Spinal administration of adrenergic agents produces analgesia in amphibians

Craig W. Stevens, George M. Brenner

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


Direct intraspinal injection of the catecholamines epinephrine and norepinephrine, and the α-adrenergic agents dexmedetomidine and clonidine, produced a dose-dependent elevation of pain thresholds in the Northern grass frog, Rana pipiens. Significant analgesic effects were noted for at least 4 h. The analgesic effect of intraspinal dexmedetomidine or epinephrine was blocked by systemic pretreatment with the α2-adrenoceptor antagonists, yohimbine and atipamezole, but not with the α1-adrenoceptor antagonist, prazosin. Dose-response analyses showed that dexmedetomidine, epinephrine, norepinephrine had similar analgesic potencies, but clonidine was significantly less potent. Analgesia was observed without accompanying motor or sedative effects. These results suggest that α2-adrenoceptor mechanisms which mediate analgesia may have evolved early in vertebrate evolution and that descending epinephrine-containing fibers in the amphibian nervous system may be the source of endogenous catecholamines regulating nociceptive sensitivity in the amphibian spinal cord.

Original languageEnglish
Pages (from-to)205-210
Number of pages6
JournalEuropean Journal of Pharmacology
Issue number2-3
StatePublished - 5 Dec 1996


  • -Adrenoceptor
  • Amphibian
  • Analgesia
  • Pain


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