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 (Pain (in press)), we assessed the effects of morphine sulphate eye drops on corneal inflammation and hyperalgesia. Topical application of a 5 μM 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 μM 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 μ and δ opioid receptors located in the rat cornea to attenuate inflammation and hyperalgesia.
|Original language||English (US)|
|Number of pages||11|
|State||Published - Oct 2003|
Bibliographical noteFunding Information:
We thank S.A. Roiko for technical assistance and J.-D. Brederson for valuable comments on earlier versions of the manuscript. This work is supported by NIH grants DA09641 and DE07288.