: Experiments were performed on male C57BL/6J mice (aged eight weeks) and prairie voles (aged eight weeks). Sham animals (five mice and six prairie voles) and CCI animals (six mice and seven prairie voles) were tested before surgery, four days after, and seven days after surgery. Each animal was rated using a modified rating scale for the scoring of nociceptive behavior. The mechanical threshold test was administered by applying arterial clips to the base of toes under isoflurane-induced sedation. Results: The right hind paw of the CCI administered side showed significant increases in the scores of nociceptive behavior on day 4 and day 7. The right hind pawof the CCI-administered side showed significant reductions in the mechanical threshold test on day 4 and day 7. Conclusions: The results of the mechanical threshold test were consistent with those of the scoring of nociceptive behavior in CCI model animals, and the method of using arterial clips under sedation was useful for the mechanical threshold test.