A model of incisional pain: the effects of dermal tail incision on pain behaviours of Sprague Dawley rats.

Hyperalgesia, a component of post-operative pain, is an enhanced responsiveness to painful challenges after the tissue damage caused by an incision. It is important to understand the mechanisms involved in the development of incisional pain, in order to treat the condition appropriately. The aim of this study was to develop a model of post-operative pain using the rat's tail. Under halothane-induced anaesthesia, female Sprague Dawley rats underwent 10mm longitudinal incisions through skin and fascia (n = 10) or 20 mm incisions through skin, fascia and muscle (n = 10) of the mid-portion of the tail. Control rats were only anaesthetised (n = 14). Withdrawal latencies to noxious mechanical and thermal challenges were recorded daily. A bar algometer was placed onto and 15 mm proximal to the incision with a force of 4N and the tail was immersed in 49 degrees C water. Daily withdrawal latencies were compared to pre-incision values using one way analysis of variance (ANOVA) with Dunnett's post-hoc test. Primary mechanical hyperalgesia lasted for 6 days after the 10 mm incisions (P < 0.0001) and for 7 days after the 20 mm incisions (P < 0.0001). Secondary mechanical hyperalgesia persisted for 1 day after the 10 mm incisions (P = 0.0013) and for 2 days after the 20 mm incisions (P = 0.0028). Thermal hyperalgesia was not elicited. This model is suitable to examine the mechanisms involved in post-operative pain.