Abstract
Some validated methods for assessing pain in laboratory animals are currently available. However, it remains to be determined whether these methods are also applicable for aged animals. Recently, grimace scale (GS) was developed for pain assessment based on facial expressions, and can effectively evaluate animal spontaneous pain. In the present study, we investigated that accuracy and reliability of the rat grimace scale (RGS) in aged rats. Six coders were trained with the RGS training manual. Unlabeled 80 facial images of which half were with no pain (baseline), the other half were with pain (2 - 4 h after laparotomy) were randomly assigned and then scored by the coders. A high degree of the reliability was found with an overall intra-class correlation coefficient value of 0.92. The average accuracy of pain detection assessed by coders’ dichotomous judgment of “global pain” or “no pain” was sufficiently high with a correct classification rate of 84.6％. Furthermore, a single subcutaneous administration with morphine (1.0 mg/kg) resulted in decrease of RGS at 4 h after laparotomy. These results suggested that RGS is a useful method for assessing spontaneous pain after laparotomy in aged rats.
