A peripheral, intracerebral, or intrathecal administration of an opioid receptor antagonist blocks illness-induced hyperalgesia in the rat.

Abstract

We used the tail-flick response of rats to study the role of opioid receptors in illness-induced hyperalgesia. An intraperitoneal injection of lithium chloride (LiCl) produced hyperalgesia that was blocked in a dose-dependent manner by subcutaneous injection of the opioid antagonist naloxone. Neither hyperalgesia nor its blockade by naloxone were due to variations in tail-skin temperature induced by LiCl. Hyperalgesia was also blocked when opioid receptor antagonism was restricted to (a) the periphery, by intraperitoneal administration of the quaternary opioid receptor antagonist naloxone methiodide; (b) the brain, by intracerebroventricular microinjection of naloxone; or (c) the spinal cord, by intrathecal microinjection of naloxone. These results document a pain facilitatory role of opioid receptors in both the peripheral and central nervous systems and are discussed with reference to their analgesic and motivational functions.

• Authors: G P McNally, I N Johnston, R F Westbrook
• Journal: Behavioral neuroscience (Behav Neurosci) Vol. 114 Issue 6 Pg. 1183-90 (Dec 2000) ISSN: 0735-7044 [Print] United States
• PMID: 11142650 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Quaternary Ammonium Compounds
• Receptors, Opioid
• Naloxone
• N-methylnaloxone
• Lithium Chloride

Topics

• Animals
• Brain (drug effects)
• Dose-Response Relationship, Drug
• Injections, Intraventricular
• Injections, Spinal
• Injections, Subcutaneous
• Lithium Chloride (toxicity)
• Male
• Naloxone (analogs & derivatives, pharmacology)
• Pain Threshold (drug effects)
• Peripheral Nerves (drug effects)
• Quaternary Ammonium Compounds
• Rats
• Rats, Wistar
• Receptors, Opioid (drug effects)
• Spinal Cord (drug effects)