Melittin selectively activates capsaicin-sensitive primary afferent fibers

Whole bee venom (WBV)-induced pain model has been reported to be very useful for the study of pain. However, the major constituent responsible for the production of pain by WBV is not apparent. Intraplantar injection of WBV and melittin dramatically reduced mechanical threshold, and increased flinchings and paw thickness. In behavioral experiments, capsaicin pretreatment almost completely prevented WBV- and melittin-induced reduction of mechanical threshold and flinchings. Intraplantar injection of melittin increased discharge rate of dorsal horn neurons only with C fiber input from peripheral receptive field, which was completely blocked by topical application of capsaicin to sciatic nerve. These results suggest that both melittin and WBV induce nociceptive responses by selective activation of capsaicin-sensitive afferent fibers.