CHARACTERIZATION OF A RAT MODEL OF INCISIONAL PAIN

In this study, we developed a rat model of incisional pain. A 1-cm lon gitudinal incision was made through skin, fascia and muscle of the pla ntar aspect of the hindpaw in halothane-anesthetized rats. Withdrawal responses were measured using von Prey filaments at different areas ar ound the wound before surgery and for the next 6 days. A cumulative pa in score based on the weight bearing behavior of the animals was also utilized. The results of tests for withdrawal responses and scores bas ed on weight bearing suggest that a surgical incision of the rat foot causes a reliable and quantifiable mechanical hyperalgesia lasting for several days after surgery. An incision that only included skin and f ascia but not muscle in the foot caused less severe hyperalgesia durin g the initial postoperative period. Distinct areas around the wound ha d different withdrawal thresholds during the study period. Even remote sites as much as 10 mm from the wound showed persistent mechanical hy peralgesia. Selective denervations of the rat hindpaw prior to foot in cision revealed both the sural and tibial nerves were responsible for transmitting input from the incision that produces hyperalgesia. This model should allow us to understand mechanisms of sensitization caused by surgery and investigate new therapies for postoperative pain in hu mans.