The Assessment of Cold Hyperalgesia After an Incision

Although cold hypersensitivity is a well-documented phenomenon in animals and humans with inflammatory and neuropathic pain, little is known about the presence of cold hyperalgesia after surgery. Therefore, we studied primary cold hyperalgesia after a surgical incision in mice. Before and after plantar incision, inflammation with complete Freund adjuvant, and spared nerve ligation, unrestrained male animals were placed on a Peltier-cooled cold plate with a surface temperature of 0 degrees C and withdrawal latencies were measured. Additionally, incision-induced cold hyperalgesia was also assessed in female animals. Furthermore, skin temperature before and after plantar incision and inflammation were assessed by using infrared thermography (Varioscan LW 3011; Infratec, Dresden, Germany). Cold hyperalgesia to a noxious cold stimulus was observed after inflammation and nerve injury but not after a surgical incision. Similar results were demonstrated for female animals after incision. Furthermore, a significant increase in skin temperature was recorded after inflammation but not after incision, indicating that a surgery evokes only minor inflammatory effects. The present data give strong evidence that a surgical incision does not cause cold hyperalgesia. Furthermore, a lack of cold hyperalgesia in unrestrained male and female mice after incision was not due to increased skin temperature after incision. Finally, we demonstrated that in contrast to a surgical incision, inflammation and nerve injury generate intense cold hyperalgesia and an increase in skin temperature, suggesting that different mechanisms are involved in surgical and inflammatory or neuropathic pain.