mu Opioid receptor knockout in mice: effects on ligand-induced analgesia and morphine lethality

Brain Res Mol Brain Res. 1998 Mar 1;54(2):321-6. doi: 10.1016/s0169-328x(97)00353-7.


The mu opioid receptor gene (MOR) was mutated in mice by a gene targeting procedure. In these MOR-knockout mice, the analgesic effects of morphine, its major metabolites, morphine-6-glucuronide (M-6-G) and morphine-6-ethereal sulfate (M-6-S), and endomorphin-2, as well as morphine-induced lethality, were drastically reduced, whereas the effects of DPDPE and U50488 remained unchanged. It is concluded that analgesic effects of mu-specific opioid ligands and acute morphine lethality are mediated by the mu receptor.

Publication types

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

MeSH terms

  • Analgesics, Opioid / toxicity*
  • Animals
  • Genotype
  • Lethal Dose 50
  • Ligands
  • Mice
  • Mice, Knockout
  • Morphine / toxicity*
  • Morphine Derivatives / toxicity
  • Oligopeptides / toxicity
  • Receptors, Opioid, mu / genetics*


  • Analgesics, Opioid
  • Ligands
  • Morphine Derivatives
  • Oligopeptides
  • Receptors, Opioid, mu
  • endomorphin 2
  • morphine-6-glucuronide
  • Morphine