Internalization of mu-opioid receptors in rat spinal cord slices

Neuroreport. 1999 Aug 2;10(11):2329-34. doi: 10.1097/00001756-199908020-00020.


Cells immunoreactive for the mu-opioid receptor (MOR) in laminae I-II of the spinal cord were identified as small neurons with rostro-caudal dendrites. In spinal cord slices, [D-Ala2,MePhe4-Gly-ol5]enkephalin (DAMGO) or etorphine (1 microM) caused naloxone-sensitive MOR endocytosis in 100% of these neurons, whereas the selective delta- and kappa-opioid agonists [D-Pen2,5]enkephalin (DPDPE) and spiradoline mesylate (U-62,066), respectively, produced negligible internalization at 1 microM. The EC50 for DAMGO was 30 nM, similar to its potency to inhibit cAMP accumulation and to increase [gamma-35S]GTP binding. MOR internalization followed an exponential timecourse with a half-life of 1.7 min. MOR internalization in spinal cord slices was faster and occurred at lower agonist concentrations than in MOR-transfected cells, suggesting that spinal cord neurons have a more effective coupling of MORs to intracellular components mediating endocytosis.

Publication types

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

MeSH terms

  • Animals
  • Dose-Response Relationship, Drug
  • Endocytosis / physiology*
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Enkephalins / pharmacology
  • Immunohistochemistry
  • In Vitro Techniques
  • Kinetics
  • Rats
  • Receptors, Opioid, mu / agonists
  • Receptors, Opioid, mu / metabolism*
  • Spinal Cord / drug effects
  • Spinal Cord / metabolism*
  • Spinal Cord / physiology
  • Tissue Distribution / physiology


  • Enkephalins
  • Receptors, Opioid, mu
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-