Cooling decreases fos-immunoreactivity in the rat after formalin injection.

The effects of cooling on inflammatory response after injection of formalin in rats were examined by counting Fos-labeled cells in the dorsal horn of the spinal cord and evaluating swelling. A small amount of dilute formalin was injected into the right hindpaw of rats. The rats were divided into Cooling (-) and Cooling (+) groups and Fos-labeled cells in the spinal cord and paw volumes were compared between the two groups. In the Cooling (+) group, Fos-labeled cells were reduced significantly and the peak time of expression was delayed compared with the Cooling (-) group. Paw volumes were significantly smaller in the Cooling (+) group than in the Cooling (-) group. These results suggest that cooling therapy is effective by delaying the progress of inflammatory reactions and provides extra time for administration of analgesics or implementation of other clinical treatments.