Changes in δ opioid receptor expression in spinal cord and dorsal root ganglias in rats with hyperalgesia induced by incisional pain-remifentanil

Abstract

Objective To investigate the changes in δ opioid receptor expression in the spinal cord and dorsal root ganglias in rats with hyperalgesia induced by incisional pain (IP)-remifentanil.Methods Thirty-two adult male Sprague-Dawley rats in which the catheter was successfully placed in the caudal vein were randomly divided into 4 groups (n =8 each):control gourp (group C),IP group (group I),remifentanil group (group R),and remifentanil + IP group (group RI).Normal saline 0.1 ml· kg-1 · min-1 was infused intravenously for 60 min in group C.In group I,normal saline 0.1 ml · kg-1 · min-1 was infused intravenously for 60 min,and IP was induced immediately after onset of infusion.In group R,remifentanil 1.0 μg· kg-1 · min-1 was infused intravenously for 60 min.In group RI,remifentanil 1.0μg· kg-1 · min-1 was infused intravenously for 60 min and IP was induced immediately after onset of infusion.At 24 h before infusion and 2,6,24 and 48 h after infusion (T0-4),paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were measured at room temperature (18-22 ℃).The rats were sacrificed after the end of the behavioral test and L4-6 segments of the spinal cord and dorsal root ganglias were removed for determination of the expression of total protein and membrane protein δ opioid receptor by Western blot.The ratio of δ opioid receptors in the membrane protein to those in the total protein (m/t ratio) was calculated.Results Compared with group C,PWT was significantly decreased and PWL was shortenedat T1-4,and the expression of total prtein and membrance protein δ opioid receptor was up-regulated and m/t ratio was increased in I,R and RI groups (P ＜ 0.05 or 0.01).Compared with group I,no significant change was found in PWT and PWL at T1-4,and the expression of total prtein and membrance protein δ opioid receptor and m/ t ratio in R group (P ＞ 0.05),and PWT was significantly decreased and PWL was shortened at T1-4 and the expression of total prtein and membrance protein δ opioid receptor was up-regulated and m/t ratio was increased in RI group (P ＜ 0.05 or 0.01).PWT was significantly lower and PWL was shorter at T1-4 and the expression of total prtein and membrance protein δ opioid receptor was up-regulated and m/t ratio was increased in RI group than in group R (P ＜ 0.05 or 0.01).Conclusion The development of IP-remifentanil-induced hyperalgesia in rats may be related to up-regulation of δ opioid receptor expression and enhanced trafficking to cell membrane in the spinal cord and dorsal root ganglias. Key words: Pain, postoperative ; Piperidines ; Hyperalgesia; Receptors, opioid, delta; Spinal cord; Ganglia, spinal