Abstract: Objective A rat model of chronic post-thoracotomy pain is used to study whether acute pain and pre-operative DNIC can predict chronic pain and how DNIC changes when pain maintains. Methods Rats were randomly divided into three groups：naive group，sham group and model group. DNIC was constantly assessed in individual rats, along with each animal’s mechanical hyperalgesia and cold allodynia after thoracotomy. Results In model group, the incidence rate of chronic post-thoracotomy pain was 55％(11 of 20), which was named CPTP group, and the other 9 rats without chronic pain was defined as non-CPTP group. The pre-operative DNIC was significantly weaker in CPTP group with lower mechanical threshold on 6 days after surgery and higher cold sensitivity on 6 days after surgery comparing with non-CPTP group. In the acute pain phase (day 3), DNIC was decreased in both CPTP group and non-CPTP group compared with pre-operative period. Besides, DNIC was recovered in non-CPTP group while kept impaired in CPTP group on 21 days after surgery. Conclusions Pre-operatively assessed DNIC efficiency and acute post-operative pain intensity were two independent predictors for CPTP. DNIC was decreased both in acute pain and chronic state, while returned to normal when pain sense was normal.

Key words: Chronic post-thoracotomy pain, Diffused noxious inhibitory controls, Acute pain, Predictors