Differential action of morphine and various opioid agonists on thermal allodynia and hyperalgesia in mononeuropathic rats.

Abstract

In a rat model of mononeuropathy produced by 4 loose ligatures around the common sciatic nerve, the effects of 1 mg/kg morphine and mu-, delta- and kappa-agonists, DAMGO (2 and 3 mg/kg), BUBUC (3 and 6 mg/kg) and U-69,593 (1.5 mg/kg), were evaluated by measuring the struggle latency (SL in sec) to immersion of the paw on the nerve-injured side in a cold (10 degrees C) or hot (42 degrees C, 44 degrees C, and 46 degrees C) water bath. Experiments were performed 2 weeks after surgery. The agonists were used at doses that produced potent antinociceptive effects on the vocalization test in this model. At 46 degrees C (clearly in the noxious range), only morphine and DAMGO had significant effects. The effect of morphine lasted for more than 2 h with a maximum at 40 min (SL = 13.8 +/- 1.6 sec, 252% of control values). For 2 and 3 mg/kg DAMGO, the dose-related effect lasted for 120 min at least, with a maximum at 20-40 min (SL = 6.0 +/- 0.5 and 8.8 +/- 0.7 sec, 148% and 170% of control values, respectively). These effects were more potent and prolonged than in normal rats and were reversed by 0.1 mg/kg naloxone i.v. By contrast, morphine and all selective agonists failed to relieve the abnormal reactions to 10 degrees C, 42 degrees C (in the non-noxious range) and 44 degrees C (at the noxious threshold) stimuli. Our data illustrate a differential effect of opioids on nociceptive tests based on different stimulus modalities and intensities in this model of mononeuropathic pain.(ABSTRACT TRUNCATED AT 250 WORDS)

• Authors: S H Lee, V Kayser, J Desmeules, G Guilbaud
• Journal: Pain (Pain) Vol. 57 Issue 2 Pg. 233-240 (May 1994) ISSN: 0304-3959 [Print] United States
• PMID: 8090518 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Receptors, Opioid
• Morphine

Topics

• Animals
• Cold Temperature
• Hot Temperature
• Hyperalgesia (drug therapy)
• Male
• Morphine (pharmacology)
• Pain (physiopathology)
• Peripheral Nervous System Diseases (physiopathology)
• Rats
• Rats, Sprague-Dawley
• Reaction Time (drug effects)
• Receptors, Opioid (drug effects)
• Sciatic Nerve (drug effects)