The effect of autophagy on hyperalgesia and astrocytic activation in rats with inflammatory pain / 中国中西医结合急救杂志

ABSTRACT

Objective To evaluate the influence of autophagy on pain behavioristics and astrocytic activation in rats with inflammatory pain.Methods Seventy-eight clean male Sprague-Dawley (SD) adult rats were randomly divided into four groups control group (n = 12), model group (n = 42), autophagy inducer rapamycin (Rap) pretreatment group (n = 12) and autophagy inhibitor 3 methyladenine (3-MA) pretreatment group (n = 12). The inflammatory pain rat model was reproduced by subcutaneous injection of freund's complete adjuvant (CFA) 100μL at foot sole, whilein control group, the same volume 0.9% normal saline 100μL was injected at the same site. One hour before modeling, Rap 10 mg/kg and 3-MA 15 mg/kg were intraperitoneally injected in rats in Rap and 3-MA pretreatment groups respectively, and the same volume of 0.9% normal saline was injected intraperitoneally in rats of control and model groups. Before modeling and 6, 12, 24 hours and 3 days after modeling, the L4-L6 spinal cord tissue was harvested from 6 rats in model group, and autophagy protein membrane microtubule-associated protein 1 light chain 3 Ⅱ (LC3 Ⅱ) and autophagy related gene Beclin-1 expressions were detected by Western Blot in the tissue; the changes of pain behavioral indexes mechanical withdraw threshold (MWT) and thermal withdrawal latency (TWL,n = 6), were observed at6, 12, 24 hours and 3 days, 7 days after modeling in the 6 rats taken from each group; in another 6 rats in each group, 24 hours after modeling, L4-L6 spinal cord tissue was collected, immunofluorescence staining was used to observe the changes of astrocytes and the positive expression of glial fibrillary acidic protein (GFAP) under a confocal microscopy, and the protein expression quantity of GFAP was detected by Western Blot in the tissue.Results ① The inflammatory pain could induce the increase of rat autophagy protein LC3Ⅱ and Beclin-1 expressions in spinal cord tissue, reaching their peaks at 24 hours (A value 0.59±0.07, 0.51±0.06, respectively), and then they were gradually decreased. ② With the prolongation of time, in the model group MWT was gradually decreased, TWL was gradually shortened, they reached their valley values at 24 hours after modeling [MWT (g) 17.8±1.9, TWL (s) 6.8±0.4], and from 12 hours they were significantly decreased compared with those in control group [12hours MWT (g) 21.5±2.4 vs. 43.4±5.1, TWL (s) 12.0±1.1 vs. 17.6±1.2, bothP < 0.05], after modeling for 3 days they were increased; Compared with model group, 12 hours after autophagy inducer Rap was given, MWT was significantly increased (g 36.8±4.9 vs. 21.5±2.4,P < 0.05), TWL was significantly prolonged (s 14.3±1.1 vs. 12.0±1.1,P < 0.05); from 12 hours after autophagy inhibitor 3-MA was given, MWT was further reduced (g 18.6±1.9 vs. 21.5±2.4, P<0.05), TWL was further shortened (s 8.4±0.6 vs. 12.0±1.1,P < 0.05). ③ Confocal microscopic findings showed, there was no significant acstrocytic change, and only litter GFAP expression was seen in control group. In model group, the inflammatory pain induced astrocyte activation, manifesting glial cell hypertrophy, hyperplasia, gelatinousnetwork deformation, and GFAP expression was obviously increased compared with that in the control group (A value 0.54±0.09 vs. 0.16±0.02,P < 0.05). Since autophagy inducer Rap can decrease astrocyte activation and inhibit GFAP expression, there was statistical significant difference between Rap pretreatment and model groups (A value 0.33±0.06 vs.0.54±0.09,P < 0.05); autophagy inhibitor 3-MA can further aggravate astrocytes activation and up-regulate GFAP expression in 3-MA pretreatment group (A value 0.73±0.08 vs. 0.54±0.09,P < 0.05).Conclusion Autophagy participates in the process of astrocytic activation and pain behavioristics in rats with inflammatory pain.