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Selective but Slight Enhancement of Delta Agonist‐Induced Antinociception by Repeated Morphine in Rhesus Monkeys
Author(s) -
Negus S. Stevens,
Banks Matthew L.,
Schrode Katrina,
Morrissey Ember,
Rice Kenner C.
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.742.7
Subject(s) - agonist , morphine , pharmacology , fentanyl , potency , opioid , nociception , chemistry , μ opioid receptor , saline , analgesic , tail flick test , partial agonist , δ opioid receptor , receptor , medicine , anesthesia , in vitro , biochemistry
Repeated treatment with mu opioid receptor agonists (e.g. morphine) may promote insertion of delta receptors into neuronal membranes and enhance the potency/efficacy of delta opioid receptor agonists. The present study compared effects of the delta agonist SNC80 and the mu agonist fentanyl after repeated saline or morphine in rhesus monkeys. In an assay of schedule‐controlled responding (FR30 for food), SNC80 and fentanyl each produced a dose‐dependent decrease in response rates after repeated saline treatment. Repeated morphine treatment (1, 1.6, 2 and 3 mg/kg at 12hr intervals, testing 12hr after last dose) had no significant effect on the potency or efficacy of either drug. In the assay of thermal nociception (tail‐withdrawal from 48 and 54°C water), SNC80 had little effect, whereas fentanyl produced full and partial antinociception at 48 and 54°C, respectively. Repeated morphine produced a significant but only slight enhancement of SNC80 effects and reduction in fentanyl effects at 54°C. Thus, under these conditions, repeated mu agonist treatment produced a selective but slight enhancement of the antinociceptive effects of SNC80 in rhesus monkeys. Supported by NIDA and NIAAA of NIH.