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Effect of Capsaicin on the Formalin-induced Fos-like Immunoreactivity in the Spinal Cord of Rat
YAKHAK HOEJI 1999;43(3):404-410
Published online June 28, 1999
© 1999 The Pharmaceutical Society of Korea.

곽지연(Ji Yeon Kwak);오우택(Uh Taek Oh)
Abstract
Administration of capsaicin produces acute pain and subsequent long-lasting antinociception. The antinociceptive action site of capsaicin is primarily small afferent nerve fibers. However, the effect of capsaicin on the neural activity of dorsal horn neurons are not well understood. The goal of the present experiment was to study the action of capsaicin on activity of dorsal horn neurons using c-fos immunoreactivity in the spinal cord. Intradermal injection of formalin in the hindpaw produced inflammation in the foot pad and increased the number of cells exhibiting Fos-like immunoreactivity (FLI) in the dorsal horn of the spinal cord, suggesting the hyperalgesia because of the apparent inflammation. Intradermal injection of capsaicin prior to formalin injeciton significantly reduced the number of cells exhibiting FLI induced by formalin and increased the paw-withdrawal latency, suggesting the hypoalgesic effect of capsaicin. Coadministeration with capsaicin of capsazepine and ruthenium red, antagonists of capsaicin receptor reversed the reduction of formalin-induced FLI by capsaicin. The antagonists also partially antagonized the antinociceptive effect of capsaicin in the paw-withdrawal test. These results further suggest that capsaicin reduces responses of dorsal horn neurons to the inflammatory nociceptive stimuli in the periphery. Thus, the reduction of FLI subserves the neural mechanisms underlying analgesia produced by capsaicin.
Keywords : Capsaicin;Fos-like immunoreactivity;analgesia;dorsal hom neurons.


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