Changes in expression of vanilioid receptor subtype 1 in dorsal root ganglion and effect of electroacupuncture on morphine tolerance in rats with inflammatory pain and morphine tolerance / 中华麻醉学杂志

ABSTRACT

Objective To investigate the changes in expression of vanilloid receptor subtype 1 (VR1) in dorsal root ganglion (DRG) and effect of electroacupuncture (EA)on morphine tolerance in rats with inflammatory pain (IP) and morphine tolerance. Methods Thirty 8 month old male SD rats in which intrathecal (IT) catheters were successfully implanted without complication were randomly divided into 6 groups ( n = 5 each) group A IP + normal saline (NS) 10 μl IT twice a day × 7 days;group B intact rats + morphine 10 μg/kg(10 μl )IT twice a day × 7 days;group C IP + morphine 10 μg/kg(10 μl) IT once;group DIP + morphine 10μg/kg(10 μl) IT twice a day × 7 days;group E and F IP + EA (frequency 2/15 Hz) + morphine 10μg/kg(10 μl) IT twice a day × 7 days. IP was induced by injecting complete Freund's adjuvant (CFA) into the anlle joint of the left hindlimb. IT morphine or NS was started on the 4th day after induction of IP. EA of Yanglingquan and Zusanli lasting 30 min was performed once a day after first IT administration of morphine for 7 days. Paw withdrawal latency (PWL) to a thermal nociceptive stimulus was measured before induction of IP (baseline), at 1 day before and 1-7days of consecutive IT administration. The animals were sacrificed after last PWL measurement. The DRGs of the lumbar segment (L4-6) were removed for determination of VR1 expression in total and membrane protein using Western blot analysis. Results There was no significant difference in the baseline PWL measured before induction of IP among the 6 groups. Morphine tolerance developed in group B and D but did not develop in group E and F.The expression of VR1 in total and membrane protein of DRG was highest in group D and was significantly lower in group E than in group F. Conclusion VR1 in DRG is involved in the development of morphine tolerance. EA can inhibit morphine tolerance by down-regulating the expression of VR1.