Sex differences in systemic morphine analgesic tolerance following intrathecal morphine injections

Brain Res. 2004 Jul 16;1014(1-2):244-6. doi: 10.1016/j.brainres.2004.03.056.


Morphine analgesic potency following systemic administration was assessed in male and female mice undergoing prior and repeated intrathecal morphine injections. Although morphine ED50 values were significantly increased in both sexes relative to their respective saline-injected controls, the magnitude of tolerance was greater in females. Intrathecal injection alone had no effect on morphine analgesia. The data suggest that spinal mechanisms contribute to sex differences in analgesic tolerance following systemic morphine administration.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics, Opioid / administration & dosage*
  • Analysis of Variance
  • Animals
  • Dose-Response Relationship, Drug
  • Drug Administration Schedule
  • Drug Tolerance
  • Female
  • Injections, Spinal
  • Male
  • Mice
  • Morphine / administration & dosage*
  • Pain / drug therapy
  • Pain Measurement
  • Reaction Time / drug effects
  • Sex Factors


  • Analgesics, Opioid
  • Morphine