Effects of footshock stress and morphine on natural killer lymphocytes in rats: studies of tolerance and cross-tolerance

Brain Res. 1986 May 7;372(2):382-5. doi: 10.1016/0006-8993(86)91149-2.


Exposure to a form of footshock stress known to cause opioid-mediated analgesia suppresses the cytotoxic activity of natural killer (NK) cells in rats. This suppression is blocked by the opioid antagonist, naltrexone and is mimicked by morphine administration, suggesting mediation by opioid receptors. Supporting this hypothesis, we now report that the morphine-induced suppression of NK activity shows tolerance after 14 daily injections. The NK-suppressive effect of stress, however, shows neither tolerance with repetition nor cross-tolerance in morphine-tolerant rats.

Publication types

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

MeSH terms

  • Animals
  • Brain / physiology*
  • Cytotoxicity, Immunologic
  • Drug Tolerance
  • Electroshock
  • Female
  • Foot
  • Killer Cells, Natural / immunology*
  • Morphine / pharmacology*
  • Rats
  • Rats, Inbred F344
  • Receptors, Opioid / physiology*
  • Stress, Physiological / immunology*


  • Receptors, Opioid
  • Morphine