Antinociceptive effect of botulinum toxin type a in rat model of carrageenan and capsaicin induced pain.

To test antinociceptive properties of botulinum toxin type A (BTX-A) in rats with carrageenan- and capsaicin-induced pain and inflammation.Pain was provoked with carrageenan (1%) or capsaicin (0.1%) injection into the plantar surface of the rat paw-pad. The effect of BTX-A 5 U/kg on carrageenan- and capsaicin-induced mechanical and thermal hypersensitivity, as well as the size of carrageenan-induced paw edema were tested 24 hours and 6 days following the toxin injection into the rat paw-pad. In the dose-response experiment, the effect of different doses of BTX-A (2, 3, 3.5, 5, and 7 U/kg) on carrageenan-induced mechanical hypersensitivity was investigated on day 5 after BTX-A application.Pretreatment with 5 U/kg BTX-A significantly reduced or completely abolished the enhanced sensitivity to mechanical and thermal stimuli provoked by peripheral carrageenan or capsaicin injections. This reduction was significant when BTX-A was applied 6 days before the induction of pain and inflammation, but the toxin was ineffective when applied 24 hours before the challenge. In the dose-response experiment, the lowest effective dose was 3.5 U/kg, but apparently the effect was not dose-dependent. In contrast to the antinociceptive effect, 5 U/kg BTX-A had no effect on the carrageenan-induced paw edema.The study demonstrated the efficacy of peripherally applied BTX-A pretreatment on the pain component of inflammatory process in experimental animals.