Spinal PKC activity and expression: role in tolerance produced by continuous spinal morphine infusion

Pain. 2000 Apr;85(3):395-404. doi: 10.1016/S0304-3959(99)00281-X.


It has been hypothesized that spinal morphine tolerance results from protein kinase C (PKC) mediated phosphorylation. Chronic lumbar intrathecal (i.t.) infusion of morphine (20 nmol/microl/h) was shown to produce antinociception on day 1 (d1) that disappeared by d5 (tolerance). On d6, a bolus i.t. probe dose of morphine (60 nmol) produced a more profound antinociception in saline-infused rats than in morphine-infused rats. Coinfusion of morphine with a PKC inhibitor, chelerythrine, prevented tolerance to the probe morphine dose. Bolus i.t. chelerythrine or GF109203X (GF), another PKC inhibitor, on d5, but not the inactive homologue of GF Bisindolymaleimide V, also blocked development of tolerance after 24 h. I.t. morphine infusion, but not saline, produced a 2-fold increase in dorsal horn PKC phosphorylating activity and in the expression of PKCalpha/gamma. Bolus chelerythrine on d5 after spinal morphine infusion blocked upon an increase in PKC activity, confirming that at the behaviorally active dose the drug had the intended biochemical effect upon spinal PKC activity. PKC activity and protein expression did not change when assessed 1 h after bolus i.t. morphine in naive rats. Thus, tolerance produced by morphine infusion is dependent upon an increase in local phosphorylating activity by PKC. Blocking the PKC activity prevents expression of the morphine tolerance.

Publication types

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

MeSH terms

  • Alkaloids
  • Animals
  • Benzophenanthridines
  • Enzyme Inhibitors / pharmacology
  • Immunoblotting
  • Injections, Spinal
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / isolation & purification
  • Isoenzymes / metabolism
  • Male
  • Morphine / pharmacology*
  • Narcotics / pharmacology*
  • Pain Measurement / drug effects
  • Phenanthridines / pharmacology
  • Phosphorylation
  • Posterior Horn Cells / drug effects
  • Posterior Horn Cells / enzymology
  • Protein Kinase C / antagonists & inhibitors
  • Protein Kinase C / isolation & purification
  • Protein Kinase C / metabolism*
  • Protein Kinase C-alpha
  • Rats
  • Rats, Sprague-Dawley
  • Spinal Cord / drug effects
  • Spinal Cord / enzymology*


  • Alkaloids
  • Benzophenanthridines
  • Enzyme Inhibitors
  • Isoenzymes
  • Narcotics
  • Phenanthridines
  • Morphine
  • chelerythrine
  • protein kinase C gamma
  • Protein Kinase C
  • Protein Kinase C-alpha