Tolerance to morphine stimulus control: role of morphine maintenance dose

Alice M. Young, Christine A. Sannerud, Elizabeth S. Steigerwald, Mechele D. Doty, William J. Lipinski, Lois E. Tetrick

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Experiments assessed the development of tolerance to morphine stimulus control during treatment with selected maintenance doses of morphine. Separate groups of rats were trained to discriminate saline and either 3.2 mg/kg or 5.6 mg/kg morphine under fixed-ratio schedules of food delivery. Dose-response functions for generalization of morphine stimulus control were determined before, during, and after repeated treatment with selected doses of morphine. Similar experiments were performed with repeated pentobarbital treatment in order to assess the pharmacological selectivity of tolerance. Repeated treatment with saline, 3.2 mg/kg morphine, or twice daily injections of 17.8 mg/kg pentobarbital produced no tolerance to morphine stimulus control. In contrast, treatment with daily injections of 10 mg/kg or twice daily injections of 10 or 17.8 mg/kg morphine produced a dose-dependent increase in the dose of morphine required for stimulus control. The magnitude of tolerance to morphine stimulus control varied directly with the maintenance dose of morphine and was slightly greater for a lower than a higher morphine training dose. Termination of repeated treatment was followed by a return to initial sensitivity, without additional training. Tolerance to morphine stimulus control was not necessarily accompanied by tolerance to its rate-suppressing effects.

Original languageEnglish (US)
Pages (from-to)59-67
Number of pages9
Issue number1
StatePublished - Sep 1990
Externally publishedYes


  • Drug discrimination
  • Morphine
  • Opioids
  • Rats
  • Tolerance

ASJC Scopus subject areas

  • Pharmacology


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