Effects of Topically Applied Capsaicin Cream on Neurogenic Inflammation and Thermal Sensitivity in Rats

Abstract

The effects of capsaicin cream on neurogenic inflammation and thermal nociceptive threshold were investigated in rats.Firstly, for topical application of capsaicin cream to hind paw, we shaped boots from dental cement to prevent the animals from licking off the drug.Capsaicin cream(1%) led to significant increases in the amounts of Evans blue and substance P(SP) released into the perfusate, and the former response was significantly suppressed by pretreatment with RP67580, an NK₁-receptor antagonist, but not by treatment with an NK₂-receptor antagonist.Subsequent electrical stimulation of the sciatic nerve resulted in a significant reduction in Evans blue and SP extravasation 24h after topical application of capsaicin cream.On the other hand, when capsaicin cream was repeatadly applied to both hind paws once a day, withdrawal latency for noxious heat stimulation decreased after 24h, and this thermal hyperalgesia was reversed 3 days later.These results suggest that capsaicin cream initially affects neurogenic inflammation mechanisms and then blocks the pain transmission mechanism.