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Updated: Aug 24, 2026
The Sciatic Nerve Cuffing Model of Neuropathic Pain in Mice
Published on: July 16, 2014
Local peripheral effects of mu-opioid receptor agonists in neuropathic pain in rats
Ilona Obara1, Ryszard Przewlocki, Barbara Przewlocka
1Department of Molecular Neuropharmacology, Institute of Pharmacology, Polish Academy of Sciences, 12 Smetna Street, 31-343 Kraków, Poland.
Abstract:
Our study was designed to demonstrate peripheral antinociception of the mu-opioid receptor agonists: morphine (MF), [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]enkephalin (DAMGO), endomorphin-1 (EM-1) and endomorphin-2 (EM-2) in Bennett's rat model of neuropathic pain. All the agonists were effective in antagonizing allodynia after their intraplantar (i.pl.) but not subcutaneous (s.c.) administration. Opioid peptides: DAMGO, EM-1 and EM-2 were more effective compared with corresponding doses of morphine (opioid alkaloid) in alleviating chronic pain. Peripheral mu-opioid receptors mediated the observed effects, as was evidenced by the i.pl. treatment with naloxone methiodide (active only at the site of injection) and by cyprodime, a selective mu-opioid receptor antagonist. These results have shown that opioid peptides are effective also after local treatment, and that their peripheral use may be of therapeutic interest in long-term management of chronic pain.
Insights
Peripheral administration of opioid peptides effectively reduced neuropathic pain in rats. These findings suggest opioid peptides may offer therapeutic potential for chronic pain management.
Area of Science:
- Pharmacology
- Neuroscience
- Pain Research
Background:
- Neuropathic pain is a debilitating condition often inadequately managed by current therapies.
- Peripheral administration of analgesics offers a potential strategy to minimize systemic side effects.
- Mu-opioid receptors are known targets for pain relief, but their peripheral efficacy requires further investigation.
Purpose of the Study:
- To investigate the peripheral antinociceptive effects of mu-opioid receptor agonists in a rat model of neuropathic pain.
- To compare the efficacy of opioid peptides (DAMGO, EM-1, EM-2) with morphine.
- To confirm the involvement of peripheral mu-opioid receptors in mediating the observed antinociception.
Main Methods:
- Utilized Bennett's rat model of neuropathic pain.
- Administered mu-opioid receptor agonists (morphine, DAMGO, EM-1, EM-2) via intraplantar (i.pl.) and subcutaneous (s.c.) routes.
- Assessed antiallodynic effects.
- Used naloxone methiodide and cyprodime (selective mu-opioid antagonist) to confirm receptor involvement.
Main Results:
- Intraplantar administration of all tested mu-opioid receptor agonists effectively antagonized allodynia.
- Subcutaneous administration did not produce significant antinociceptive effects.
- Opioid peptides (DAMGO, EM-1, EM-2) demonstrated greater efficacy than morphine at equivalent doses.
- Peripheral mu-opioid receptor blockade with naloxone methiodide and cyprodime reversed the antiallodynia.
Conclusions:
- Peripheral administration of opioid peptides provides effective antinociception in neuropathic pain.
- Opioid peptides show superior efficacy compared to morphine for peripheral pain relief.
- Targeting peripheral mu-opioid receptors with opioid peptides represents a promising therapeutic avenue for chronic pain management.
