Similarities and differences in the action of resiniferatoxin and capsaicin on central and peripheral endings of primary sensory neurons

Neuroscience. 1990;37(2):531-9. doi: 10.1016/0306-4522(90)90421-y.

Abstract

We have compared the ability of capsaicin and resiniferatoxin, a natural diterpene present in the latex of plants of the Euphorbia family to excite and desensitize capsaicin-sensitive primary afferents in a variety of models. Both capsaicin and resiniferatoxin inhibited the twitch contractions of the rat isolated vas deferens and prevented, in a concentration-related manner, the effect of a subsequent challenge with 1 microM capsaicin (desensitization). Resiniferatoxin was 1000-10,000 times more potent than capsaicin in both cases. The time course of action of resiniferatoxin was much slower than that of capsaicin, suggesting a slower penetration rate in the tissue. The action of resiniferatoxin was blocked by Ruthenium Red, a proposed antagonist at the cation channel coupled to the capsaicin receptor. Both capsaicin and resiniferatoxin produced a contraction of the rat isolated urinary bladder. Resiniferatoxin was about as potent as capsaicin in this assay although it was 500-1000 times more potent than capsaicin in desensitizing the primary afferents to a subsequent challenge with capsaicin itself. Resiniferatoxin did not affect motility in the isolated vasa deferentia or urinary bladder from capsaicin-pretreated rats. After topical application onto the rat urinary bladder both resiniferatoxin (10 nM) and capsaicin (10 microM) increased bladder capacity as assessed in a volume-evoked micturition reflex model in rats without affecting micturition contraction. Intrarterial injection of resiniferatoxin or capsaicin in the ear of anesthetized rabbits evoked a systemic depressor reflex due to activation of paravascular nociceptors, resiniferatoxin being about three times more potent than capsaicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anesthesia
  • Animals
  • Calcitonin Gene-Related Peptide / metabolism
  • Capsaicin / antagonists & inhibitors
  • Capsaicin / pharmacology*
  • Diterpenes / antagonists & inhibitors
  • Diterpenes / pharmacology*
  • Ear, External / innervation
  • In Vitro Techniques
  • Male
  • Muscle Contraction / drug effects
  • Nerve Endings / drug effects*
  • Nerve Endings / metabolism
  • Neurons, Afferent / drug effects*
  • Neurons, Afferent / metabolism
  • Peripheral Nerves / drug effects*
  • Peripheral Nerves / metabolism
  • Rabbits
  • Rats
  • Rats, Inbred Strains
  • Reflex / drug effects
  • Ruthenium Red / pharmacology
  • Spinal Cord / cytology
  • Spinal Cord / drug effects*
  • Spinal Cord / metabolism
  • Substance P / metabolism
  • Urinary Bladder / innervation
  • Urination / drug effects
  • Vas Deferens / innervation

Substances

  • Diterpenes
  • Ruthenium Red
  • Substance P
  • resiniferatoxin
  • Calcitonin Gene-Related Peptide
  • Capsaicin