Local and remote modifications of nociceptive sensitivity during carrageenin-induced inflammation in the rat.

The modifications of the threshold for vocalization induced by pressure on the paws (both hind paws and both forepaws) were monitored at different times (15 min-96 h) following intraplantar injection of the polysaccharide carrageenin in the rat. During the first 2 h following the carrageenin injection, a decrease in vocalization threshold was observed not only for the right, injected hind paw, but also, in some rats, on paws distant from the inflamed plantar region, especially the right forepaw. This hyperalgesic effect was suppressed by locally administered Xylocaine into the right hind paw. During the 4 days following the injection, the number of rats hyperalgesic in the injected paw progressively declined. Twenty-four hours after the carrageenin injection, only a few rats still presented a clear hyperalgesia in the non-injected paws.