ABSTRACT
Objective A rat model of chronic post-thoracotomy pain is used to study whether acute pain and pre-operative diffused noxious inhibitory controls(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 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 as 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.