Naloxone-induced facilitation of C-fiber reflexes is reduced by chronic morphine.
The effects of chronic morphine on endogenous opioid function were examined in feline spinal cord. Naloxone-induced facilitation (disinhibition) of the C-fiber reflex was used as a model to reflect endogenous opioid function. Facilitation was reduced 24 h after withdrawal of chronic morphine (14 days). Acute morphine failed to depress C-fiber reflexes in the abstinent cats, indicating tolerance. Thus, these results demonstrated that, after chronic morphine, spinal endogenous opioid function was reduced due to tolerance.
Bell
J A
JA
Neuroscience Branch, National Institute on Drug Abuse, Baltimore, MD 21224.
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002415:Cats; D004594:Electrophysiology; D005260:Female; D007262:Infusions, Intravenous; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects*; D012018:Reflex / Q000187:drug effects*; D013997:Time Factors
D009270:Naloxone; D009020:Morphine