Korean J Anesthesiol.  2001 Feb;40(2):244-251. 10.4097/kjae.2001.40.2.244.

The Mechanism of Antiallodynic Effect of Intrathecal Morphine in Neuropathic Pain Induced by Spinal Nerve Ligation

• Hwang JH
• Kim YK
• Park JY
• Lee EJ

• KMID: 2236830
• DOI: http://doi.org/10.4097/kjae.2001.40.2.244

Abstract

BACKGROUND: Although the efficacy of morphine in a neuropathic pain state is somewhat controversial, intrathecally administered morphine reversed the mechanical allodynia in a previous animal study. Using a behavioral test, we investigated the mechanism of the antiallodynic action of intrathecal morphine by administering opioids, alpha2 adrenergic and cholinergic receptor antagonists in a rat model of neuropathic pain induced by a spinal nerve ligation injury.
METHODS
Male Sprague Dawley rats were prepared with a tight ligation of the left lumbar 5th and 6th spinal nerves and insertion of a chronic lumbar intrathecal catheter. Morphine 1 microgram was administered intrathecally to attenuate the mechanical allodynia. Naloxone 10 microgram, yohimbine 30 microgram, prazosin 30 microgram, atropine 10 microgram, pirenzepine 10 microgram, and methoctramine 10 microgram was administered intrathecally before and after the injection of morphine in order to investigate the reversal of an increased allodynic threshold by morphine. The allodynic thresholds for the left hindpaw withdrawal to von Frey hairs were assessed and converted to %MPE.
RESULTS
A reduction of mechanical allodynia by intrathecal morphine was produced. Naloxone pretreatment, but not posttreatment, reversed the antiallodynic effect of intrathecal morphine (P < 0.01). All alpha2 adrenergic and cholinergic receptor antagonists used here did not reverse it.
CONCLUSIONS
The results suggest that the reversal mechanism of mechanical allodynia by intrathecal morphine appears to be mediated mostly by the opioid receptor system, but not the alpha2 adrenergic and cholinergic receptor systems, at the spinal level in a rat model of a spinal nerve ligation injury.

Keyword

Analgesics: morphine; Animals: rats; Antagonists, narcotic: naloxone; Pain: allodynia; measurement; Receptors: adrenergic; cholinergic; opioid

MeSH Terms

Analgesics, Opioid
Animals
Atropine
Catheters
Cholinergic Antagonists
Hair
Humans
Hyperalgesia
Ligation*
Male
Models, Animal
Morphine*
Naloxone
Neuralgia*
Pirenzepine
Prazosin
Rats, Sprague-Dawley
Receptors, Opioid
Spinal Nerves*
Yohimbine
Analgesics, Opioid
Atropine
Cholinergic Antagonists
Morphine
Naloxone
Pirenzepine
Prazosin
Receptors, Opioid
Yohimbine