Direct evidence for the up-regulation of spinal micro-opioid receptor function after repeated stimulation of kappa-opioid receptors in the mouse

Eur J Neurosci. 2003 Nov;18(9):2498-504. doi: 10.1046/j.1460-9568.2003.02980.x.


The present study was designed to investigate the possible change in spinal micro -opioid receptor function after repeated administration of a selective kappa-opioid receptor agonist (1S-trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]-benzeneacetamide hydrochloride [(-)U-50,488H] in the ICR mouse. A single s.c. or i.t. injection of (-)U-50,488H produced a dose-dependent antinociception. Repeated s.c. or i.t. administration of (-)U-50,488H resulted in the development of tolerance to (-)U-50,488H-induced antinociception. Under these conditions, we demonstrated here that repeated s.c. injection of (-)U-50,488H significantly enhanced the antinociceptive effect induced by the i.t. administration of a selective micro -opioid receptor agonist [d-Ala2,N-Me-Phe4,Gly5-ol] enkephalin (DAMGO). Using the guanosine-5'-o-(3-[35S]thio) triphosphate ([35S]GTPgammaS) binding assay, we found that (-)U-50,488H was able to produce a dose-dependent increase in [35S]GTPgammaS binding to membranes of the mouse spinal cord. Repeated administration of (-)U-50,488H caused a significant reduction in the (-)U-50,488H-stimulated [35S]GTPgammaS binding in this region, whereas repeated treatment with (-)U-50,488H exhibited an increase in the DAMGO-stimulated [35S]GTPgammaS binding in membranes of the spinal cord. Using a receptor binding assay, repeated treatment with (-)U-50,488H significantly increased the density of [3H]DAMGO binding sites in membranes of the mouse spinal cord. In contrast, the expression of micro -opioid receptor was not affected after repeated treatment with (-)U-50,488H. These results suggest that repeated stimulation of kappa-opioid receptors leads to the up-regulation of micro -opioid receptor functions in the spinal cord, which may be associated with an increase in the number of functional micro -opioid receptors in the mouse spinal cord.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer / pharmacology*
  • Analgesics, Non-Narcotic / pharmacology*
  • Analgesics, Opioid / pharmacology
  • Animals
  • Dose-Response Relationship, Drug
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / pharmacology
  • Guanosine 5'-O-(3-Thiotriphosphate) / metabolism
  • Male
  • Mice
  • Mice, Inbred ICR
  • Pain / metabolism
  • Receptors, Opioid, kappa / agonists*
  • Receptors, Opioid, kappa / metabolism*
  • Receptors, Opioid, mu / drug effects*
  • Receptors, Opioid, mu / metabolism*
  • Reverse Transcriptase Polymerase Chain Reaction
  • Spinal Cord / drug effects
  • Spinal Cord / metabolism*
  • Up-Regulation / drug effects


  • Analgesics, Non-Narcotic
  • Analgesics, Opioid
  • Receptors, Opioid, kappa
  • Receptors, Opioid, mu
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Guanosine 5'-O-(3-Thiotriphosphate)
  • 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer