Role of autophagy in development of neuropathic pain in rats

Abstract

Objective To evaluate the role of autophagy in the development of neuropathic pain (NP) in rats.Methods Thirty male Sprague-Dawley rats,weighing 200-220 g,were randomly divided into 3 groups (n =10 each) using a random number table:sham operation group (sham group),NP group and rapamycin (autophagy inducer) group (Rap group).Intrathecal catheter was inserted into the subarachnoid space and advanced caudally until the tip reached L4,5 segment.NP was induced by ligation of the left L5 spinal nerve (SNL) in NP and Rap groups.The L5 spinal nerve was only exposed,but not ligated in group sham.At 30 min before ligation and 2 days after operation,rapamycin 60 μg was injected intrathecally via the intrathecal catheter in Rap group,while the equal volume of vehicle (5％ dimethyl sulfoxide) was injected in sham and NP groups.The mechanical and thermal pain thresholds were measured on 1,3,5 and 7 days after ligation (T-4).The rats were sacrificed after the last measurement of pain threshold at T4.The ipsilateral L5 segment of spinal dorsal horn was removed for examination of autophagosomes (using transmission electron microscope) and for determination of the expression of LC3 Ⅱ and p62 (by Western blot) and content of IL-1β (by ELISA).Results Compared with sham group,the mechanical pain threshold at each time point and thermal pain threshold at T2-4 were significantly decreased,and the LC3 Ⅱ and p62 expression and IL-1β content were increased at T4 in group NP (P ＜ 0.05).Compared with NP group,the mechanical pain threshold at each time point,thermal pain threshold at T2-4 and LC3 Ⅱ expression at T4 were significantly increased,and the p62 expression and IL-1β content were decreased at T4 in group Rap (P ＜ 0.05).Microscopic examination showed that autophagosomes were observed in the spinal dorsal horn in NP and Rap groups,and the damage to organelles was lighter in Rap group than in NP group.Conclusion The development of NP is related to autophagic dysfunction in rats. Key words: Autophagy; Neuralgia