Using the CatWalk method to assess weight-bearing and pain behaviour in walking rats with ankle joint monoarthritis induced by carrageenan: effects of morphine and rofecoxib.

The CatWalk automated quantitative gait analysis technique has been validated as a method to quantify behaviour in rodent models of neuropathic and arthritic pain. Its suitability for pharmacological testing of pain relief has been questioned, however, based on findings using paw soft tissue plantar inflammation as stimulus. In this study, we investigated the effectiveness of morphine and rofecoxib in reducing pain behaviour in monoarthritic rats. The CatWalk was used to assess print area, weight load and duration of stance for each paw, as well as interlimb coordination, before and 3, 5 and 24h after injection of lambda-carrageenan into one ankle joint. The monoarthritic rat showed a reduced print area, weight load and duration of stance for the injected paw at all times tested, and a significant loss of interlimb coordination at 3 and 5h after injection. Both morphine (3.75 and 15 micromol/kg s.c.) and rofecoxib (7.5 and 30 micromol/kg p.o.) reduced the effects of carrageenan. In conclusion, behavioural effects interpreted as reflecting movement-related pain in monoarthritic rats and pharmacological treatment of the monoarthritis can objectively and efficiently be quantified in detail by the CatWalk method.