Nociceptin receptors in the rat spinal cord during morphine tolerance

Brain Res. 1999 Aug 14;838(1-2):85-94. doi: 10.1016/s0006-8993(99)01713-8.


The anatomical localization of nociceptin receptors was examined by in vitro quantitative autoradiography techniques in rat spinal cord sections by using [(125)I-Tyr(14)]nociceptin. [(125)I-Tyr(14)]nociceptin appeared to interact with a single class of binding sites (K(D)=0.1 nM) present in the grey matter in all laminae of the spinal cord from cervical to sacral levels. Pre-incubation of sections in the presence of 150 mM NaCl, did not modify the radioligand affinity but significantly augmented the number of accessible binding sites and increased specific binding of [(125)I-Tyr(14)]nociceptin differentially on each laminae. In particular, the superficial layers of the dorsal horn exhibited the highest density of sites after pre-wash. Continuous intrathecal infusion of morphine produced a tolerance accompanied by a significant increase in nociceptin site density in the superficial layers. Thus, nociceptin binding sites may have different properties dependent upon the layer and may be up-regulated during the process of opioid-induced tolerance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Analgesics, Opioid / pharmacology*
  • Animals
  • Autoradiography
  • Drug Tolerance
  • Iodine Radioisotopes
  • Male
  • Molecular Sequence Data
  • Morphine / pharmacology*
  • Radioligand Assay
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Opioid / analysis
  • Receptors, Opioid / drug effects*
  • Spinal Cord / chemistry
  • Spinal Cord / drug effects*


  • Analgesics, Opioid
  • Iodine Radioisotopes
  • Receptors, Opioid
  • Morphine
  • nociceptin receptor