In order to evaluate pain in animal models of arthritis, various methods such as measuring paw elevation time of arthritic rat, walking on a rotating cylinder, measuring latency of paw withdrawal response to radiant heat and subjective scoring of loco motor behavior have been widely used. However, none of these methods are sufficiently practical and reliable to assess arthritic pain. The aim of this study was to provide a more practical, objective and quantitative method of assessing arthritic pain.
Rats were injected with 2% kaolin and 3% carrageen an (suspended in 50 p1 normal saline) into the right knee joint cavity under enflurane anesthesia (0.5--2%). Before and after the injection, rats were allowed to walk freely through a pathway constructed to record the weight load by means of 8 weight sensors (strain gauges) attached to 8 plates which function independently. The weight bearing was measured before the injection and from 2 hours to 7 days after the injection.
Following the kaolin and carrageen an injection, the weight bearing on the injected side reduced to the lowest level at 6.5 hours, and returned to the pre-injection level on the 7th day. Intra-peritoneal morphine injection reversed the reduction of weight bearing in a dose-dependent manner.
These results clearly demonstrated that decreased weight load in arthritic leg is a pain-related behavior. These results suggest that our device is a reliable and practical measure for assessing arthritic pain quantitatively. Our device is an appropriate tool for the screening of analgesic drug and widely applicable method.
|