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SPINAL µ‐OPIOID RECEPTOR EXPRESSION AND HYPERALGESIA WITH DEXAMETHASONE IN CHRONIC ADJUVANT‐INDUCED ARTHRITIS IN RATS
Author(s) -
Zaringhalam Jalal,
Manaheji Homa,
Mghsoodi Nader,
Farokhi Babak,
Mirzaiee Vahideh
Publication year - 2008
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.2008.05009.x
Subject(s) - hyperalgesia , dexamethasone , opioid , opioid receptor , endocrinology , medicine , receptor , pharmacology , nociception
SUMMARY1 It is known that inflammation influences peripheral and central µ‐opioid receptor expression. Previous studies have indicated that glucocorticoids may influence the density of µ‐opioid receptors. In the present study, we investigated the fluctuations of spinal µ‐opioid receptor expression and hyperalgesia induced by complete Freund's adjuvant (CFA) under long‐term administration of dexamethasone. 2 Adjuvant arthritis (AA) was induced by subcutaneous injection of CFA in the right hindpaw of male Wistar rats. Spinal µ‐opioid receptor expression was detected by semiquantitative reverse transcription–polymerase chain reaction on Days 6 and 21 following AA induction. Dexamethasone (0.1 mg/kg) was administered intraperitoneally for 21 days. Variations in thermal hyperalgesia were checked by radiant heat on the same days as µ‐opioid receptor expression was determined. 3 The results indicated a significant increase in spinal µ‐opioid receptor expression on Days 6 and 21 after AA induction compared with the control group. Spinal µ‐opioid receptor expression decreased significantly only on Day 21 in the AA + dexamethasone group compared with the AA alone group. Thermal hyperalgesia on Day 6 after AA induction showed a significant increase compared with the control group. Hyperalgesia decreased significantly on Day 21 after AA compared with Day 6. The AA + dexamethasone group showed a significant decrease in hyperalgesia on Day 6 compared with the AA group, but hyperalgesia increased significantly on Day 21 in the AA + dexamethasone group compared with the AA group. 4 The effects of long‐term dexamethasone on both spinal µ‐opioid receptor expression and hyperalgesia during persistent AA inflammation are time dependent. In addition, the effect of long‐term dexamethasone administration on hyperalgesia during persistent arthritis inflammation needs to be investigated further.