Effect of morphine sulphate eye drops on hyperalgesia in the rat cornea.
In addition to their traditional role in centrally mediated analgesia, opiate compounds produce significant effects when administered peripherally. Using a recently characterized model of acute chemical injury to the rat cornea, we assessed the effects of morphine sulphate eye drops on corneal inflammation and hyperalgesia. Topical application of a 5 microM morphine sulphate eye drop preparation attenuated capsaicin-induced blinking in a concentration-dependent manner. However, morphine had no effect on capsaicin-induced blinking when applied to healthy, non-inflamed rat cornea. In addition, 5 microM morphine given every 2 h following cauterization retarded the development of both stromal edema and the infiltration of immune cells. Both the analgesic and anti-inflammatory effects of morphine were prevented by the opioid receptor antagonists naloxone, CTAP, and naltrindole. We conclude that morphine acts on mu and delta opioid receptors located in the rat cornea to attenuate inflammation and hyperalgesia.
Wenk
N H
NH
Department of Neuroscience and Graduate Program in Neuroscience, University of Minnesota, 6-145 Jackson Hall, 312 Church Street SE, Minneapolis, MN 55455-0329, USA.
Nannenga
N M
NM
Honda
N C
NC
D000818:Animals; D004305:Dose-Response Relationship, Drug; D006930:Hyperalgesia / Q000188:drug therapy* / Q000473:pathology; D007634:Keratitis / Q000188:drug therapy* / Q000473:pathology; D008297:Male; D009020:Morphine / Q000627:therapeutic use*; D009883:Ophthalmic Solutions / Q000627:therapeutic use*; D051381:Rats; D017207:Rats, Sprague-Dawley
D009883:Ophthalmic Solutions; D009020:Morphine