Spinal delta 2-, but not delta 1-, mu-, or kappa-opioid receptors are involved in the tail-flick inhibition induced by beta-endorphin from nucleus raphe obscurus in the pentobarbital-anesthetized rat

Eur J Pharmacol. 1995 Apr 24;277(2-3):251-6. doi: 10.1016/0014-2999(95)00084-x.

Abstract

The antinociception induced by beta-endorphin given supraspinally has been previously demonstrated to be mediated by the release of [Met5]enkephalin acting on delta-opioid receptors in the spinal cord. The present study was designed to determine what type of opioid receptors in the spinal cord is involved in beta-endorphin-induced antinociception in the rat. Antinociception was induced by beta-endorphin (0.6 nmol) given into nucleus raphe obscurus and was assessed by the tail-flick test in pentobarbital-anesthesized rats. Naltriben (0.6-6.0 nmol), a selective delta 2-opioid receptor antagonist, given intrathecally dose-dependently attenuated beta-endorphin-induced inhibition of the tail-flick response. On the other hand, 7-benzylidene naltrexone (2.1-64.3 nmol), CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2, 0.09-2.8 nmol), or nor-binaltorphimine (1.4-40.8 nmol), selective delta 1-, mu-, and kappa-opioid receptor antagonists, respectively, did not block beta-endorphin-induced antinociception. The results of present study in rats are consistent with previous experiments in mice indicating that spinal delta 2-, but not delta 1-, mu- or kappa-opioid receptors are involved in beta-endorphin-induced inhibition of the tail-flick response.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Analgesia
  • Animals
  • Benzylidene Compounds / pharmacology
  • Dose-Response Relationship, Drug
  • Enkephalin, Methionine / metabolism
  • Injections, Intraventricular
  • Injections, Spinal
  • Male
  • Molecular Sequence Data
  • Naltrexone / administration & dosage
  • Naltrexone / analogs & derivatives
  • Naltrexone / pharmacology
  • Narcotic Antagonists / administration & dosage
  • Narcotic Antagonists / pharmacology
  • Pentobarbital / administration & dosage
  • Pentobarbital / pharmacology
  • Raphe Nuclei / drug effects*
  • Raphe Nuclei / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Opioid, delta / drug effects*
  • Receptors, Opioid, delta / metabolism
  • Receptors, Opioid, kappa / drug effects*
  • Receptors, Opioid, kappa / metabolism
  • Receptors, Opioid, mu / drug effects*
  • Receptors, Opioid, mu / metabolism
  • Somatostatin / administration & dosage
  • Somatostatin / analogs & derivatives
  • Somatostatin / pharmacology
  • Spinal Cord / drug effects
  • Spinal Cord / metabolism
  • Tail
  • beta-Endorphin / administration & dosage
  • beta-Endorphin / toxicity*

Substances

  • Benzylidene Compounds
  • Narcotic Antagonists
  • Receptors, Opioid, delta
  • Receptors, Opioid, kappa
  • Receptors, Opioid, mu
  • phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide
  • naltrindole benzofuran
  • 7-benzylidenenaltrexone
  • norbinaltorphimine
  • Somatostatin
  • Enkephalin, Methionine
  • Naltrexone
  • beta-Endorphin
  • Pentobarbital