Relationship between bilateral paw mechanical pain and the proinflammatory expression in spinal cord in a rat model of spinal nerve ligation

Objective: To analyze the mRNAs expression of IL-1β,IL-6 in spinal dorsal horn and their effects on mechanical pain sensitivity following spinal nerve ligation in rats.Methods: Healthy adult male SD rats were randomly divided into the spinal nerve ligation group(Tx),sham operation group(S),control group.The 50% mechanical paw withdrawal threshold(50%MWT) of left or right feet was determined by up-down method;RT-qPCR measured the mRNA expression levels of IL-1β and IL-6 in left or right spinal dorsal horn at different time point after surgery.Results: The 50%MWT of ipsilateral feet decreased significantly on 3rd day after L5 and L6 spinal nerve ligation(P0.001) and reached the minimum on 21st day(P0.001).The mechanical pain sensitivity of the contralateral feet enhanced significantly only on 10th day and 14th day after nerve ligation(P0.01,P0.05).The mRNA expression of IL-1β and IL-6 upregulated in ipsilateral dorsal horn on 7th day after nerve ligation when compared to group S or control group(P0.05);on 14th day,the level of IL-6 mRNA in ipsilateral side was still higher than group S or control group(P0.05).The mRNAs of IL-1β,IL-6 in contralateral spinal dorsal horn showed no significant increase on 10th,14th day after nerve ligation.Conclusion: Unilateral L5 and L6 nerve ligation contributed to mechanical hyperalgesia development of bilateral feet,however,the mechanical pain sensitivity of ipsilateral feet after nerve ligation occurred earlier and maintained longer.IL-1β、IL-6 mRNA in bilateral spinal dorsal horn showed different characteristic expression in the time course,they played an important role in neuropathic pain.