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Systemic morphine administration attenuates the perceived intensity of noxious heat in the monkey
David A Thomas1, Jean-Louis Oliveras, William Maixner
1Neurobiology and Anesthesiology Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, MD 20892 USA.
Abstract:
We examined the ability of systemic morphine to diminish the sensory discriminative features of noxious heating. Monkeys were trained to perform a thermal detection task, and the time until their detection of small increases in heating was used as a measure of the perceived intensity of pain. Relatively small doses of morphine sulfate (0.1, 0.3 and 1.0 mg/kg, i.m.) increased the time until detection of graded temperature increases (0.4-1.0 degrees C) from a noxious 46 degrees C baseline. These effects were generally dose-dependent, reversed by systemic naloxone, and did not result from changes in attentional, motivational or motoric aspects of the monkeys' behavior. Furthermore, the effects of morphine were more pronounced on detection of temperature shifts that were near threshold. These findings indicate that doses of morphine in the therapeutic dose range for humans alter the perceived intensity of noxious heat in monkeys.
Insights
Systemic morphine, a pain reliever, was found to reduce the perceived intensity of noxious heat in monkeys. Even low, therapeutic doses increased pain detection times, indicating altered pain perception.
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- Morphine is a widely used analgesic.
- Understanding its effects on sensory discrimination of pain is crucial for optimizing pain management.
- Previous research has explored morphine's analgesic properties, but its specific impact on the discriminative aspects of noxious heat perception requires further elucidation.
Purpose of the Study:
- To investigate the effect of systemic morphine administration on the sensory discriminative aspects of noxious heat pain in a non-human primate model.
- To quantify the impact of varying morphine doses on the perception of thermal stimuli.
Main Methods:
- Monkeys were trained on a thermal detection task to measure the time to detect noxious heat increases.
- Systemic morphine sulfate was administered at doses of 0.1, 0.3, and 1.0 mg/kg (intramuscularly).
- Naloxone was used to reverse morphine's effects, and behavioral measures controlled for attentional, motivational, and motoric changes.
Main Results:
- Morphine administration dose-dependently increased the time required to detect noxious heat stimuli.
- These effects were reversed by systemic naloxone, confirming opioid receptor involvement.
- Morphine's impact was more significant for temperature changes near the detection threshold.
- No significant changes in attentional, motivational, or motoric behaviors were observed.
Conclusions:
- Systemic morphine, even at therapeutic doses relevant to human treatment, alters the perceived intensity of noxious heat.
- These findings suggest that morphine affects the sensory discriminative pathways of pain perception.
- The study provides valuable insights into the mechanisms by which morphine modulates pain in a preclinical model.