A rat model of persistent postoperative pain evoked by skin/muscle incision and retraction

Abstract

Objective To establish a rat model of persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR)and to test its efficacy. Methods Thirty-six male SD rats were randomly divided into three groups (n= 12): control group, sham group and model group. SMIR was produced as Flatters described and the threshold with von Frey filament and radiant heat stimulation were measured before operation (baseline) and at 1st, 3rd, 7th, 12th, 22nd and 32nd postoperative day. The structural damages to myelin sheath of saphenous nerve in 4 rats of each group randomly were observed with electron microscope at 12th postoperative day. Results SMIR surgery induced signi?cantly persistent mechanical hypersensitivity to von Frey stimulation of the plantar ipsilateral hindpaw. Compared to the responses of control group rats, the threshold to mechanical stimuli started to decrease at 1 d (P=0.015＜0.05) and peaked at 12 d (P=0.001＜0.01) after operation. There was no significant difference between the SMIR group and control group at 32 d after surgery (P=0.772＞0.05). Mechanical sensitivity of control group and sham group did not significantly change. SMIR did not induce significant heat hyperalgesia. Electron microscopy of saphenous nerve sections did not show demyelination or oedema in the saphenous nerve of the model group or sham group. Conclusion The results of the present study suggest that the model of persistent postoperative pain evoked by SMIR is stable and repeatable, which may provide a new stage for the study on the mechanisms and treatment of postoperative pain. Key words: Postoperative pain; Animal model; Pain behavior