Journal article
Differential cross-tolerance to opioid agonists in morphine-tolerant pigeons responding under a schedule of food presentation
The Journal of pharmacology and experimental therapeutics, Vol.249(2), pp.386-393
05/1989
Handle:
https://hdl.handle.net/2376/106671
PMID: 2542528
Abstract
Effects of the opioid agonists morphine, l-methadone, ethylketazocine, U50,488 [trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl) cyclohexyl]benzeneacetamide methanesulfonate hydrate], cyclazocine and bremazocine, and the nonopioid chlorpromazine were determined in pigeons responding under a fixed-ratio 30 schedule of food presentation before, during and after chronic morphine administration. Before chronic morphine administration, all drugs produced dose-dependent decreases in response rates. After daily administration of up to 56 mg/kg of morphine for 7 weeks, dose-effect curves for the mu agonists morphine and l-methadone, as well as the mu/kappa agonist ethylketazocine shifted to the right approximately 1 1/4, 3/4 and 1/2 log units, respectively. In contrast, dose-effect curves for the mixed agonist/antagonists cyclazocine and bremazocine each shifted to the left approximately 3/4 log unit, whereas dose-effect curves for the kappa agonist U50,488 and the nonopioid chlorpromazine did not shift during chronic morphine administration. Dose-effect curves for all drugs except bremazocine returned to their prechronic positions within the period 3 to 8 weeks after termination of chronic morphine administration. The present study demonstrates that repeated administration of morphine produces tolerance to its rate-decreasing effects as well as cross-tolerance selective to other opioids possessing mu agonist properties. The cross-tolerance to ethylketazocine observed in morphine-tolerant pigeons corroborates studies of the discriminative stimulus effects of ethylketazocine in pigeons, suggesting that in this species ethylketazocine possesses predominantly mu agonist properties.
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Details
- Title
- Differential cross-tolerance to opioid agonists in morphine-tolerant pigeons responding under a schedule of food presentation
- Creators
- R M Craft - Department of Psychology, University of North Carolina, Chapel HillM J PickerL A Dykstra
- Publication Details
- The Journal of pharmacology and experimental therapeutics, Vol.249(2), pp.386-393
- Academic Unit
- Psychology, Department of
- Publisher
- United States
- Grant note
- DA 02749 / NIDA NIH HHS KO5-DA00033 / NIDA NIH HHS
- Identifiers
- 99900546879501842
- Language
- English
- Resource Type
- Journal article